Fix truncation of long filenames in attachments

Currently mutt truncates long filenames in attachments and doesn't
take into account UTF-8 character size. If filename is truncated in
the middle of multi-byte UTF-8 character (last character is bad),
then some mail clients assume whole attachment name bad and don't
display its name (use 'Noname' instead).

Filenames can be up to 255 *characters* long depending on used
filesystem. ReiserFS, NFTS, FAT, APFS and some other supports up to
255 characters.
In the worst case 255 characters in UTF-8 will take 255*4 = 1020
bytes. Every non-ascii byte in the filename will be encoded using 3
bytes (for example, %8D).
So 'Content-Disposition' will take in the worst case up to: 1020*3 =
3060 bytes. Therefore even LONG_STRING (1024) isn't enough.

Co-authored-by: Richard Russon <rich@flatcap.org>

diff --git a/sendlib.c b/sendlib.c
index 752ef940a164634b7962b866a6761cdcacc2eda5..a7ba320faebf5e4b19d46d39005ac77cf5471a62 100644 (file)
--- a/sendlib.c
+++ b/sendlib.c
@@ -371,8 +371,7 @@ int mutt_write_mime_header(struct Body *a, FILE *fp)
 
       fputc(';', fp);
 
-      char buf[256];
-      buf[0] = '\0';
+      char buf[8192] = { 0 };
       tmp = mutt_str_strdup(np->value);
       const int encode = rfc2231_encode_string(&tmp);
       mutt_addr_cat(buf, sizeof(buf), tmp, MimeSpecials);