Fix Content-Length with obsolete line folding

Content-Length with line folding was accepted with invalid input. Treat
obsolete line folding as space and continue parsing

Fixes: https://github.com/nodejs/http-parser/issues/456
PR-URL: https://github.com/nodejs/http-parser/pull/458
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

http_parser.c

@@ -1436,6 +1436,11 @@ reexecute:
             parser->header_state = h_content_length_num;
             break;
 
+          /* when obsolete line folding is encountered for content length
+           * continue to the s_header_value state */
+          case h_content_length_ws:
+            break;
+
           case h_connection:
             /* looking for 'Connection: keep-alive' */
             if (c == 'k') {
@@ -1679,6 +1684,10 @@ reexecute:
       case s_header_value_lws:
       {
         if (ch == ' ' || ch == '\t') {
+          if (parser->header_state == h_content_length_num) {
+              /* treat obsolete line folding as space */
+              parser->header_state = h_content_length_ws;
+          }
           UPDATE_STATE(s_header_value_start);
           REEXECUTE();
         }

test.c

@@ -4203,6 +4203,20 @@ main (void)
       HPE_INVALID_CONTENT_LENGTH,
       HTTP_REQUEST);
 
+  test_simple_type(
+      "POST / HTTP/1.1\r\n"
+      "Content-Length:  42\r\n"
+      " Hello world!\r\n",
+      HPE_INVALID_CONTENT_LENGTH,
+      HTTP_REQUEST);
+
+  test_simple_type(
+      "POST / HTTP/1.1\r\n"
+      "Content-Length:  42\r\n"
+      " \r\n",
+      HPE_OK,
+      HTTP_REQUEST);
+
   //// RESPONSES
 
   test_simple_type("HTP/1.1 200 OK\r\n\r\n", HPE_INVALID_VERSION, HTTP_RESPONSE);