ESP8266WifiServer timeout when requesting through external IP #8853
Description
I have a basic ESP8266WebServer that sends roughly 1000 characters worth of response via send(). Everything works fine when the traffic is over the local IPv4 address 192.168.xx.xx.
However, I have set up port forwarding over my external IP to be directed to the NodeMCU device, and when the request is made over the external IP 87.xx.xx.xx via a device connected to the local network, the server times out during send() operation. Upon closer inspection, it seems that ClientContext::availableForWrite() / tcp_sndbuf returns 0 in this case. Increasing the timeout to 10s didn't help. Seems the buffer is never available.
As an additional step, I set up a VPN on the request device to make the request device's IP as 105.xx.xx.xx and made the same request. This time ClientContext::availableForWrite() / tcp_sndbuf returned a non-zero value and the request was successful.
Any ideas why the tcp_sndbuf would not work when a request is made by a device connected on the same network but via external IP that is port forwarded to my NodeMCU?