mysnprintf.c: Massive rewrite of PyOS_snprintf and PyOS_vsnprintf, to

use wrappers on all platforms, to make this as consistent as possible x-
platform (in particular, make sure there's at least one \0 byte in
the output buffer).  Also document more of the truth about what these do.

getargs.c, seterror():  Three computations of remaining buffer size were
backwards, thus telling PyOS_snprintf the buffer is larger than it
actually is.  This matters a lot now that PyOS_snprintf ensures there's a
trailing \0 byte (because it didn't get the truth about the buffer size,
it was storing \0 beyond the true end of the buffer).

sysmodule.c, mywrite():  Simplify, now that PyOS_vsnprintf guarantees to
produce a \0 byte.

1 files changed, 1 insertions, 8 deletions

diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index faa63ab7a3..ff49adcece 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -1025,18 +1025,11 @@ mywrite(char *name, FILE *fp, const char *format, va_list va)
 		char buffer[1001];
 		const int written = PyOS_vsnprintf(buffer, sizeof(buffer),
 						   format, va);
-		const int trouble = written < 0 || written >= sizeof(buffer);
-		if (trouble) {
-			/* Ensure there's a trailing null byte -- MS
-			   vsnprintf fills the buffer to the very end
-			   if it's not big enough. */
-			buffer[sizeof(buffer) - 1] = '\0';
-		}
 		if (PyFile_WriteString(buffer, file) != 0) {
 			PyErr_Clear();
 			fputs(buffer, fp);
 		}
-		if (trouble) {
+		if (written < 0 || written >= sizeof(buffer)) {
 			const char *truncated = "... truncated";
 			if (PyFile_WriteString(truncated, file) != 0) {
 				PyErr_Clear();