imap-send: increase command size limit

nfvasprintf() has a 8KB limit, but it's not relevant, as its result is
combined with other strings and added to a 1KB buffer by its caller.
That 1KB limit is not mentioned in RFC 9051, which specifies IMAP.

While 1KB is plenty for user names, passwords and mailbox names,
there's no point in limiting our commands like that.  Call xstrvfmt()
instead of open-coding it and use strbuf to format the command to
send, as we need its length.  Fail hard if it exceeds INT_MAX, because
socket_write() can't take more than that.

Suggested-by: Jeff King <[email protected]>
Signed-off-by: René Scharfe <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: rscharfe

imap-send.c

@@ -68,20 +68,6 @@ static void imap_warn(const char *, ...);
 
 static char *next_arg(char **);
 
-static int nfvasprintf(char **strp, const char *fmt, va_list ap)
-{
-	int len;
-	char tmp[8192];
-
-	len = vsnprintf(tmp, sizeof(tmp), fmt, ap);
-	if (len < 0)
-		die("Fatal: Out of memory");
-	if (len >= sizeof(tmp))
-		die("imap command overflow!");
-	*strp = xmemdupz(tmp, len);
-	return len;
-}
-
 struct imap_server_conf {
 	const char *name;
 	const char *tunnel;
@@ -503,11 +489,11 @@ static struct imap_cmd *issue_imap_cmd(struct imap_store *ctx,
 {
 	struct imap *imap = ctx->imap;
 	struct imap_cmd *cmd;
-	int n, bufl;
-	char buf[1024];
+	int n;
+	struct strbuf buf = STRBUF_INIT;
 
 	cmd = xmalloc(sizeof(struct imap_cmd));
-	nfvasprintf(&cmd->cmd, fmt, ap);
+	cmd->cmd = xstrvfmt(fmt, ap);
 	cmd->tag = ++imap->nexttag;
 
 	if (cb)
@@ -519,27 +505,30 @@ static struct imap_cmd *issue_imap_cmd(struct imap_store *ctx,
 		get_cmd_result(ctx, NULL);
 
 	if (!cmd->cb.data)
-		bufl = xsnprintf(buf, sizeof(buf), "%d %s\r\n", cmd->tag, cmd->cmd);
+		strbuf_addf(&buf, "%d %s\r\n", cmd->tag, cmd->cmd);
 	else
-		bufl = xsnprintf(buf, sizeof(buf), "%d %s{%d%s}\r\n",
-				 cmd->tag, cmd->cmd, cmd->cb.dlen,
-				 CAP(LITERALPLUS) ? "+" : "");
+		strbuf_addf(&buf, "%d %s{%d%s}\r\n", cmd->tag, cmd->cmd,
+			    cmd->cb.dlen, CAP(LITERALPLUS) ? "+" : "");
+	if (buf.len > INT_MAX)
+		die("imap command overflow!");
 
 	if (0 < verbosity) {
 		if (imap->num_in_progress)
 			printf("(%d in progress) ", imap->num_in_progress);
 		if (!starts_with(cmd->cmd, "LOGIN"))
-			printf(">>> %s", buf);
+			printf(">>> %s", buf.buf);
 		else
 			printf(">>> %d LOGIN <user> <pass>\n", cmd->tag);
 	}
-	if (socket_write(&imap->buf.sock, buf, bufl) != bufl) {
+	if (socket_write(&imap->buf.sock, buf.buf, buf.len) != buf.len) {
 		free(cmd->cmd);
 		free(cmd);
 		if (cb)
 			free(cb->data);
+		strbuf_release(&buf);
 		return NULL;
 	}
+	strbuf_release(&buf);
 	if (cmd->cb.data) {
 		if (CAP(LITERALPLUS)) {
 			n = socket_write(&imap->buf.sock, cmd->cb.data, cmd->cb.dlen);