ConnectionExists: respect the max_concurrent_streams limits

A regression made the code use 'multiplexed' as a boolean instead of the
counter it is intended to be. This made curl try to "over-populate"
connections with new streams.

This regression came with 41fcdf71a1, shipped in curl 7.65.0.

Also, respect the CURLMOPT_MAX_CONCURRENT_STREAMS value in the same
check.

Reported-by: Kunal Ekawde
Fixes #4779
Closes #4784

1 files changed, 10 insertions, 3 deletions

diff --git a/lib/url.c b/lib/url.c
index 4797b5182..b001e87f8 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -1073,7 +1073,7 @@ ConnectionExists(struct Curl_easy *data,
     curr = bundle->conn_list.head;
     while(curr) {
       bool match = FALSE;
-      size_t multiplexed;
+      size_t multiplexed = 0;
 
       /*
        * Note that if we use a HTTP proxy in normal mode (no tunneling), we
@@ -1086,8 +1086,8 @@ ConnectionExists(struct Curl_easy *data,
         /* connect-only or to-be-closed connections will not be reused */
         continue;
 
-      multiplexed = CONN_INUSE(check) &&
-        (bundle->multiuse == BUNDLE_MULTIPLEX);
+      if(bundle->multiuse == BUNDLE_MULTIPLEX)
+        multiplexed = CONN_INUSE(check);
 
       if(canmultiplex) {
         ;
@@ -1347,6 +1347,13 @@ ConnectionExists(struct Curl_easy *data,
                     multiplexed);
               continue;
             }
+            else if(multiplexed >=
+                    Curl_multi_max_concurrent_streams(needle->data->multi)) {
+              infof(data, "client side MAX_CONCURRENT_STREAMS reached"
+                    ", skip (%zu)\n",
+                    multiplexed);
+              continue;
+            }
           }
 #endif
           /* When not multiplexed, we have a match here! */