Python/codecs.c

/* ------------------------------------------------------------------------

   Python Codec Registry and support functions

Written by Marc-Andre Lemburg (mal@lemburg.com).

(c) Copyright CNRI, All Rights Reserved. NO WARRANTY.

   ------------------------------------------------------------------------ */

#include "Python.h"
#include <ctype.h>

/* --- Globals ------------------------------------------------------------ */

static PyObject *_PyCodec_SearchPath;
static PyObject *_PyCodec_SearchCache;

/* Flag used for lazy import of the standard encodings package */
static int import_encodings_called = 0;

/* --- Codec Registry ----------------------------------------------------- */

/* Import the standard encodings package which will register the first
   codec search function. 

   This is done in a lazy way so that the Unicode implementation does
   not downgrade startup time of scripts not needing it.

   Errors are silently ignored by this function. Only one try is made.

*/

static
void import_encodings() 
{
    PyObject *mod;
    
    import_encodings_called = 1;
    mod = PyImport_ImportModule("encodings");
    if (mod == NULL) {
	PyErr_Clear();
	return;
    }
    Py_DECREF(mod);
}

/* Register a new codec search function.

   The search_function's refcount is incremented by this function. */

int PyCodec_Register(PyObject *search_function)
{
    if (!import_encodings_called)
	import_encodings();
    if (search_function == NULL) {
	PyErr_BadArgument();
	return -1;
    }
    if (!PyCallable_Check(search_function)) {
	PyErr_SetString(PyExc_TypeError,
			"argument must be callable");
	return -1;
    }
    return PyList_Append(_PyCodec_SearchPath, search_function);
}

static
PyObject *lowercasestring(const char *string)
{
    register int i;
    int len = strlen(string);
    char *p;
    PyObject *v;
    
    v = PyString_FromStringAndSize(NULL, len);
    if (v == NULL)
	return NULL;
    p = PyString_AS_STRING(v);
    for (i = 0; i < len; i++)
	p[i] = tolower(string[i]);
    return v;
}

/* Lookup the given encoding and return a tuple providing the codec
   facilities.

   The encoding string is looked up converted to all lower-case
   characters. This makes encodings looked up through this mechanism
   effectively case-insensitive.

   If no codec is found, a KeyError is set and NULL returned.  */

PyObject *_PyCodec_Lookup(const char *encoding)
{
    PyObject *result, *args = NULL, *v;
    int i, len;

    if (!import_encodings_called)
	import_encodings();

    /* Convert the encoding to a lower-cased Python string */
    v = lowercasestring(encoding);
    if (v == NULL)
	goto onError;
    PyString_InternInPlace(&v);

    /* First, try to lookup the name in the registry dictionary */
    result = PyDict_GetItem(_PyCodec_SearchCache, v);
    if (result != NULL) {
	Py_INCREF(result);
	return result;
    }
    
    /* Next, scan the search functions in order of registration */
    len = PyList_Size(_PyCodec_SearchPath);
    if (len < 0)
	goto onError;

    args = PyTuple_New(1);
    if (args == NULL)
	goto onError;
    PyTuple_SET_ITEM(args,0,v);

    for (i = 0; i < len; i++) {
	PyObject *func;
	
	func = PyList_GetItem(_PyCodec_SearchPath, i);
	if (func == NULL)
	    goto onError;
	result = PyEval_CallObject(func,args);
	if (result == NULL)
	    goto onError;
	if (result == Py_None) {
	    Py_DECREF(result);
	    continue;
	}
	if (!PyTuple_Check(result) || PyTuple_GET_SIZE(result) != 4) {
	    PyErr_SetString(PyExc_TypeError,
			    "codec search functions must return 4-tuples");
	    Py_DECREF(result);
	    goto onError;
	}
	break;
    }
    if (i == len) {
	/* XXX Perhaps we should cache misses too ? */
	PyErr_SetString(PyExc_LookupError,
			"unkown encoding");
	goto onError;
    }

    /* Cache and return the result */
    PyDict_SetItem(_PyCodec_SearchCache, v, result);
    Py_DECREF(args);
    return result;

 onError:
    Py_XDECREF(args);
    return NULL;
}

static
PyObject *args_tuple(PyObject *object,
		     const char *errors)
{
    PyObject *args;
    
    args = PyTuple_New(1 + (errors != NULL));
    if (args == NULL)
	return NULL;
    Py_INCREF(object);
    PyTuple_SET_ITEM(args,0,object);
    if (errors) {
	PyObject *v;
	
	v = PyString_FromString(errors);
	if (v == NULL) {
	    Py_DECREF(args);
	    return NULL;
	}
	PyTuple_SET_ITEM(args, 1, v);
    }
    return args;
}

/* Build a codec by calling factory(stream[,errors]) or just
   factory(errors) depending on whether the given parameters are
   non-NULL. */

static
PyObject *build_stream_codec(PyObject *factory,
			     PyObject *stream,
			     const char *errors)
{
    PyObject *args, *codec;

    args = args_tuple(stream, errors);
    if (args == NULL)
	return NULL;
    
    codec = PyEval_CallObject(factory, args);
    Py_DECREF(args);
    return codec;
}

/* Convenience APIs to query the Codec registry. 
   
   All APIs return a codec object with incremented refcount.
   
 */

PyObject *PyCodec_Encoder(const char *encoding)
{
    PyObject *codecs;
    PyObject *v;

    codecs = _PyCodec_Lookup(encoding);
    if (codecs == NULL)
	goto onError;
    v = PyTuple_GET_ITEM(codecs,0);
    Py_INCREF(v);
    return v;

 onError:
    return NULL;
}

PyObject *PyCodec_Decoder(const char *encoding)
{
    PyObject *codecs;
    PyObject *v;

    codecs = _PyCodec_Lookup(encoding);
    if (codecs == NULL)
	goto onError;
    v = PyTuple_GET_ITEM(codecs,1);
    Py_INCREF(v);
    return v;

 onError:
    return NULL;
}

PyObject *PyCodec_StreamReader(const char *encoding,
			       PyObject *stream,
			       const char *errors)
{
    PyObject *codecs;

    codecs = _PyCodec_Lookup(encoding);
    if (codecs == NULL)
	goto onError;
    return build_stream_codec(PyTuple_GET_ITEM(codecs,2),stream,errors);

 onError:
    return NULL;
}

PyObject *PyCodec_StreamWriter(const char *encoding,
			       PyObject *stream,
			       const char *errors)
{
    PyObject *codecs;

    codecs = _PyCodec_Lookup(encoding);
    if (codecs == NULL)
	goto onError;
    return build_stream_codec(PyTuple_GET_ITEM(codecs,3),stream,errors);

 onError:
    return NULL;
}

/* Encode an object (e.g. an Unicode object) using the given encoding
   and return the resulting encoded object (usually a Python string).

   errors is passed to the encoder factory as argument if non-NULL. */

PyObject *PyCodec_Encode(PyObject *object,
			 const char *encoding,
			 const char *errors)
{
    PyObject *encoder = NULL;
    PyObject *args = NULL, *result;
    PyObject *v;

    encoder = PyCodec_Encoder(encoding);
    if (encoder == NULL)
	goto onError;

    args = args_tuple(object, errors);
    if (args == NULL)
	goto onError;
    
    result = PyEval_CallObject(encoder,args);
    if (result == NULL)
	goto onError;

    if (!PyTuple_Check(result) || 
	PyTuple_GET_SIZE(result) != 2) {
	PyErr_SetString(PyExc_TypeError,
			"encoder must return a tuple (object,integer)");
	goto onError;
    }
    v = PyTuple_GET_ITEM(result,0);
    Py_INCREF(v);
    /* We don't check or use the second (integer) entry. */

    Py_DECREF(args);
    Py_DECREF(encoder);
    Py_DECREF(result);
    return v;
	
 onError:
    Py_XDECREF(args);
    Py_XDECREF(encoder);
    return NULL;
}

/* Decode an object (usually a Python string) using the given encoding
   and return an equivalent object (e.g. an Unicode object).

   errors is passed to the decoder factory as argument if non-NULL. */

PyObject *PyCodec_Decode(PyObject *object,
			 const char *encoding,
			 const char *errors)
{
    PyObject *decoder = NULL;
    PyObject *args = NULL, *result = NULL;
    PyObject *v;

    decoder = PyCodec_Decoder(encoding);
    if (decoder == NULL)
	goto onError;

    args = args_tuple(object, errors);
    if (args == NULL)
	goto onError;
    
    result = PyEval_CallObject(decoder,args);
    if (result == NULL)
	goto onError;
    if (!PyTuple_Check(result) || 
	PyTuple_GET_SIZE(result) != 2) {
	PyErr_SetString(PyExc_TypeError,
			"decoder must return a tuple (object,integer)");
	goto onError;
    }
    v = PyTuple_GET_ITEM(result,0);
    Py_INCREF(v);
    /* We don't check or use the second (integer) entry. */

    Py_DECREF(args);
    Py_DECREF(decoder);
    Py_DECREF(result);
    return v;
	
 onError:
    Py_XDECREF(args);
    Py_XDECREF(decoder);
    Py_XDECREF(result);
    return NULL;
}

void _PyCodecRegistry_Init()
{
    if (_PyCodec_SearchPath == NULL)
	_PyCodec_SearchPath = PyList_New(0);
    if (_PyCodec_SearchCache == NULL)
	_PyCodec_SearchCache = PyDict_New();
    if (_PyCodec_SearchPath == NULL || 
	_PyCodec_SearchCache == NULL)
	Py_FatalError("can't intialize codec registry");
}

void _PyCodecRegistry_Fini()
{
    Py_XDECREF(_PyCodec_SearchPath);
    Py_XDECREF(_PyCodec_SearchCache);
}