From f81b0811a879d4a54ff697b31627406620d7dfc4 Mon Sep 17 00:00:00 2001
From: Theis Pieter Hollebeek <tphollebeek@gmail.com>
Date: Wed, 25 Mar 2026 14:08:43 +0100
Subject: [PATCH] backend: poll/wake impl

---
 backend/src/errno_shim.hpp | 12 +++++
 backend/src/event_loop.cpp | 53 ++++++++++++++++++++++
 backend/src/event_loop.hpp | 33 ++++++++++++++
 backend/src/main.cpp       | 10 ++---
 backend/src/result.hpp     |  5 +++
 backend/src/server.cpp     | 61 +++++++++++++++++++++++++
 backend/src/server.hpp     | 35 +++++++++++++++
 backend/src/tcp.cpp        | 92 ++++----------------------------------
 backend/src/tcp.hpp        | 31 +++----------
 9 files changed, 218 insertions(+), 114 deletions(-)
 create mode 100644 backend/src/errno_shim.hpp
 create mode 100644 backend/src/event_loop.cpp
 create mode 100644 backend/src/event_loop.hpp
 create mode 100644 backend/src/result.hpp

diff --git a/backend/src/errno_shim.hpp b/backend/src/errno_shim.hpp
new file mode 100644
index 0000000..9646f47
--- /dev/null
+++ b/backend/src/errno_shim.hpp
@@ -0,0 +1,12 @@
+#pragma once
+#include <cerrno>
+#include <cstring>
+#include <format>
+#include <string_view>
+
+namespace mst {
+auto inline errno_shim(std::string_view message) -> std::string
+{
+    return std::format("{} ({})", message, strerror(errno));
+}
+}
diff --git a/backend/src/event_loop.cpp b/backend/src/event_loop.cpp
new file mode 100644
index 0000000..ace6c90
--- /dev/null
+++ b/backend/src/event_loop.cpp
@@ -0,0 +1,53 @@
+#include "event_loop.hpp"
+#include "errno_shim.hpp"
+#include "server.hpp"
+#include <print>
+#include <sys/epoll.h>
+
+namespace mst::event {
+
+auto Manager::start() -> Result<void>
+{
+    epoll_event events[128] = { };
+    while (true) {
+        auto events_len = ::epoll_wait(this->epoll_fd, events, 128, -1);
+        if (events_len < 0) {
+            return std::unexpected(errno_shim("could not poll"));
+        }
+        for (int i = 0; i < events_len; ++i) {
+            auto event = (event::Event*)events[i].data.ptr;
+
+            switch (event->variant) {
+                case event::Server: {
+                    auto ptr = (mst::Server*)event->data;
+                    auto res = ptr->wake(*this);
+                    if (!res) {
+                        return std::unexpected(res.error());
+                    }
+
+                    break;
+                }
+                case event::Client: {
+                    std::println("client call scheduled");
+                    auto ptr = (mst::Client*)event->data;
+                    auto res = ptr->wake();
+                    if (!res) {
+                        return std::unexpected(res.error());
+                    }
+                    break;
+                }
+            }
+        }
+    }
+}
+
+auto Manager::create() -> Result<Manager>
+{
+    auto epoll_fd = ::epoll_create1(0);
+    if (epoll_fd < 0) {
+        std::unexpected(mst::errno_shim("could not create epoll"));
+    }
+
+    return Manager(epoll_fd);
+}
+}
diff --git a/backend/src/event_loop.hpp b/backend/src/event_loop.hpp
new file mode 100644
index 0000000..aac3358
--- /dev/null
+++ b/backend/src/event_loop.hpp
@@ -0,0 +1,33 @@
+#pragma once
+#include "result.hpp"
+namespace mst::event {
+enum Variant { Server, Client };
+struct Event {
+    Variant variant;
+    int fd;
+    void* data;
+};
+
+template <typename Data> auto make_event(Variant variant, Data data) -> Event*
+{
+    auto event = (Event*)malloc(sizeof(Event));
+    auto ptr = (Data*)std::malloc(sizeof(Data));
+    *ptr = data;
+
+    event->variant = variant;
+    event->data = ptr;
+
+    return event;
+}
+
+class Manager {
+public:
+    auto start() -> Result<void>;
+    int epoll_fd;
+    static auto create() -> Result<Manager>;
+
+private:
+    Manager(int epoll_fd)
+        : epoll_fd(epoll_fd) { };
+};
+}
diff --git a/backend/src/main.cpp b/backend/src/main.cpp
index ddc550c..fa7565f 100644
--- a/backend/src/main.cpp
+++ b/backend/src/main.cpp
@@ -1,6 +1,6 @@
-#include "tcp.hpp"
+#include "event_loop.hpp"
+#include "server.hpp"
 #include <print>
-#include <stdio.h>
 #include <sys/select.h>
 #include <sys/socket.h>
 #include <sys/types.h>
@@ -9,15 +9,15 @@
 
 int main(void)
 {
-    auto x = mst::TcpListener::bind("0.0.0.0", PORT);
+    auto mgr = mst::event::Manager::create().value();
+    auto x = mst::Server::bind(mgr, "0.0.0.0", PORT);
     if (!x) {
         std::println("{}", x.error());
         return 1;
     }
     std::println("starting");
-    auto listener = x.value();
     {
-        auto x = listener.loop();
+        auto x = mgr.start();
     }
     return 0;
 }
diff --git a/backend/src/result.hpp b/backend/src/result.hpp
new file mode 100644
index 0000000..ebd8a58
--- /dev/null
+++ b/backend/src/result.hpp
@@ -0,0 +1,5 @@
+#pragma once
+#include <expected>
+#include <string>
+
+template <typename T> using Result = std::expected<T, std::string>;
diff --git a/backend/src/server.cpp b/backend/src/server.cpp
index e69de29..b1ea4cb 100644
--- a/backend/src/server.cpp
+++ b/backend/src/server.cpp
@@ -0,0 +1,61 @@
+#include "server.hpp"
+#include "errno_shim.hpp"
+#include "event_loop.hpp"
+#include <print>
+#include <sys/epoll.h>
+
+namespace mst {
+
+auto Client::wake() -> Result<void>
+{
+    uint8_t buffer[128] = { };
+    auto x = this->connection.read(buffer, 128);
+    if (!x) {
+        return std::unexpected(x.error());
+    }
+    auto bytes_read = x.value();
+    for (size_t i = 0; i < bytes_read; ++i) {
+        std::println("{:c}", buffer[i]);
+    }
+
+    return { };
+}
+
+auto Server::bind(mst::event::Manager& mgr, const std::string& host,
+    uint16_t port) -> Result<void>
+{
+    auto x = TcpListener::bind(host, port);
+    if (!x) {
+        return std::unexpected(x.error());
+    }
+    auto listener = x.value();
+    auto context = event::make_event(event::Server, Server(listener));
+    auto poll_event
+        = epoll_event { .events = EPOLLIN, .data = { .ptr = context } };
+    if (::epoll_ctl(mgr.epoll_fd, EPOLL_CTL_ADD, listener.fd, &poll_event)
+        < 0) {
+        return std::unexpected(errno_shim("could not add listener to epoll"));
+    }
+    return { };
+}
+
+auto Server::wake(event::Manager& mgr) -> Result<void>
+{
+    auto x = this->listener.accept();
+    auto connection = x.value();
+
+    auto context
+        = event::make_event(event::Client, mst::Client(*this, connection));
+
+    auto poll_event
+        = epoll_event { .events = EPOLLIN, .data = { .ptr = context } };
+
+    if (::epoll_ctl(mgr.epoll_fd, EPOLL_CTL_ADD, connection.fd, &poll_event)
+        < 0) {
+        return std::unexpected(
+            mst::errno_shim("could not add connection to epoll"));
+    }
+    return { };
+}
+
+}
diff --git a/backend/src/server.hpp b/backend/src/server.hpp
index 6f70f09..351bdb6 100644
--- a/backend/src/server.hpp
+++ b/backend/src/server.hpp
@@ -1 +1,36 @@
 #pragma once
+
+#include "event_loop.hpp"
+#include "tcp.hpp"
+
+namespace mst {
+
+class Server {
+public:
+    auto wake(mst::event::Manager& mgr) -> Result<void>;
+    static auto bind(mst::event::Manager& mgr, const std::string& host,
+        uint16_t port) -> Result<void>;
+
+private:
+    TcpListener listener;
+
+    Server(TcpListener listener)
+        : listener(listener)
+    {
+    }
+};
+
+class Client {
+public:
+    auto wake() -> Result<void>;
+
+    Client(Server&, TcpConnection connection)
+        : connection(connection)
+    {
+    }
+
+private:
+    TcpConnection connection;
+};
+
+}
diff --git a/backend/src/tcp.cpp b/backend/src/tcp.cpp
index 68dee7b..be3155d 100644
--- a/backend/src/tcp.cpp
+++ b/backend/src/tcp.cpp
@@ -1,50 +1,19 @@
 #include "tcp.hpp"
+#include "errno_shim.hpp"
 #include <arpa/inet.h>
 #include <cstdlib>
-#include <errno.h>
 #include <expected>
-#include <format>
 #include <netdb.h>
 #include <netinet/in.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
 #include <string>
-#include <string_view>
 #include <sys/epoll.h>
 #include <sys/socket.h>
 #include <unistd.h>
 
 namespace mst {
 
-auto event::make_listener_event(int fd) -> Event*
-{
-    auto ev = (Event*)malloc(sizeof(Event));
-
-    ev->variant = Listener;
-    ev->data.listener_fd = fd;
-
-    return ev;
-}
-
-auto event::make_connection_event(TcpConnection connection) -> Event*
-{
-    auto ev = (Event*)malloc(sizeof(Event));
-    auto ptr = (TcpConnection*)std::malloc(sizeof(TcpConnection));
-    *ptr = connection;
-
-    ev->variant = Connection;
-    ev->data.connection = ptr;
-
-    return ev;
-}
-
-auto errno_shim(std::string_view message) -> std::string
-{
-    auto x = strerror(errno);
-    return std::format("{} ({})", message, x);
-}
-
 auto TcpConnection::write(uint8_t* buffer, size_t len) -> Result<size_t>
 {
     ssize_t bytes_written = ::write(this->fd, buffer, len);
@@ -86,61 +55,18 @@ auto TcpListener::bind(const std::string& host, uint16_t port)
         return std::unexpected(errno_shim("could not listen"));
     }
 
-    auto epoll_fd = ::epoll_create1(0);
-
-    auto context = event::make_listener_event(socket_fd);
-
-    auto event = epoll_event { .events = EPOLLIN, .data = { .ptr = context } };
-    if (::epoll_ctl(epoll_fd, EPOLL_CTL_ADD, socket_fd, &event) < 0) {
-        return std::unexpected(errno_shim("could not connect to epoll"));
-    }
-
-    return TcpListener(epoll_fd, address);
+    return TcpListener(address, socket_fd);
 }
 
-auto TcpListener::start() -> Result<void>
+auto TcpListener::accept() -> Result<TcpConnection>
 {
-    epoll_event events[128] = { };
-    while (true) {
-
-        auto events_len = ::epoll_wait(this->epoll_fd, events, 128, -1);
-        if (events_len < 0) {
-            return std::unexpected(errno_shim("could not poll"));
-        }
-        for (int i = 0; i < events_len; ++i) {
-            auto event = (event::Event*)events[i].data.ptr;
-
-            switch (event->variant) {
-                case event::Listener: {
-                    socklen_t size = sizeof(address);
-                    int client = ::accept(
-                        events[0].data.fd, (struct sockaddr*)&address, &size);
-                    if (client < 0) {
-                        return std::unexpected(errno_shim("could not accept"));
-                    }
-
-                    auto context = event::make_connection_event(
-                        TcpConnection(*this, client));
-
-                    auto poll_event = epoll_event { .events = EPOLLIN,
-                        .data = { .ptr = context } };
-
-                    if (::epoll_ctl(
-                            epoll_fd, EPOLL_CTL_ADD, client, &poll_event)
-                        < 0) {
-                        return std::unexpected(
-                            errno_shim("could not add connection to epoll"));
-                    }
-
-                    break;
-                }
-                case event::Connection: {
-                    event->data.connection.wake();
-                    break;
-                }
-            }
-        }
+    socklen_t size = sizeof(this->address);
+    int client = ::accept(this->fd, (struct sockaddr*)&address, &size);
+    if (client < 0) {
+        return std::unexpected(errno_shim("could not accept"));
     }
+
+    return TcpConnection(*this, client);
 }
 
 }
diff --git a/backend/src/tcp.hpp b/backend/src/tcp.hpp
index 30b6538..b1ce2ca 100644
--- a/backend/src/tcp.hpp
+++ b/backend/src/tcp.hpp
@@ -1,32 +1,13 @@
 #pragma once
 
+#include "result.hpp"
 #include <cstdint>
-#include <expected>
 #include <netinet/in.h>
 #include <string>
 #include <unistd.h>
 
 namespace mst {
 
-template <typename T> using Result = std::expected<T, std::string>;
-
-class TcpConnection;
-
-namespace event {
-    enum Variant { Listener, Connection };
-    typedef union {
-        int listener_fd;
-        TcpConnection* connection;
-    } Data;
-    struct Event {
-        Variant variant;
-        Data data;
-    };
-
-    auto make_listener_event(int fd) -> Event*;
-    auto make_connection_event(TcpConnection connection) -> Event*;
-}
-
 class TcpListener;
 
 class TcpConnection {
@@ -36,9 +17,7 @@ public:
     TcpConnection(TcpListener&, int fd)
         : fd(fd) { };
 
-private:
     int fd;
-    event::Event event;
 };
 
 class TcpListener {
@@ -46,13 +25,13 @@ class TcpListener {
 public:
     static auto bind(const std::string& host, uint16_t port)
         -> Result<TcpListener>;
-    auto start() -> Result<void>;
+    auto accept() -> Result<TcpConnection>;
+    int fd;
 
 private:
-    TcpListener(int epoll_fd, sockaddr_in address)
-        : epoll_fd(epoll_fd)
+    TcpListener(sockaddr_in address, int fd)
+        : fd(fd)
         , address(address) { };
-    int epoll_fd;
     sockaddr_in address;
 };
 }