ProtocolServer+LibProtocol: Introduce a server for handling downloads

This patch adds ProtocolServer, a server that handles network requests
on behalf of its clients. The first protocol implemented is HTTP.

The idea here is to use a plug-in architecture where any number of
protocols can be added and implemented without having to mess around
with each client program that wants to use the protocol.

A simple client API is provided through LibProtocol::Client. :^)

Libraries/LibProtocol/Client.cpp

@@ -0,0 +1,45 @@
+#include <LibProtocol/Client.h>
+#include <SharedBuffer.h>
+
+namespace LibProtocol {
+
+Client::Client()
+    : ConnectionNG(*this, "/tmp/psportal")
+{
+}
+
+void Client::handshake()
+{
+    auto response = send_sync<ProtocolServer::Greet>(getpid());
+    set_server_pid(response->server_pid());
+    set_my_client_id(response->client_id());
+}
+
+bool Client::is_supported_protocol(const String& protocol)
+{
+    return send_sync<ProtocolServer::IsSupportedProtocol>(protocol)->supported();
+}
+
+i32 Client::start_download(const String& url)
+{
+    return send_sync<ProtocolServer::StartDownload>(url)->download_id();
+}
+
+bool Client::stop_download(i32 download_id)
+{
+    return send_sync<ProtocolServer::StopDownload>(download_id)->success();
+}
+
+void Client::handle(const ProtocolClient::DownloadFinished& message)
+{
+    if (on_download_finish)
+        on_download_finish(message.download_id(), message.success());
+}
+
+void Client::handle(const ProtocolClient::DownloadProgress& message)
+{
+    if (on_download_progress)
+        on_download_progress(message.download_id(), message.total_size(), message.downloaded_size());
+}
+
+}

Libraries/LibProtocol/Client.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <LibCore/CoreIPCClient.h>
+#include <ProtocolServer/ProtocolClientEndpoint.h>
+#include <ProtocolServer/ProtocolServerEndpoint.h>
+
+namespace LibProtocol {
+
+class Client : public IPC::Client::ConnectionNG<ProtocolClientEndpoint, ProtocolServerEndpoint>
+    , public ProtocolClientEndpoint {
+    C_OBJECT(Client)
+public:
+    Client();
+
+    virtual void handshake() override;
+
+    bool is_supported_protocol(const String&);
+    i32 start_download(const String& url);
+    bool stop_download(i32 download_id);
+
+    Function<void(i32 download_id, bool success)> on_download_finish;
+    Function<void(i32 download_id, u64 total_size, u64 downloaded_size)> on_download_progress;
+
+private:
+    virtual void handle(const ProtocolClient::DownloadProgress&) override;
+    virtual void handle(const ProtocolClient::DownloadFinished&) override;
+};
+
+}

Libraries/LibProtocol/Makefile

@@ -0,0 +1,20 @@
+include ../../Makefile.common
+
+OBJS = \
+    Client.o
+
+LIBRARY = libprotocol.a
+DEFINES += -DUSERLAND
+
+all: $(LIBRARY)
+
+$(LIBRARY): $(OBJS)
+	@echo "LIB $@"; $(AR) rcs $@ $(OBJS) $(LIBS)
+
+.cpp.o:
+	@echo "CXX $<"; $(CXX) $(CXXFLAGS) -o $@ -c $<
+
+-include $(OBJS:%.o=%.d)
+
+clean:
+	@echo "CLEAN"; rm -f $(LIBRARY) $(OBJS) *.d