easy: allow connect-only handle reuse with easy_perform

- Detach and disconnect an attached connection before performing.

Prior to this change it was not possible to safely reuse an easy handle
with an attached connection in a second call to curl_easy_perform. The
only known case of this is a connect-only type handle where the
connection was detached when curl_easy_perform returned, only to be
reattached by either curl_easy_send/recv.

This commit effectively reverts 2f8ecd5d and be82a360, the latter of
which treated the reuse as an error. Prior to that change undefined
behavior may occur in such a case.

Bug: https://curl.se/mail/lib-2025-01/0044.html
Reported-by: Aleksander Mazur
Closes https://github.com/curl/curl/pull/16008

diff --git a/docs/libcurl/opts/CURLOPT_CONNECT_ONLY.md b/docs/libcurl/opts/CURLOPT_CONNECT_ONLY.md
index 90d17c7e9de68c63c3b2a8dc400271b51b1ca086..61cf2b802cd7aac6663e6430dfba94dc8bc6cb8f 100644 (file)
--- a/docs/libcurl/opts/CURLOPT_CONNECT_ONLY.md
+++ b/docs/libcurl/opts/CURLOPT_CONNECT_ONLY.md
@@ -34,8 +34,8 @@ and then return.
 
 The option can be used to simply test a connection to a server, but is more
 useful when used with the CURLINFO_ACTIVESOCKET(3) option to
-curl_easy_getinfo(3) as the library can set up the connection and then the
-application can obtain the most recently used socket for special data
+curl_easy_getinfo(3) as the library can set up the connection and then
+the application can obtain the most recently used socket for special data
 transfers.
 
 Since 7.86.0, this option can be set to '2' and if HTTP or WebSocket are used,
@@ -43,16 +43,13 @@ libcurl performs the request and reads all response headers before handing
 over control to the application.
 
 Transfers marked connect only do not reuse any existing connections and
-connections marked connect only are not allowed to get reused. For this
-reason, an easy handle cannot be reused for a second transfer when
-CURLOPT_CONNECT_ONLY(3) is set, it must be closed with curl_easy_cleanup(3)
-once the application is done with it.
+connections marked connect only are not allowed to get reused.
 
 If the connect only transfer is done using the multi interface, the particular
 easy handle must remain added to the multi handle for as long as the
 application wants to use it. Once it has been removed with
-curl_multi_remove_handle(3), curl_easy_send(3) and curl_easy_recv(3) do not
-function.
+curl_multi_remove_handle(3), curl_easy_send(3) and
+curl_easy_recv(3) do not function.
 
 # DEFAULT
 

diff --git a/lib/easy.c b/lib/easy.c
index 657e007a94bb5f4a1ac4ce10a969a0e86ffc9613..1573a9d9297b01be3d370171e318a39b5158243e 100644 (file)
--- a/lib/easy.c
+++ b/lib/easy.c
@@ -751,11 +751,6 @@ static CURLcode easy_perform(struct Curl_easy *data, bool events)
   if(!data)
     return CURLE_BAD_FUNCTION_ARGUMENT;
 
-  if(data->conn) {
-    failf(data, "cannot use again while associated with a connection");
-    return CURLE_BAD_FUNCTION_ARGUMENT;
-  }
-
   if(data->set.errorbuffer)
     /* clear this as early as possible */
     data->set.errorbuffer[0] = 0;
@@ -767,6 +762,19 @@ static CURLcode easy_perform(struct Curl_easy *data, bool events)
     return CURLE_FAILED_INIT;
   }
 
+  /* if the handle has a connection still attached (it is/was a connect-only
+     handle) then disconnect before performing */
+  if(data->conn) {
+    struct connectdata *c;
+    curl_socket_t s;
+    Curl_detach_connection(data);
+    s = Curl_getconnectinfo(data, &c);
+    if((s != CURL_SOCKET_BAD) && c) {
+      Curl_cpool_disconnect(data, c, TRUE);
+    }
+    DEBUGASSERT(!data->conn);
+  }
+
   if(data->multi_easy)
     multi = data->multi_easy;
   else {

diff --git a/tests/data/test696 b/tests/data/test696
index 8b0bfd430970041f738ea3b538f0ef2dbbaabf19..1af5fc7a841e9ce877235dcc87eae841028678b6 100644 (file)
--- a/tests/data/test696
+++ b/tests/data/test696
@@ -7,7 +7,7 @@ HTTP GET
 </info>
 
 <reply>
-<data>
+<data nocheck="yes">
 HTTP/1.1 200 OK swsclose\r
 Server: test-server/fake\r
 Last-Modified: Tue, 13 Jun 2000 12:10:00 GMT\r
@@ -38,15 +38,33 @@ http://%HOSTIP:%HTTPPORT
 #
 # Verify data after the test has been "shot"
 <verify>
+<stdout>
+HTTP/1.1 200 OK swsclose\r
+Server: test-server/fake\r
+Last-Modified: Tue, 13 Jun 2000 12:10:00 GMT\r
+Content-Length: 6\r
+Connection: close\r
+\r
+-foo-
+HTTP/1.1 200 OK swsclose\r
+Server: test-server/fake\r
+Last-Modified: Tue, 13 Jun 2000 12:10:00 GMT\r
+Content-Length: 6\r
+Connection: close\r
+\r
+-foo-
+</stdout>
 <protocol>
 GET /556 HTTP/1.1\r
 Host: ninja\r
 \r
+GET /556 HTTP/1.1\r
+Host: ninja\r
+\r
 </protocol>
 
-# 43 == CURLE_BAD_FUNCTION_ARGUMENT
 <errorcode>
-43
+0
 </errorcode>
 </verify>
 </testcase>

diff --git a/tests/libtest/lib556.c b/tests/libtest/lib556.c
index 31818dc8a2f0a83c49fe215468dbe23935010ab3..da9aea091e33d34ed3ad77261c4b34e1bef341cc 100644 (file)
--- a/tests/libtest/lib556.c
+++ b/tests/libtest/lib556.c
@@ -41,6 +41,9 @@ CURLcode test(char *URL)
 {
   CURLcode res;
   CURL *curl;
+#ifdef LIB696
+  int transfers = 0;
+#endif
 
   if(curl_global_init(CURL_GLOBAL_ALL) != CURLE_OK) {
     fprintf(stderr, "curl_global_init() failed\n");
@@ -58,6 +61,10 @@ CURLcode test(char *URL)
   test_setopt(curl, CURLOPT_CONNECT_ONLY, 1L);
   test_setopt(curl, CURLOPT_VERBOSE, 1L);
 
+#ifdef LIB696
+again:
+#endif
+
   res = curl_easy_perform(curl);
 
   if(!res) {
@@ -87,8 +94,12 @@ CURLcode test(char *URL)
 
       if(nread) {
         /* send received stuff to stdout */
-        if(!write(STDOUT_FILENO, buf, nread))
+        if((size_t)write(STDOUT_FILENO, buf, nread) != nread) {
+          fprintf(stderr, "write() failed: errno %d (%s)\n",
+                  errno, strerror(errno));
+          res = TEST_ERR_FAILURE;
           break;
+        }
       }
 
     } while((res == CURLE_OK && nread) || (res == CURLE_AGAIN));
@@ -98,12 +109,10 @@ CURLcode test(char *URL)
   }
 
 #ifdef LIB696
-  /* attempt to use the handle again */
-  test_setopt(curl, CURLOPT_URL, URL);
-  test_setopt(curl, CURLOPT_CONNECT_ONLY, 1L);
-  test_setopt(curl, CURLOPT_VERBOSE, 1L);
-
-  res = curl_easy_perform(curl);
+  ++transfers;
+  /* perform the transfer a second time */
+  if(!res && transfers == 1)
+    goto again;
 #endif
 
 test_cleanup: