Net: Fix WebSocket sendFrame delay by enabling TCP_NODELAY by Copilot · Pull Request #5077 · pocoproject/poco

Copilot · 2025-12-08T01:37:26Z

WebSocket sendFrame() experiences ~2 second delays because Nagle's algorithm buffers small frames. While client-side WebSockets inherit TCP_NODELAY from HTTPClientSession, server-side WebSockets created from HTTPServerRequest do not.

Changes

WebSocketImpl.cpp: Enable TCP_NODELAY in constructor for all WebSocket connections
- Skip Unix domain sockets which don't support TCP options
- Gracefully handle socket configuration errors
WebSocket.h: Document TCP_NODELAY behavior

Implementation

// WebSocketImpl constructor now sets TCP_NODELAY
try
{
    if (_pStreamSocketImpl->address().family() != SocketAddress::UNIX_LOCAL)
        _pStreamSocketImpl->setNoDelay(true);
}
catch (NetException&) { /* ignore */ }
catch (Poco::Exception&) { /* ignore */ }

This eliminates the artificial delays caused by Nagle's algorithm buffering small WebSocket frames, making frame sends immediate regardless of whether the WebSocket originated from a client or server connection.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

192.168.168.192
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest /tmp/ccsAxjaq.s ork/�� ch=" --green --p-I -I nit/include -I k/poco/poco/Net/-I t.cpp.o -D_LARGEFILE64_-I -qui�� /bin/c++ -DPOCO_-I /home/REDACTED/wor/home/REDACTED/work/poco/poco/CppUnit/include nit/include /home/REDACTED/woras -I /home/REDACTED/wor/home/REDACTED/work/poco/poco/Net/include FFSET_BITS=64 -D-I (packet block)
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest CMakeFiles/Net.dir/src/WebSocketImpl.cpp.d -MF t/testsuite/all -MT Net/CMakeFiles/Net.dir/src/WebSocketImpl.cpp.o -D_GNU_SOURCE -D Net_EXPORTS -D -DPO�� cpp.o -DPOCO_ENABLE_CPP20 dation/include _FD_EPOLL -DPOCOas nit/include -D_FILE_OFFSET_B/home/REDACTED/work/poco/poco/Net/include FFSET_BITS=64 -D-I (packet block)
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest FFSET_BITS=64 -D_LARGEFILE64_SOURCE -D_REENTRAN -DPO�� include -DPOCO_ENABLE_CPP20 dation/include -DPOCO_OS_FAMILYbash nit/include -DUTF8PROC_STATI--noprofile FFSET_BITS=64 -D_LARGEFILE64_SOU872727f6db7dcd22990d7845dae167444594bf63 -DPO�� include -DPOCO_ENABLE_CPP20 dation/include -DPOCO_HAVE_SEND/bin/sh nit/include -DUTF8PROC_STATIcd /home/REDACTED/work/poco/poco/cmake-build && /usr/local/bin/cmake -E cmake_depends "Unix Makefiles" /home/REDACTED/work/poco/poco /home/REDACTED/work/poco/poco/Foundation /home/REDACTED/work/poco/poco/cmake-build /home/REDACTED/work/poco/poco/cmak e-build/Foundat (packet block)
239.255.1.2
- Triggering command: REDACTED, pid is -1 (packet block)
255.255.255.255
- Triggering command: REDACTED, pid is -1 (packet block)
86.195.122.80.in-addr.arpa
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest /tmp/ccsAxjaq.s ork/�� ch=" --green --p-I -I nit/include -I k/poco/poco/Net/-I t.cpp.o -D_LARGEFILE64_-I -qui�� /bin/c++ -DPOCO_-I /home/REDACTED/wor/home/REDACTED/work/poco/poco/CppUnit/include nit/include /home/REDACTED/woras -I /home/REDACTED/wor/home/REDACTED/work/poco/poco/Net/include FFSET_BITS=64 -D-I (dns block)
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest CMakeFiles/Net.dir/src/WebSocketImpl.cpp.d -MF t/testsuite/all -MT Net/CMakeFiles/Net.dir/src/WebSocketImpl.cpp.o -D_GNU_SOURCE -D Net_EXPORTS -D -DPO�� cpp.o -DPOCO_ENABLE_CPP20 dation/include _FD_EPOLL -DPOCOas nit/include -D_FILE_OFFSET_B/home/REDACTED/work/poco/poco/Net/include FFSET_BITS=64 -D-I (dns block)
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest FFSET_BITS=64 -D_LARGEFILE64_SOURCE -D_REENTRAN -DPO�� include -DPOCO_ENABLE_CPP20 dation/include -DPOCO_OS_FAMILYbash nit/include -DUTF8PROC_STATI--noprofile FFSET_BITS=64 -D_LARGEFILE64_SOU872727f6db7dcd22990d7845dae167444594bf63 -DPO�� include -DPOCO_ENABLE_CPP20 dation/include -DPOCO_HAVE_SEND/bin/sh nit/include -DUTF8PROC_STATIcd /home/REDACTED/work/poco/poco/cmake-build && /usr/local/bin/cmake -E cmake_depends "Unix Makefiles" /home/REDACTED/work/poco/poco /home/REDACTED/work/poco/poco/Foundation /home/REDACTED/work/poco/poco/cmake-build /home/REDACTED/work/poco/poco/cmak e-build/Foundat (dns block)
aliastest.pocoproject.org
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest /tmp/ccsAxjaq.s ork/�� ch=" --green --p-I -I nit/include -I k/poco/poco/Net/-I t.cpp.o -D_LARGEFILE64_-I -qui�� /bin/c++ -DPOCO_-I /home/REDACTED/wor/home/REDACTED/work/poco/poco/CppUnit/include nit/include /home/REDACTED/woras -I /home/REDACTED/wor/home/REDACTED/work/poco/poco/Net/include FFSET_BITS=64 -D-I (dns block)
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest CMakeFiles/Net.dir/src/WebSocketImpl.cpp.d -MF t/testsuite/all -MT Net/CMakeFiles/Net.dir/src/WebSocketImpl.cpp.o -D_GNU_SOURCE -D Net_EXPORTS -D -DPO�� cpp.o -DPOCO_ENABLE_CPP20 dation/include _FD_EPOLL -DPOCOas nit/include -D_FILE_OFFSET_B/home/REDACTED/work/poco/poco/Net/include FFSET_BITS=64 -D-I (dns block)
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest FFSET_BITS=64 -D_LARGEFILE64_SOURCE -D_REENTRAN -DPO�� include -DPOCO_ENABLE_CPP20 dation/include -DPOCO_OS_FAMILYbash nit/include -DUTF8PROC_STATI--noprofile FFSET_BITS=64 -D_LARGEFILE64_SOU872727f6db7dcd22990d7845dae167444594bf63 -DPO�� include -DPOCO_ENABLE_CPP20 dation/include -DPOCO_HAVE_SEND/bin/sh nit/include -DUTF8PROC_STATIcd /home/REDACTED/work/poco/poco/cmake-build && /usr/local/bin/cmake -E cmake_depends "Unix Makefiles" /home/REDACTED/work/poco/poco /home/REDACTED/work/poco/poco/Foundation /home/REDACTED/work/poco/poco/cmake-build /home/REDACTED/work/poco/poco/cmak e-build/Foundat (dns block)
pocoproject.org
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest /tmp/ccsAxjaq.s ork/�� ch=" --green --p-I -I nit/include -I k/poco/poco/Net/-I t.cpp.o -D_LARGEFILE64_-I -qui�� /bin/c++ -DPOCO_-I /home/REDACTED/wor/home/REDACTED/work/poco/poco/CppUnit/include nit/include /home/REDACTED/woras -I /home/REDACTED/wor/home/REDACTED/work/poco/poco/Net/include FFSET_BITS=64 -D-I (dns block)
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest CMakeFiles/Net.dir/src/WebSocketImpl.cpp.d -MF t/testsuite/all -MT Net/CMakeFiles/Net.dir/src/WebSocketImpl.cpp.o -D_GNU_SOURCE -D Net_EXPORTS -D -DPO�� cpp.o -DPOCO_ENABLE_CPP20 dation/include _FD_EPOLL -DPOCOas nit/include -D_FILE_OFFSET_B/home/REDACTED/work/poco/poco/Net/include FFSET_BITS=64 -D-I (dns block)
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest FFSET_BITS=64 -D_LARGEFILE64_SOURCE -D_REENTRAN -DPO�� include -DPOCO_ENABLE_CPP20 dation/include -DPOCO_OS_FAMILYbash nit/include -DUTF8PROC_STATI--noprofile FFSET_BITS=64 -D_LARGEFILE64_SOU872727f6db7dcd22990d7845dae167444594bf63 -DPO�� include -DPOCO_ENABLE_CPP20 dation/include -DPOCO_HAVE_SEND/bin/sh nit/include -DUTF8PROC_STATIcd /home/REDACTED/work/poco/poco/cmake-build && /usr/local/bin/cmake -E cmake_depends "Unix Makefiles" /home/REDACTED/work/poco/poco /home/REDACTED/work/poco/poco/Foundation /home/REDACTED/work/poco/poco/cmake-build /home/REDACTED/work/poco/poco/cmak e-build/Foundat (dns block)
pool.ntp.org
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest /tmp/ccsAxjaq.s ork/�� ch=" --green --p-I -I nit/include -I k/poco/poco/Net/-I t.cpp.o -D_LARGEFILE64_-I -qui�� /bin/c++ -DPOCO_-I /home/REDACTED/wor/home/REDACTED/work/poco/poco/CppUnit/include nit/include /home/REDACTED/woras -I /home/REDACTED/wor/home/REDACTED/work/poco/poco/Net/include FFSET_BITS=64 -D-I (dns block)
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest CMakeFiles/Net.dir/src/WebSocketImpl.cpp.d -MF t/testsuite/all -MT Net/CMakeFiles/Net.dir/src/WebSocketImpl.cpp.o -D_GNU_SOURCE -D Net_EXPORTS -D -DPO�� cpp.o -DPOCO_ENABLE_CPP20 dation/include _FD_EPOLL -DPOCOas nit/include -D_FILE_OFFSET_B/home/REDACTED/work/poco/poco/Net/include FFSET_BITS=64 -D-I (dns block)
- Triggering command: ./bin/Net-testREDACTED ./bin/Net-testREDACTED -all WebSocketTest FFSET_BITS=64 -D_LARGEFILE64_SOURCE -D_REENTRAN -DPO�� include -DPOCO_ENABLE_CPP20 dation/include -DPOCO_OS_FAMILYbash nit/include -DUTF8PROC_STATI--noprofile FFSET_BITS=64 -D_LARGEFILE64_SOU872727f6db7dcd22990d7845dae167444594bf63 -DPO�� include -DPOCO_ENABLE_CPP20 dation/include -DPOCO_HAVE_SEND/bin/sh nit/include -DUTF8PROC_STATIcd /home/REDACTED/work/poco/poco/cmake-build && /usr/local/bin/cmake -E cmake_depends "Unix Makefiles" /home/REDACTED/work/poco/poco /home/REDACTED/work/poco/poco/Foundation /home/REDACTED/work/poco/poco/cmake-build /home/REDACTED/work/poco/poco/cmak e-build/Foundat (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

Configure Actions setup steps to set up my environment, which run before the firewall is enabled
Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

This section details on the original issue you should resolve

<issue_title>WebSocket sendFrame Delay and ReceiveTimeout Dependency - Need Help</issue_title>
<issue_description>Hi,
I'm having a problem with Poco::Net::WebSocket.sendFrame(). It takes forever (about 2 seconds) to execute in a non-blocking context. It seems that sendFrame() only works when a receive timeout happens, which makes the receiving end laggy and timeouty. I tried setting the WebSocket to non-blocking mode with ws->setBlocking(false), but that didn't help. If I set ws->setReceiveTimeout(Poco::Timespan(0, 1000)), the receive timeout keeps getting called, and sendFrame() doesn't lag at all.

What am I missing? Should I set the timeout low, catch it, and then ignore it? I'd appreciate any help or suggestions.
I've attached a sample code below.

#include <chrono>
#include <iostream>
#include <thread>

#include "Poco/Net/HTTPRequest.h"
#include "Poco/Net/HTTPResponse.h"
#include "Poco/Net/HTTPSClientSession.h"
#include "Poco/Net/SSLManager.h"
#include "Poco/Net/WebSocket.h"

class WebSocketClient {
   private:
    Poco::Net::WebSocket* ws;
    std::thread receiveThread;
    std::atomic<bool> running{true};

   public:
    WebSocketClient(const std::string& host, uint16_t port, const std::string& path) {
        Poco::Net::Context::Ptr context = new Poco::Net::Context(
            Poco::Net::Context::CLIENT_USE, "", "", "", Poco::Net::Context::VERIFY_NONE, 9, false,
            "ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH");

        Poco::Net::HTTPSClientSession session(host, port, context);
        session.setTimeout(Poco::Timespan(5, 0)); 
        Poco::Net::HTTPRequest request(Poco::Net::HTTPRequest::HTTP_GET, path,
                                       Poco::Net::HTTPMessage::HTTP_1_1);
        Poco::Net::HTTPResponse response;

        ws = new Poco::Net::WebSocket(session, request, response);
        // ws->setReceiveTimeout(Poco::Timespan(0, 1000)); 
        receiveThread = std::thread(&WebSocketClient::receiveLoop, this);
    }

    ~WebSocketClient() {
        running = false;
        if (receiveThread.joinable()) {
            receiveThread.join();
        }
        delete ws;
    }

    bool sendMessage(const std::string& message) {
        try {
            auto start = std::chrono::steady_clock::now();

            int flags = Poco::Net::WebSocket::FRAME_TEXT;
            int sent = ws->sendFrame(message.data(), message.length(), flags);

            auto end = std::chrono::steady_clock::now();
            auto duration = std::chrono::duration_cast<std::chrono::milliseconds>(end - start);

            std::cout << "Time taken for sendFrame: " << duration.count() << " ms\n";

            return sent == message.length();
        } catch (const Poco::TimeoutException& e) {
            std::cerr << "Timeout sending message: " << e.what() << std::endl;
            return false;
        } catch (const Poco::Exception& e) {
            std::cerr << "Error sending message: " << e.what() << std::endl;
            return false;
        }
    }

   private:
    void receiveLoop() {
        const int BUFFER_SIZE = 1024;
        char buffer[BUFFER_SIZE];
        int flags = 0;

        while (running) {
            try {
                int received = ws->receiveFrame(buffer, sizeof(buffer), flags);
                if (received > 0) {
                    std::string message(buffer, received);
                    std::cout << "Received message: " << message << std::endl;
                }
            } catch (const Poco::TimeoutException&) {
                std::cerr << "Timeout receiving message\n";
                std::this_thread::sleep_for(std::chrono::milliseconds(100));
                continue;
            } catch (const Poco::Exception& e) {
                std::cerr << "Error in receive loop: " << e.what() << std::endl;
                break;
            }
        }
    }
};

int main() {
    try {
        WebSocketClient client("echo.websocket.org", 443, "/");

        while (true) {
            std::cout << "Sending message: test\n";
            client.sendMessage("test");
            std::this_thread::sleep_for(std::chrono::seconds(3));
        }
    } catch (const Poco::Exception& e) {
        std::cerr << "Error: " << e.what() << std::endl;
        return 1;
    }
    return 0;
}```

</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

Fixes WebSocket sendFrame Delay and ReceiveTimeout Dependency - Need Help #4756

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

- Enable TCP_NODELAY in WebSocketImpl constructor to prevent Nagle's algorithm from buffering small WebSocket frames - Add check to skip TCP_NODELAY for Unix domain sockets - Add documentation about TCP_NODELAY behavior to WebSocket class - Tested with existing WebSocket test suite - all tests pass Co-authored-by: aleks-f <2429093+aleks-f@users.noreply.github.com>

- Avoid unnecessary SocketAddress object construction by calling family() directly - Use specific exception type (Poco::Exception) instead of catch-all Co-authored-by: aleks-f <2429093+aleks-f@users.noreply.github.com>

- Catch specific exception types (NetException, IOException, InvalidArgumentException) instead of broad Poco::Exception - Improve error handling comments for clarity Co-authored-by: aleks-f <2429093+aleks-f@users.noreply.github.com>

- Combine catch blocks since all exceptions are handled identically - Improve code clarity with more descriptive comments Co-authored-by: aleks-f <2429093+aleks-f@users.noreply.github.com>

Initial plan

56f28c5

Copilot AI assigned Copilot and aleks-f Dec 8, 2025

Copilot started work on behalf of aleks-f December 8, 2025 01:38 View session

Copilot AI and others added 4 commits December 8, 2025 01:55

Address code review feedback

8a3b177

- Avoid unnecessary SocketAddress object construction by calling family() directly - Use specific exception type (Poco::Exception) instead of catch-all Co-authored-by: aleks-f <2429093+aleks-f@users.noreply.github.com>

Consolidate exception handling for better maintainability

f187973

- Combine catch blocks since all exceptions are handled identically - Improve code clarity with more descriptive comments Co-authored-by: aleks-f <2429093+aleks-f@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix delay in WebSocket sendFrame method~~ Fix WebSocket sendFrame delay by enabling TCP_NODELAY Dec 8, 2025

Copilot AI requested a review from aleks-f December 8, 2025 02:06

Copilot finished work on behalf of aleks-f December 8, 2025 02:06

aleks-f requested a review from obiltschnig December 8, 2025 06:01

aleks-f approved these changes Dec 8, 2025

View reviewed changes

aleks-f marked this pull request as ready for review December 8, 2025 18:38

aleks-f merged commit b35f44c into main Dec 9, 2025
77 of 111 checks passed

aleks-f deleted the copilot/fix-websocket-sendframe-delay branch December 9, 2025 01:05

matejk changed the title ~~Fix WebSocket sendFrame delay by enabling TCP_NODELAY~~ Net: Fix WebSocket sendFrame delay by enabling TCP_NODELAY Dec 20, 2025

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Net: Fix WebSocket sendFrame delay by enabling TCP_NODELAY#5077

Net: Fix WebSocket sendFrame delay by enabling TCP_NODELAY#5077
aleks-f merged 5 commits intomainfrom
copilot/fix-websocket-sendframe-delay

Copilot AI commented Dec 8, 2025 •

edited

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Copilot AI commented Dec 8, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Changes

Implementation

I tried to connect to the following addresses, but was blocked by firewall rules:

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Copilot AI commented Dec 8, 2025 •

edited

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