rfc822: Fix bug parsing headers when body begins with linear whitespace

next_header_parse() had a bug which would mis-parse an extra header if the
body of the message began with a linear whitespace character (space or
tab).  This patch fixes it and adds a suitable testcase.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

ccan/rfc822/rfc822.c

@@ -150,29 +150,33 @@ static struct rfc822_header *next_header_parse(struct rfc822_msg *msg)
 	if (msg->body && (msg->remainder >= msg->body))
 		return NULL;
 
-	eh = h = msg->remainder;
-	do {
-		eh = next_line(eh, msg->end);
-	} while ((eh < msg->end) && rfc822_iswsp(*eh));
-
-	if (eh >= msg->end)
-		msg->remainder = NULL;
-	else
-		msg->remainder = eh;
+	h = msg->remainder;
+	eh = next_line(h, msg->end);
 
 	ev = eh;
 	if ((ev > h) && (ev[-1] == '\n'))
 		ev--;
 	if ((ev > h) && (ev[-1] == '\r'))
 		ev--;
-
 	if (ev == h) {
 		/* Found the end of the headers */
+
+		assert(!msg->body || (msg->body == eh));
+
 		if (eh < msg->end)
 			msg->body = eh;
 		return NULL;
 	}
 
+	while ((eh < msg->end) && rfc822_iswsp(*eh))
+		eh = next_line(eh, msg->end);
+
+	if (eh >= msg->end)
+		msg->remainder = NULL;
+	else
+		msg->remainder = eh;
+
+
 	hi = talloc_zero(msg, struct rfc822_header);
 	ALLOC_CHECK(hi, NULL);
 

ccan/rfc822/test/testdata.h

@@ -53,11 +53,15 @@ AEXAMPLE(test_msg_nlnl_crlf);
 const char test_msg_nlnl_mixed_body[] = "Message containing both \n\n and \r\n\r\n inside body\n\r\n";
 AEXAMPLE(test_msg_nlnl_mixed);
 
+#define test_msg_space_body_hdrs test_msg_1_hdrs
+const char test_msg_space_body_body[] = " Message with LWS at start of body\n";
+AEXAMPLE(test_msg_space_body);
 
 #define for_each_aexample(_e)				     \
 	foreach_ptr((_e), &test_msg_1, &test_msg_empty_body, \
 		    &test_msg_nlnl_lf, &test_msg_nlnl_crlf, \
-		    &test_msg_nlnl_mixed)
+		    &test_msg_nlnl_mixed, \
+		    &test_msg_space_body)
 
 #define for_each_aexample_buf(_e, _buf, _len)	\
 	for_each_aexample((_e)) 		\