Patch #788249: Pass an explicit buffer to setvbuf in PyFile_SetBufSize().

Fixes #603724. Will backport to 2.3.

Include/fileobject.h

@@ -19,6 +19,7 @@ typedef struct {
 	char* f_buf;		/* Allocated readahead buffer */
 	char* f_bufend;		/* Points after last occupied position */
 	char* f_bufptr;		/* Current buffer position */
+	char *f_setbuf;		/* Buffer for setbuf(3) and setvbuf(3) */
 #ifdef WITH_UNIVERSAL_NEWLINES
 	int f_univ_newline;	/* Handle any newline convention */
 	int f_newlinetypes;	/* Types of newlines seen */

Objects/fileobject.c

@@ -283,25 +283,37 @@ PyFile_FromString(char *name, char *mode)
 void
 PyFile_SetBufSize(PyObject *f, int bufsize)
 {
+	PyFileObject *file = (PyFileObject *)f;
 	if (bufsize >= 0) {
-#ifdef HAVE_SETVBUF
 		int type;
 		switch (bufsize) {
 		case 0:
 			type = _IONBF;
 			break;
+#ifdef HAVE_SETVBUF
 		case 1:
 			type = _IOLBF;
 			bufsize = BUFSIZ;
 			break;
+#endif
 		default:
 			type = _IOFBF;
+#ifndef HAVE_SETVBUF
+			bufsize = BUFSIZ;
+#endif
+			break;
+		}
+		fflush(file->f_fp);
+		if (type == _IONBF) {
+			PyMem_Free(file->f_setbuf);
+			file->f_setbuf = NULL;
+		} else {
+			file->f_setbuf = PyMem_Realloc(file->f_setbuf, bufsize);
 		}
-		setvbuf(((PyFileObject *)f)->f_fp, (char *)NULL,
-			type, bufsize);
+#ifdef HAVE_SETVBUF
+		setvbuf(file->f_fp, file->f_setbuf, type, bufsize);
 #else /* !HAVE_SETVBUF */
-		if (bufsize <= 1)
-			setbuf(((PyFileObject *)f)->f_fp, (char *)NULL);
+		setbuf(file->f_fp, file->f_setbuf);
 #endif /* !HAVE_SETVBUF */
 	}
 }
@@ -376,6 +388,7 @@ static PyObject *
 file_close(PyFileObject *f)
 {
 	int sts = 0;
+	PyMem_Free(f->f_setbuf);
 	if (f->f_fp != NULL) {
 		if (f->f_close != NULL) {
 			Py_BEGIN_ALLOW_THREADS
@@ -1928,6 +1941,7 @@ file_init(PyObject *self, PyObject *args, PyObject *kwds)
 	}
 	if (open_the_file(foself, name, mode) == NULL)
 		goto Error;
+	foself->f_setbuf = NULL;
 	PyFile_SetBufSize(self, bufsize);
 	goto Done;