ProtocolServer: Stream the downloaded data if possible

This patchset makes ProtocolServer stream the downloads to its client
(LibProtocol), and as such changes the download API; a possible
download lifecycle could be as such:
notation = client->server:'>', server->client:'<', pipe activity:'*'
```
> StartDownload(GET, url, headers, {})
< Response(0, fd 8)
* {data, 1024b}
< HeadersBecameAvailable(0, response_headers, 200)
< DownloadProgress(0, 4K, 1024)
* {data, 1024b}
* {data, 1024b}
< DownloadProgress(0, 4K, 2048)
* {data, 1024b}
< DownloadProgress(0, 4K, 1024)
< DownloadFinished(0, true, 4K)
```

Since managing the received file descriptor is a pain, LibProtocol
implements `Download::stream_into(OutputStream)`, which can be used to
stream the download into any given output stream (be it a file, or
memory, or writing stuff with a delay, etc.).
Also, as some of the users of this API require all the downloaded data
upfront, LibProtocol also implements `set_should_buffer_all_input()`,
which causes the download instance to buffer all the data until the
download is complete, and to call the `on_buffered_download_finish`
hook.

Applications/Browser/DownloadWidget.cpp

@@ -29,6 +29,7 @@
 #include <AK/SharedBuffer.h>
 #include <AK/StringBuilder.h>
 #include <LibCore/File.h>
+#include <LibCore/FileStream.h>
 #include <LibCore/StandardPaths.h>
 #include <LibDesktop/Launcher.h>
 #include <LibGUI/BoxLayout.h>
@@ -61,9 +62,19 @@ DownloadWidget::DownloadWidget(const URL& url)
     m_download->on_progress = [this](Optional<u32> total_size, u32 downloaded_size) {
         did_progress(total_size.value(), downloaded_size);
     };
-    m_download->on_finish = [this](bool success, auto payload, auto payload_storage, auto& response_headers, auto) {
-        did_finish(success, payload, payload_storage, response_headers);
-    };
+
+    {
+        auto file_or_error = Core::File::open(m_destination_path, Core::IODevice::WriteOnly);
+        if (file_or_error.is_error()) {
+            GUI::MessageBox::show(window(), String::formatted("Cannot open {} for writing", m_destination_path), "Download failed", GUI::MessageBox::Type::Error);
+            window()->close();
+            return;
+        }
+        m_output_file_stream = make<Core::OutputFileStream>(*file_or_error.value());
+    }
+
+    m_download->on_finish = [this](bool success, auto) { did_finish(success); };
+    m_download->stream_into(*m_output_file_stream);
 
     set_fill_with_background_color(true);
     auto& layout = set_layout<GUI::VerticalBoxLayout>();
@@ -149,7 +160,7 @@ void DownloadWidget::did_progress(Optional<u32> total_size, u32 downloaded_size)
     }
 }
 
-void DownloadWidget::did_finish(bool success, [[maybe_unused]] ReadonlyBytes payload, [[maybe_unused]] RefPtr<SharedBuffer> payload_storage, [[maybe_unused]] const HashMap<String, String, CaseInsensitiveStringTraits>& response_headers)
+void DownloadWidget::did_finish(bool success)
 {
     dbg() << "did_finish, success=" << success;
 
@@ -166,17 +177,6 @@ void DownloadWidget::did_finish(bool success, [[maybe_unused]] ReadonlyBytes pay
         window()->close();
         return;
     }
-
-    auto file_or_error = Core::File::open(m_destination_path, Core::IODevice::WriteOnly);
-    if (file_or_error.is_error()) {
-        GUI::MessageBox::show(window(), String::formatted("Cannot open {} for writing", m_destination_path), "Download failed", GUI::MessageBox::Type::Error);
-        window()->close();
-        return;
-    }
-
-    auto& file = *file_or_error.value();
-    bool write_success = file.write(payload.data(), payload.size());
-    ASSERT(write_success);
 }
 
 }

Applications/Browser/DownloadWidget.h

@@ -28,6 +28,7 @@
 
 #include <AK/URL.h>
 #include <LibCore/ElapsedTimer.h>
+#include <LibCore/FileStream.h>
 #include <LibGUI/ProgressBar.h>
 #include <LibGUI/Widget.h>
 #include <LibProtocol/Download.h>
@@ -44,7 +45,7 @@ private:
     explicit DownloadWidget(const URL&);
 
     void did_progress(Optional<u32> total_size, u32 downloaded_size);
-    void did_finish(bool success, ReadonlyBytes payload, RefPtr<SharedBuffer> payload_storage, const HashMap<String, String, CaseInsensitiveStringTraits>& response_headers);
+    void did_finish(bool success);
 
     URL m_url;
     String m_destination_path;
@@ -53,6 +54,7 @@ private:
     RefPtr<GUI::Label> m_progress_label;
     RefPtr<GUI::Button> m_cancel_button;
     RefPtr<GUI::Button> m_close_button;
+    OwnPtr<Core::OutputFileStream> m_output_file_stream;
     Core::ElapsedTimer m_elapsed_timer;
 };
 

Applications/Browser/main.cpp

@@ -68,7 +68,7 @@ int main(int argc, char** argv)
         return 1;
     }
 
-    if (pledge("stdio shared_buffer accept unix cpath rpath wpath fattr", nullptr) < 0) {
+    if (pledge("stdio shared_buffer accept unix cpath rpath wpath fattr sendfd recvfd", nullptr) < 0) {
         perror("pledge");
         return 1;
     }
@@ -86,7 +86,7 @@ int main(int argc, char** argv)
     Web::ResourceLoader::the();
 
     // FIXME: Once there is a standalone Download Manager, we can drop the "unix" pledge.
-    if (pledge("stdio shared_buffer accept unix cpath rpath wpath", nullptr) < 0) {
+    if (pledge("stdio shared_buffer accept unix cpath rpath wpath sendfd recvfd", nullptr) < 0) {
         perror("pledge");
         return 1;
     }