adding max channels per upstream connection as configurable item

README.md

@@ -70,6 +70,7 @@ You probably want to modify `/etc/systemd/system/amqproxy.service` and configure
 | Listen port             | Port to listen on. This is the port which will be the target of clients                                                                                                                                                                                                                                                                                                         | `--port` / `-p`                             | `LISTEN_PORT`             | `[listen] > port`                             | `5673`        |
 | Log level               | Controls log verbosity.<br><br>Available levels (see [84codes/logger.cr](https://github.com/84codes/logger.cr/blob/main/src/logger.cr#L86)):<br> - `DEBUG`: Low-level information for developers<br> - `INFO`: Generic (useful) information about system operation<br> - `WARN`: Warnings<br> - `ERROR`: Handleable error conditions<br> - `FATAL`: Unhandleable errors that results in a program crash | `--debug` / `-d`: Sets the level to `DEBUG` | -                         | `[main] > log_level`                         | `INFO`          |
 | Idle connection timeout | Maximum time in seconds an unused pooled connection stays open                                                                                                                                                                                                                                                                                                                  | `--idle-connection-timeout` / `-t`          | `IDLE_CONNECTION_TIMEOUT` | `[main] > idle_connection_timeout`           | `5`           |
+| Max upstream channels   | Maximum number of channels per upstream connection. The effective limit will be the lowest value between this setting and the upstream server's channel_max from the connection tune packet                                                                                                                                                                                     | `--max-upstream-channels`                   | `MAX_UPSTREAM_CHANNELS`   | `[main] > max_upstream_channels`             | `65535`       |
 | Upstream                | AMQP URL that points to the upstream RabbitMQ server to which the proxy should connect to. May only contain scheme, host & port (optional). Example: `amqps://rabbitmq.example.com`                                                                                                                                                                                             | Pass as argument after all options          | `AMQP_URL`                | `[main] > upstream`                          |               |
 
 ### How to configure

config/example.ini

@@ -1,6 +1,7 @@
 [main]
 log_level = info
 idle_connection_timeout = 5
+max_upstream_channels = 65535
 upstream = amqp://localhost:5672
 
 [listen]

spec/amqproxy/server_spec.cr

@@ -90,6 +90,19 @@ describe AMQProxy::Server do
     end
   end
 
+  it "creates multiple upstreams when max_upstream_channels is low" do
+    with_server(max_upstream_channels: 10_u16) do |server, proxy_url|
+      AMQP::Client.start(proxy_url) do |conn|
+        25.times { conn.channel }
+        server.client_connections.should eq 1
+        server.upstream_connections.should be >= 3
+      end
+      sleep 0.1.seconds
+      server.client_connections.should eq 0
+      server.upstream_connections.should eq 3
+    end
+  end
+
   it "can reconnect if upstream closes" do
     with_server do |server, proxy_url|
       Fiber.yield

spec/spec_helper.cr

@@ -16,8 +16,12 @@ rescue e : URI::Error
   exit 1
 end
 
-def with_server(idle_connection_timeout = 5, &)
-  server = AMQProxy::Server.new(UPSTREAM_URL)
+def with_server(idle_connection_timeout = 5, max_upstream_channels = UInt16::MAX, &)
+  tls = UPSTREAM_URL.scheme == "amqps"
+  host = UPSTREAM_URL.host || "127.0.0.1"
+  port = UPSTREAM_URL.port || 5672
+  port = 5671 if tls && UPSTREAM_URL.port.nil?
+  server = AMQProxy::Server.new(host, port, tls, idle_connection_timeout, max_upstream_channels)
   tcp_server = TCPServer.new("127.0.0.1", 0)
   amqp_url = "amqp://#{tcp_server.local_address}"
   spawn { server.listen(tcp_server) }

src/amqproxy/channel_pool.cr

@@ -9,7 +9,7 @@ module AMQProxy
     @lock = Mutex.new
     @upstreams = Deque(Upstream).new
 
-    def initialize(@host : String, @port : Int32, @tls_ctx : OpenSSL::SSL::Context::Client?, @credentials : Credentials, @idle_connection_timeout : Int32)
+    def initialize(@host : String, @port : Int32, @tls_ctx : OpenSSL::SSL::Context::Client?, @credentials : Credentials, @idle_connection_timeout : Int32, @max_upstream_channels : UInt16)
       spawn shrink_pool_loop, name: "shrink pool loop"
     end
 
@@ -36,7 +36,7 @@ module AMQProxy
     end
 
     private def add_upstream
-      upstream = Upstream.new(@host, @port, @tls_ctx, @credentials)
+      upstream = Upstream.new(@host, @port, @tls_ctx, @credentials, @max_upstream_channels)
       Log.info { "Adding upstream connection" }
       @upstreams.unshift upstream
       spawn(name: "Upstream#read_loop") do

src/amqproxy/cli.cr

@@ -14,6 +14,7 @@ class AMQProxy::CLI
   @http_port = 15673
   @log_level : ::Log::Severity = ::Log::Severity::Info
   @idle_connection_timeout : Int32 = 5
+  @max_upstream_channels : UInt16 = UInt16::MAX
   @term_timeout = -1
   @term_client_close_timeout = 0
   @server : AMQProxy::Server? = nil
@@ -27,6 +28,7 @@ class AMQProxy::CLI
           when "upstream"                  then @upstream = value
           when "log_level"                 then @log_level = ::Log::Severity.parse(value)
           when "idle_connection_timeout"   then @idle_connection_timeout = value.to_i
+          when "max_upstream_channels"     then @max_upstream_channels = value.to_u16
           when "term_timeout"              then @term_timeout = value.to_i
           when "term_client_close_timeout" then @term_client_close_timeout = value.to_i
           else                                  raise "Unsupported config #{name}/#{key}"
@@ -54,6 +56,7 @@ class AMQProxy::CLI
     @http_port = ENV["HTTP_PORT"]?.try &.to_i || @http_port
     @log_level = ENV["LOG_LEVEL"]?.try { |level| ::Log::Severity.parse(level) } || @log_level
     @idle_connection_timeout = ENV["IDLE_CONNECTION_TIMEOUT"]?.try &.to_i || @idle_connection_timeout
+    @max_upstream_channels = ENV["MAX_UPSTREAM_CHANNELS"]?.try &.to_u16 || @max_upstream_channels
     @term_timeout = ENV["TERM_TIMEOUT"]?.try &.to_i || @term_timeout
     @term_client_close_timeout = ENV["TERM_CLIENT_CLOSE_TIMEOUT"]?.try &.to_i || @term_client_close_timeout
     @upstream = ENV["AMQP_URL"]? || @upstream
@@ -81,6 +84,9 @@ class AMQProxy::CLI
       parser.on("-t IDLE_CONNECTION_TIMEOUT", "--idle-connection-timeout=SECONDS", "Maximum time in seconds an unused pooled connection stays open (default 5s)") do |v|
         @idle_connection_timeout = v.to_i
       end
+      parser.on("--max-upstream-channels=CHANNELS", "Maximum channels per upstream connection (default: server max or 65535)") do |v|
+        @max_upstream_channels = v.to_u16
+      end
       parser.on("--term-timeout=SECONDS", "At TERM the server waits SECONDS seconds for clients to gracefully close their sockets after Close has been sent (default: infinite)") do |v|
         @term_timeout = v.to_i
       end
@@ -117,7 +123,7 @@ class AMQProxy::CLI
     Signal::INT.trap &->self.initiate_shutdown(Signal)
     Signal::TERM.trap &->self.initiate_shutdown(Signal)
 
-    server = @server = AMQProxy::Server.new(u.hostname || "", port, tls, @idle_connection_timeout)
+    server = @server = AMQProxy::Server.new(u.hostname || "", port, tls, @idle_connection_timeout, @max_upstream_channels)
 
     HTTPServer.new(server, @listen_address, @http_port.to_i)
     server.listen(@listen_address, @listen_port.to_i)

src/amqproxy/server.cr

@@ -21,10 +21,10 @@ module AMQProxy
       new(host, port, tls, idle_connection_timeout)
     end
 
-    def initialize(upstream_host, upstream_port, upstream_tls, idle_connection_timeout = 5)
+    def initialize(upstream_host, upstream_port, upstream_tls, idle_connection_timeout = 5, max_upstream_channels = UInt16::MAX)
       tls_ctx = OpenSSL::SSL::Context::Client.new if upstream_tls
       @channel_pools = Hash(Credentials, ChannelPool).new do |hash, credentials|
-        hash[credentials] = ChannelPool.new(upstream_host, upstream_port, tls_ctx, credentials, idle_connection_timeout)
+        hash[credentials] = ChannelPool.new(upstream_host, upstream_port, tls_ctx, credentials, idle_connection_timeout, max_upstream_channels)
       end
       Log.info { "Proxy upstream: #{upstream_host}:#{upstream_port} #{upstream_tls ? "TLS" : ""}" }
     end

src/amqproxy/upstream.cr

@@ -16,7 +16,7 @@ module AMQProxy
     @channel_max : UInt16
     @frame_max : UInt32
 
-    def initialize(@host : String, @port : Int32, @tls_ctx : OpenSSL::SSL::Context::Client?, credentials)
+    def initialize(@host : String, @port : Int32, @tls_ctx : OpenSSL::SSL::Context::Client?, credentials, @max_upstream_channels : UInt16 = UInt16::MAX)
       tcp_socket = TCPSocket.new(@host, @port)
       tcp_socket.sync = false
       tcp_socket.keepalive = true
@@ -203,7 +203,9 @@ module AMQProxy
 
       case tune = AMQ::Protocol::Frame.from_io(@socket)
       when AMQ::Protocol::Frame::Connection::Tune
-        channel_max = tune.channel_max.zero? ? UInt16::MAX : tune.channel_max
+        server_max = tune.channel_max.zero? ? UInt16::MAX : tune.channel_max
+        max_upstream_channels = @max_upstream_channels.zero? ? UInt16::MAX : @max_upstream_channels 
+        channel_max = Math.min(server_max, max_upstream_channels)
         frame_max = tune.frame_max.zero? ? 131072_u32 : Math.min(131072_u32, tune.frame_max)
         tune_ok = AMQ::Protocol::Frame::Connection::TuneOk.new(channel_max, frame_max, tune.heartbeat)
         @socket.write_bytes tune_ok, IO::ByteFormat::NetworkEndian