Curl_getconnectinfo: avoid checking if the connection is closed

It doesn't benefit us much as the connection could get closed at
any time, and also by checking we lose the ability to determine
if the socket was closed by reading zero bytes.

Reported-by: Michael Kaufmann

Closes https://github.com/curl/curl/pull/1134

lib/connect.c

@@ -1247,24 +1247,6 @@ curl_socket_t Curl_getconnectinfo(struct Curl_easy *data,
       /* only store this if the caller cares for it */
       *connp = c;
     sockfd = c->sock[FIRSTSOCKET];
-    /* we have a socket connected, let's determine if the server shut down */
-    /* determine if ssl */
-    if(c->ssl[FIRSTSOCKET].use) {
-      /* use the SSL context */
-      if(!Curl_ssl_check_cxn(c))
-        return CURL_SOCKET_BAD;   /* FIN received */
-    }
-/* Minix 3.1 doesn't support any flags on recv; just assume socket is OK */
-#ifdef MSG_PEEK
-    else if(sockfd != CURL_SOCKET_BAD) {
-      /* use the socket */
-      char buf;
-      if(recv((RECV_TYPE_ARG1)sockfd, (RECV_TYPE_ARG2)&buf,
-              (RECV_TYPE_ARG3)1, (RECV_TYPE_ARG4)MSG_PEEK) == 0) {
-        return CURL_SOCKET_BAD;   /* FIN received */
-      }
-    }
-#endif
   }
   else
     return CURL_SOCKET_BAD;
@@ -1272,6 +1254,33 @@ curl_socket_t Curl_getconnectinfo(struct Curl_easy *data,
   return sockfd;
 }
 
+/*
+ * Check if a connection seems to be alive.
+ */
+bool Curl_connalive(struct connectdata *conn)
+{
+  /* First determine if ssl */
+  if(conn->ssl[FIRSTSOCKET].use) {
+    /* use the SSL context */
+    if(!Curl_ssl_check_cxn(conn))
+      return false;   /* FIN received */
+  }
+/* Minix 3.1 doesn't support any flags on recv; just assume socket is OK */
+#ifdef MSG_PEEK
+  else if(conn->sock[FIRSTSOCKET] == CURL_SOCKET_BAD)
+    return false;
+  else {
+    /* use the socket */
+    char buf;
+    if(recv((RECV_TYPE_ARG1)conn->sock[FIRSTSOCKET], (RECV_TYPE_ARG2)&buf,
+            (RECV_TYPE_ARG3)1, (RECV_TYPE_ARG4)MSG_PEEK) == 0) {
+      return false;   /* FIN received */
+    }
+  }
+#endif
+  return true;
+}
+
 /*
  * Close a socket.
  *

lib/connect.h

@@ -52,6 +52,11 @@ time_t Curl_timeleft(struct Curl_easy *data,
 curl_socket_t Curl_getconnectinfo(struct Curl_easy *data,
                                   struct connectdata **connp);
 
+/*
+ * Check if a connection seems to be alive.
+ */
+bool Curl_connalive(struct connectdata *conn);
+
 #ifdef USE_WINSOCK
 /* When you run a program that uses the Windows Sockets API, you may
    experience slow performance when you copy data to a TCP server.

lib/rtsp.c

@@ -140,7 +140,7 @@ static CURLcode rtsp_setup_connection(struct connectdata *conn)
  * want to block the application forever while receiving a stream. Therefore,
  * we cannot assume that an RTSP socket is dead just because it is readable.
  *
- * Instead, if it is readable, run Curl_getconnectinfo() to peek at the socket
+ * Instead, if it is readable, run Curl_connalive() to peek at the socket
  * and distinguish between closed and data.
  */
 bool Curl_rtsp_connisdead(struct connectdata *check)
@@ -157,12 +157,9 @@ bool Curl_rtsp_connisdead(struct connectdata *check)
     /* socket is in an error state */
     ret_val = TRUE;
   }
-  else if((sval & CURL_CSELECT_IN) && check->data) {
+  else if(sval & CURL_CSELECT_IN) {
-    /* readable with no error. could be closed or could be alive but we can
+    /* readable with no error. could still be closed */
-       only check if we have a proper Curl_easy for the connection */
+    ret_val = !Curl_connalive(check);
-    curl_socket_t connectinfo = Curl_getconnectinfo(check->data, &check);
-    if(connectinfo != CURL_SOCKET_BAD)
-      ret_val = FALSE;
   }
 
   return ret_val;