improve web kit to be more stable

* when data is not available on nonblocking socket, retry it later
* disable SIGPIPE on web server's socket, this prevents svm crashing
  under high traffic load

fix #27

src/kits/inet/native/std/inet_TcpServerSocket_std.c

@@ -107,6 +107,16 @@ Cell inet_TcpServerSocket_accept(SedonaVM* vm, Cell* params)
     return falseCell;
   }
 
+#ifdef SO_NOSIGPIPE
+  int val = 1;
+  if (setsockopt(acceptedSock, SOL_SOCKET, SO_NOSIGPIPE, 
+              (void*)&val, sizeof(val)) != 0)
+  {
+    closesocket(acceptedSock);
+    return falseCell;
+  }
+#endif
+
   // mark as open
   setSocket(accepted, acceptedSock);
   setClosed(accepted, 0);

src/kits/inet/native/std/inet_TcpSocket_std.c

@@ -176,6 +176,9 @@ Cell inet_TcpSocket_write(SedonaVM* vm, Cell* params)
   Cell result;
 
   buf = buf + off;
+  //NOTE: MSG_NOSIGNAL is not defined under macOS(BSD like
+  //      system?), should use `setsockopt` to set 
+  //      SO_NOSIGPIPE after socket is created
   result.ival = send(sock, buf, len, MSG_NOSIGNAL);
   if (result.ival >= 0) return result;  // 0+ is ok
   if (inet_errorIsWouldBlock()) return zeroCell;

src/kits/web/Handler.sedona

@@ -74,10 +74,16 @@ internal class Handler
 
     // read request bytes
     int read = socket.read(buf, pos, bufLen)
-    if (read <= 0) 
+
+    if (read == 0) // no data available yet (nonblocking)
+      return true
+    else if (read < 0) // some error happened
     { 
-      res.writeStatus(HttpCode.badRequest).finishHeaders().close()
-      return true 
+      if (socket.isClosed())
+        WebService.log.trace("socket has been closed, skip request handling")
+      else
+        res.writeStatus(HttpCode.badRequest).finishHeaders().close()
+      return false 
     }
 
     // update read offset