From 2b458747f8f997202aaa4392237348a954e35120 Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Tue, 19 Aug 2025 12:04:13 -0400
Subject: [PATCH] Use writev

---
 src/main.cpp | 62 ++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 45 insertions(+), 17 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index 3c195ee..687cb1f 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -10,11 +10,13 @@
 #include <fcntl.h>
 #include <inttypes.h>
 #include <iostream>
+#include <limits.h>
 #include <netdb.h>
 #include <netinet/tcp.h>
 #include <sys/epoll.h>
 #include <sys/socket.h>
 #include <sys/types.h>
+#include <sys/uio.h>
 #include <sys/un.h>
 #include <thread>
 #include <unistd.h>
@@ -147,18 +149,13 @@ struct Connection {
     }
   }
 
-  struct Message {
-    // Owned by Connection::arena
-    std::string_view s;
-    int written = 0;
-  };
-  std::deque<Message, ArenaStlAllocator<Message>> messages{
-      ArenaStlAllocator<Message>{&arena}};
+  std::deque<std::string_view, ArenaStlAllocator<std::string_view>> messages{
+      ArenaStlAllocator<std::string_view>{&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);
+    messages.emplace_back(arena_str, s.size());
   }
   // Whether or not to close the connection after completing writing the
   // response
@@ -192,11 +189,28 @@ struct Connection {
 
   bool writeBytes() {
     while (!messages.empty()) {
-      auto &front = messages.front();
-      int w;
+      // Build iovec array up to IOV_MAX limit
+      struct iovec iov[IOV_MAX];
+      int iov_count = 0;
+
+      for (auto it = messages.begin();
+           it != messages.end() && iov_count < IOV_MAX; ++it) {
+        const auto &msg = *it;
+        if (msg.size() > 0) {
+          iov[iov_count] = {
+              const_cast<void *>(static_cast<const void *>(msg.data())),
+              msg.size()};
+          iov_count++;
+        }
+      }
+
+      if (iov_count == 0) {
+        break;
+      }
+
+      ssize_t w;
       for (;;) {
-        w = write(fd, front.s.data() + front.written,
-                  front.s.size() - front.written);
+        w = writev(fd, iov, iov_count);
         if (w == -1) {
           if (errno == EINTR) {
             continue; // Standard practice: retry on signal interruption
@@ -204,15 +218,29 @@ struct Connection {
           if (errno == EAGAIN) {
             return false;
           }
-          perror("write");
+          perror("writev");
           return true;
         }
         break;
       }
-      assert(w != 0);
-      front.written += w;
-      if (front.written == int(front.s.size())) {
-        messages.pop_front();
+
+      assert(w > 0);
+
+      // Handle partial writes by updating string_view data/size
+      size_t bytes_written = static_cast<size_t>(w);
+      while (bytes_written > 0 && !messages.empty()) {
+        auto &front = messages.front();
+
+        if (bytes_written >= front.size()) {
+          // This message is completely written
+          bytes_written -= front.size();
+          messages.pop_front();
+        } else {
+          // Partial write of this message - update string_view
+          front = std::string_view(front.data() + bytes_written,
+                                   front.size() - bytes_written);
+          bytes_written = 0;
+        }
       }
     }
     assert(messages.empty());