From: Daniel Stenberg <daniel@haxx.se>
Date: Tue, 4 Jun 2024 15:00:05 +0000 (+0200)
Subject: url: allow DoH transfers to override max connection limit
X-Git-Tag: curl-8_9_0~297
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=b049388d473a9a0189f3180e57e04a39a3793382;p=thirdparty%2Fcurl.git

url: allow DoH transfers to override max connection limit

When reaching the set maximum limit of allowed connections, allow a new
connection anyway if the transfer is created for the (internal) purpose
of doing a DoH name resolve. Otherwise, unrelated "normal" transfers can
starve out new DoH requests making it impossible to name resolve for new
transfers.

Bug: https://curl.se/mail/lib-2024-06/0001.html
Reported-by: kartatz
Closes #13880
---

diff --git a/lib/url.c b/lib/url.c
index 41e35e1531..4eabf0c876 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -3662,10 +3662,16 @@ static CURLcode create_conn(struct Curl_easy *data,
       conn_candidate = Curl_conncache_extract_oldest(data);
       if(conn_candidate)
         Curl_disconnect(data, conn_candidate, FALSE);
-      else {
-        infof(data, "No connections available in cache");
-        connections_available = FALSE;
-      }
+      else
+#ifndef CURL_DISABLE_DOH
+        if(data->set.dohfor)
+          infof(data, "Allowing DoH to override max connection limit");
+        else
+#endif
+        {
+          infof(data, "No connections available in cache");
+          connections_available = FALSE;
+        }
     }
 
     if(!connections_available) {