Issue #6215: backport the 3.1 io lib
diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
new file mode 100644
index 0000000..c129303
--- /dev/null
+++ b/Modules/_io/textio.c
@@ -0,0 +1,2606 @@
+/*
+    An implementation of Text I/O as defined by PEP 3116 - "New I/O"
+
+    Classes defined here: TextIOBase, IncrementalNewlineDecoder, TextIOWrapper.
+
+    Written by Amaury Forgeot d'Arc and Antoine Pitrou
+*/
+
+#define PY_SSIZE_T_CLEAN
+#include "Python.h"
+#include "structmember.h"
+#include "_iomodule.h"
+
+/* TextIOBase */
+
+PyDoc_STRVAR(textiobase_doc,
+    "Base class for text I/O.\n"
+    "\n"
+    "This class provides a character and line based interface to stream\n"
+    "I/O. There is no readinto method because Python's character strings\n"
+    "are immutable. There is no public constructor.\n"
+    );
+
+static PyObject *
+_unsupported(const char *message)
+{
+    PyErr_SetString(_PyIO_unsupported_operation, message);
+    return NULL;
+}
+
+PyDoc_STRVAR(textiobase_detach_doc,
+    "Separate the underlying buffer from the TextIOBase and return it.\n"
+    "\n"
+    "After the underlying buffer has been detached, the TextIO is in an\n"
+    "unusable state.\n"
+    );
+
+static PyObject *
+textiobase_detach(PyObject *self)
+{
+    return _unsupported("detach");
+}
+
+PyDoc_STRVAR(textiobase_read_doc,
+    "Read at most n characters from stream.\n"
+    "\n"
+    "Read from underlying buffer until we have n characters or we hit EOF.\n"
+    "If n is negative or omitted, read until EOF.\n"
+    );
+
+static PyObject *
+textiobase_read(PyObject *self, PyObject *args)
+{
+    return _unsupported("read");
+}
+
+PyDoc_STRVAR(textiobase_readline_doc,
+    "Read until newline or EOF.\n"
+    "\n"
+    "Returns an empty string if EOF is hit immediately.\n"
+    );
+
+static PyObject *
+textiobase_readline(PyObject *self, PyObject *args)
+{
+    return _unsupported("readline");
+}
+
+PyDoc_STRVAR(textiobase_write_doc,
+    "Write string to stream.\n"
+    "Returns the number of characters written (which is always equal to\n"
+    "the length of the string).\n"
+    );
+
+static PyObject *
+textiobase_write(PyObject *self, PyObject *args)
+{
+    return _unsupported("write");
+}
+
+PyDoc_STRVAR(textiobase_encoding_doc,
+    "Encoding of the text stream.\n"
+    "\n"
+    "Subclasses should override.\n"
+    );
+
+static PyObject *
+textiobase_encoding_get(PyObject *self, void *context)
+{
+    Py_RETURN_NONE;
+}
+
+PyDoc_STRVAR(textiobase_newlines_doc,
+    "Line endings translated so far.\n"
+    "\n"
+    "Only line endings translated during reading are considered.\n"
+    "\n"
+    "Subclasses should override.\n"
+    );
+
+static PyObject *
+textiobase_newlines_get(PyObject *self, void *context)
+{
+    Py_RETURN_NONE;
+}
+
+PyDoc_STRVAR(textiobase_errors_doc,
+    "The error setting of the decoder or encoder.\n"
+    "\n"
+    "Subclasses should override.\n"
+    );
+
+static PyObject *
+textiobase_errors_get(PyObject *self, void *context)
+{
+    Py_RETURN_NONE;
+}
+
+
+static PyMethodDef textiobase_methods[] = {
+    {"detach", (PyCFunction)textiobase_detach, METH_NOARGS, textiobase_detach_doc},
+    {"read", textiobase_read, METH_VARARGS, textiobase_read_doc},
+    {"readline", textiobase_readline, METH_VARARGS, textiobase_readline_doc},
+    {"write", textiobase_write, METH_VARARGS, textiobase_write_doc},
+    {NULL, NULL}
+};
+
+static PyGetSetDef textiobase_getset[] = {
+    {"encoding", (getter)textiobase_encoding_get, NULL, textiobase_encoding_doc},
+    {"newlines", (getter)textiobase_newlines_get, NULL, textiobase_newlines_doc},
+    {"errors", (getter)textiobase_errors_get, NULL, textiobase_errors_doc},
+    {NULL}
+};
+
+PyTypeObject PyTextIOBase_Type = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    "_io._TextIOBase",          /*tp_name*/
+    0,                          /*tp_basicsize*/
+    0,                          /*tp_itemsize*/
+    0,                          /*tp_dealloc*/
+    0,                          /*tp_print*/
+    0,                          /*tp_getattr*/
+    0,                          /*tp_setattr*/
+    0,                          /*tp_compare */
+    0,                          /*tp_repr*/
+    0,                          /*tp_as_number*/
+    0,                          /*tp_as_sequence*/
+    0,                          /*tp_as_mapping*/
+    0,                          /*tp_hash */
+    0,                          /*tp_call*/
+    0,                          /*tp_str*/
+    0,                          /*tp_getattro*/
+    0,                          /*tp_setattro*/
+    0,                          /*tp_as_buffer*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  /*tp_flags*/
+    textiobase_doc,             /* tp_doc */
+    0,                          /* tp_traverse */
+    0,                          /* tp_clear */
+    0,                          /* tp_richcompare */
+    0,                          /* tp_weaklistoffset */
+    0,                          /* tp_iter */
+    0,                          /* tp_iternext */
+    textiobase_methods,         /* tp_methods */
+    0,                          /* tp_members */
+    textiobase_getset,          /* tp_getset */
+    &PyIOBase_Type,             /* tp_base */
+    0,                          /* tp_dict */
+    0,                          /* tp_descr_get */
+    0,                          /* tp_descr_set */
+    0,                          /* tp_dictoffset */
+    0,                          /* tp_init */
+    0,                          /* tp_alloc */
+    0,                          /* tp_new */
+};
+
+
+/* IncrementalNewlineDecoder */
+
+PyDoc_STRVAR(incrementalnewlinedecoder_doc,
+    "Codec used when reading a file in universal newlines mode.  It wraps\n"
+    "another incremental decoder, translating \\r\\n and \\r into \\n.  It also\n"
+    "records the types of newlines encountered.  When used with\n"
+    "translate=False, it ensures that the newline sequence is returned in\n"
+    "one piece. When used with decoder=None, it expects unicode strings as\n"
+    "decode input and translates newlines without first invoking an external\n"
+    "decoder.\n"
+    );
+
+typedef struct {
+    PyObject_HEAD
+    PyObject *decoder;
+    PyObject *errors;
+    int pendingcr:1;
+    int translate:1;
+    unsigned int seennl:3;
+} nldecoder_object;
+
+static int
+incrementalnewlinedecoder_init(nldecoder_object *self,
+                               PyObject *args, PyObject *kwds)
+{
+    PyObject *decoder;
+    int translate;
+    PyObject *errors = NULL;
+    char *kwlist[] = {"decoder", "translate", "errors", NULL};
+
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "Oi|O:IncrementalNewlineDecoder",
+                                     kwlist, &decoder, &translate, &errors))
+        return -1;
+
+    self->decoder = decoder;
+    Py_INCREF(decoder);
+
+    if (errors == NULL) {
+        self->errors = PyUnicode_FromString("strict");
+        if (self->errors == NULL)
+            return -1;
+    }
+    else {
+        Py_INCREF(errors);
+        self->errors = errors;
+    }
+
+    self->translate = translate;
+    self->seennl = 0;
+    self->pendingcr = 0;
+
+    return 0;
+}
+
+static void
+incrementalnewlinedecoder_dealloc(nldecoder_object *self)
+{
+    Py_CLEAR(self->decoder);
+    Py_CLEAR(self->errors);
+    Py_TYPE(self)->tp_free((PyObject *)self);
+}
+
+#define SEEN_CR   1
+#define SEEN_LF   2
+#define SEEN_CRLF 4
+#define SEEN_ALL (SEEN_CR | SEEN_LF | SEEN_CRLF)
+
+PyObject *
+_PyIncrementalNewlineDecoder_decode(PyObject *_self,
+                                    PyObject *input, int final)
+{
+    PyObject *output;
+    Py_ssize_t output_len;
+    nldecoder_object *self = (nldecoder_object *) _self;
+
+    if (self->decoder == NULL) {
+        PyErr_SetString(PyExc_ValueError,
+                        "IncrementalNewlineDecoder.__init__ not called");
+        return NULL;
+    }
+
+    /* decode input (with the eventual \r from a previous pass) */
+    if (self->decoder != Py_None) {
+        output = PyObject_CallMethodObjArgs(self->decoder,
+            _PyIO_str_decode, input, final ? Py_True : Py_False, NULL);
+    }
+    else {
+        output = input;
+        Py_INCREF(output);
+    }
+
+    if (output == NULL)
+        return NULL;
+
+    if (!PyUnicode_Check(output)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "decoder should return a string result");
+        goto error;
+    }
+
+    output_len = PyUnicode_GET_SIZE(output);
+    if (self->pendingcr && (final || output_len > 0)) {
+        Py_UNICODE *out;
+        PyObject *modified = PyUnicode_FromUnicode(NULL, output_len + 1);
+        if (modified == NULL)
+            goto error;
+        out = PyUnicode_AS_UNICODE(modified);
+        out[0] = '\r';
+        memcpy(out + 1, PyUnicode_AS_UNICODE(output),
+               output_len * sizeof(Py_UNICODE));
+        Py_DECREF(output);
+        output = modified;
+        self->pendingcr = 0;
+        output_len++;
+    }
+
+    /* retain last \r even when not translating data:
+     * then readline() is sure to get \r\n in one pass
+     */
+    if (!final) {
+        if (output_len > 0
+            && PyUnicode_AS_UNICODE(output)[output_len - 1] == '\r') {
+
+            if (Py_REFCNT(output) == 1) {
+                if (PyUnicode_Resize(&output, output_len - 1) < 0)
+                    goto error;
+            }
+            else {
+                PyObject *modified = PyUnicode_FromUnicode(
+                    PyUnicode_AS_UNICODE(output),
+                    output_len - 1);
+                if (modified == NULL)
+                    goto error;
+                Py_DECREF(output);
+                output = modified;
+            }
+            self->pendingcr = 1;
+        }
+    }
+
+    /* Record which newlines are read and do newline translation if desired,
+       all in one pass. */
+    {
+        Py_UNICODE *in_str;
+        Py_ssize_t len;
+        int seennl = self->seennl;
+        int only_lf = 0;
+
+        in_str = PyUnicode_AS_UNICODE(output);
+        len = PyUnicode_GET_SIZE(output);
+
+        if (len == 0)
+            return output;
+
+        /* If, up to now, newlines are consistently \n, do a quick check
+           for the \r *byte* with the libc's optimized memchr.
+           */
+        if (seennl == SEEN_LF || seennl == 0) {
+            only_lf = (memchr(in_str, '\r', len * sizeof(Py_UNICODE)) == NULL);
+        }
+
+        if (only_lf) {
+            /* If not already seen, quick scan for a possible "\n" character.
+               (there's nothing else to be done, even when in translation mode)
+            */
+            if (seennl == 0 &&
+                memchr(in_str, '\n', len * sizeof(Py_UNICODE)) != NULL) {
+                Py_UNICODE *s, *end;
+                s = in_str;
+                end = in_str + len;
+                for (;;) {
+                    Py_UNICODE c;
+                    /* Fast loop for non-control characters */
+                    while (*s > '\n')
+                        s++;
+                    c = *s++;
+                    if (c == '\n') {
+                        seennl |= SEEN_LF;
+                        break;
+                    }
+                    if (s > end)
+                        break;
+                }
+            }
+            /* Finished: we have scanned for newlines, and none of them
+               need translating */
+        }
+        else if (!self->translate) {
+            Py_UNICODE *s, *end;
+            /* We have already seen all newline types, no need to scan again */
+            if (seennl == SEEN_ALL)
+                goto endscan;
+            s = in_str;
+            end = in_str + len;
+            for (;;) {
+                Py_UNICODE c;
+                /* Fast loop for non-control characters */
+                while (*s > '\r')
+                    s++;
+                c = *s++;
+                if (c == '\n')
+                    seennl |= SEEN_LF;
+                else if (c == '\r') {
+                    if (*s == '\n') {
+                        seennl |= SEEN_CRLF;
+                        s++;
+                    }
+                    else
+                        seennl |= SEEN_CR;
+                }
+                if (s > end)
+                    break;
+                if (seennl == SEEN_ALL)
+                    break;
+            }
+        endscan:
+            ;
+        }
+        else {
+            PyObject *translated = NULL;
+            Py_UNICODE *out_str;
+            Py_UNICODE *in, *out, *end;
+            if (Py_REFCNT(output) != 1) {
+                /* We could try to optimize this so that we only do a copy
+                   when there is something to translate. On the other hand,
+                   most decoders should only output non-shared strings, i.e.
+                   translation is done in place. */
+                translated = PyUnicode_FromUnicode(NULL, len);
+                if (translated == NULL)
+                    goto error;
+                assert(Py_REFCNT(translated) == 1);
+                memcpy(PyUnicode_AS_UNICODE(translated),
+                       PyUnicode_AS_UNICODE(output),
+                       len * sizeof(Py_UNICODE));
+            }
+            else {
+                translated = output;
+            }
+            out_str = PyUnicode_AS_UNICODE(translated);
+            in = in_str;
+            out = out_str;
+            end = in_str + len;
+            for (;;) {
+                Py_UNICODE c;
+                /* Fast loop for non-control characters */
+                while ((c = *in++) > '\r')
+                    *out++ = c;
+                if (c == '\n') {
+                    *out++ = c;
+                    seennl |= SEEN_LF;
+                    continue;
+                }
+                if (c == '\r') {
+                    if (*in == '\n') {
+                        in++;
+                        seennl |= SEEN_CRLF;
+                    }
+                    else
+                        seennl |= SEEN_CR;
+                    *out++ = '\n';
+                    continue;
+                }
+                if (in > end)
+                    break;
+                *out++ = c;
+            }
+            if (translated != output) {
+                Py_DECREF(output);
+                output = translated;
+            }
+            if (out - out_str != len) {
+                if (PyUnicode_Resize(&output, out - out_str) < 0)
+                    goto error;
+            }
+        }
+        self->seennl |= seennl;
+    }
+
+    return output;
+
+  error:
+    Py_DECREF(output);
+    return NULL;
+}
+
+static PyObject *
+incrementalnewlinedecoder_decode(nldecoder_object *self,
+                                 PyObject *args, PyObject *kwds)
+{
+    char *kwlist[] = {"input", "final", NULL};
+    PyObject *input;
+    int final = 0;
+
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|i:IncrementalNewlineDecoder",
+                                     kwlist, &input, &final))
+        return NULL;
+    return _PyIncrementalNewlineDecoder_decode((PyObject *) self, input, final);
+}
+
+static PyObject *
+incrementalnewlinedecoder_getstate(nldecoder_object *self, PyObject *args)
+{
+    PyObject *buffer;
+    unsigned PY_LONG_LONG flag;
+
+    if (self->decoder != Py_None) {
+        PyObject *state = PyObject_CallMethodObjArgs(self->decoder,
+           _PyIO_str_getstate, NULL);
+        if (state == NULL)
+            return NULL;
+        if (!PyArg_Parse(state, "(OK)", &buffer, &flag)) {
+            Py_DECREF(state);
+            return NULL;
+        }
+        Py_INCREF(buffer);
+        Py_DECREF(state);
+    }
+    else {
+        buffer = PyBytes_FromString("");
+        flag = 0;
+    }
+    flag <<= 1;
+    if (self->pendingcr)
+        flag |= 1;
+    return Py_BuildValue("NK", buffer, flag);
+}
+
+static PyObject *
+incrementalnewlinedecoder_setstate(nldecoder_object *self, PyObject *state)
+{
+    PyObject *buffer;
+    unsigned PY_LONG_LONG flag;
+
+    if (!PyArg_Parse(state, "(OK)", &buffer, &flag))
+        return NULL;
+
+    self->pendingcr = (int) flag & 1;
+    flag >>= 1;
+
+    if (self->decoder != Py_None)
+        return PyObject_CallMethod(self->decoder,
+                                   "setstate", "((OK))", buffer, flag);
+    else
+        Py_RETURN_NONE;
+}
+
+static PyObject *
+incrementalnewlinedecoder_reset(nldecoder_object *self, PyObject *args)
+{
+    self->seennl = 0;
+    self->pendingcr = 0;
+    if (self->decoder != Py_None)
+        return PyObject_CallMethodObjArgs(self->decoder, _PyIO_str_reset, NULL);
+    else
+        Py_RETURN_NONE;
+}
+
+static PyObject *
+incrementalnewlinedecoder_newlines_get(nldecoder_object *self, void *context)
+{
+    switch (self->seennl) {
+    case SEEN_CR:
+        return PyUnicode_FromString("\r");
+    case SEEN_LF:
+        return PyUnicode_FromString("\n");
+    case SEEN_CRLF:
+        return PyUnicode_FromString("\r\n");
+    case SEEN_CR | SEEN_LF:
+        return Py_BuildValue("ss", "\r", "\n");
+    case SEEN_CR | SEEN_CRLF:
+        return Py_BuildValue("ss", "\r", "\r\n");
+    case SEEN_LF | SEEN_CRLF:
+        return Py_BuildValue("ss", "\n", "\r\n");
+    case SEEN_CR | SEEN_LF | SEEN_CRLF:
+        return Py_BuildValue("sss", "\r", "\n", "\r\n");
+    default:
+        Py_RETURN_NONE;
+   }
+
+}
+
+
+static PyMethodDef incrementalnewlinedecoder_methods[] = {
+    {"decode", (PyCFunction)incrementalnewlinedecoder_decode, METH_VARARGS|METH_KEYWORDS},
+    {"getstate", (PyCFunction)incrementalnewlinedecoder_getstate, METH_NOARGS},
+    {"setstate", (PyCFunction)incrementalnewlinedecoder_setstate, METH_O},
+    {"reset", (PyCFunction)incrementalnewlinedecoder_reset, METH_NOARGS},
+    {NULL}
+};
+
+static PyGetSetDef incrementalnewlinedecoder_getset[] = {
+    {"newlines", (getter)incrementalnewlinedecoder_newlines_get, NULL, NULL},
+    {NULL}
+};
+
+PyTypeObject PyIncrementalNewlineDecoder_Type = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    "_io.IncrementalNewlineDecoder", /*tp_name*/
+    sizeof(nldecoder_object), /*tp_basicsize*/
+    0,                          /*tp_itemsize*/
+    (destructor)incrementalnewlinedecoder_dealloc, /*tp_dealloc*/
+    0,                          /*tp_print*/
+    0,                          /*tp_getattr*/
+    0,                          /*tp_setattr*/
+    0,                          /*tp_compare */
+    0,                          /*tp_repr*/
+    0,                          /*tp_as_number*/
+    0,                          /*tp_as_sequence*/
+    0,                          /*tp_as_mapping*/
+    0,                          /*tp_hash */
+    0,                          /*tp_call*/
+    0,                          /*tp_str*/
+    0,                          /*tp_getattro*/
+    0,                          /*tp_setattro*/
+    0,                          /*tp_as_buffer*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  /*tp_flags*/
+    incrementalnewlinedecoder_doc,          /* tp_doc */
+    0,                          /* tp_traverse */
+    0,                          /* tp_clear */
+    0,                          /* tp_richcompare */
+    0,                          /*tp_weaklistoffset*/
+    0,                          /* tp_iter */
+    0,                          /* tp_iternext */
+    incrementalnewlinedecoder_methods, /* tp_methods */
+    0,                          /* tp_members */
+    incrementalnewlinedecoder_getset, /* tp_getset */
+    0,                          /* tp_base */
+    0,                          /* tp_dict */
+    0,                          /* tp_descr_get */
+    0,                          /* tp_descr_set */
+    0,                          /* tp_dictoffset */
+    (initproc)incrementalnewlinedecoder_init, /* tp_init */
+    0,                          /* tp_alloc */
+    PyType_GenericNew,          /* tp_new */
+};
+
+
+/* TextIOWrapper */
+
+PyDoc_STRVAR(textiowrapper_doc,
+    "Character and line based layer over a BufferedIOBase object, buffer.\n"
+    "\n"
+    "encoding gives the name of the encoding that the stream will be\n"
+    "decoded or encoded with. It defaults to locale.getpreferredencoding.\n"
+    "\n"
+    "errors determines the strictness of encoding and decoding (see the\n"
+    "codecs.register) and defaults to \"strict\".\n"
+    "\n"
+    "newline can be None, '', '\\n', '\\r', or '\\r\\n'.  It controls the\n"
+    "handling of line endings. If it is None, universal newlines is\n"
+    "enabled.  With this enabled, on input, the lines endings '\\n', '\\r',\n"
+    "or '\\r\\n' are translated to '\\n' before being returned to the\n"
+    "caller. Conversely, on output, '\\n' is translated to the system\n"
+    "default line seperator, os.linesep. If newline is any other of its\n"
+    "legal values, that newline becomes the newline when the file is read\n"
+    "and it is returned untranslated. On output, '\\n' is converted to the\n"
+    "newline.\n"
+    "\n"
+    "If line_buffering is True, a call to flush is implied when a call to\n"
+    "write contains a newline character."
+    );
+
+typedef PyObject *
+        (*encodefunc_t)(PyObject *, PyObject *);
+
+typedef struct
+{
+    PyObject_HEAD
+    int ok; /* initialized? */
+    int detached;
+    Py_ssize_t chunk_size;
+    PyObject *buffer;
+    PyObject *encoding;
+    PyObject *encoder;
+    PyObject *decoder;
+    PyObject *readnl;
+    PyObject *errors;
+    const char *writenl; /* utf-8 encoded, NULL stands for \n */
+    char line_buffering;
+    char readuniversal;
+    char readtranslate;
+    char writetranslate;
+    char seekable;
+    char telling;
+    /* Specialized encoding func (see below) */
+    encodefunc_t encodefunc;
+    /* Whether or not it's the start of the stream */
+    char encoding_start_of_stream;
+
+    /* Reads and writes are internally buffered in order to speed things up.
+       However, any read will first flush the write buffer if itsn't empty.
+
+       Please also note that text to be written is first encoded before being
+       buffered. This is necessary so that encoding errors are immediately
+       reported to the caller, but it unfortunately means that the
+       IncrementalEncoder (whose encode() method is always written in Python)
+       becomes a bottleneck for small writes.
+    */
+    PyObject *decoded_chars;       /* buffer for text returned from decoder */
+    Py_ssize_t decoded_chars_used; /* offset into _decoded_chars for read() */
+    PyObject *pending_bytes;       /* list of bytes objects waiting to be
+                                      written, or NULL */
+    Py_ssize_t pending_bytes_count;
+    PyObject *snapshot;
+    /* snapshot is either None, or a tuple (dec_flags, next_input) where
+     * dec_flags is the second (integer) item of the decoder state and
+     * next_input is the chunk of input bytes that comes next after the
+     * snapshot point.  We use this to reconstruct decoder states in tell().
+     */
+
+    /* Cache raw object if it's a FileIO object */
+    PyObject *raw;
+
+    PyObject *weakreflist;
+    PyObject *dict;
+} textio;
+
+
+/* A couple of specialized cases in order to bypass the slow incremental
+   encoding methods for the most popular encodings. */
+
+static PyObject *
+ascii_encode(textio *self, PyObject *text)
+{
+    return PyUnicode_EncodeASCII(PyUnicode_AS_UNICODE(text),
+                                 PyUnicode_GET_SIZE(text),
+                                 PyBytes_AS_STRING(self->errors));
+}
+
+static PyObject *
+utf16be_encode(textio *self, PyObject *text)
+{
+    return PyUnicode_EncodeUTF16(PyUnicode_AS_UNICODE(text),
+                                 PyUnicode_GET_SIZE(text),
+                                 PyBytes_AS_STRING(self->errors), 1);
+}
+
+static PyObject *
+utf16le_encode(textio *self, PyObject *text)
+{
+    return PyUnicode_EncodeUTF16(PyUnicode_AS_UNICODE(text),
+                                 PyUnicode_GET_SIZE(text),
+                                 PyBytes_AS_STRING(self->errors), -1);
+}
+
+static PyObject *
+utf16_encode(textio *self, PyObject *text)
+{
+    if (!self->encoding_start_of_stream) {
+        /* Skip the BOM and use native byte ordering */
+#if defined(WORDS_BIGENDIAN)
+        return utf16be_encode(self, text);
+#else
+        return utf16le_encode(self, text);
+#endif
+    }
+    return PyUnicode_EncodeUTF16(PyUnicode_AS_UNICODE(text),
+                                 PyUnicode_GET_SIZE(text),
+                                 PyBytes_AS_STRING(self->errors), 0);
+}
+
+static PyObject *
+utf32be_encode(textio *self, PyObject *text)
+{
+    return PyUnicode_EncodeUTF32(PyUnicode_AS_UNICODE(text),
+                                 PyUnicode_GET_SIZE(text),
+                                 PyBytes_AS_STRING(self->errors), 1);
+}
+
+static PyObject *
+utf32le_encode(textio *self, PyObject *text)
+{
+    return PyUnicode_EncodeUTF32(PyUnicode_AS_UNICODE(text),
+                                 PyUnicode_GET_SIZE(text),
+                                 PyBytes_AS_STRING(self->errors), -1);
+}
+
+static PyObject *
+utf32_encode(textio *self, PyObject *text)
+{
+    if (!self->encoding_start_of_stream) {
+        /* Skip the BOM and use native byte ordering */
+#if defined(WORDS_BIGENDIAN)
+        return utf32be_encode(self, text);
+#else
+        return utf32le_encode(self, text);
+#endif
+    }
+    return PyUnicode_EncodeUTF32(PyUnicode_AS_UNICODE(text),
+                                 PyUnicode_GET_SIZE(text),
+                                 PyBytes_AS_STRING(self->errors), 0);
+}
+
+static PyObject *
+utf8_encode(textio *self, PyObject *text)
+{
+    return PyUnicode_EncodeUTF8(PyUnicode_AS_UNICODE(text),
+                                PyUnicode_GET_SIZE(text),
+                                PyBytes_AS_STRING(self->errors));
+}
+
+static PyObject *
+latin1_encode(textio *self, PyObject *text)
+{
+    return PyUnicode_EncodeLatin1(PyUnicode_AS_UNICODE(text),
+                                  PyUnicode_GET_SIZE(text),
+                                  PyBytes_AS_STRING(self->errors));
+}
+
+/* Map normalized encoding names onto the specialized encoding funcs */
+
+typedef struct {
+    const char *name;
+    encodefunc_t encodefunc;
+} encodefuncentry;
+
+static encodefuncentry encodefuncs[] = {
+    {"ascii",       (encodefunc_t) ascii_encode},
+    {"iso8859-1",   (encodefunc_t) latin1_encode},
+    {"utf-8",       (encodefunc_t) utf8_encode},
+    {"utf-16-be",   (encodefunc_t) utf16be_encode},
+    {"utf-16-le",   (encodefunc_t) utf16le_encode},
+    {"utf-16",      (encodefunc_t) utf16_encode},
+    {"utf-32-be",   (encodefunc_t) utf32be_encode},
+    {"utf-32-le",   (encodefunc_t) utf32le_encode},
+    {"utf-32",      (encodefunc_t) utf32_encode},
+    {NULL, NULL}
+};
+
+
+static int
+textiowrapper_init(textio *self, PyObject *args, PyObject *kwds)
+{
+    char *kwlist[] = {"buffer", "encoding", "errors",
+                      "newline", "line_buffering",
+                      NULL};
+    PyObject *buffer, *raw;
+    char *encoding = NULL;
+    char *errors = NULL;
+    char *newline = NULL;
+    int line_buffering = 0;
+
+    PyObject *res;
+    int r;
+
+    self->ok = 0;
+    self->detached = 0;
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|zzzi:fileio",
+                                     kwlist, &buffer, &encoding, &errors,
+                                     &newline, &line_buffering))
+        return -1;
+
+    if (newline && newline[0] != '\0'
+        && !(newline[0] == '\n' && newline[1] == '\0')
+        && !(newline[0] == '\r' && newline[1] == '\0')
+        && !(newline[0] == '\r' && newline[1] == '\n' && newline[2] == '\0')) {
+        PyErr_Format(PyExc_ValueError,
+                     "illegal newline value: %s", newline);
+        return -1;
+    }
+
+    Py_CLEAR(self->buffer);
+    Py_CLEAR(self->encoding);
+    Py_CLEAR(self->encoder);
+    Py_CLEAR(self->decoder);
+    Py_CLEAR(self->readnl);
+    Py_CLEAR(self->decoded_chars);
+    Py_CLEAR(self->pending_bytes);
+    Py_CLEAR(self->snapshot);
+    Py_CLEAR(self->errors);
+    Py_CLEAR(self->raw);
+    self->decoded_chars_used = 0;
+    self->pending_bytes_count = 0;
+    self->encodefunc = NULL;
+    self->writenl = NULL;
+
+    if (encoding == NULL && self->encoding == NULL) {
+        if (_PyIO_locale_module == NULL) {
+            _PyIO_locale_module = PyImport_ImportModule("locale");
+            if (_PyIO_locale_module == NULL)
+                goto catch_ImportError;
+            else
+                goto use_locale;
+        }
+        else {
+          use_locale:
+            self->encoding = PyObject_CallMethod(
+                _PyIO_locale_module, "getpreferredencoding", NULL);
+            if (self->encoding == NULL) {
+              catch_ImportError:
+                /*
+                 Importing locale can raise a ImportError because of
+                 _functools, and locale.getpreferredencoding can raise a
+                 ImportError if _locale is not available.  These will happen
+                 during module building.
+                */
+                if (PyErr_ExceptionMatches(PyExc_ImportError)) {
+                    PyErr_Clear();
+                    self->encoding = PyString_FromString("ascii");
+                }
+                else
+                    goto error;
+            }
+            else if (!PyString_Check(self->encoding))
+                Py_CLEAR(self->encoding);
+        }
+    }
+    if (self->encoding != NULL)
+        encoding = PyString_AsString(self->encoding);
+    else if (encoding != NULL) {
+        self->encoding = PyString_FromString(encoding);
+        if (self->encoding == NULL)
+            goto error;
+    }
+    else {
+        PyErr_SetString(PyExc_IOError,
+                        "could not determine default encoding");
+    }
+
+    if (errors == NULL)
+        errors = "strict";
+    self->errors = PyBytes_FromString(errors);
+    if (self->errors == NULL)
+        goto error;
+
+    self->chunk_size = 8192;
+    self->readuniversal = (newline == NULL || newline[0] == '\0');
+    self->line_buffering = line_buffering;
+    self->readtranslate = (newline == NULL);
+    if (newline) {
+        self->readnl = PyString_FromString(newline);
+        if (self->readnl == NULL)
+            return -1;
+    }
+    self->writetranslate = (newline == NULL || newline[0] != '\0');
+    if (!self->readuniversal && self->writetranslate) {
+        self->writenl = PyString_AsString(self->readnl);
+        if (!strcmp(self->writenl, "\n"))
+            self->writenl = NULL;
+    }
+#ifdef MS_WINDOWS
+    else
+        self->writenl = "\r\n";
+#endif
+
+    /* Build the decoder object */
+    res = PyObject_CallMethod(buffer, "readable", NULL);
+    if (res == NULL)
+        goto error;
+    r = PyObject_IsTrue(res);
+    Py_DECREF(res);
+    if (r == -1)
+        goto error;
+    if (r == 1) {
+        self->decoder = PyCodec_IncrementalDecoder(
+            encoding, errors);
+        if (self->decoder == NULL)
+            goto error;
+
+        if (self->readuniversal) {
+            PyObject *incrementalDecoder = PyObject_CallFunction(
+                (PyObject *)&PyIncrementalNewlineDecoder_Type,
+                "Oi", self->decoder, (int)self->readtranslate);
+            if (incrementalDecoder == NULL)
+                goto error;
+            Py_CLEAR(self->decoder);
+            self->decoder = incrementalDecoder;
+        }
+    }
+
+    /* Build the encoder object */
+    res = PyObject_CallMethod(buffer, "writable", NULL);
+    if (res == NULL)
+        goto error;
+    r = PyObject_IsTrue(res);
+    Py_DECREF(res);
+    if (r == -1)
+        goto error;
+    if (r == 1) {
+        PyObject *ci;
+        self->encoder = PyCodec_IncrementalEncoder(
+            encoding, errors);
+        if (self->encoder == NULL)
+            goto error;
+        /* Get the normalized named of the codec */
+        ci = _PyCodec_Lookup(encoding);
+        if (ci == NULL)
+            goto error;
+        res = PyObject_GetAttrString(ci, "name");
+        Py_DECREF(ci);
+        if (res == NULL) {
+            if (PyErr_ExceptionMatches(PyExc_AttributeError))
+                PyErr_Clear();
+            else
+                goto error;
+        }
+        else if (PyString_Check(res)) {
+            encodefuncentry *e = encodefuncs;
+            while (e->name != NULL) {
+                if (!strcmp(PyString_AS_STRING(res), e->name)) {
+                    self->encodefunc = e->encodefunc;
+                    break;
+                }
+                e++;
+            }
+        }
+        Py_XDECREF(res);
+    }
+
+    self->buffer = buffer;
+    Py_INCREF(buffer);
+
+    if (Py_TYPE(buffer) == &PyBufferedReader_Type ||
+        Py_TYPE(buffer) == &PyBufferedWriter_Type ||
+        Py_TYPE(buffer) == &PyBufferedRandom_Type) {
+        raw = PyObject_GetAttrString(buffer, "raw");
+        /* Cache the raw FileIO object to speed up 'closed' checks */
+        if (raw == NULL) {
+            if (PyErr_ExceptionMatches(PyExc_AttributeError))
+                PyErr_Clear();
+            else
+                goto error;
+        }
+        else if (Py_TYPE(raw) == &PyFileIO_Type)
+            self->raw = raw;
+        else
+            Py_DECREF(raw);
+    }
+
+    res = PyObject_CallMethod(buffer, "seekable", NULL);
+    if (res == NULL)
+        goto error;
+    self->seekable = self->telling = PyObject_IsTrue(res);
+    Py_DECREF(res);
+
+    self->encoding_start_of_stream = 0;
+    if (self->seekable && self->encoder) {
+        PyObject *cookieObj;
+        int cmp;
+
+        self->encoding_start_of_stream = 1;
+
+        cookieObj = PyObject_CallMethodObjArgs(buffer, _PyIO_str_tell, NULL);
+        if (cookieObj == NULL)
+            goto error;
+
+        cmp = PyObject_RichCompareBool(cookieObj, _PyIO_zero, Py_EQ);
+        Py_DECREF(cookieObj);
+        if (cmp < 0) {
+            goto error;
+        }
+
+        if (cmp == 0) {
+            self->encoding_start_of_stream = 0;
+            res = PyObject_CallMethodObjArgs(self->encoder, _PyIO_str_setstate,
+                                             _PyIO_zero, NULL);
+            if (res == NULL)
+                goto error;
+            Py_DECREF(res);
+        }
+    }
+
+    self->ok = 1;
+    return 0;
+
+  error:
+    return -1;
+}
+
+static int
+_textiowrapper_clear(textio *self)
+{
+    if (self->ok && _PyIOBase_finalize((PyObject *) self) < 0)
+        return -1;
+    self->ok = 0;
+    Py_CLEAR(self->buffer);
+    Py_CLEAR(self->encoding);
+    Py_CLEAR(self->encoder);
+    Py_CLEAR(self->decoder);
+    Py_CLEAR(self->readnl);
+    Py_CLEAR(self->decoded_chars);
+    Py_CLEAR(self->pending_bytes);
+    Py_CLEAR(self->snapshot);
+    Py_CLEAR(self->errors);
+    Py_CLEAR(self->raw);
+    return 0;
+}
+
+static void
+textiowrapper_dealloc(textio *self)
+{
+    if (_textiowrapper_clear(self) < 0)
+        return;
+    _PyObject_GC_UNTRACK(self);
+    if (self->weakreflist != NULL)
+        PyObject_ClearWeakRefs((PyObject *)self);
+    Py_CLEAR(self->dict);
+    Py_TYPE(self)->tp_free((PyObject *)self);
+}
+
+static int
+textiowrapper_traverse(textio *self, visitproc visit, void *arg)
+{
+    Py_VISIT(self->buffer);
+    Py_VISIT(self->encoding);
+    Py_VISIT(self->encoder);
+    Py_VISIT(self->decoder);
+    Py_VISIT(self->readnl);
+    Py_VISIT(self->decoded_chars);
+    Py_VISIT(self->pending_bytes);
+    Py_VISIT(self->snapshot);
+    Py_VISIT(self->errors);
+    Py_VISIT(self->raw);
+
+    Py_VISIT(self->dict);
+    return 0;
+}
+
+static int
+textiowrapper_clear(textio *self)
+{
+    if (_textiowrapper_clear(self) < 0)
+        return -1;
+    Py_CLEAR(self->dict);
+    return 0;
+}
+
+static PyObject *
+textiowrapper_closed_get(textio *self, void *context);
+
+/* This macro takes some shortcuts to make the common case faster. */
+#define CHECK_CLOSED(self) \
+    do { \
+        int r; \
+        PyObject *_res; \
+        if (Py_TYPE(self) == &PyTextIOWrapper_Type) { \
+            if (self->raw != NULL) \
+                r = _PyFileIO_closed(self->raw); \
+            else { \
+                _res = textiowrapper_closed_get(self, NULL); \
+                if (_res == NULL) \
+                    return NULL; \
+                r = PyObject_IsTrue(_res); \
+                Py_DECREF(_res); \
+                if (r < 0) \
+                    return NULL; \
+            } \
+            if (r > 0) { \
+                PyErr_SetString(PyExc_ValueError, \
+                                "I/O operation on closed file."); \
+                return NULL; \
+            } \
+        } \
+        else if (_PyIOBase_check_closed((PyObject *)self, Py_True) == NULL) \
+            return NULL; \
+    } while (0)
+
+#define CHECK_INITIALIZED(self) \
+    if (self->ok <= 0) { \
+        if (self->detached) { \
+            PyErr_SetString(PyExc_ValueError, \
+                 "underlying buffer has been detached"); \
+        } else {                                   \
+            PyErr_SetString(PyExc_ValueError, \
+                "I/O operation on uninitialized object"); \
+        } \
+        return NULL; \
+    }
+
+#define CHECK_INITIALIZED_INT(self) \
+    if (self->ok <= 0) { \
+        if (self->detached) { \
+            PyErr_SetString(PyExc_ValueError, \
+                 "underlying buffer has been detached"); \
+        } else {                                   \
+            PyErr_SetString(PyExc_ValueError, \
+                "I/O operation on uninitialized object"); \
+        } \
+        return -1; \
+    }
+
+
+static PyObject *
+textiowrapper_detach(textio *self)
+{
+    PyObject *buffer, *res;
+    CHECK_INITIALIZED(self);
+    res = PyObject_CallMethodObjArgs((PyObject *)self, _PyIO_str_flush, NULL);
+    if (res == NULL)
+        return NULL;
+    Py_DECREF(res);
+    buffer = self->buffer;
+    self->buffer = NULL;
+    self->detached = 1;
+    self->ok = 0;
+    return buffer;
+}
+
+Py_LOCAL_INLINE(const Py_UNICODE *)
+findchar(const Py_UNICODE *s, Py_ssize_t size, Py_UNICODE ch)
+{
+    /* like wcschr, but doesn't stop at NULL characters */
+    while (size-- > 0) {
+        if (*s == ch)
+            return s;
+        s++;
+    }
+    return NULL;
+}
+
+/* Flush the internal write buffer. This doesn't explicitly flush the
+   underlying buffered object, though. */
+static int
+_textiowrapper_writeflush(textio *self)
+{
+    PyObject *b, *ret;
+
+    if (self->pending_bytes == NULL)
+        return 0;
+    b = _PyBytes_Join(_PyIO_empty_bytes, self->pending_bytes);
+    if (b == NULL)
+        return -1;
+    ret = PyObject_CallMethodObjArgs(self->buffer,
+                                     _PyIO_str_write, b, NULL);
+    Py_DECREF(b);
+    if (ret == NULL)
+        return -1;
+    Py_DECREF(ret);
+    Py_CLEAR(self->pending_bytes);
+    self->pending_bytes_count = 0;
+    return 0;
+}
+
+static PyObject *
+textiowrapper_write(textio *self, PyObject *args)
+{
+    PyObject *ret;
+    PyObject *text; /* owned reference */
+    PyObject *b;
+    Py_ssize_t textlen;
+    int haslf = 0;
+    int needflush = 0;
+
+    CHECK_INITIALIZED(self);
+
+    if (!PyArg_ParseTuple(args, "U:write", &text)) {
+        return NULL;
+    }
+
+    CHECK_CLOSED(self);
+
+    if (self->encoder == NULL) {
+        PyErr_SetString(PyExc_IOError, "not writable");
+        return NULL;
+    }
+
+    Py_INCREF(text);
+
+    textlen = PyUnicode_GetSize(text);
+
+    if ((self->writetranslate && self->writenl != NULL) || self->line_buffering)
+        if (findchar(PyUnicode_AS_UNICODE(text),
+                     PyUnicode_GET_SIZE(text), '\n'))
+            haslf = 1;
+
+    if (haslf && self->writetranslate && self->writenl != NULL) {
+        PyObject *newtext = PyObject_CallMethod(
+            text, "replace", "ss", "\n", self->writenl);
+        Py_DECREF(text);
+        if (newtext == NULL)
+            return NULL;
+        text = newtext;
+    }
+
+    if (self->line_buffering &&
+        (haslf ||
+         findchar(PyUnicode_AS_UNICODE(text),
+                  PyUnicode_GET_SIZE(text), '\r')))
+        needflush = 1;
+
+    /* XXX What if we were just reading? */
+    if (self->encodefunc != NULL) {
+        b = (*self->encodefunc)((PyObject *) self, text);
+        self->encoding_start_of_stream = 0;
+    }
+    else
+        b = PyObject_CallMethodObjArgs(self->encoder,
+                                       _PyIO_str_encode, text, NULL);
+    Py_DECREF(text);
+    if (b == NULL)
+        return NULL;
+
+    if (self->pending_bytes == NULL) {
+        self->pending_bytes = PyList_New(0);
+        if (self->pending_bytes == NULL) {
+            Py_DECREF(b);
+            return NULL;
+        }
+        self->pending_bytes_count = 0;
+    }
+    if (PyList_Append(self->pending_bytes, b) < 0) {
+        Py_DECREF(b);
+        return NULL;
+    }
+    self->pending_bytes_count += PyBytes_GET_SIZE(b);
+    Py_DECREF(b);
+    if (self->pending_bytes_count > self->chunk_size || needflush) {
+        if (_textiowrapper_writeflush(self) < 0)
+            return NULL;
+    }
+
+    if (needflush) {
+        ret = PyObject_CallMethodObjArgs(self->buffer, _PyIO_str_flush, NULL);
+        if (ret == NULL)
+            return NULL;
+        Py_DECREF(ret);
+    }
+
+    Py_CLEAR(self->snapshot);
+
+    if (self->decoder) {
+        ret = PyObject_CallMethod(self->decoder, "reset", NULL);
+        if (ret == NULL)
+            return NULL;
+        Py_DECREF(ret);
+    }
+
+    return PyLong_FromSsize_t(textlen);
+}
+
+/* Steal a reference to chars and store it in the decoded_char buffer;
+ */
+static void
+textiowrapper_set_decoded_chars(textio *self, PyObject *chars)
+{
+    Py_CLEAR(self->decoded_chars);
+    self->decoded_chars = chars;
+    self->decoded_chars_used = 0;
+}
+
+static PyObject *
+textiowrapper_get_decoded_chars(textio *self, Py_ssize_t n)
+{
+    PyObject *chars;
+    Py_ssize_t avail;
+
+    if (self->decoded_chars == NULL)
+        return PyUnicode_FromStringAndSize(NULL, 0);
+
+    avail = (PyUnicode_GET_SIZE(self->decoded_chars)
+             - self->decoded_chars_used);
+
+    assert(avail >= 0);
+
+    if (n < 0 || n > avail)
+        n = avail;
+
+    if (self->decoded_chars_used > 0 || n < avail) {
+        chars = PyUnicode_FromUnicode(
+            PyUnicode_AS_UNICODE(self->decoded_chars)
+            + self->decoded_chars_used, n);
+        if (chars == NULL)
+            return NULL;
+    }
+    else {
+        chars = self->decoded_chars;
+        Py_INCREF(chars);
+    }
+
+    self->decoded_chars_used += n;
+    return chars;
+}
+
+/* Read and decode the next chunk of data from the BufferedReader.
+ */
+static int
+textiowrapper_read_chunk(textio *self)
+{
+    PyObject *dec_buffer = NULL;
+    PyObject *dec_flags = NULL;
+    PyObject *input_chunk = NULL;
+    PyObject *decoded_chars, *chunk_size;
+    int eof;
+
+    /* The return value is True unless EOF was reached.  The decoded string is
+     * placed in self._decoded_chars (replacing its previous value).  The
+     * entire input chunk is sent to the decoder, though some of it may remain
+     * buffered in the decoder, yet to be converted.
+     */
+
+    if (self->decoder == NULL) {
+        PyErr_SetString(PyExc_IOError, "not readable");
+        return -1;
+    }
+
+    if (self->telling) {
+        /* To prepare for tell(), we need to snapshot a point in the file
+         * where the decoder's input buffer is empty.
+         */
+
+        PyObject *state = PyObject_CallMethodObjArgs(self->decoder,
+                                                     _PyIO_str_getstate, NULL);
+        if (state == NULL)
+            return -1;
+        /* Given this, we know there was a valid snapshot point
+         * len(dec_buffer) bytes ago with decoder state (b'', dec_flags).
+         */
+        if (PyArg_Parse(state, "(OO)", &dec_buffer, &dec_flags) < 0) {
+            Py_DECREF(state);
+            return -1;
+        }
+        Py_INCREF(dec_buffer);
+        Py_INCREF(dec_flags);
+        Py_DECREF(state);
+    }
+
+    /* Read a chunk, decode it, and put the result in self._decoded_chars. */
+    chunk_size = PyLong_FromSsize_t(self->chunk_size);
+    if (chunk_size == NULL)
+        goto fail;
+    input_chunk = PyObject_CallMethodObjArgs(self->buffer,
+        _PyIO_str_read1, chunk_size, NULL);
+    Py_DECREF(chunk_size);
+    if (input_chunk == NULL)
+        goto fail;
+    assert(PyBytes_Check(input_chunk));
+
+    eof = (PyBytes_Size(input_chunk) == 0);
+
+    if (Py_TYPE(self->decoder) == &PyIncrementalNewlineDecoder_Type) {
+        decoded_chars = _PyIncrementalNewlineDecoder_decode(
+            self->decoder, input_chunk, eof);
+    }
+    else {
+        decoded_chars = PyObject_CallMethodObjArgs(self->decoder,
+            _PyIO_str_decode, input_chunk, eof ? Py_True : Py_False, NULL);
+    }
+
+    /* TODO sanity check: isinstance(decoded_chars, unicode) */
+    if (decoded_chars == NULL)
+        goto fail;
+    textiowrapper_set_decoded_chars(self, decoded_chars);
+    if (PyUnicode_GET_SIZE(decoded_chars) > 0)
+        eof = 0;
+
+    if (self->telling) {
+        /* At the snapshot point, len(dec_buffer) bytes before the read, the
+         * next input to be decoded is dec_buffer + input_chunk.
+         */
+        PyObject *next_input = PyNumber_Add(dec_buffer, input_chunk);
+        if (next_input == NULL)
+            goto fail;
+        assert (PyBytes_Check(next_input));
+        Py_DECREF(dec_buffer);
+        Py_CLEAR(self->snapshot);
+        self->snapshot = Py_BuildValue("NN", dec_flags, next_input);
+    }
+    Py_DECREF(input_chunk);
+
+    return (eof == 0);
+
+  fail:
+    Py_XDECREF(dec_buffer);
+    Py_XDECREF(dec_flags);
+    Py_XDECREF(input_chunk);
+    return -1;
+}
+
+static PyObject *
+textiowrapper_read(textio *self, PyObject *args)
+{
+    Py_ssize_t n = -1;
+    PyObject *result = NULL, *chunks = NULL;
+
+    CHECK_INITIALIZED(self);
+
+    if (!PyArg_ParseTuple(args, "|n:read", &n))
+        return NULL;
+
+    CHECK_CLOSED(self);
+
+    if (self->decoder == NULL) {
+        PyErr_SetString(PyExc_IOError, "not readable");
+        return NULL;
+    }
+
+    if (_textiowrapper_writeflush(self) < 0)
+        return NULL;
+
+    if (n < 0) {
+        /* Read everything */
+        PyObject *bytes = PyObject_CallMethod(self->buffer, "read", NULL);
+        PyObject *decoded, *final;
+        if (bytes == NULL)
+            goto fail;
+        decoded = PyObject_CallMethodObjArgs(self->decoder, _PyIO_str_decode,
+                                             bytes, Py_True, NULL);
+        Py_DECREF(bytes);
+        if (decoded == NULL)
+            goto fail;
+
+        result = textiowrapper_get_decoded_chars(self, -1);
+
+        if (result == NULL) {
+            Py_DECREF(decoded);
+            return NULL;
+        }
+
+        final = PyUnicode_Concat(result, decoded);
+        Py_DECREF(result);
+        Py_DECREF(decoded);
+        if (final == NULL)
+            goto fail;
+
+        Py_CLEAR(self->snapshot);
+        return final;
+    }
+    else {
+        int res = 1;
+        Py_ssize_t remaining = n;
+
+        result = textiowrapper_get_decoded_chars(self, n);
+        if (result == NULL)
+            goto fail;
+        remaining -= PyUnicode_GET_SIZE(result);
+
+        /* Keep reading chunks until we have n characters to return */
+        while (remaining > 0) {
+            res = textiowrapper_read_chunk(self);
+            if (res < 0)
+                goto fail;
+            if (res == 0)  /* EOF */
+                break;
+            if (chunks == NULL) {
+                chunks = PyList_New(0);
+                if (chunks == NULL)
+                    goto fail;
+            }
+            if (PyList_Append(chunks, result) < 0)
+                goto fail;
+            Py_DECREF(result);
+            result = textiowrapper_get_decoded_chars(self, remaining);
+            if (result == NULL)
+                goto fail;
+            remaining -= PyUnicode_GET_SIZE(result);
+        }
+        if (chunks != NULL) {
+            if (result != NULL && PyList_Append(chunks, result) < 0)
+                goto fail;
+            Py_CLEAR(result);
+            result = PyUnicode_Join(_PyIO_empty_str, chunks);
+            if (result == NULL)
+                goto fail;
+            Py_CLEAR(chunks);
+        }
+        return result;
+    }
+  fail:
+    Py_XDECREF(result);
+    Py_XDECREF(chunks);
+    return NULL;
+}
+
+
+/* NOTE: `end` must point to the real end of the Py_UNICODE storage,
+   that is to the NUL character. Otherwise the function will produce
+   incorrect results. */
+static Py_UNICODE *
+find_control_char(Py_UNICODE *start, Py_UNICODE *end, Py_UNICODE ch)
+{
+    Py_UNICODE *s = start;
+    for (;;) {
+        while (*s > ch)
+            s++;
+        if (*s == ch)
+            return s;
+        if (s == end)
+            return NULL;
+        s++;
+    }
+}
+
+Py_ssize_t
+_PyIO_find_line_ending(
+    int translated, int universal, PyObject *readnl,
+    Py_UNICODE *start, Py_UNICODE *end, Py_ssize_t *consumed)
+{
+    Py_ssize_t len = end - start;
+
+    if (translated) {
+        /* Newlines are already translated, only search for \n */
+        Py_UNICODE *pos = find_control_char(start, end, '\n');
+        if (pos != NULL)
+            return pos - start + 1;
+        else {
+            *consumed = len;
+            return -1;
+        }
+    }
+    else if (universal) {
+        /* Universal newline search. Find any of \r, \r\n, \n
+         * The decoder ensures that \r\n are not split in two pieces
+         */
+        Py_UNICODE *s = start;
+        for (;;) {
+            Py_UNICODE ch;
+            /* Fast path for non-control chars. The loop always ends
+               since the Py_UNICODE storage is NUL-terminated. */
+            while (*s > '\r')
+                s++;
+            if (s >= end) {
+                *consumed = len;
+                return -1;
+            }
+            ch = *s++;
+            if (ch == '\n')
+                return s - start;
+            if (ch == '\r') {
+                if (*s == '\n')
+                    return s - start + 1;
+                else
+                    return s - start;
+            }
+        }
+    }
+    else {
+        /* Non-universal mode. */
+        Py_ssize_t readnl_len = PyString_GET_SIZE(readnl);
+        unsigned char *nl = (unsigned char *) PyString_AS_STRING(readnl);
+        if (readnl_len == 1) {
+            Py_UNICODE *pos = find_control_char(start, end, nl[0]);
+            if (pos != NULL)
+                return pos - start + 1;
+            *consumed = len;
+            return -1;
+        }
+        else {
+            Py_UNICODE *s = start;
+            Py_UNICODE *e = end - readnl_len + 1;
+            Py_UNICODE *pos;
+            if (e < s)
+                e = s;
+            while (s < e) {
+                Py_ssize_t i;
+                Py_UNICODE *pos = find_control_char(s, end, nl[0]);
+                if (pos == NULL || pos >= e)
+                    break;
+                for (i = 1; i < readnl_len; i++) {
+                    if (pos[i] != nl[i])
+                        break;
+                }
+                if (i == readnl_len)
+                    return pos - start + readnl_len;
+                s = pos + 1;
+            }
+            pos = find_control_char(e, end, nl[0]);
+            if (pos == NULL)
+                *consumed = len;
+            else
+                *consumed = pos - start;
+            return -1;
+        }
+    }
+}
+
+static PyObject *
+_textiowrapper_readline(textio *self, Py_ssize_t limit)
+{
+    PyObject *line = NULL, *chunks = NULL, *remaining = NULL;
+    Py_ssize_t start, endpos, chunked, offset_to_buffer;
+    int res;
+
+    CHECK_CLOSED(self);
+
+    if (_textiowrapper_writeflush(self) < 0)
+        return NULL;
+
+    chunked = 0;
+
+    while (1) {
+        Py_UNICODE *ptr;
+        Py_ssize_t line_len;
+        Py_ssize_t consumed = 0;
+
+        /* First, get some data if necessary */
+        res = 1;
+        while (!self->decoded_chars ||
+               !PyUnicode_GET_SIZE(self->decoded_chars)) {
+            res = textiowrapper_read_chunk(self);
+            if (res < 0)
+                goto error;
+            if (res == 0)
+                break;
+        }
+        if (res == 0) {
+            /* end of file */
+            textiowrapper_set_decoded_chars(self, NULL);
+            Py_CLEAR(self->snapshot);
+            start = endpos = offset_to_buffer = 0;
+            break;
+        }
+
+        if (remaining == NULL) {
+            line = self->decoded_chars;
+            start = self->decoded_chars_used;
+            offset_to_buffer = 0;
+            Py_INCREF(line);
+        }
+        else {
+            assert(self->decoded_chars_used == 0);
+            line = PyUnicode_Concat(remaining, self->decoded_chars);
+            start = 0;
+            offset_to_buffer = PyUnicode_GET_SIZE(remaining);
+            Py_CLEAR(remaining);
+            if (line == NULL)
+                goto error;
+        }
+
+        ptr = PyUnicode_AS_UNICODE(line);
+        line_len = PyUnicode_GET_SIZE(line);
+
+        endpos = _PyIO_find_line_ending(
+            self->readtranslate, self->readuniversal, self->readnl,
+            ptr + start, ptr + line_len, &consumed);
+        if (endpos >= 0) {
+            endpos += start;
+            if (limit >= 0 && (endpos - start) + chunked >= limit)
+                endpos = start + limit - chunked;
+            break;
+        }
+
+        /* We can put aside up to `endpos` */
+        endpos = consumed + start;
+        if (limit >= 0 && (endpos - start) + chunked >= limit) {
+            /* Didn't find line ending, but reached length limit */
+            endpos = start + limit - chunked;
+            break;
+        }
+
+        if (endpos > start) {
+            /* No line ending seen yet - put aside current data */
+            PyObject *s;
+            if (chunks == NULL) {
+                chunks = PyList_New(0);
+                if (chunks == NULL)
+                    goto error;
+            }
+            s = PyUnicode_FromUnicode(ptr + start, endpos - start);
+            if (s == NULL)
+                goto error;
+            if (PyList_Append(chunks, s) < 0) {
+                Py_DECREF(s);
+                goto error;
+            }
+            chunked += PyUnicode_GET_SIZE(s);
+            Py_DECREF(s);
+        }
+        /* There may be some remaining bytes we'll have to prepend to the
+           next chunk of data */
+        if (endpos < line_len) {
+            remaining = PyUnicode_FromUnicode(
+                    ptr + endpos, line_len - endpos);
+            if (remaining == NULL)
+                goto error;
+        }
+        Py_CLEAR(line);
+        /* We have consumed the buffer */
+        textiowrapper_set_decoded_chars(self, NULL);
+    }
+
+    if (line != NULL) {
+        /* Our line ends in the current buffer */
+        self->decoded_chars_used = endpos - offset_to_buffer;
+        if (start > 0 || endpos < PyUnicode_GET_SIZE(line)) {
+            if (start == 0 && Py_REFCNT(line) == 1) {
+                if (PyUnicode_Resize(&line, endpos) < 0)
+                    goto error;
+            }
+            else {
+                PyObject *s = PyUnicode_FromUnicode(
+                        PyUnicode_AS_UNICODE(line) + start, endpos - start);
+                Py_CLEAR(line);
+                if (s == NULL)
+                    goto error;
+                line = s;
+            }
+        }
+    }
+    if (remaining != NULL) {
+        if (chunks == NULL) {
+            chunks = PyList_New(0);
+            if (chunks == NULL)
+                goto error;
+        }
+        if (PyList_Append(chunks, remaining) < 0)
+            goto error;
+        Py_CLEAR(remaining);
+    }
+    if (chunks != NULL) {
+        if (line != NULL && PyList_Append(chunks, line) < 0)
+            goto error;
+        Py_CLEAR(line);
+        line = PyUnicode_Join(_PyIO_empty_str, chunks);
+        if (line == NULL)
+            goto error;
+        Py_DECREF(chunks);
+    }
+    if (line == NULL)
+        line = PyUnicode_FromStringAndSize(NULL, 0);
+
+    return line;
+
+  error:
+    Py_XDECREF(chunks);
+    Py_XDECREF(remaining);
+    Py_XDECREF(line);
+    return NULL;
+}
+
+static PyObject *
+textiowrapper_readline(textio *self, PyObject *args)
+{
+    PyObject *limitobj = NULL;
+    Py_ssize_t limit = -1;
+
+    CHECK_INITIALIZED(self);
+    if (!PyArg_ParseTuple(args, "|O:readline", &limitobj)) {
+        return NULL;
+    }
+    if (limitobj) {
+        if (!PyNumber_Check(limitobj)) {
+            PyErr_Format(PyExc_TypeError,
+                         "integer argument expected, got '%.200s'",
+                         Py_TYPE(limitobj)->tp_name);
+            return NULL;
+        }
+        limit = PyNumber_AsSsize_t(limitobj, PyExc_OverflowError);
+        if (limit == -1 && PyErr_Occurred())
+            return NULL;
+    }
+    return _textiowrapper_readline(self, limit);
+}
+
+/* Seek and Tell */
+
+typedef struct {
+    Py_off_t start_pos;
+    int dec_flags;
+    int bytes_to_feed;
+    int chars_to_skip;
+    char need_eof;
+} cookie_type;
+
+/*
+   To speed up cookie packing/unpacking, we store the fields in a temporary
+   string and call _PyLong_FromByteArray() or _PyLong_AsByteArray (resp.).
+   The following macros define at which offsets in the intermediary byte
+   string the various CookieStruct fields will be stored.
+ */
+
+#define COOKIE_BUF_LEN      (sizeof(Py_off_t) + 3 * sizeof(int) + sizeof(char))
+
+#if defined(WORDS_BIGENDIAN)
+
+# define IS_LITTLE_ENDIAN   0
+
+/* We want the least significant byte of start_pos to also be the least
+   significant byte of the cookie, which means that in big-endian mode we
+   must copy the fields in reverse order. */
+
+# define OFF_START_POS      (sizeof(char) + 3 * sizeof(int))
+# define OFF_DEC_FLAGS      (sizeof(char) + 2 * sizeof(int))
+# define OFF_BYTES_TO_FEED  (sizeof(char) + sizeof(int))
+# define OFF_CHARS_TO_SKIP  (sizeof(char))
+# define OFF_NEED_EOF       0
+
+#else
+
+# define IS_LITTLE_ENDIAN   1
+
+/* Little-endian mode: the least significant byte of start_pos will
+   naturally end up the least significant byte of the cookie. */
+
+# define OFF_START_POS      0
+# define OFF_DEC_FLAGS      (sizeof(Py_off_t))
+# define OFF_BYTES_TO_FEED  (sizeof(Py_off_t) + sizeof(int))
+# define OFF_CHARS_TO_SKIP  (sizeof(Py_off_t) + 2 * sizeof(int))
+# define OFF_NEED_EOF       (sizeof(Py_off_t) + 3 * sizeof(int))
+
+#endif
+
+static int
+textiowrapper_parse_cookie(cookie_type *cookie, PyObject *cookieObj)
+{
+    unsigned char buffer[COOKIE_BUF_LEN];
+    PyLongObject *cookieLong = (PyLongObject *)PyNumber_Long(cookieObj);
+    if (cookieLong == NULL)
+        return -1;
+
+    if (_PyLong_AsByteArray(cookieLong, buffer, sizeof(buffer),
+                            IS_LITTLE_ENDIAN, 0) < 0) {
+        Py_DECREF(cookieLong);
+        return -1;
+    }
+    Py_DECREF(cookieLong);
+
+    memcpy(&cookie->start_pos, buffer + OFF_START_POS, sizeof(cookie->start_pos));
+    memcpy(&cookie->dec_flags, buffer + OFF_DEC_FLAGS, sizeof(cookie->dec_flags));
+    memcpy(&cookie->bytes_to_feed, buffer + OFF_BYTES_TO_FEED, sizeof(cookie->bytes_to_feed));
+    memcpy(&cookie->chars_to_skip, buffer + OFF_CHARS_TO_SKIP, sizeof(cookie->chars_to_skip));
+    memcpy(&cookie->need_eof, buffer + OFF_NEED_EOF, sizeof(cookie->need_eof));
+
+    return 0;
+}
+
+static PyObject *
+textiowrapper_build_cookie(cookie_type *cookie)
+{
+    unsigned char buffer[COOKIE_BUF_LEN];
+
+    memcpy(buffer + OFF_START_POS, &cookie->start_pos, sizeof(cookie->start_pos));
+    memcpy(buffer + OFF_DEC_FLAGS, &cookie->dec_flags, sizeof(cookie->dec_flags));
+    memcpy(buffer + OFF_BYTES_TO_FEED, &cookie->bytes_to_feed, sizeof(cookie->bytes_to_feed));
+    memcpy(buffer + OFF_CHARS_TO_SKIP, &cookie->chars_to_skip, sizeof(cookie->chars_to_skip));
+    memcpy(buffer + OFF_NEED_EOF, &cookie->need_eof, sizeof(cookie->need_eof));
+
+    return _PyLong_FromByteArray(buffer, sizeof(buffer), IS_LITTLE_ENDIAN, 0);
+}
+#undef IS_LITTLE_ENDIAN
+
+static int
+_textiowrapper_decoder_setstate(textio *self, cookie_type *cookie)
+{
+    PyObject *res;
+    /* When seeking to the start of the stream, we call decoder.reset()
+       rather than decoder.getstate().
+       This is for a few decoders such as utf-16 for which the state value
+       at start is not (b"", 0) but e.g. (b"", 2) (meaning, in the case of
+       utf-16, that we are expecting a BOM).
+    */
+    if (cookie->start_pos == 0 && cookie->dec_flags == 0)
+        res = PyObject_CallMethodObjArgs(self->decoder, _PyIO_str_reset, NULL);
+    else
+        res = PyObject_CallMethod(self->decoder, "setstate",
+                                  "((si))", "", cookie->dec_flags);
+    if (res == NULL)
+        return -1;
+    Py_DECREF(res);
+    return 0;
+}
+
+static int
+_textiowrapper_encoder_setstate(textio *self, cookie_type *cookie)
+{
+    PyObject *res;
+    /* Same as _textiowrapper_decoder_setstate() above. */
+    if (cookie->start_pos == 0 && cookie->dec_flags == 0) {
+        res = PyObject_CallMethodObjArgs(self->encoder, _PyIO_str_reset, NULL);
+        self->encoding_start_of_stream = 1;
+    }
+    else {
+        res = PyObject_CallMethodObjArgs(self->encoder, _PyIO_str_setstate,
+                                         _PyIO_zero, NULL);
+        self->encoding_start_of_stream = 0;
+    }
+    if (res == NULL)
+        return -1;
+    Py_DECREF(res);
+    return 0;
+}
+
+static PyObject *
+textiowrapper_seek(textio *self, PyObject *args)
+{
+    PyObject *cookieObj, *posobj;
+    cookie_type cookie;
+    int whence = 0;
+    PyObject *res;
+    int cmp;
+
+    CHECK_INITIALIZED(self);
+
+    if (!PyArg_ParseTuple(args, "O|i:seek", &cookieObj, &whence))
+        return NULL;
+    CHECK_CLOSED(self);
+
+    Py_INCREF(cookieObj);
+
+    if (!self->seekable) {
+        PyErr_SetString(PyExc_IOError,
+                        "underlying stream is not seekable");
+        goto fail;
+    }
+
+    if (whence == 1) {
+        /* seek relative to current position */
+        cmp = PyObject_RichCompareBool(cookieObj, _PyIO_zero, Py_EQ);
+        if (cmp < 0)
+            goto fail;
+
+        if (cmp == 0) {
+            PyErr_SetString(PyExc_IOError,
+                            "can't do nonzero cur-relative seeks");
+            goto fail;
+        }
+
+        /* Seeking to the current position should attempt to
+         * sync the underlying buffer with the current position.
+         */
+        Py_DECREF(cookieObj);
+        cookieObj = PyObject_CallMethod((PyObject *)self, "tell", NULL);
+        if (cookieObj == NULL)
+            goto fail;
+    }
+    else if (whence == 2) {
+        /* seek relative to end of file */
+
+        cmp = PyObject_RichCompareBool(cookieObj, _PyIO_zero, Py_EQ);
+        if (cmp < 0)
+            goto fail;
+
+        if (cmp == 0) {
+            PyErr_SetString(PyExc_IOError,
+                            "can't do nonzero end-relative seeks");
+            goto fail;
+        }
+
+        res = PyObject_CallMethod((PyObject *)self, "flush", NULL);
+        if (res == NULL)
+            goto fail;
+        Py_DECREF(res);
+
+        textiowrapper_set_decoded_chars(self, NULL);
+        Py_CLEAR(self->snapshot);
+        if (self->decoder) {
+            res = PyObject_CallMethod(self->decoder, "reset", NULL);
+            if (res == NULL)
+                goto fail;
+            Py_DECREF(res);
+        }
+
+        res = PyObject_CallMethod(self->buffer, "seek", "ii", 0, 2);
+        Py_XDECREF(cookieObj);
+        return res;
+    }
+    else if (whence != 0) {
+        PyErr_Format(PyExc_ValueError,
+                     "invalid whence (%d, should be 0, 1 or 2)", whence);
+        goto fail;
+    }
+
+    cmp = PyObject_RichCompareBool(cookieObj, _PyIO_zero, Py_LT);
+    if (cmp < 0)
+        goto fail;
+
+    if (cmp == 1) {
+        PyObject *repr = PyObject_Repr(cookieObj);
+        if (repr != NULL) {
+            PyErr_Format(PyExc_ValueError,
+                         "negative seek position %s",
+                         PyString_AS_STRING(repr));
+            Py_DECREF(repr);
+        }
+        goto fail;
+    }
+
+    res = PyObject_CallMethodObjArgs((PyObject *)self, _PyIO_str_flush, NULL);
+    if (res == NULL)
+        goto fail;
+    Py_DECREF(res);
+
+    /* The strategy of seek() is to go back to the safe start point
+     * and replay the effect of read(chars_to_skip) from there.
+     */
+    if (textiowrapper_parse_cookie(&cookie, cookieObj) < 0)
+        goto fail;
+
+    /* Seek back to the safe start point. */
+    posobj = PyLong_FromOff_t(cookie.start_pos);
+    if (posobj == NULL)
+        goto fail;
+    res = PyObject_CallMethodObjArgs(self->buffer,
+                                     _PyIO_str_seek, posobj, NULL);
+    Py_DECREF(posobj);
+    if (res == NULL)
+        goto fail;
+    Py_DECREF(res);
+
+    textiowrapper_set_decoded_chars(self, NULL);
+    Py_CLEAR(self->snapshot);
+
+    /* Restore the decoder to its state from the safe start point. */
+    if (self->decoder) {
+        if (_textiowrapper_decoder_setstate(self, &cookie) < 0)
+            goto fail;
+    }
+
+    if (cookie.chars_to_skip) {
+        /* Just like _read_chunk, feed the decoder and save a snapshot. */
+        PyObject *input_chunk = PyObject_CallMethod(
+            self->buffer, "read", "i", cookie.bytes_to_feed);
+        PyObject *decoded;
+
+        if (input_chunk == NULL)
+            goto fail;
+
+        assert (PyBytes_Check(input_chunk));
+
+        self->snapshot = Py_BuildValue("iN", cookie.dec_flags, input_chunk);
+        if (self->snapshot == NULL) {
+            Py_DECREF(input_chunk);
+            goto fail;
+        }
+
+        decoded = PyObject_CallMethod(self->decoder, "decode",
+                                      "Oi", input_chunk, (int)cookie.need_eof);
+
+        if (decoded == NULL)
+            goto fail;
+
+        textiowrapper_set_decoded_chars(self, decoded);
+
+        /* Skip chars_to_skip of the decoded characters. */
+        if (PyUnicode_GetSize(self->decoded_chars) < cookie.chars_to_skip) {
+            PyErr_SetString(PyExc_IOError, "can't restore logical file position");
+            goto fail;
+        }
+        self->decoded_chars_used = cookie.chars_to_skip;
+    }
+    else {
+        self->snapshot = Py_BuildValue("is", cookie.dec_flags, "");
+        if (self->snapshot == NULL)
+            goto fail;
+    }
+
+    /* Finally, reset the encoder (merely useful for proper BOM handling) */
+    if (self->encoder) {
+        if (_textiowrapper_encoder_setstate(self, &cookie) < 0)
+            goto fail;
+    }
+    return cookieObj;
+  fail:
+    Py_XDECREF(cookieObj);
+    return NULL;
+
+}
+
+static PyObject *
+textiowrapper_tell(textio *self, PyObject *args)
+{
+    PyObject *res;
+    PyObject *posobj = NULL;
+    cookie_type cookie = {0,0,0,0,0};
+    PyObject *next_input;
+    Py_ssize_t chars_to_skip, chars_decoded;
+    PyObject *saved_state = NULL;
+    char *input, *input_end;
+
+    CHECK_INITIALIZED(self);
+    CHECK_CLOSED(self);
+
+    if (!self->seekable) {
+        PyErr_SetString(PyExc_IOError,
+                        "underlying stream is not seekable");
+        goto fail;
+    }
+    if (!self->telling) {
+        PyErr_SetString(PyExc_IOError,
+                        "telling position disabled by next() call");
+        goto fail;
+    }
+
+    if (_textiowrapper_writeflush(self) < 0)
+        return NULL;
+    res = PyObject_CallMethod((PyObject *)self, "flush", NULL);
+    if (res == NULL)
+        goto fail;
+    Py_DECREF(res);
+
+    posobj = PyObject_CallMethod(self->buffer, "tell", NULL);
+    if (posobj == NULL)
+        goto fail;
+
+    if (self->decoder == NULL || self->snapshot == NULL) {
+        assert (self->decoded_chars == NULL || PyUnicode_GetSize(self->decoded_chars) == 0);
+        return posobj;
+    }
+
+#if defined(HAVE_LARGEFILE_SUPPORT)
+    cookie.start_pos = PyLong_AsLongLong(posobj);
+#else
+    cookie.start_pos = PyLong_AsLong(posobj);
+#endif
+    if (PyErr_Occurred())
+        goto fail;
+
+    /* Skip backward to the snapshot point (see _read_chunk). */
+    if (!PyArg_Parse(self->snapshot, "(iO)", &cookie.dec_flags, &next_input))
+        goto fail;
+
+    assert (PyBytes_Check(next_input));
+
+    cookie.start_pos -= PyBytes_GET_SIZE(next_input);
+
+    /* How many decoded characters have been used up since the snapshot? */
+    if (self->decoded_chars_used == 0)  {
+        /* We haven't moved from the snapshot point. */
+        Py_DECREF(posobj);
+        return textiowrapper_build_cookie(&cookie);
+    }
+
+    chars_to_skip = self->decoded_chars_used;
+
+    /* Starting from the snapshot position, we will walk the decoder
+     * forward until it gives us enough decoded characters.
+     */
+    saved_state = PyObject_CallMethodObjArgs(self->decoder,
+                                             _PyIO_str_getstate, NULL);
+    if (saved_state == NULL)
+        goto fail;
+
+    /* Note our initial start point. */
+    if (_textiowrapper_decoder_setstate(self, &cookie) < 0)
+        goto fail;
+
+    /* Feed the decoder one byte at a time.  As we go, note the
+     * nearest "safe start point" before the current location
+     * (a point where the decoder has nothing buffered, so seek()
+     * can safely start from there and advance to this location).
+     */
+    chars_decoded = 0;
+    input = PyBytes_AS_STRING(next_input);
+    input_end = input + PyBytes_GET_SIZE(next_input);
+    while (input < input_end) {
+        PyObject *state;
+        char *dec_buffer;
+        Py_ssize_t dec_buffer_len;
+        int dec_flags;
+
+        PyObject *decoded = PyObject_CallMethod(
+            self->decoder, "decode", "s#", input, 1);
+        if (decoded == NULL)
+            goto fail;
+        assert (PyUnicode_Check(decoded));
+        chars_decoded += PyUnicode_GET_SIZE(decoded);
+        Py_DECREF(decoded);
+
+        cookie.bytes_to_feed += 1;
+
+        state = PyObject_CallMethodObjArgs(self->decoder,
+                                           _PyIO_str_getstate, NULL);
+        if (state == NULL)
+            goto fail;
+        if (!PyArg_Parse(state, "(s#i)", &dec_buffer, &dec_buffer_len, &dec_flags)) {
+            Py_DECREF(state);
+            goto fail;
+        }
+        Py_DECREF(state);
+
+        if (dec_buffer_len == 0 && chars_decoded <= chars_to_skip) {
+            /* Decoder buffer is empty, so this is a safe start point. */
+            cookie.start_pos += cookie.bytes_to_feed;
+            chars_to_skip -= chars_decoded;
+            cookie.dec_flags = dec_flags;
+            cookie.bytes_to_feed = 0;
+            chars_decoded = 0;
+        }
+        if (chars_decoded >= chars_to_skip)
+            break;
+        input++;
+    }
+    if (input == input_end) {
+        /* We didn't get enough decoded data; signal EOF to get more. */
+        PyObject *decoded = PyObject_CallMethod(
+            self->decoder, "decode", "si", "", /* final = */ 1);
+        if (decoded == NULL)
+            goto fail;
+        assert (PyUnicode_Check(decoded));
+        chars_decoded += PyUnicode_GET_SIZE(decoded);
+        Py_DECREF(decoded);
+        cookie.need_eof = 1;
+
+        if (chars_decoded < chars_to_skip) {
+            PyErr_SetString(PyExc_IOError,
+                            "can't reconstruct logical file position");
+            goto fail;
+        }
+    }
+
+    /* finally */
+    Py_XDECREF(posobj);
+    res = PyObject_CallMethod(self->decoder, "setstate", "(O)", saved_state);
+    Py_DECREF(saved_state);
+    if (res == NULL)
+        return NULL;
+    Py_DECREF(res);
+
+    /* The returned cookie corresponds to the last safe start point. */
+    cookie.chars_to_skip = Py_SAFE_DOWNCAST(chars_to_skip, Py_ssize_t, int);
+    return textiowrapper_build_cookie(&cookie);
+
+  fail:
+    Py_XDECREF(posobj);
+    if (saved_state) {
+        PyObject *type, *value, *traceback;
+        PyErr_Fetch(&type, &value, &traceback);
+
+        res = PyObject_CallMethod(self->decoder, "setstate", "(O)", saved_state);
+        Py_DECREF(saved_state);
+        if (res == NULL)
+            return NULL;
+        Py_DECREF(res);
+
+        PyErr_Restore(type, value, traceback);
+    }
+    return NULL;
+}
+
+static PyObject *
+textiowrapper_truncate(textio *self, PyObject *args)
+{
+    PyObject *pos = Py_None;
+    PyObject *res;
+
+    CHECK_INITIALIZED(self)
+    if (!PyArg_ParseTuple(args, "|O:truncate", &pos)) {
+        return NULL;
+    }
+
+    res = PyObject_CallMethodObjArgs((PyObject *) self, _PyIO_str_flush, NULL);
+    if (res == NULL)
+        return NULL;
+    Py_DECREF(res);
+
+    if (pos != Py_None) {
+        res = PyObject_CallMethodObjArgs((PyObject *) self,
+                                          _PyIO_str_seek, pos, NULL);
+        if (res == NULL)
+            return NULL;
+        Py_DECREF(res);
+    }
+
+    return PyObject_CallMethodObjArgs(self->buffer, _PyIO_str_truncate, NULL);
+}
+
+static PyObject *
+textiowrapper_repr(textio *self)
+{
+    PyObject *nameobj, *res;
+    PyObject *namerepr = NULL, *encrepr = NULL;
+
+    CHECK_INITIALIZED(self);
+
+    nameobj = PyObject_GetAttrString((PyObject *) self, "name");
+    if (nameobj == NULL) {
+        if (PyErr_ExceptionMatches(PyExc_AttributeError))
+            PyErr_Clear();
+        else
+            goto error;
+        encrepr = PyObject_Repr(self->encoding);
+        res = PyString_FromFormat("<_io.TextIOWrapper encoding=%s>",
+                                   PyString_AS_STRING(encrepr));
+    }
+    else {
+        encrepr = PyObject_Repr(self->encoding);
+        namerepr = PyObject_Repr(nameobj);
+        res = PyString_FromFormat("<_io.TextIOWrapper name=%s encoding=%s>",
+                                   PyString_AS_STRING(namerepr),
+                                   PyString_AS_STRING(encrepr));
+        Py_DECREF(nameobj);
+    }
+    Py_XDECREF(namerepr);
+    Py_XDECREF(encrepr);
+    return res;
+
+error:
+    Py_XDECREF(namerepr);
+    Py_XDECREF(encrepr);
+    return NULL;
+}
+
+
+/* Inquiries */
+
+static PyObject *
+textiowrapper_fileno(textio *self, PyObject *args)
+{
+    CHECK_INITIALIZED(self);
+    return PyObject_CallMethod(self->buffer, "fileno", NULL);
+}
+
+static PyObject *
+textiowrapper_seekable(textio *self, PyObject *args)
+{
+    CHECK_INITIALIZED(self);
+    return PyObject_CallMethod(self->buffer, "seekable", NULL);
+}
+
+static PyObject *
+textiowrapper_readable(textio *self, PyObject *args)
+{
+    CHECK_INITIALIZED(self);
+    return PyObject_CallMethod(self->buffer, "readable", NULL);
+}
+
+static PyObject *
+textiowrapper_writable(textio *self, PyObject *args)
+{
+    CHECK_INITIALIZED(self);
+    return PyObject_CallMethod(self->buffer, "writable", NULL);
+}
+
+static PyObject *
+textiowrapper_isatty(textio *self, PyObject *args)
+{
+    CHECK_INITIALIZED(self);
+    return PyObject_CallMethod(self->buffer, "isatty", NULL);
+}
+
+static PyObject *
+textiowrapper_flush(textio *self, PyObject *args)
+{
+    CHECK_INITIALIZED(self);
+    CHECK_CLOSED(self);
+    self->telling = self->seekable;
+    if (_textiowrapper_writeflush(self) < 0)
+        return NULL;
+    return PyObject_CallMethod(self->buffer, "flush", NULL);
+}
+
+static PyObject *
+textiowrapper_close(textio *self, PyObject *args)
+{
+    PyObject *res;
+    CHECK_INITIALIZED(self);
+    res = PyObject_CallMethod((PyObject *)self, "flush", NULL);
+    if (res == NULL) {
+        /* If flush() fails, just give up */
+        PyErr_Clear();
+    }
+    else
+        Py_DECREF(res);
+
+    return PyObject_CallMethod(self->buffer, "close", NULL);
+}
+
+static PyObject *
+textiowrapper_iternext(textio *self)
+{
+    PyObject *line;
+
+    CHECK_INITIALIZED(self);
+
+    self->telling = 0;
+    if (Py_TYPE(self) == &PyTextIOWrapper_Type) {
+        /* Skip method call overhead for speed */
+        line = _textiowrapper_readline(self, -1);
+    }
+    else {
+        line = PyObject_CallMethodObjArgs((PyObject *)self,
+                                           _PyIO_str_readline, NULL);
+        if (line && !PyUnicode_Check(line)) {
+            PyErr_Format(PyExc_IOError,
+                         "readline() should have returned an str object, "
+                         "not '%.200s'", Py_TYPE(line)->tp_name);
+            Py_DECREF(line);
+            return NULL;
+        }
+    }
+
+    if (line == NULL)
+        return NULL;
+
+    if (PyUnicode_GET_SIZE(line) == 0) {
+        /* Reached EOF or would have blocked */
+        Py_DECREF(line);
+        Py_CLEAR(self->snapshot);
+        self->telling = self->seekable;
+        return NULL;
+    }
+
+    return line;
+}
+
+static PyObject *
+textiowrapper_name_get(textio *self, void *context)
+{
+    CHECK_INITIALIZED(self);
+    return PyObject_GetAttrString(self->buffer, "name");
+}
+
+static PyObject *
+textiowrapper_closed_get(textio *self, void *context)
+{
+    CHECK_INITIALIZED(self);
+    return PyObject_GetAttr(self->buffer, _PyIO_str_closed);
+}
+
+static PyObject *
+textiowrapper_newlines_get(textio *self, void *context)
+{
+    PyObject *res;
+    CHECK_INITIALIZED(self);
+    if (self->decoder == NULL)
+        Py_RETURN_NONE;
+    res = PyObject_GetAttr(self->decoder, _PyIO_str_newlines);
+    if (res == NULL) {
+        if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
+            PyErr_Clear();
+            Py_RETURN_NONE;
+        }
+        else {
+            return NULL;
+        }
+    }
+    return res;
+}
+
+static PyObject *
+textiowrapper_errors_get(textio *self, void *context)
+{
+    CHECK_INITIALIZED(self);
+    Py_INCREF(self->errors);
+    return self->errors;
+}
+
+static PyObject *
+textiowrapper_chunk_size_get(textio *self, void *context)
+{
+    CHECK_INITIALIZED(self);
+    return PyLong_FromSsize_t(self->chunk_size);
+}
+
+static int
+textiowrapper_chunk_size_set(textio *self, PyObject *arg, void *context)
+{
+    Py_ssize_t n;
+    CHECK_INITIALIZED_INT(self);
+    n = PyNumber_AsSsize_t(arg, PyExc_TypeError);
+    if (n == -1 && PyErr_Occurred())
+        return -1;
+    if (n <= 0) {
+        PyErr_SetString(PyExc_ValueError,
+                        "a strictly positive integer is required");
+        return -1;
+    }
+    self->chunk_size = n;
+    return 0;
+}
+
+static PyMethodDef textiowrapper_methods[] = {
+    {"detach", (PyCFunction)textiowrapper_detach, METH_NOARGS},
+    {"write", (PyCFunction)textiowrapper_write, METH_VARARGS},
+    {"read", (PyCFunction)textiowrapper_read, METH_VARARGS},
+    {"readline", (PyCFunction)textiowrapper_readline, METH_VARARGS},
+    {"flush", (PyCFunction)textiowrapper_flush, METH_NOARGS},
+    {"close", (PyCFunction)textiowrapper_close, METH_NOARGS},
+
+    {"fileno", (PyCFunction)textiowrapper_fileno, METH_NOARGS},
+    {"seekable", (PyCFunction)textiowrapper_seekable, METH_NOARGS},
+    {"readable", (PyCFunction)textiowrapper_readable, METH_NOARGS},
+    {"writable", (PyCFunction)textiowrapper_writable, METH_NOARGS},
+    {"isatty", (PyCFunction)textiowrapper_isatty, METH_NOARGS},
+
+    {"seek", (PyCFunction)textiowrapper_seek, METH_VARARGS},
+    {"tell", (PyCFunction)textiowrapper_tell, METH_NOARGS},
+    {"truncate", (PyCFunction)textiowrapper_truncate, METH_VARARGS},
+    {NULL, NULL}
+};
+
+static PyMemberDef textiowrapper_members[] = {
+    {"encoding", T_OBJECT, offsetof(textio, encoding), READONLY},
+    {"buffer", T_OBJECT, offsetof(textio, buffer), READONLY},
+    {"line_buffering", T_BOOL, offsetof(textio, line_buffering), READONLY},
+    {NULL}
+};
+
+static PyGetSetDef textiowrapper_getset[] = {
+    {"name", (getter)textiowrapper_name_get, NULL, NULL},
+    {"closed", (getter)textiowrapper_closed_get, NULL, NULL},
+/*    {"mode", (getter)TextIOWrapper_mode_get, NULL, NULL},
+*/
+    {"newlines", (getter)textiowrapper_newlines_get, NULL, NULL},
+    {"errors", (getter)textiowrapper_errors_get, NULL, NULL},
+    {"_CHUNK_SIZE", (getter)textiowrapper_chunk_size_get,
+                    (setter)textiowrapper_chunk_size_set, NULL},
+    {NULL}
+};
+
+PyTypeObject PyTextIOWrapper_Type = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    "_io.TextIOWrapper",        /*tp_name*/
+    sizeof(textio), /*tp_basicsize*/
+    0,                          /*tp_itemsize*/
+    (destructor)textiowrapper_dealloc, /*tp_dealloc*/
+    0,                          /*tp_print*/
+    0,                          /*tp_getattr*/
+    0,                          /*tps_etattr*/
+    0,                          /*tp_compare */
+    (reprfunc)textiowrapper_repr,/*tp_repr*/
+    0,                          /*tp_as_number*/
+    0,                          /*tp_as_sequence*/
+    0,                          /*tp_as_mapping*/
+    0,                          /*tp_hash */
+    0,                          /*tp_call*/
+    0,                          /*tp_str*/
+    0,                          /*tp_getattro*/
+    0,                          /*tp_setattro*/
+    0,                          /*tp_as_buffer*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
+            | Py_TPFLAGS_HAVE_GC, /*tp_flags*/
+    textiowrapper_doc,          /* tp_doc */
+    (traverseproc)textiowrapper_traverse, /* tp_traverse */
+    (inquiry)textiowrapper_clear, /* tp_clear */
+    0,                          /* tp_richcompare */
+    offsetof(textio, weakreflist), /*tp_weaklistoffset*/
+    0,                          /* tp_iter */
+    (iternextfunc)textiowrapper_iternext, /* tp_iternext */
+    textiowrapper_methods,      /* tp_methods */
+    textiowrapper_members,      /* tp_members */
+    textiowrapper_getset,       /* tp_getset */
+    0,                          /* tp_base */
+    0,                          /* tp_dict */
+    0,                          /* tp_descr_get */
+    0,                          /* tp_descr_set */
+    offsetof(textio, dict), /*tp_dictoffset*/
+    (initproc)textiowrapper_init, /* tp_init */
+    0,                          /* tp_alloc */
+    PyType_GenericNew,          /* tp_new */
+};