Fix segfault on delayed connection errors.

Connection errors could cause a segfault if the error was delayed enough to pass the initial call to sckClientOpenWait() and the error was instead thrown by a subsequent call to sckClientOpenWait(), which was not correctly initializing a variable required for error handling.

While this can be produced fairly easily in a test environment, I was unable to craft a unit test to hit this exact condition, probably due to timing. The new code still has full coverage and I added several comments to help prevent regressions.

doc/xml/release/2024/2.54.xml

@@ -14,6 +14,19 @@
                 <p>Fix permissions when <cmd>restore</cmd> run as root user.</p>
             </release-item>
 
+            <release-item>
+                <github-issue id="2420"/>
+                <github-pull-request id="2422"/>
+
+                <release-item-contributor-list>
+                    <release-item-ideator id="anton.glushakov"/>
+                    <release-item-contributor id="david.steele"/>
+                    <release-item-reviewer id="david.christensen"/>
+                </release-item-contributor-list>
+
+                <p>Fix segfault on delayed connection errors.</p>
+            </release-item>
+
             <release-item>
                 <github-issue id="2418"/>
                 <github-pull-request id="2421"/>

src/common/io/socket/client.c

@@ -159,10 +159,17 @@ sckClientOpen(THIS_VOID)
                 {
                     SckClientOpenData *const openDataWait = lstGet(openDataList, openDataIdx);
 
-                    if (openDataWait->fd != 0 && sckClientOpenWait(openDataWait, 0))
+                    if (openDataWait->fd != 0)
                     {
+                        // Set so the connection will be closed on error
                         openData = openDataWait;
-                        break;
+
+                        // Check if the connection has completed without waiting
+                        if (sckClientOpenWait(openData, 0))
+                            break;
+
+                        // Reset to NULL if the connection is still waiting so another connection can be attempted
+                        openData = NULL;
                     }
                 }
 
@@ -233,6 +240,8 @@ sckClientOpen(THIS_VOID)
             }
             CATCH_ANY()
             {
+                ASSERT(openData != NULL);
+
                 // Close socket
                 close(openData->fd);