# HG changeset patch
# User Kim Alvefur <zash@zash.se>
# Date 1699740514 -3600
# Node ID 6d6291dfe735119acf7f2c220785ed0ea2e60fe6
# Parent  4a437dd62cc9d237430bf8f30cd3d18f1edbe7d5
net.http: Add simple connection pooling

This should speed up repeated requests to the same site by keeping their
connections around and sending more requests on them.

Sending multiple requests at the same time is not supported, instead a
request started while another to the same authority is in progress would
open a new one and the first one to complete would go back in the pool.
This could be investigated in the future.

Some http servers limit the number of requests per connection and this
is not tested and could cause one request to fail, but hopefully it will
close the connection and prevent it from being reused.

diff -r 4a437dd62cc9 -r 6d6291dfe735 net/http.lua
--- a/net/http.lua	Mon Jul 17 04:30:35 2023 +0200
+++ b/net/http.lua	Sat Nov 11 23:08:34 2023 +0100
@@ -51,10 +51,19 @@
 	return ...;
 end
 
-local function destroy_request(request)
+local function destroy_request(request, force)
 	local conn = request.conn;
 	if conn then
 		request.conn = nil;
+		local pool = request.http.pool;
+		if pool and not force then
+			local pool_id = request.scheme .. "://" .. request.authority;
+			if not pool[pool_id] then
+				pool[conn] = pool_id;
+				pool[pool_id] = conn;
+				return;
+			end
+		end
 		conn:close()
 	end
 end
@@ -193,6 +202,13 @@
 	if request and request.conn then
 		request:reader(nil, err or "closed");
 	end
+	if request and request.http.pool then
+		local pool = request.http.pool;
+		local pool_id = pool[conn];
+		if pool_id then
+			pool[pool_id], pool[conn] = nil, nil;
+		end
+	end
 	requests[conn] = nil;
 end
 
@@ -296,6 +312,23 @@
 		end
 	end
 
+	if self.pool then
+		local pool_id = req.scheme .. "://" .. req.authority;
+		local conn = self.pool[pool_id];
+		if conn then
+			log("debug", "Re-using connection to %s from pool", req.host);
+			self.pool[pool_id] = nil;
+			self.pool[conn] = nil;
+			req.conn = conn;
+			requests[conn] = req;
+			self.events.fire_event("request", { http = self, request = req, url = u });
+			listener.onconnect(conn);
+			return req;
+		else
+			log("debug", "Opening a new connection for this request");
+		end
+	end
+
 	local http_service = basic_resolver.new(host, port_number, "tcp", { servername = req.host; use_dane = use_dane });
 	connect(http_service, listener, { sslctx = sslctx }, req);
 
@@ -332,6 +365,10 @@
 		end or new;
 		events = events.new();
 	};
+	if options and options.connection_pooling then
+		-- util.cache in the future?
+		http.pool = {};
+	end
 	return http;
 end