initial rate limit support

driver/main.cpp

@@ -37,7 +37,6 @@ auto configure_sasl(const Settings &settings) -> std::unique_ptr<SaslMechanism>
         settings.sasl_mechanism == "ECDSA" &&
         not settings.sasl_authcid.empty() &&
         not settings.sasl_key_file.empty()
-
     ) {
         if (auto sasl_key = key_from_file(settings.sasl_key_file, settings.sasl_key_password))
             return std::make_unique<SaslEcdsa>(
@@ -62,18 +61,17 @@ static auto start(boost::asio::io_context &io, const Settings &settings) -> void
         tls_key = key_from_file(settings.tls_key_file, settings.tls_key_password);
     }
 
-    auto sasl_mech = configure_sasl(settings);
-
     const auto connection = std::make_shared<Connection>(io);
     const auto client = Client::start(connection);
+    const auto bot = Bot::start(client);
+
     Registration::start({
         .nickname = settings.nickname,
         .realname = settings.realname,
         .username = settings.username,
         .password = settings.password,
-        .sasl_mechanism = std::move(sasl_mech),
+        .sasl_mechanism = configure_sasl(settings),
     }, client);
-    const auto bot = Bot::start(client);
 
     // Configure CHALLENGE on registration if applicable
     if (not settings.challenge_username.empty() && not settings.challenge_key_file.empty()) {
@@ -84,7 +82,7 @@ static auto start(boost::asio::io_context &io, const Settings &settings) -> void
         }
     }
 
-    // On disconnect tear down the various layers and reconnect in 5 seconds
+    // On disconnect reconnect in 5 seconds
     // connection is captured in the disconnect handler so it can keep itself alive
     connection->sig_disconnect.connect(
         [&io, &settings, connection]() {

myirc/CMakeLists.txt

@@ -17,6 +17,7 @@ add_library(myirc STATIC
   ircmsg.cpp
   openssl_utils.cpp
   registration.cpp
+  ratelimit.cpp
   sasl_mechanism.cpp
   snote.cpp
 )

myirc/connection.cpp

@@ -1,5 +1,6 @@
 #include "connection.hpp"
 
+#include "boost/asio/steady_timer.hpp"
 #include "linebuffer.hpp"
 
 #include <mybase64.hpp>
@@ -25,16 +26,51 @@ Connection::Connection(boost::asio::io_context &io)
 
 auto Connection::write_buffers() -> void
 {
+    const auto available = write_strings_.size();
+    const auto [delay, count]
+        = rate_limit
+        ? rate_limit->query(available)
+        : std::pair{0ms, available};
+
+    if (delay > 0ms) {
+        auto timer = std::make_shared<boost::asio::steady_timer>(stream_.get_executor(), delay);
+        timer->async_wait([timer, count, self = weak_from_this()](auto) {
+            if (auto lock = self.lock()) {
+                lock->write_buffers(count);
+            }
+        });
+    } else {
+        write_buffers(count);
+    }
+}
+
+auto Connection::write_buffers(size_t n) -> void
+{
+    std::list<std::string> strings;
     std::vector<boost::asio::const_buffer> buffers;
-    buffers.reserve(write_strings_.size());
-    for (const auto &elt : write_strings_)
+
+    if (n == write_strings_.size()) {
+        strings = std::move(write_strings_);
+        write_strings_.clear();
+    } else {
+        strings.splice(
+            strings.begin(), // insert at
+           write_strings_, // remove from
+            write_strings_.begin(), // start removing at
+            std::next(write_strings_.begin(), n) // stop removing at
+        );
+    }
+
+    buffers.reserve(n);
+    for (const auto &elt : strings)
     {
         buffers.push_back(boost::asio::buffer(elt));
     }
+
     boost::asio::async_write(
         stream_,
         buffers,
-        [this, strings = std::move(write_strings_)](const boost::system::error_code &error, std::size_t) {
+        [this, strings = std::move(strings)](const boost::system::error_code &error, std::size_t) {
             if (not error)
             {
                 if (write_strings_.empty())
@@ -48,7 +84,6 @@ auto Connection::write_buffers() -> void
             }
         }
     );
-    write_strings_.clear();
 }
 
 auto Connection::watchdog() -> void
@@ -154,14 +189,17 @@ auto Connection::write_irc(std::string message) -> void
 
 auto Connection::write_irc(std::string front, std::string_view last) -> void
 {
-    if (last.find_first_of("\r\n\0"sv) != last.npos)
-    {
-        throw std::runtime_error{"bad irc argument"};
+    bool colon = last.starts_with(":");
+    for (const auto c : last) {
+        switch (c) {
+            case '\r': case '\n': case '\0': throw std::runtime_error{"bad irc argument"};
+            case ' ': colon = true;
+            default: break;
+        }
     }
-
-    front += " :";
+    front += colon ? " :" : " ";
     front += last;
-    write_irc(std::move(front));
+    write_line(std::move(front));
 }
 
 auto Connection::send_ping(std::string_view txt) -> void

myirc/include/connection.hpp

@@ -2,6 +2,7 @@
 
 #include "irc_command.hpp"
 #include "ircmsg.hpp"
+#include "ratelimit.hpp"
 #include "ref.hpp"
 #include "snote.hpp"
 #include "stream.hpp"
@@ -46,7 +47,12 @@ private:
     // AUTHENTICATE support
     std::string authenticate_buffer_;
 
+    /// write buffers after consulting with rate limit
     auto write_buffers() -> void;
+
+    /// write a specific number of messages now
+    auto write_buffers(size_t) -> void;
+
     auto dispatch_line(char *line) -> void;
 
     static constexpr std::chrono::seconds watchdog_duration = std::chrono::seconds{30};
@@ -68,6 +74,7 @@ public:
     boost::signals2::signal<void(IrcCommand, const IrcMsg &)> sig_ircmsg;
     boost::signals2::signal<void(SnoteMatch &)> sig_snote;
     boost::signals2::signal<void(std::string_view)> sig_authenticate;
+    std::unique_ptr<RateLimit> rate_limit;
 
     Connection(boost::asio::io_context &io);
 

myirc/include/ratelimit.hpp

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <chrono>
+#include <utility>
+
+struct RateLimit {
+    virtual ~RateLimit();
+    auto virtual query(size_t want_to_send) -> std::pair<std::chrono::milliseconds, size_t> = 0;
+};
+
+struct Rfc1459RateLimit final : RateLimit
+{
+    using clock = std::chrono::steady_clock;
+
+    std::chrono::milliseconds cost_ {2'000};
+    std::chrono::milliseconds allowance_ {10'000};
+    clock::time_point horizon_{};
+
+    auto query(size_t want_to_send) -> std::pair<std::chrono::milliseconds, size_t> override;
+};

myirc/ratelimit.cpp

@@ -0,0 +1,23 @@
+#include "ratelimit.hpp"
+#include <chrono>
+
+using namespace std::literals;
+using ms = std::chrono::milliseconds;
+
+auto Rfc1459RateLimit::query(size_t want_to_send) -> std::pair<ms, size_t>
+{
+    const auto now = clock::now();
+    if (horizon_ < now) horizon_ = now;
+
+    auto gap = std::chrono::floor<ms>(now + allowance_ - horizon_);
+    auto send = gap / cost_;
+    if (std::cmp_greater(send, want_to_send)) send = want_to_send;
+
+    if (send > 0) {
+        horizon_ += send * cost_;
+        return {0ms, send};
+    } else {
+        horizon_ += cost_;
+        return {cost_ - gap, 1};
+    }
+}