RequestServer+LibHTTP+LibGemini: Cache connections to the same host

This makes connections (particularly TLS-based ones) do the handshaking
stuff only once.
Currently the cache is configured to keep at most two connections evenly
balanced in queue size, and with a grace period of 10s after the last
queued job has finished (after which the connection will be dropped).

22 files changed, 295 insertions, 51 deletions

diff --git a/Userland/Libraries/LibCore/IODevice.h b/Userland/Libraries/LibCore/IODevice.h
index a13f6ea996..86e4ac8f8a 100644
--- a/Userland/Libraries/LibCore/IODevice.h
+++ b/Userland/Libraries/LibCore/IODevice.h
@@ -82,6 +82,7 @@ public:
     bool can_read_line() const;
 
     bool can_read() const;
+    bool can_read_only_from_buffer() const { return !m_buffered_data.is_empty() && !can_read_from_fd(); }
 
     bool seek(i64, SeekMode = SeekMode::SetPosition, off_t* = nullptr);
 
diff --git a/Userland/Libraries/LibCore/NetworkJob.cpp b/Userland/Libraries/LibCore/NetworkJob.cpp
index f393cc93af..dd8b15ed00 100644
--- a/Userland/Libraries/LibCore/NetworkJob.cpp
+++ b/Userland/Libraries/LibCore/NetworkJob.cpp
@@ -19,7 +19,7 @@ NetworkJob::~NetworkJob()
 {
 }
 
-void NetworkJob::start()
+void NetworkJob::start(NonnullRefPtr<Core::Socket>)
 {
 }
 
diff --git a/Userland/Libraries/LibCore/NetworkJob.h b/Userland/Libraries/LibCore/NetworkJob.h
index 911a556ac7..781dc825a8 100644
--- a/Userland/Libraries/LibCore/NetworkJob.h
+++ b/Userland/Libraries/LibCore/NetworkJob.h
@@ -35,7 +35,7 @@ public:
     NetworkResponse* response() { return m_response.ptr(); }
     const NetworkResponse* response() const { return m_response.ptr(); }
 
-    virtual void start() = 0;
+    virtual void start(NonnullRefPtr<Core::Socket>) = 0;
     virtual void shutdown() = 0;
 
     void cancel()
diff --git a/Userland/Libraries/LibGemini/GeminiJob.cpp b/Userland/Libraries/LibGemini/GeminiJob.cpp
index 6ab80ae571..340d470644 100644
--- a/Userland/Libraries/LibGemini/GeminiJob.cpp
+++ b/Userland/Libraries/LibGemini/GeminiJob.cpp
@@ -14,15 +14,11 @@
 
 namespace Gemini {
 
-void GeminiJob::start()
+void GeminiJob::start(NonnullRefPtr<Core::Socket> socket)
 {
     VERIFY(!m_socket);
-    m_socket = TLS::TLSv12::construct(this);
-    m_socket->set_root_certificates(m_override_ca_certificates ? *m_override_ca_certificates : DefaultRootCACertificates::the().certificates());
-    m_socket->on_tls_connected = [this] {
-        dbgln_if(GEMINIJOB_DEBUG, "GeminiJob: on_connected callback");
-        on_socket_connected();
-    };
+    VERIFY(is<TLS::TLSv12>(*socket));
+    m_socket = static_ptr_cast<TLS::TLSv12>(socket);
     m_socket->on_tls_error = [this](TLS::AlertDescription error) {
         if (error == TLS::AlertDescription::HandshakeFailure) {
             deferred_invoke([this] {
@@ -45,11 +41,20 @@ void GeminiJob::start()
         if (on_certificate_requested)
             on_certificate_requested(*this);
     };
-    bool success = ((TLS::TLSv12&)*m_socket).connect(m_request.url().host(), m_request.url().port_or_default());
-    if (!success) {
-        deferred_invoke([this] {
-            return did_fail(Core::NetworkJob::Error::ConnectionFailed);
-        });
+
+    if (m_socket->is_established()) {
+        deferred_invoke([this] { on_socket_connected(); });
+    } else {
+        m_socket->set_root_certificates(m_override_ca_certificates ? *m_override_ca_certificates : DefaultRootCACertificates::the().certificates());
+        m_socket->on_tls_connected = [this] {
+            on_socket_connected();
+        };
+        bool success = ((TLS::TLSv12&)*m_socket).connect(m_request.url().host(), m_request.url().port_or_default());
+        if (!success) {
+            deferred_invoke([this] {
+                return did_fail(Core::NetworkJob::Error::ConnectionFailed);
+            });
+        }
     }
 }
 
@@ -59,7 +64,6 @@ void GeminiJob::shutdown()
         return;
     m_socket->on_tls_ready_to_read = nullptr;
     m_socket->on_tls_connected = nullptr;
-    remove_child(*m_socket);
     m_socket = nullptr;
 }
 
diff --git a/Userland/Libraries/LibGemini/GeminiJob.h b/Userland/Libraries/LibGemini/GeminiJob.h
index 2407d2cca5..20cc8afcf9 100644
--- a/Userland/Libraries/LibGemini/GeminiJob.h
+++ b/Userland/Libraries/LibGemini/GeminiJob.h
@@ -27,10 +27,13 @@ public:
     {
     }
 
-    virtual void start() override;
+    virtual void start(NonnullRefPtr<Core::Socket>) override;
     virtual void shutdown() override;
     void set_certificate(String certificate, String key);
 
+    Core::Socket const* socket() const { return m_socket; }
+    URL url() const { return m_request.url(); }
+
     Function<void(GeminiJob&)> on_certificate_requested;
 
 protected:
diff --git a/Userland/Libraries/LibGemini/Job.h b/Userland/Libraries/LibGemini/Job.h
index 01eac13e11..5bc50216f7 100644
--- a/Userland/Libraries/LibGemini/Job.h
+++ b/Userland/Libraries/LibGemini/Job.h
@@ -19,7 +19,7 @@ public:
     explicit Job(const GeminiRequest&, OutputStream&);
     virtual ~Job() override;
 
-    virtual void start() override = 0;
+    virtual void start(NonnullRefPtr<Core::Socket>) override = 0;
     virtual void shutdown() override = 0;
 
     GeminiResponse* response() { return static_cast<GeminiResponse*>(Core::NetworkJob::response()); }
diff --git a/Userland/Libraries/LibHTTP/HttpJob.cpp b/Userland/Libraries/LibHTTP/HttpJob.cpp
index 98ffbace48..58ab0e28d6 100644
--- a/Userland/Libraries/LibHTTP/HttpJob.cpp
+++ b/Userland/Libraries/LibHTTP/HttpJob.cpp
@@ -12,26 +12,35 @@
 #include <unistd.h>
 
 namespace HTTP {
-void HttpJob::start()
+void HttpJob::start(NonnullRefPtr<Core::Socket> socket)
 {
     VERIFY(!m_socket);
-    m_socket = Core::TCPSocket::construct(this);
-    m_socket->on_connected = [this] {
-        dbgln_if(CHTTPJOB_DEBUG, "HttpJob: on_connected callback");
-        on_socket_connected();
-    };
+    m_socket = move(socket);
     m_socket->on_error = [this] {
         dbgln_if(CHTTPJOB_DEBUG, "HttpJob: on_error callback");
         deferred_invoke([this] {
             did_fail(Core::NetworkJob::Error::ConnectionFailed);
         });
     };
-    bool success = m_socket->connect(m_request.url().host(), m_request.url().port_or_default());
-    if (!success) {
+    if (m_socket->is_connected()) {
+        dbgln("Reusing previous connection for {}", url());
         deferred_invoke([this] {
-            return did_fail(Core::NetworkJob::Error::ConnectionFailed);
+            dbgln_if(CHTTPJOB_DEBUG, "HttpJob: on_connected callback");
+            on_socket_connected();
         });
-    }
+    } else {
+        dbgln("Creating new connection for {}", url());
+        m_socket->on_connected = [this] {
+            dbgln_if(CHTTPJOB_DEBUG, "HttpJob: on_connected callback");
+            on_socket_connected();
+        };
+        bool success = m_socket->connect(m_request.url().host(), m_request.url().port_or_default());
+        if (!success) {
+            deferred_invoke([this] {
+                return did_fail(Core::NetworkJob::Error::ConnectionFailed);
+            });
+        }
+    };
 }
 
 void HttpJob::shutdown()
@@ -40,13 +49,24 @@ void HttpJob::shutdown()
         return;
     m_socket->on_ready_to_read = nullptr;
     m_socket->on_connected = nullptr;
-    remove_child(*m_socket);
     m_socket = nullptr;
 }
 
 void HttpJob::register_on_ready_to_read(Function<void()> callback)
 {
-    m_socket->on_ready_to_read = move(callback);
+    m_socket->on_ready_to_read = [callback = move(callback), this] {
+        callback();
+        // As IODevice so graciously buffers everything, there's a possible
+        // scenario where it buffers the entire response, and we get stuck waiting
+        // for select() in the notifier (which will never return).
+        // So handle this case by exhausting the buffer here.
+        if (m_socket->can_read_only_from_buffer() && m_state != State::Finished && !has_error()) {
+            deferred_invoke([this] {
+                if (m_socket && m_socket->on_ready_to_read)
+                    m_socket->on_ready_to_read();
+            });
+        }
+    };
 }
 
 void HttpJob::register_on_ready_to_write(Function<void()> callback)
diff --git a/Userland/Libraries/LibHTTP/HttpJob.h b/Userland/Libraries/LibHTTP/HttpJob.h
index 07100cd0a0..16ccb3abfb 100644
--- a/Userland/Libraries/LibHTTP/HttpJob.h
+++ b/Userland/Libraries/LibHTTP/HttpJob.h
@@ -27,9 +27,12 @@ public:
     {
     }
 
-    virtual void start() override;
+    virtual void start(NonnullRefPtr<Core::Socket>) override;
     virtual void shutdown() override;
 
+    Core::Socket const* socket() const { return m_socket; }
+    URL url() const { return m_request.url(); }
+
 protected:
     virtual bool should_fail_on_empty_payload() const override { return false; }
     virtual void register_on_ready_to_read(Function<void()>) override;
diff --git a/Userland/Libraries/LibHTTP/HttpRequest.cpp b/Userland/Libraries/LibHTTP/HttpRequest.cpp
index 2bf198290b..5175f75d9c 100644
--- a/Userland/Libraries/LibHTTP/HttpRequest.cpp
+++ b/Userland/Libraries/LibHTTP/HttpRequest.cpp
@@ -55,7 +55,6 @@ ByteBuffer HttpRequest::to_raw_request() const
         builder.append(header.value);
         builder.append("\r\n");
     }
-    builder.append("Connection: close\r\n");
     if (!m_body.is_empty()) {
         builder.appendff("Content-Length: {}\r\n\r\n", m_body.size());
         builder.append((char const*)m_body.data(), m_body.size());
diff --git a/Userland/Libraries/LibHTTP/HttpsJob.cpp b/Userland/Libraries/LibHTTP/HttpsJob.cpp
index 37e4b7502e..0f249fc5fb 100644
--- a/Userland/Libraries/LibHTTP/HttpsJob.cpp
+++ b/Userland/Libraries/LibHTTP/HttpsJob.cpp
@@ -14,15 +14,12 @@
 
 namespace HTTP {
 
-void HttpsJob::start()
+void HttpsJob::start(NonnullRefPtr<Core::Socket> socket)
 {
     VERIFY(!m_socket);
-    m_socket = TLS::TLSv12::construct(this);
-    m_socket->set_root_certificates(m_override_ca_certificates ? *m_override_ca_certificates : DefaultRootCACertificates::the().certificates());
-    m_socket->on_tls_connected = [this] {
-        dbgln_if(HTTPSJOB_DEBUG, "HttpsJob: on_connected callback");
-        on_socket_connected();
-    };
+    VERIFY(is<TLS::TLSv12>(*socket));
+
+    m_socket = static_ptr_cast<TLS::TLSv12>(socket);
     m_socket->on_tls_error = [&](TLS::AlertDescription error) {
         if (error == TLS::AlertDescription::HandshakeFailure) {
             deferred_invoke([this] {
@@ -46,11 +43,22 @@ void HttpsJob::start()
         if (on_certificate_requested)
             on_certificate_requested(*this);
     };
-    bool success = ((TLS::TLSv12&)*m_socket).connect(m_request.url().host(), m_request.url().port_or_default());
-    if (!success) {
-        deferred_invoke([this] {
-            return did_fail(Core::NetworkJob::Error::ConnectionFailed);
-        });
+    if (m_socket->is_established()) {
+        dbgln("Reusing previous connection for {}", url());
+        deferred_invoke([this] { on_socket_connected(); });
+    } else {
+        dbgln("Creating a new connection for {}", url());
+        m_socket->set_root_certificates(m_override_ca_certificates ? *m_override_ca_certificates : DefaultRootCACertificates::the().certificates());
+        m_socket->on_tls_connected = [this] {
+            dbgln_if(HTTPSJOB_DEBUG, "HttpsJob: on_connected callback");
+            on_socket_connected();
+        };
+        bool success = ((TLS::TLSv12&)*m_socket).connect(m_request.url().host(), m_request.url().port_or_default());
+        if (!success) {
+            deferred_invoke([this] {
+                return did_fail(Core::NetworkJob::Error::ConnectionFailed);
+            });
+        }
     }
 }
 
@@ -60,7 +68,6 @@ void HttpsJob::shutdown()
         return;
     m_socket->on_tls_ready_to_read = nullptr;
     m_socket->on_tls_connected = nullptr;
-    remove_child(*m_socket);
     m_socket = nullptr;
 }
 
diff --git a/Userland/Libraries/LibHTTP/HttpsJob.h b/Userland/Libraries/LibHTTP/HttpsJob.h
index d3fce85aeb..c7c20ea7e6 100644
--- a/Userland/Libraries/LibHTTP/HttpsJob.h
+++ b/Userland/Libraries/LibHTTP/HttpsJob.h
@@ -28,10 +28,13 @@ public:
     {
     }
 
-    virtual void start() override;
+    virtual void start(NonnullRefPtr<Core::Socket>) override;
     virtual void shutdown() override;
     void set_certificate(String certificate, String key);
 
+    Core::Socket const* socket() const { return m_socket; }
+    URL url() const { return m_request.url(); }
+
     Function<void(HttpsJob&)> on_certificate_requested;
 
 protected:
diff --git a/Userland/Libraries/LibHTTP/Job.cpp b/Userland/Libraries/LibHTTP/Job.cpp
index 5c75997db8..97c4b317bd 100644
--- a/Userland/Libraries/LibHTTP/Job.cpp
+++ b/Userland/Libraries/LibHTTP/Job.cpp
@@ -85,7 +85,7 @@ void Job::flush_received_buffers()
 {
     if (!m_can_stream_response || m_buffered_size == 0)
         return;
-    dbgln_if(JOB_DEBUG, "Job: Flushing received buffers: have {} bytes in {} buffers", m_buffered_size, m_received_buffers.size());
+    dbgln_if(JOB_DEBUG, "Job: Flushing received buffers: have {} bytes in {} buffers for {}", m_buffered_size, m_received_buffers.size(), m_request.url());
     for (size_t i = 0; i < m_received_buffers.size(); ++i) {
         auto& payload = m_received_buffers[i];
         auto written = do_write(payload);
@@ -100,7 +100,7 @@ void Job::flush_received_buffers()
         payload = payload.slice(written, payload.size() - written);
         break;
     }
-    dbgln_if(JOB_DEBUG, "Job: Flushing received buffers done: have {} bytes in {} buffers", m_buffered_size, m_received_buffers.size());
+    dbgln_if(JOB_DEBUG, "Job: Flushing received buffers done: have {} bytes in {} buffers for {}", m_buffered_size, m_received_buffers.size(), m_request.url());
 }
 
 void Job::on_socket_connected()
@@ -121,6 +121,7 @@ void Job::on_socket_connected()
             deferred_invoke([this] { did_fail(Core::NetworkJob::Error::TransmissionFailed); });
     });
     register_on_ready_to_read([&] {
+        dbgln_if(JOB_DEBUG, "Ready to read for {}, state = {}, cancelled = {}", m_request.url(), to_underlying(m_state), is_cancelled());
         if (is_cancelled())
             return;
 
@@ -132,9 +133,12 @@ void Job::on_socket_connected()
         }
 
         if (m_state == State::InStatus) {
-            if (!can_read_line())
+            if (!can_read_line()) {
+                dbgln_if(JOB_DEBUG, "Job {} cannot read line", m_request.url());
                 return;
+            }
             auto line = read_line(PAGE_SIZE);
+            dbgln_if(JOB_DEBUG, "Job {} read line of length {}", m_request.url(), line.length());
             if (line.is_null()) {
                 dbgln("Job: Expected HTTP status");
                 return deferred_invoke([this] { did_fail(Core::NetworkJob::Error::TransmissionFailed); });
@@ -287,7 +291,9 @@ void Job::on_socket_connected()
                 }
             }
 
+            dbgln_if(JOB_DEBUG, "Waiting for payload for {}", m_request.url());
             auto payload = receive(read_size);
+            dbgln_if(JOB_DEBUG, "Received {} bytes of payload from {}", payload.size(), m_request.url());
             if (payload.is_empty()) {
                 if (eof()) {
                     finish_up();
diff --git a/Userland/Libraries/LibHTTP/Job.h b/Userland/Libraries/LibHTTP/Job.h
index 338d43192f..99a6e0607f 100644
--- a/Userland/Libraries/LibHTTP/Job.h
+++ b/Userland/Libraries/LibHTTP/Job.h
@@ -21,7 +21,7 @@ public:
     explicit Job(const HttpRequest&, OutputStream&);
     virtual ~Job() override;
 
-    virtual void start() override = 0;
+    virtual void start(NonnullRefPtr<Core::Socket>) override = 0;
     virtual void shutdown() override = 0;
 
     HttpResponse* response() { return static_cast<HttpResponse*>(Core::NetworkJob::response()); }
diff --git a/Userland/Services/RequestServer/CMakeLists.txt b/Userland/Services/RequestServer/CMakeLists.txt
index 5033367604..3ad98628bc 100644
--- a/Userland/Services/RequestServer/CMakeLists.txt
+++ b/Userland/Services/RequestServer/CMakeLists.txt
@@ -8,6 +8,7 @@ compile_ipc(RequestClient.ipc RequestClientEndpoint.h)
 
 set(SOURCES
     ClientConnection.cpp
+    ConnectionCache.cpp
     Request.cpp
     RequestClientEndpoint.h
     RequestServerEndpoint.h
diff --git a/Userland/Services/RequestServer/ConnectionCache.cpp b/Userland/Services/RequestServer/ConnectionCache.cpp
new file mode 100644
index 0000000000..e9ef533240
--- /dev/null
+++ b/Userland/Services/RequestServer/ConnectionCache.cpp
@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "ConnectionCache.h"
+#include <LibCore/EventLoop.h>
+
+namespace RequestServer::ConnectionCache {
+
+HashMap<ConnectionKey, Vector<Connection<Core::TCPSocket>>> g_tcp_connection_cache {};
+HashMap<ConnectionKey, Vector<Connection<TLS::TLSv12>>> g_tls_connection_cache {};
+
+void request_did_finish(URL const& url, Core::Socket const* socket)
+{
+    if (!socket) {
+        dbgln("Request with a null socket finished for URL {}", url);
+        return;
+    }
+
+    dbgln("Request for {} finished", url);
+
+    ConnectionKey key { url.host(), url.port_or_default() };
+    auto fire_off_next_job = [&](auto& cache) {
+        auto it = cache.find(key);
+        if (it == cache.end()) {
+            dbgln("Request for URL {} finished, but we don't own that!", url);
+            return;
+        }
+        auto connection_it = it->value.find_if([&](auto& connection) { return connection.socket == socket; });
+        if (connection_it.is_end()) {
+            dbgln("Request for URL {} finished, but we don't have a socket for that!", url);
+            return;
+        }
+
+        auto& connection = *connection_it;
+        if (connection.request_queue.is_empty()) {
+            connection.has_started = false;
+            connection.removal_timer->on_timeout = [&connection, &cache_entry = it->value] {
+                Core::deferred_invoke([&] {
+                    dbgln("Removing no-longer-used connection {}", &connection);
+                    cache_entry.remove_first_matching([&](auto& entry) { return &entry == &connection; });
+                });
+            };
+            connection.removal_timer->start();
+        } else {
+            using SocketType = RemoveCVReference<decltype(*connection.socket)>;
+            bool is_connected;
+            if constexpr (IsSame<SocketType, TLS::TLSv12>)
+                is_connected = connection.socket->is_established();
+            else
+                is_connected = connection.socket->is_connected();
+            if (!is_connected) {
+                // Create another socket for the connection.
+                dbgln("Creating a new socket for {}", url);
+                connection.socket = SocketType::construct(nullptr);
+            }
+            dbgln("Running next job in queue for connection {}", &connection);
+            auto request = connection.request_queue.take_first();
+            request(connection.socket);
+        }
+    };
+
+    if (is<TLS::TLSv12>(socket))
+        fire_off_next_job(g_tls_connection_cache);
+    else if (is<Core::TCPSocket>(socket))
+        fire_off_next_job(g_tcp_connection_cache);
+    else
+        dbgln("Unknown socket {} finished for URL {}", *socket, url);
+}
+
+}
diff --git a/Userland/Services/RequestServer/ConnectionCache.h b/Userland/Services/RequestServer/ConnectionCache.h
new file mode 100644
index 0000000000..d9bbc0975c
--- /dev/null
+++ b/Userland/Services/RequestServer/ConnectionCache.h
@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/HashMap.h>
+#include <AK/URL.h>
+#include <AK/Vector.h>
+#include <LibCore/TCPSocket.h>
+#include <LibCore/Timer.h>
+#include <LibTLS/TLSv12.h>
+
+namespace RequestServer::ConnectionCache {
+
+template<typename Socket>
+struct Connection {
+    using QueueType = Vector<Function<void(Core::Socket&)>>;
+    using SocketType = Socket;
+
+    NonnullRefPtr<Socket> socket;
+    QueueType request_queue;
+    NonnullRefPtr<Core::Timer> removal_timer;
+    bool has_started { false };
+};
+
+struct ConnectionKey {
+    String hostname;
+    u16 port { 0 };
+
+    bool operator==(ConnectionKey const&) const = default;
+};
+
+};
+
+template<>
+struct AK::Traits<RequestServer::ConnectionCache::ConnectionKey> : public AK::GenericTraits<RequestServer::ConnectionCache::ConnectionKey> {
+    static u32 hash(RequestServer::ConnectionCache::ConnectionKey const& key)
+    {
+        return pair_int_hash(key.hostname.hash(), key.port);
+    }
+};
+
+namespace RequestServer::ConnectionCache {
+
+extern HashMap<ConnectionKey, Vector<Connection<Core::TCPSocket>>> g_tcp_connection_cache;
+extern HashMap<ConnectionKey, Vector<Connection<TLS::TLSv12>>> g_tls_connection_cache;
+
+void request_did_finish(URL const&, Core::Socket const*);
+
+constexpr static inline size_t MaxConcurrentConnectionsPerURL = 2;
+constexpr static inline size_t ConnectionKeepAliveTimeMilliseconds = 10'000;
+
+decltype(auto) get_or_create_connection(auto& cache, URL const& url, auto& job)
+{
+    auto start_job = [&job](auto& socket) {
+        job.start(socket);
+    };
+    auto& sockets_for_url = cache.ensure({ url.host(), url.port_or_default() });
+    auto it = sockets_for_url.find_if([](auto& connection) { return connection.request_queue.is_empty(); });
+    auto did_add_new_connection = false;
+    if (it.is_end() && sockets_for_url.size() < ConnectionCache::MaxConcurrentConnectionsPerURL) {
+        sockets_for_url.append({
+            RemoveCVReference<decltype(cache.begin()->value.at(0))>::SocketType::construct(nullptr),
+            {},
+            Core::Timer::create_single_shot(ConnectionKeepAliveTimeMilliseconds, nullptr),
+        });
+        did_add_new_connection = true;
+    }
+    size_t index;
+    if (it.is_end()) {
+        if (did_add_new_connection) {
+            index = sockets_for_url.size() - 1;
+        } else {
+            // Find the least backed-up connection (based on how many entries are in their request queue.
+            index = 0;
+            auto min_queue_size = (size_t)-1;
+            for (auto it = sockets_for_url.begin(); it != sockets_for_url.end(); ++it) {
+                if (auto queue_size = it->request_queue.size(); min_queue_size > queue_size) {
+                    index = it.index();
+                    min_queue_size = queue_size;
+                }
+            }
+        }
+    } else {
+        index = it.index();
+    }
+    auto& connection = sockets_for_url[index];
+    if (!connection.has_started) {
+        dbgln("Immediately start request for url {} in {}", url, &connection);
+        connection.has_started = true;
+        connection.removal_timer->stop();
+        start_job(*connection.socket);
+    } else {
+        dbgln("Enqueue request for URL {} in {}", url, &connection);
+        connection.request_queue.append(move(start_job));
+    }
+    return connection;
+}
+
+}
diff --git a/Userland/Services/RequestServer/GeminiProtocol.cpp b/Userland/Services/RequestServer/GeminiProtocol.cpp
index e02ed8413f..45686caa75 100644
--- a/Userland/Services/RequestServer/GeminiProtocol.cpp
+++ b/Userland/Services/RequestServer/GeminiProtocol.cpp
@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include "ConnectionCache.h"
 #include <LibGemini/GeminiJob.h>
 #include <LibGemini/GeminiRequest.h>
 #include <RequestServer/GeminiProtocol.h>
@@ -34,7 +35,9 @@ OwnPtr<Request> GeminiProtocol::start_request(ClientConnection& client, const St
     auto job = Gemini::GeminiJob::construct(request, *output_stream);
     auto protocol_request = GeminiRequest::create_with_job({}, client, (Gemini::GeminiJob&)*job, move(output_stream));
     protocol_request->set_request_fd(pipe_result.value().read_fd);
-    job->start();
+
+    ConnectionCache::get_or_create_connection(ConnectionCache::g_tls_connection_cache, url, *job);
+
     return protocol_request;
 }
 
diff --git a/Userland/Services/RequestServer/GeminiRequest.cpp b/Userland/Services/RequestServer/GeminiRequest.cpp
index 6ff619af88..d98feb0546 100644
--- a/Userland/Services/RequestServer/GeminiRequest.cpp
+++ b/Userland/Services/RequestServer/GeminiRequest.cpp
@@ -4,6 +4,8 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include "ConnectionCache.h"
+#include <LibCore/EventLoop.h>
 #include <LibGemini/GeminiJob.h>
 #include <LibGemini/GeminiResponse.h>
 #include <RequestServer/GeminiRequest.h>
@@ -15,6 +17,9 @@ GeminiRequest::GeminiRequest(ClientConnection& client, NonnullRefPtr<Gemini::Gem
     , m_job(job)
 {
     m_job->on_finish = [this](bool success) {
+        Core::deferred_invoke([url = m_job->url(), socket = m_job->socket()] {
+            ConnectionCache::request_did_finish(url, socket);
+        });
         if (auto* response = m_job->response()) {
             set_downloaded_size(this->output_stream().size());
             if (!response->meta().is_empty()) {
diff --git a/Userland/Services/RequestServer/GeminiRequest.h b/Userland/Services/RequestServer/GeminiRequest.h
index 1111a416d0..c481da653d 100644
--- a/Userland/Services/RequestServer/GeminiRequest.h
+++ b/Userland/Services/RequestServer/GeminiRequest.h
@@ -18,6 +18,8 @@ public:
     virtual ~GeminiRequest() override;
     static NonnullOwnPtr<GeminiRequest> create_with_job(Badge<GeminiProtocol>, ClientConnection&, NonnullRefPtr<Gemini::GeminiJob>, NonnullOwnPtr<OutputFileStream>&&);
 
+    Gemini::GeminiJob const& job() const { return *m_job; }
+
 private:
     explicit GeminiRequest(ClientConnection&, NonnullRefPtr<Gemini::GeminiJob>, NonnullOwnPtr<OutputFileStream>&&);
 
diff --git a/Userland/Services/RequestServer/HttpCommon.h b/Userland/Services/RequestServer/HttpCommon.h
index bdc158faa6..5a4866a53d 100644
--- a/Userland/Services/RequestServer/HttpCommon.h
+++ b/Userland/Services/RequestServer/HttpCommon.h
@@ -15,6 +15,7 @@
 #include <AK/Types.h>
 #include <LibHTTP/HttpRequest.h>
 #include <RequestServer/ClientConnection.h>
+#include <RequestServer/ConnectionCache.h>
 #include <RequestServer/Request.h>
 
 namespace RequestServer::Detail {
@@ -29,6 +30,9 @@ void init(TSelf* self, TJob job)
     };
 
     job->on_finish = [self](bool success) {
+        Core::deferred_invoke([url = self->job().url(), socket = self->job().socket()] {
+            ConnectionCache::request_did_finish(url, socket);
+        });
         if (auto* response = self->job().response()) {
             self->set_status_code(response->code());
             self->set_response_headers(response->headers());
@@ -80,7 +84,12 @@ OwnPtr<Request> start_request(TBadgedProtocol&& protocol, ClientConnection& clie
     auto job = TJob::construct(request, *output_stream);
     auto protocol_request = TRequest::create_with_job(forward<TBadgedProtocol>(protocol), client, (TJob&)*job, move(output_stream));
     protocol_request->set_request_fd(pipe_result.value().read_fd);
-    job->start();
+
+    if constexpr (IsSame<typename TBadgedProtocol::Type, HttpsProtocol>)
+        ConnectionCache::get_or_create_connection(ConnectionCache::g_tls_connection_cache, url, *job);
+    else
+        ConnectionCache::get_or_create_connection(ConnectionCache::g_tcp_connection_cache, url, *job);
+
     return protocol_request;
 }
 
diff --git a/Userland/Services/RequestServer/HttpRequest.h b/Userland/Services/RequestServer/HttpRequest.h
index aa7e7f999d..d2968061c1 100644
--- a/Userland/Services/RequestServer/HttpRequest.h
+++ b/Userland/Services/RequestServer/HttpRequest.h
@@ -20,6 +20,7 @@ public:
     static NonnullOwnPtr<HttpRequest> create_with_job(Badge<HttpProtocol>&&, ClientConnection&, NonnullRefPtr<HTTP::HttpJob>, NonnullOwnPtr<OutputFileStream>&&);
 
     HTTP::HttpJob& job() { return m_job; }
+    HTTP::HttpJob const& job() const { return m_job; }
 
 private:
     explicit HttpRequest(ClientConnection&, NonnullRefPtr<HTTP::HttpJob>, NonnullOwnPtr<OutputFileStream>&&);
diff --git a/Userland/Services/RequestServer/HttpsRequest.h b/Userland/Services/RequestServer/HttpsRequest.h
index 7d15fb4792..2f26b0d6fe 100644
--- a/Userland/Services/RequestServer/HttpsRequest.h
+++ b/Userland/Services/RequestServer/HttpsRequest.h
@@ -19,6 +19,7 @@ public:
     static NonnullOwnPtr<HttpsRequest> create_with_job(Badge<HttpsProtocol>&&, ClientConnection&, NonnullRefPtr<HTTP::HttpsJob>, NonnullOwnPtr<OutputFileStream>&&);
 
     HTTP::HttpsJob& job() { return m_job; }
+    HTTP::HttpsJob const& job() const { return m_job; }
 
 private:
     explicit HttpsRequest(ClientConnection&, NonnullRefPtr<HTTP::HttpsJob>, NonnullOwnPtr<OutputFileStream>&&);