From 5dc800a088778aaf3067f93cd2fdec2c2fb0a93d Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Tue, 19 Aug 2025 11:51:44 -0400
Subject: [PATCH] Add Connection::arena

---
 src/main.cpp | 58 +++++++++++++++++++++++++++++++++-------------------
 1 file changed, 37 insertions(+), 21 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index 785a680..3c195ee 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,3 +1,4 @@
+#include "arena_allocator.hpp"
 #include "config.hpp"
 #include <atomic>
 #include <cassert>
@@ -130,6 +131,7 @@ struct Connection {
   const int fd;
   const int64_t id;
   struct sockaddr_storage addr; // sockaddr_storage handles IPv4/IPv6
+  ArenaAllocator arena;
 
   Connection(struct sockaddr_storage addr, int fd, int64_t id)
       : fd(fd), id(id), addr(addr) {
@@ -145,15 +147,24 @@ struct Connection {
     }
   }
 
-  struct Task {
-    std::string s;
-    bool closeConnection{false};
+  struct Message {
+    // Owned by Connection::arena
+    std::string_view s;
     int written = 0;
   };
+  std::deque<Message, ArenaStlAllocator<Message>> messages{
+      ArenaStlAllocator<Message>{&arena}};
+  // Copies s into arena, and appends to messages
+  void appendMessage(std::string_view s) {
+    char *arena_str = arena.allocate<char>(s.size());
+    std::memcpy(arena_str, s.data(), s.size());
+    messages.emplace_back(std::string_view(arena_str, s.size()), 0);
+  }
+  // Whether or not to close the connection after completing writing the
+  // response
+  bool closeConnection{false};
 
-  std::deque<Task> tasks;
-
-  void readBytes(size_t max_request_size) {
+  bool readBytes(size_t max_request_size) {
     // Use smaller buffer size but respect max request size
     // TODO revisit
     size_t buf_size = std::min(size_t(4096), max_request_size);
@@ -165,28 +176,23 @@ struct Connection {
           continue;
         }
         if (errno == EAGAIN) {
-          return;
+          return false;
         }
         perror("read");
-        goto close_connection;
+        return true;
       }
       if (r == 0) {
-        goto close_connection;
+        return true;
       }
       // "pump parser"
       // TODO revisit
-      tasks.emplace_back(std::string{buf.data(), size_t(r)});
+      appendMessage({buf.data(), size_t(r)});
     }
-  close_connection:
-    tasks.emplace_back(std::string{}, true);
   }
 
   bool writeBytes() {
-    while (!tasks.empty()) {
-      auto &front = tasks.front();
-      if (front.closeConnection) {
-        return true;
-      }
+    while (!messages.empty()) {
+      auto &front = messages.front();
       int w;
       for (;;) {
         w = write(fd, front.s.data() + front.written,
@@ -206,10 +212,12 @@ struct Connection {
       assert(w != 0);
       front.written += w;
       if (front.written == int(front.s.size())) {
-        tasks.pop_front();
+        messages.pop_front();
       }
     }
-    return false;
+    assert(messages.empty());
+    arena.reset();
+    return closeConnection;
   }
 
   // This is necessary because tsan doesn't (yet?) understand that there's a
@@ -346,8 +354,16 @@ int main(int argc, char *argv[]) {
                 continue;
               }
 
+              // When we register our epoll interest, if we have something to
+              // write, we write. Otherwise we read.
+              assert(!((events[i].events & EPOLLIN) &&
+                       (events[i].events & EPOLLOUT)));
+
               if (events[i].events & EPOLLIN) {
-                conn->readBytes(max_request_size);
+                bool done = conn->readBytes(max_request_size);
+                if (done) {
+                  continue;
+                }
               }
 
               if (events[i].events & EPOLLOUT) {
@@ -357,7 +373,7 @@ int main(int argc, char *argv[]) {
                 }
               }
 
-              if (conn->tasks.empty()) {
+              if (conn->messages.empty()) {
                 events[i].events = EPOLLIN | EPOLLONESHOT | EPOLLRDHUP;
               } else {
                 events[i].events = EPOLLOUT | EPOLLONESHOT | EPOLLRDHUP;