bpo-30249: Improve struct.unpack_from() error messages (GH-6059)
diff --git a/Modules/_struct.c b/Modules/_struct.c
index 66f74d6..0539706 100644
--- a/Modules/_struct.c
+++ b/Modules/_struct.c
@@ -1553,7 +1553,8 @@
Values are unpacked according to the format string Struct.format.
-The buffer's size in bytes, minus offset, must be at least Struct.size.
+The buffer's size in bytes, starting at position offset, must be
+at least Struct.size.
See help(struct) for more on format strings.
[clinic start generated code]*/
@@ -1561,16 +1562,38 @@
static PyObject *
Struct_unpack_from_impl(PyStructObject *self, Py_buffer *buffer,
Py_ssize_t offset)
-/*[clinic end generated code: output=57fac875e0977316 input=97ade52422f8962f]*/
+/*[clinic end generated code: output=57fac875e0977316 input=cafd4851d473c894]*/
{
assert(self->s_codes != NULL);
- if (offset < 0)
+ if (offset < 0) {
+ if (offset + self->s_size > 0) {
+ PyErr_Format(StructError,
+ "not enough data to unpack %zd bytes at offset %zd",
+ self->s_size,
+ offset);
+ return NULL;
+ }
+
+ if (offset + buffer->len < 0) {
+ PyErr_Format(StructError,
+ "offset %zd out of range for %zd-byte buffer",
+ offset,
+ buffer->len);
+ return NULL;
+ }
offset += buffer->len;
- if (offset < 0 || buffer->len - offset < self->s_size) {
+ }
+
+ if ((buffer->len - offset) < self->s_size) {
PyErr_Format(StructError,
- "unpack_from requires a buffer of at least %zd bytes",
- self->s_size);
+ "unpack_from requires a buffer of at least %zu bytes for "
+ "unpacking %zd bytes at offset %zd "
+ "(actual buffer size is %zd)",
+ (size_t)self->s_size + (size_t)offset,
+ self->s_size,
+ offset,
+ buffer->len);
return NULL;
}
return s_unpack_internal(self, (char*)buffer->buf + offset);