From 3d4b551b7766b3cfa2c6475531dbf273e8272319 Mon Sep 17 00:00:00 2001
From: Anatoly Zaretsky <anatoly.zaretsky@gmail.com>
Date: Sat, 4 May 2019 18:57:07 +0300
Subject: [PATCH] Add an ability to disable body parsing

Currently the on_headers_complete callback can return 0 to proceed
with the response body, 1 to skip the body, and 2 to skip the body
and stop looking for further messages, and this decision on what to do
with the body can only be made inside the on_headers_complete callback.

This commit adds an ability to alter the parser behaviour later
after on_headers_complete pauses the parser and returns 0.
---
 http_parser.c | 49 +++++++++++++++++++++++++++++++++++--------------
 http_parser.h |  8 ++++++++
 2 files changed, 43 insertions(+), 14 deletions(-)

diff --git a/http_parser.c b/http_parser.c
index 48963853..c9fd6477 100644
--- a/http_parser.c
+++ b/http_parser.c
@@ -160,6 +160,25 @@ do {                                                                 \
   }                                                                  \
 } while (0)
 
+#define APPLY_ON_HEADERS_COMPLETE_RESULT(V, DEFAULT)                 \
+do {                                                                 \
+  switch (V) {                                                       \
+    case 0:                                                          \
+      break;                                                         \
+                                                                     \
+    case 2:                                                          \
+      parser->upgrade = 1;                                           \
+                                                                     \
+      /* fall through */                                             \
+    case 1:                                                          \
+      parser->flags |= F_SKIPBODY;                                   \
+      break;                                                         \
+                                                                     \
+    default:                                                         \
+      DEFAULT                                                        \
+  }                                                                  \
+} while (0)
+
 
 #define PROXY_CONNECTION "proxy-connection"
 #define CONNECTION "connection"
@@ -1798,22 +1817,10 @@ size_t http_parser_execute (http_parser *parser,
          * we have to simulate it by handling a change in errno below.
          */
         if (settings->on_headers_complete) {
-          switch (settings->on_headers_complete(parser)) {
-            case 0:
-              break;
-
-            case 2:
-              parser->upgrade = 1;
-
-              /* fall through */
-            case 1:
-              parser->flags |= F_SKIPBODY;
-              break;
-
-            default:
+          APPLY_ON_HEADERS_COMPLETE_RESULT(settings->on_headers_complete(parser),
               SET_ERRNO(HPE_CB_headers_complete);
               RETURN(p - data); /* Error */
-          }
+          );
         }
 
         if (HTTP_PARSER_ERRNO(parser) != HPE_OK) {
@@ -2480,6 +2487,20 @@ http_parser_pause(http_parser *parser, int paused) {
   }
 }
 
+void
+http_parser_continue_after_on_headers_complete(http_parser *parser, int result) {
+  uint32_t nread;
+  assert(parser->state == s_headers_done &&
+         (HTTP_PARSER_ERRNO(parser) == HPE_OK ||
+          HTTP_PARSER_ERRNO(parser) == HPE_PAUSED));
+  APPLY_ON_HEADERS_COMPLETE_RESULT(result,
+    ;
+  );
+  nread = parser->nread; /* used by the SET_ERRNO macro */
+  /* unpause the parser - after all, it says "continue", right? */
+  SET_ERRNO(HPE_OK);
+}
+
 int
 http_body_is_final(const struct http_parser *parser) {
     return parser->state == s_message_done;
diff --git a/http_parser.h b/http_parser.h
index 16b5281d..72b8f295 100644
--- a/http_parser.h
+++ b/http_parser.h
@@ -427,6 +427,14 @@ int http_parser_parse_url(const char *buf, size_t buflen,
 /* Pause or un-pause the parser; a nonzero value pauses */
 void http_parser_pause(http_parser *parser, int paused);
 
+/* Change the parser state as if the on_headers_complete callback
+ * returned `result` and un-pause the parser - only makes sense
+ * between two consecutive invocations of http_parser_execute
+ * when the first one returned due to the on_headers_complete pausing
+ * the parser and returning 0.
+ */
+void http_parser_continue_after_on_headers_complete(http_parser *parser, int result);
+
 /* Checks if this is the final chunk of the body. */
 int http_body_is_final(const http_parser *parser);