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//! The client implementation.
use futures::sink::SinkExt;
use mpd_protocol::{response::Frame, Command, CommandList, MpdCodec, MpdCodecError, Response};
use tokio::{
io::{self, split, AsyncRead, AsyncWrite},
stream::{Stream, StreamExt},
sync::{
mpsc::{self, UnboundedReceiver, UnboundedSender},
oneshot,
},
};
use tokio_util::codec::{FramedRead, FramedWrite};
use std::collections::VecDeque;
use std::iter;
use crate::errors::{CommandError, StateChangeError};
use crate::util::Subsystem;
static IDLE: &str = "idle";
static CANCEL_IDLE: &str = "noidle";
type CommandResponder = oneshot::Sender<Result<Response, CommandError>>;
/// Client for MPD.
#[derive(Clone, Debug)]
pub struct Client(UnboundedSender<(CommandList, CommandResponder)>);
impl Client {
/// Connect to the MPD server using the given connection.
///
/// Returns a `Client` you can use to issue commands, and a stream of state change events as
/// returned by MPD.
///
/// Since this is generic over the connection type, you can use it with both TCP and Unix
/// socket connections.
///
/// # Panics
///
/// Since this spawns a task internally, this will panic when called outside a tokio runtime.
///
/// # Errors
///
/// This will return an error if sending the initial commands over the given transport fails.
pub async fn connect<C>(
connection: C,
) -> Result<
(
Self,
impl Stream<Item = Result<Subsystem, StateChangeError>>,
),
MpdCodecError,
>
where
C: AsyncRead + AsyncWrite + Send + 'static,
{
let (state_changes_sender, state_changes) = mpsc::unbounded_channel();
let (commands, commands_receiver) = mpsc::unbounded_channel();
let connection = connect(connection).await?;
tokio::spawn(run_loop(
connection,
commands_receiver,
state_changes_sender,
));
Ok((Self(commands), state_changes))
}
/// Send the given command, and return the response to it.
///
/// # Errors
///
/// This will return an error if the connection to MPD is closed (cleanly) or a protocol error
/// occurs (including IO errors), or if the command results in an MPD error.
pub async fn command(&self, command: Command) -> Result<Frame, CommandError> {
self.do_send(CommandList::new(command))
.await?
.single_frame()
.map_err(Into::into)
}
/// Send the given command list, and return the responses to the contained commands.
///
/// # Errors
///
/// Errors will be returned in the same conditions as with [`command`], but if *any* of the
/// commands in the list return an error condition, the entire list will be treated as an
/// error. You may recover possible succesful fields in a response from the [error variant].
///
/// [`command`]: #method.command
/// [error variant]: ../errors/enum.CommandError.html#variant.ErrorResponse
pub async fn command_list(&self, commands: CommandList) -> Result<Vec<Frame>, CommandError> {
let res = self.do_send(commands).await?;
let mut frames = Vec::with_capacity(res.len());
for frame in res {
match frame {
Ok(f) => frames.push(f),
Err(error) => {
return Err(CommandError::ErrorResponse {
error,
succesful_frames: frames,
});
}
}
}
Ok(frames)
}
async fn do_send(&self, commands: CommandList) -> Result<Response, CommandError> {
let (tx, rx) = oneshot::channel();
self.0.send((commands, tx))?;
rx.await?
}
}
struct Connection<C: AsyncRead + AsyncWrite> {
read: FramedRead<io::ReadHalf<C>, MpdCodec>,
write: FramedWrite<io::WriteHalf<C>, MpdCodec>,
}
async fn connect<C: AsyncRead + AsyncWrite>(connection: C) -> Result<Connection<C>, MpdCodecError> {
let (read, write) = split(connection);
let read = FramedRead::new(read, MpdCodec::new());
let mut write = FramedWrite::new(write, MpdCodec::new());
// Immediately send an idle command, to prevent the connection from timing out
write.send(CommandList::new(Command::new(IDLE))).await?;
Ok(Connection { read, write })
}
async fn run_loop<C>(
connection: Connection<C>,
mut commands: UnboundedReceiver<(CommandList, CommandResponder)>,
state_changes: UnboundedSender<Result<Subsystem, StateChangeError>>,
) where
C: AsyncRead + AsyncWrite,
{
let Connection {
mut read,
mut write,
} = connection;
let mut current_command_responder: Option<CommandResponder> = None;
let mut command_queue = VecDeque::new();
let mut commands_channel_open = true;
while commands_channel_open || current_command_responder.is_some() || !command_queue.is_empty()
{
tokio::select! {
command = commands.next(), if commands_channel_open => {
let command = match command {
Some(c) => c,
None => {
commands_channel_open = false;
continue;
}
};
// Add the command to the queue to be processed during a later iteration of this
// loop.
command_queue.push_back(command);
if current_command_responder.is_none() {
// If there is no current responder, we are currently idling, so cancel that.
if let Err(e) = write.send(CommandList::new(Command::new(CANCEL_IDLE))).await {
// Get back the responder (and command) we just pushed
let (_, responder) = command_queue.pop_back().unwrap();
let _ = responder.send(Err(e.into()));
}
}
}
msg = read.next() => {
let msg = match msg {
Some(m) => m,
// If the connection is closed, exit the loop. This will drop all remaining
// responders, which signals error conditions.
None => break,
};
// If there is a current responder set, the message we just received was a reply to
// an explicit command.
if let Some(responder) = current_command_responder.take() {
// The response channel may have already been dropped if the future
// representing the command request was cancelled dropped, but there's nothing
// we can do about it.
let _ = responder.send(msg.map_err(Into::into));
} else {
// If not responder is available, the message is a state change notification.
let msg = msg.map_err(Into::into).and_then(response_to_subsystem);
// The notification may be empty if no changes occured.
if let Some(msg) = msg.transpose() {
// Just like above, the state change notification channel may be dropped.
let _ = state_changes.send(msg);
}
}
// Get the next command with an open response channel (closed channels represent
// cancelled command futures).
if let Some((command, responder)) = next_command(&mut command_queue) {
// If there is a command in the queue, send it immediately and store the
// responder
current_command_responder = Some(responder);
if let Err(e) = write.send(command).await {
let responder = current_command_responder.take().unwrap();
let _ = responder.send(Err(e.into()));
}
} else {
// If there is no command in the queue, start idling
if let Err(e) = write.send(CommandList::new(Command::new(IDLE))).await {
let _ = state_changes.send(Err(e.into()));
}
}
}
}
}
}
fn next_command(
queue: &mut VecDeque<(CommandList, CommandResponder)>,
) -> Option<(CommandList, CommandResponder)> {
iter::from_fn(|| queue.pop_front()).find(|(_, responder)| !responder.is_closed())
}
fn response_to_subsystem(res: Response) -> Result<Option<Subsystem>, StateChangeError> {
let values = res.single_frame()?.values;
if values.is_empty() {
Ok(None)
} else {
let raw = values
.into_iter()
.find(|(k, _)| k == "changed")
.ok_or(StateChangeError::MissingChangedKey)?
.1;
Ok(Some(Subsystem::from(raw)))
}
}