Overhauled SSL to use explicit BIO buffers

luprex/cpp/drv/driver-mingw.cpp

@@ -152,37 +152,46 @@ static SOCKET accept_on_socket(SOCKET listen_socket, std::string &err) {
     }
 }
 
+// the return values for socket_send:
+//
+//  positive: sent bytes successfully
+//  negative: error.
+//     If the error message is empty, then it's "would block"
+//     Any other error generates an error message.
+//
+
 static int socket_send(SOCKET socket, const char *bytes, int nbytes, std::string &err) {
-    err.clear();
     int wbytes = send(socket, bytes, nbytes, 0);
     if (wbytes == SOCKET_ERROR) {
         int errcode = WSAGetLastError();
         if (errcode == WSAEWOULDBLOCK) {
-            return 0;
+            err.clear();
         } else {
             err = "send failure";
-            return -1;
         }
+        return -1;
     } else {
         assert(wbytes > 0);
+        err.clear();
         return wbytes;
     }
 }
 
 static int socket_recv(SOCKET socket, char *bytes, int nbytes, std::string &err) {
-    err.clear();
     int nrecv = recv(socket, bytes, nbytes, 0);
     if (nrecv < 0) {
         int errcode = WSAGetLastError();
         if (errcode == WSAEWOULDBLOCK) {
-            return 0;
+            err = "";
         } else {
             err = "recv failure";
-            return -1;
         }
-    } else if (nrecv == 0) {
         return -1;
+    } else if (nrecv == 0) {
+        err.clear();
+        return 0;
     } else {
+        err.clear();
         return nrecv;
     }
 }