On macOS, use Mach port messaging instead of Unix domain sockets for
all IPC transport. This makes the transport capable of carrying Mach
port rights as message attachments, which is a prerequisite for sending
IOSurface handles over the main IPC channel (currently sent via a
separate out-of-band path). It also avoids the need for the FD
acknowledgement protocol that TransportSocket requires, since Mach port
right transfers are atomic in the kernel.
Three connection establishment patterns:
- Spawned helper processes (WebContent, RequestServer, etc.) use the
existing MachPortServer: the child sends its task port with a reply
port, and the parent responds with a pre-created port pair.
- Socket-bootstrapped connections (WebDriver, BrowserProcess) exchange
Mach port names over the socket, then drop the socket.
- Pre-created pairs for IPC tests and in-message transport transfer.
Attachment on macOS now wraps a MachPort instead of a file descriptor,
converting between the two via fileport_makeport()/fileport_makefd().
The LibIPC socket transport tests are disabled on macOS since they are
socket-specific.
The new ImageDecoder service (available for members of "image" via
/tmp/portal/image) allows you to decode images in a separate process.
This will allow programs to confidently load untrusted images, since
the bulk of the security concerns are sandboxed to a separate process.
The only API right now is a synchronous IPC DecodeImage() call that
takes a shbuf with encoded image data and returns a shared buffer and
metadata for the decoded image.
It also comes with a very simple library for interfacing with the
ImageDecoder service: LibImageDecoderClient. The name is a bit of a
mouthful but I guess we can rename it later if we think of something
nicer to call it.
There's obviously a bit of overhead to spawning a separate process
for every image decode, so this is mostly only appropriate for
untrusted images (e.g stuff downloaded from the web) and not necessary
for trusted local images (e.g stuff in /res)
