netbase: Make SOCKS5 negotiation interruptible

Avoids that SOCKS5 negotiation will hold up the shutdown process.

- Sockets can stay in non-blocking mode, no need to switch it on/off
  anymore
- Adds a timeout (20 seconds) on SOCK5 negotiation. This should be
  enough for even Tor to get a connection to a hidden service, and
  avoids blocking the opencon thread indefinitely on a hanging proxy.

Fixes #2954.

src/net.cpp

@@ -488,10 +488,6 @@ CNode* ConnectNode(CAddress addrConnect, const char *pszDest)
     {
         addrman.Attempt(addrConnect);
 
-        // Set to non-blocking
-        if (!SetSocketNonBlocking(hSocket, true))
-            LogPrintf("ConnectNode: Setting socket to non-blocking failed, error %s\n", NetworkErrorString(WSAGetLastError()));
-
         // Add node
         CNode* pnode = new CNode(hSocket, addrConnect, pszDest ? pszDest : "", false);
         pnode->AddRef();

src/netbase.cpp

@@ -45,6 +45,9 @@ bool fNameLookup = false;
 
 static const unsigned char pchIPv4[12] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff };
 
+// Need ample time for negotiation for very slow proxies such as Tor (milliseconds)
+static const int SOCKS5_RECV_TIMEOUT = 20 * 1000;
+
 enum Network ParseNetwork(std::string net) {
     boost::to_lower(net);
     if (net == "ipv4") return NET_IPV4;
@@ -225,6 +228,63 @@ bool LookupNumeric(const char *pszName, CService& addr, int portDefault)
     return Lookup(pszName, addr, portDefault, false);
 }
 
+/**
+ * Convert milliseconds to a struct timeval for select.
+ */
+struct timeval static MillisToTimeval(int64_t nTimeout)
+{
+    struct timeval timeout;
+    timeout.tv_sec  = nTimeout / 1000;
+    timeout.tv_usec = (nTimeout % 1000) * 1000;
+    return timeout;
+}
+
+/**
+ * Read bytes from socket. This will either read the full number of bytes requested
+ * or return False on error or timeout.
+ * This function can be interrupted by boost thread interrupt.
+ *
+ * @param data Buffer to receive into
+ * @param len  Length of data to receive
+ * @param timeout  Timeout in milliseconds for receive operation
+ *
+ * @note This function requires that hSocket is in non-blocking mode.
+ */
+bool static InterruptibleRecv(char* data, size_t len, int timeout, SOCKET& hSocket)
+{
+    int64_t curTime = GetTimeMillis();
+    int64_t endTime = curTime + timeout;
+    // Maximum time to wait in one select call. It will take up until this time (in millis)
+    // to break off in case of an interruption.
+    const int64_t maxWait = 1000;
+    while (len > 0 && curTime < endTime) {
+        ssize_t ret = recv(hSocket, data, len, 0); // Optimistically try the recv first
+        if (ret > 0) {
+            len -= ret;
+            data += ret;
+        } else if (ret == 0) { // Unexpected disconnection
+            return false;
+        } else { // Other error or blocking
+            int nErr = WSAGetLastError();
+            if (nErr == WSAEINPROGRESS || nErr == WSAEWOULDBLOCK || nErr == WSAEINVAL) {
+                struct timeval tval = MillisToTimeval(std::min(endTime - curTime, maxWait));
+                fd_set fdset;
+                FD_ZERO(&fdset);
+                FD_SET(hSocket, &fdset);
+                int nRet = select(hSocket + 1, &fdset, NULL, NULL, &tval);
+                if (nRet == SOCKET_ERROR) {
+                    return false;
+                }
+            } else {
+                return false;
+            }
+        }
+        boost::this_thread::interruption_point();
+        curTime = GetTimeMillis();
+    }
+    return len == 0;
+}
+
 bool static Socks5(string strDest, int port, SOCKET& hSocket)
 {
     LogPrintf("SOCKS5 connecting %s\n", strDest);
@@ -243,7 +303,7 @@ bool static Socks5(string strDest, int port, SOCKET& hSocket)
         return error("Error sending to proxy");
     }
     char pchRet1[2];
-    if (recv(hSocket, pchRet1, 2, 0) != 2)
+    if (!InterruptibleRecv(pchRet1, 2, SOCKS5_RECV_TIMEOUT, hSocket))
     {
         CloseSocket(hSocket);
         return error("Error reading proxy response");
@@ -266,7 +326,7 @@ bool static Socks5(string strDest, int port, SOCKET& hSocket)
         return error("Error sending to proxy");
     }
     char pchRet2[4];
-    if (recv(hSocket, pchRet2, 4, 0) != 4)
+    if (!InterruptibleRecv(pchRet2, 4, SOCKS5_RECV_TIMEOUT, hSocket))
     {
         CloseSocket(hSocket);
         return error("Error reading proxy response");
@@ -300,27 +360,27 @@ bool static Socks5(string strDest, int port, SOCKET& hSocket)
     char pchRet3[256];
     switch (pchRet2[3])
     {
-        case 0x01: ret = recv(hSocket, pchRet3, 4, 0) != 4; break;
-        case 0x04: ret = recv(hSocket, pchRet3, 16, 0) != 16; break;
+        case 0x01: ret = InterruptibleRecv(pchRet3, 4, SOCKS5_RECV_TIMEOUT, hSocket); break;
+        case 0x04: ret = InterruptibleRecv(pchRet3, 16, SOCKS5_RECV_TIMEOUT, hSocket); break;
         case 0x03:
         {
-            ret = recv(hSocket, pchRet3, 1, 0) != 1;
-            if (ret) {
+            ret = InterruptibleRecv(pchRet3, 1, SOCKS5_RECV_TIMEOUT, hSocket);
+            if (!ret) {
                 CloseSocket(hSocket);
                 return error("Error reading from proxy");
             }
             int nRecv = pchRet3[0];
-            ret = recv(hSocket, pchRet3, nRecv, 0) != nRecv;
+            ret = InterruptibleRecv(pchRet3, nRecv, SOCKS5_RECV_TIMEOUT, hSocket);
             break;
         }
         default: CloseSocket(hSocket); return error("Error: malformed proxy response");
     }
-    if (ret)
+    if (!ret)
     {
         CloseSocket(hSocket);
         return error("Error reading from proxy");
     }
-    if (recv(hSocket, pchRet3, 2, 0) != 2)
+    if (!InterruptibleRecv(pchRet3, 2, SOCKS5_RECV_TIMEOUT, hSocket))
     {
         CloseSocket(hSocket);
         return error("Error reading from proxy");
@@ -360,10 +420,7 @@ bool static ConnectSocketDirectly(const CService &addrConnect, SOCKET& hSocketRe
         // WSAEINVAL is here because some legacy version of winsock uses it
         if (nErr == WSAEINPROGRESS || nErr == WSAEWOULDBLOCK || nErr == WSAEINVAL)
         {
-            struct timeval timeout;
-            timeout.tv_sec  = nTimeout / 1000;
-            timeout.tv_usec = (nTimeout % 1000) * 1000;
-
+            struct timeval timeout = MillisToTimeval(nTimeout);
             fd_set fdset;
             FD_ZERO(&fdset);
             FD_SET(hSocket, &fdset);
@@ -410,11 +467,6 @@ bool static ConnectSocketDirectly(const CService &addrConnect, SOCKET& hSocketRe
         }
     }
 
-    // This is required when using SOCKS5 proxy!
-    // CNode::ConnectNode turns the socket back to non-blocking.
-    if (!SetSocketNonBlocking(hSocket, false))
-        return error("ConnectSocketDirectly: Setting socket to blocking failed, error %s\n", NetworkErrorString(WSAGetLastError()));
-
     hSocketRet = hSocket;
     return true;
 }