[FFmpeg-devel] [PATCH] avutil/error: Provide better feedback about unknown error codes

[Andrew Sayers]

AVERROR messages should always be less than zero,
and are usually based on three or four ASCII characters.

For error codes that aren't explicitly handled by error.c (e.g. FFERROR_REDO),
print the ASCII code so the user has a little more information.

If a non-negative number somehow gets passed to this function,
print a message saying this shouldn't happen.
---
 libavutil/error.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/libavutil/error.c b/libavutil/error.c
index 90bab7b9d3..c40b54b1f9 100644
--- a/libavutil/error.c
+++ b/libavutil/error.c
@@ -119,6 +119,38 @@ int av_strerror(int errnum, char *errbuf, size_t errbuf_size)
     }
     if (entry) {
         av_strlcpy(errbuf, entry->str, errbuf_size);
+    } else if (
+        -errnum <= 0xFFFFFFFF
+        && ((-errnum >>  0) & 0xFF) >= 0x20 && ((-errnum >>  0) & 0xFF) <= 0x7F
+        && ((-errnum >>  8) & 0xFF) >= 0x20 && ((-errnum >>  8) & 0xFF) <= 0x7F
+        && ((-errnum >> 16) & 0xFF) >= 0x20 && ((-errnum >> 16) & 0xFF) <= 0x7F
+        && (
+           (((-errnum >> 24) & 0xFF) >= 0x20 && ((-errnum >> 24) & 0xFF) <= 0x7F)
+           || !((-errnum >> 24) & 0xFF)
+        )
+    ) {
+        if ((-errnum >> 24) & 0xFF) {
+            snprintf(
+                errbuf,
+                errbuf_size,
+                "Unrecognised error code \"%c%c%c%c\" occurred",
+                (-errnum >>  0) & 0xFF,
+                (-errnum >>  8) & 0xFF,
+                (-errnum >> 16) & 0xFF,
+                (-errnum >> 24) & 0xFF
+            );
+        } else {
+            snprintf(
+                errbuf,
+                errbuf_size,
+                "Unrecognised error code \"%c%c%c\" occurred",
+                (-errnum >>  0) & 0xFF,
+                (-errnum >>  8) & 0xFF,
+                (-errnum >> 16) & 0xFF
+            );
+        }
+    } else if (errnum >= 0) {
+        snprintf(errbuf, errbuf_size, "Impossible: non-negative error number %d occurred", errnum);
     } else {
 #if HAVE_STRERROR_R
         ret = AVERROR(strerror_r(AVUNERROR(errnum), errbuf, errbuf_size));
-- 
2.45.2