CURL_PUSH_ERROROUT: allow the push callback to fail the parent stream

... by adding support for a new dedicated return code.

Suggested-by: Jonathan Cardoso
Assisted-by: Erik Johansson
URL: https://curl.haxx.se/mail/lib-2020-06/0099.html
Closes #5636

docs/TODO

@@ -36,7 +36,6 @@
  1.17 Add support for IRIs
  1.18 try next proxy if one doesn't work
  1.20 SRV and URI DNS records
- 1.21 Add return code to CURLMOPT_PUSHFUNCTION to fail the connection
  1.22 CURLINFO_PAUSE_STATE
  1.23 Offer API to flush the connection pool
  1.24 TCP Fast Open for windows
@@ -358,13 +357,6 @@
  Offer support for resolving SRV and URI DNS records for libcurl to know which
  server to connect to for various protocols (including HTTP!).
 
-1.21 Add return code to CURLMOPT_PUSHFUNCTION to fail the connection
-
- Allow the callback to return a value that would stop the entire operation,
- like it can be done from most other callbacks.
-
- See https://curl.haxx.se/mail/lib-2020-06/0099.html
-
 1.22 CURLINFO_PAUSE_STATE
 
  Return information about the transfer's current pause state, in both

docs/libcurl/opts/CURLMOPT_PUSHFUNCTION.3

@@ -86,6 +86,9 @@ the ownership of the CURL handle has been taken over by the application.
 .IP "CURL_PUSH_DENY (1)"
 The callback denies the stream and no data for this will reach the
 application, the easy handle will be destroyed by libcurl.
+.IP "CURL_PUSH_ERROROUT (2)"
+Returning this will reject the pushed stream and return an error back on the
+parent stream making it get closed with an error. (Added in curl 7.72.0)
 .IP *
 All other return codes are reserved for future use.
 .SH DEFAULT

docs/libcurl/symbols-in-versions

@@ -892,6 +892,7 @@ CURL_PROGRESSFUNC_CONTINUE      7.68.0
 CURL_PROGRESS_BAR               7.1.1         -           7.4.1
 CURL_PROGRESS_STATS             7.1.1         -           7.4.1
 CURL_PUSH_DENY                  7.44.0
+CURL_PUSH_ERROROUT              7.72.0
 CURL_PUSH_OK                    7.44.0
 CURL_READFUNC_ABORT             7.12.1
 CURL_READFUNC_PAUSE             7.18.0

include/curl/multi.h

@@ -427,12 +427,14 @@ CURL_EXTERN CURLMcode curl_multi_assign(CURLM *multi_handle,
  * Name: curl_push_callback
  *
  * Desc: This callback gets called when a new stream is being pushed by the
- *       server. It approves or denies the new stream.
+ *       server. It approves or denies the new stream. It can also decide
+ *       to completely fail the connection.
  *
- * Returns: CURL_PUSH_OK or CURL_PUSH_DENY.
+ * Returns: CURL_PUSH_OK, CURL_PUSH_DENY or CURL_PUSH_ERROROUT
  */
-#define CURL_PUSH_OK   0
-#define CURL_PUSH_DENY 1
+#define CURL_PUSH_OK       0
+#define CURL_PUSH_DENY     1
+#define CURL_PUSH_ERROROUT 2 /* added in 7.72.0 */
 
 struct curl_pushheaders;  /* forward declaration only */
 

lib/http2.c

@@ -514,7 +514,7 @@ static int push_promise(struct Curl_easy *data,
                         struct connectdata *conn,
                         const nghttp2_push_promise *frame)
 {
-  int rv;
+  int rv; /* one of the CURL_PUSH_* defines */
   H2BUGF(infof(data, "PUSH_PROMISE received, stream %u!\n",
                frame->promised_stream_id));
   if(data->multi->push_cb) {
@@ -528,7 +528,7 @@ static int push_promise(struct Curl_easy *data,
     struct Curl_easy *newhandle = duphandle(data);
     if(!newhandle) {
       infof(data, "failed to duplicate handle\n");
-      rv = 1; /* FAIL HARD */
+      rv = CURL_PUSH_DENY; /* FAIL HARD */
       goto fail;
     }
 
@@ -541,13 +541,15 @@ static int push_promise(struct Curl_easy *data,
     if(!stream) {
       failf(data, "Internal NULL stream!\n");
       (void)Curl_close(&newhandle);
-      rv = 1;
+      rv = CURL_PUSH_DENY;
       goto fail;
     }
 
     rv = set_transfer_url(newhandle, &heads);
-    if(rv)
+    if(rv) {
+      rv = CURL_PUSH_DENY;
       goto fail;
+    }
 
     Curl_set_in_callback(data, true);
     rv = data->multi->push_cb(data, newhandle,
@@ -563,6 +565,7 @@ static int push_promise(struct Curl_easy *data,
     stream->push_headers_used = 0;
 
     if(rv) {
+      DEBUGASSERT((rv > CURL_PUSH_OK) && (rv <= CURL_PUSH_ERROROUT));
       /* denied, kill off the new handle again */
       http2_stream_free(newhandle->req.protop);
       newhandle->req.protop = NULL;
@@ -583,7 +586,7 @@ static int push_promise(struct Curl_easy *data,
       http2_stream_free(newhandle->req.protop);
       newhandle->req.protop = NULL;
       Curl_close(&newhandle);
-      rv = 1;
+      rv = CURL_PUSH_DENY;
       goto fail;
     }
 
@@ -595,12 +598,13 @@ static int push_promise(struct Curl_easy *data,
       infof(data, "failed to set user_data for stream %d\n",
             frame->promised_stream_id);
       DEBUGASSERT(0);
+      rv = CURL_PUSH_DENY;
       goto fail;
     }
   }
   else {
     H2BUGF(infof(data, "Got PUSH_PROMISE, ignore it!\n"));
-    rv = 1;
+    rv = CURL_PUSH_DENY;
   }
   fail:
   return rv;
@@ -737,11 +741,16 @@ static int on_frame_recv(nghttp2_session *session, const nghttp2_frame *frame,
   case NGHTTP2_PUSH_PROMISE:
     rv = push_promise(data_s, conn, &frame->push_promise);
     if(rv) { /* deny! */
-      rv = nghttp2_submit_rst_stream(session, NGHTTP2_FLAG_NONE,
+      int h2;
+      DEBUGASSERT((rv > CURL_PUSH_OK) && (rv <= CURL_PUSH_ERROROUT));
+      h2 = nghttp2_submit_rst_stream(session, NGHTTP2_FLAG_NONE,
                                      frame->push_promise.promised_stream_id,
                                      NGHTTP2_CANCEL);
-      if(nghttp2_is_fatal(rv)) {
-        return rv;
+      if(nghttp2_is_fatal(h2))
+        return NGHTTP2_ERR_CALLBACK_FAILURE;
+      else if(rv == CURL_PUSH_ERROROUT) {
+        DEBUGF(infof(data_s, "Fail the parent stream (too)\n"));
+        return NGHTTP2_ERR_CALLBACK_FAILURE;
       }
     }
     break;