[PATCH v4 3/5] dump: Disallow \n in message IDs

[Austin Clements <amdragon@MIT.EDU>]

When we switch to using regular Xapian queries in the dump format, \n
will cause problems, so we disallow it.  Specially, while Xapian can
quote and parse queries containing \n without difficultly, quoted
queries containing \n still span multiple lines, which breaks the
line-orientedness of the dump format.  Strictly speaking, we could
still round-trip these, but it would significantly complicate restore
as well as scripts that deal with tag dumps.  This complexity would
come at absolutely no benefit: because of the RFC 2822 unfolding
rules, no amount of standards negligence can produce a message with a
message ID containing a line break (not even Outlook can do it!).

Hence, we simply disallow it.
---
 notmuch-dump.c       |    9 +++++++++
 test/random-corpus.c |    4 +++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/notmuch-dump.c b/notmuch-dump.c
index d2dad40..29d79da 100644
--- a/notmuch-dump.c
+++ b/notmuch-dump.c
@@ -132,6 +132,15 @@ notmuch_dump_command (unused (void *ctx), int argc, char *argv[])
 	if (output_format == DUMP_FORMAT_SUP) {
 	    fputs (")\n", output);
 	} else {
+	    if (strchr (message_id, '\n')) {
+		/* This will produce a line break in the output, which
+		 * would be difficult to handle in tools.  However,
+		 * it's also impossible to produce an email containing
+		 * a line break in a message ID because of unfolding,
+		 * so we can safely disallow it. */
+		fprintf (stderr, "Error: cannot dump message id containing line break: %s\n", message_id);
+		return 1;
+	    }
 	    if (hex_encode (notmuch, message_id,
 			    &buffer, &buffer_size) != HEX_SUCCESS) {
 		    fprintf (stderr, "Error: failed to hex-encode msg-id %s\n",
diff --git a/test/random-corpus.c b/test/random-corpus.c
index f354d4b..8b7748e 100644
--- a/test/random-corpus.c
+++ b/test/random-corpus.c
@@ -96,7 +96,9 @@ random_utf8_string (void *ctx, size_t char_count)
 	    buf = talloc_realloc (ctx, buf, gchar, buf_size);
 	}
 
-	randomchar = random_unichar ();
+	do {
+	    randomchar = random_unichar ();
+	} while (randomchar == '\n');
 
 	written = g_unichar_to_utf8 (randomchar, buf + offset);
 
-- 
1.7.10.4