nushell/crates/nu-plugin-core/src/interface/mod.rs

//! Implements the stream multiplexing interface for both the plugin side and the engine side.

use nu_plugin_protocol::{ByteStreamInfo, ListStreamInfo, PipelineDataHeader, StreamMessage};
use nu_protocol::{
    engine::Sequence, shell_error::io::IoError, ByteStream, ListStream, PipelineData, Reader,
    ShellError, Signals,
};
use std::{
    io::{Read, Write},
    sync::Mutex,
    thread,
};

pub mod stream;

use crate::Encoder;

use self::stream::{StreamManager, StreamManagerHandle, StreamWriter, WriteStreamMessage};

pub mod test_util;

#[cfg(test)]
mod tests;

/// The maximum number of list stream values to send without acknowledgement. This should be tuned
/// with consideration for memory usage.
const LIST_STREAM_HIGH_PRESSURE: i32 = 100;

/// The maximum number of raw stream buffers to send without acknowledgement. This should be tuned
/// with consideration for memory usage.
const RAW_STREAM_HIGH_PRESSURE: i32 = 50;

/// Read input/output from the stream.
pub trait PluginRead<T> {
    /// Returns `Ok(None)` on end of stream.
    fn read(&mut self) -> Result<Option<T>, ShellError>;
}

impl<R, E, T> PluginRead<T> for (R, E)
where
    R: std::io::BufRead,
    E: Encoder<T>,
{
    fn read(&mut self) -> Result<Option<T>, ShellError> {
        self.1.decode(&mut self.0)
    }
}

impl<R, T> PluginRead<T> for &mut R
where
    R: PluginRead<T>,
{
    fn read(&mut self) -> Result<Option<T>, ShellError> {
        (**self).read()
    }
}

/// Write input/output to the stream.
///
/// The write should be atomic, without interference from other threads.
pub trait PluginWrite<T>: Send + Sync {
    fn write(&self, data: &T) -> Result<(), ShellError>;

    /// Flush any internal buffers, if applicable.
    fn flush(&self) -> Result<(), ShellError>;

    /// True if this output is stdout, so that plugins can avoid using stdout for their own purpose
    fn is_stdout(&self) -> bool {
        false
    }
}

impl<E, T> PluginWrite<T> for (std::io::Stdout, E)
where
    E: Encoder<T>,
{
    fn write(&self, data: &T) -> Result<(), ShellError> {
        let mut lock = self.0.lock();
        self.1.encode(data, &mut lock)
    }

    fn flush(&self) -> Result<(), ShellError> {
        self.0.lock().flush().map_err(|err| {
            ShellError::Io(IoError::new_internal(
                err.kind(),
                "PluginWrite could not flush",
                nu_protocol::location!(),
            ))
        })
    }

    fn is_stdout(&self) -> bool {
        true
    }
}

impl<W, E, T> PluginWrite<T> for (Mutex<W>, E)
where
    W: std::io::Write + Send,
    E: Encoder<T>,
{
    fn write(&self, data: &T) -> Result<(), ShellError> {
        let mut lock = self.0.lock().map_err(|_| ShellError::NushellFailed {
            msg: "writer mutex poisoned".into(),
        })?;
        self.1.encode(data, &mut *lock)
    }

    fn flush(&self) -> Result<(), ShellError> {
        let mut lock = self.0.lock().map_err(|_| ShellError::NushellFailed {
            msg: "writer mutex poisoned".into(),
        })?;
        lock.flush().map_err(|err| {
            ShellError::Io(IoError::new_internal(
                err.kind(),
                "PluginWrite could not flush",
                nu_protocol::location!(),
            ))
        })
    }
}

impl<W, T> PluginWrite<T> for &W
where
    W: PluginWrite<T>,
{
    fn write(&self, data: &T) -> Result<(), ShellError> {
        (**self).write(data)
    }

    fn flush(&self) -> Result<(), ShellError> {
        (**self).flush()
    }

    fn is_stdout(&self) -> bool {
        (**self).is_stdout()
    }
}

/// An interface manager handles I/O and state management for communication between a plugin and
/// the engine. See `PluginInterfaceManager` in `nu-plugin-engine` for communication from the engine
/// side to a plugin, or `EngineInterfaceManager` in `nu-plugin` for communication from the plugin
/// side to the engine.
///
/// There is typically one [`InterfaceManager`] consuming input from a background thread, and
/// managing shared state.
pub trait InterfaceManager {
    /// The corresponding interface type.
    type Interface: Interface + 'static;

    /// The input message type.
    type Input;

    /// Make a new interface that communicates with this [`InterfaceManager`].
    fn get_interface(&self) -> Self::Interface;

    /// Consume an input message.
    ///
    /// When implementing, call [`.consume_stream_message()`](Self::consume_stream_message) for any encapsulated
    /// [`StreamMessage`]s received.
    fn consume(&mut self, input: Self::Input) -> Result<(), ShellError>;

    /// Get the [`StreamManager`] for handling operations related to stream messages.
    fn stream_manager(&self) -> &StreamManager;

    /// Prepare [`PipelineData`] after reading. This is called by `read_pipeline_data()` as
    /// a hook so that values that need special handling can be taken care of.
    fn prepare_pipeline_data(&self, data: PipelineData) -> Result<PipelineData, ShellError>;

    /// Consume an input stream message.
    ///
    /// This method is provided for implementors to use.
    fn consume_stream_message(&mut self, message: StreamMessage) -> Result<(), ShellError> {
        self.stream_manager().handle_message(message)
    }

    /// Generate `PipelineData` for reading a stream, given a [`PipelineDataHeader`] that was
    /// received from the other side.
    ///
    /// This method is provided for implementors to use.
    fn read_pipeline_data(
        &self,
        header: PipelineDataHeader,
        signals: &Signals,
    ) -> Result<PipelineData, ShellError> {
        self.prepare_pipeline_data(match header {
            PipelineDataHeader::Empty => PipelineData::Empty,
            PipelineDataHeader::Value(value, metadata) => PipelineData::Value(value, metadata),
            PipelineDataHeader::ListStream(info) => {
                let handle = self.stream_manager().get_handle();
                let reader = handle.read_stream(info.id, self.get_interface())?;
                let ls = ListStream::new(reader, info.span, signals.clone());
                PipelineData::ListStream(ls, info.metadata)
            }
            PipelineDataHeader::ByteStream(info) => {
                let handle = self.stream_manager().get_handle();
                let reader = handle.read_stream(info.id, self.get_interface())?;
                let bs =
                    ByteStream::from_result_iter(reader, info.span, signals.clone(), info.type_);
                PipelineData::ByteStream(bs, info.metadata)
            }
        })
    }
}

/// An interface provides an API for communicating with a plugin or the engine and facilitates
/// stream I/O. See `PluginInterface` in `nu-plugin-engine` for the API from the engine side to a
/// plugin, or `EngineInterface` in `nu-plugin` for the API from the plugin side to the engine.
///
/// There can be multiple copies of the interface managed by a single [`InterfaceManager`].
pub trait Interface: Clone + Send {
    /// The output message type, which must be capable of encapsulating a [`StreamMessage`].
    type Output: From<StreamMessage>;

    /// Any context required to construct [`PipelineData`]. Can be `()` if not needed.
    type DataContext;

    /// Write an output message.
    fn write(&self, output: Self::Output) -> Result<(), ShellError>;

    /// Flush the output buffer, so messages are visible to the other side.
    fn flush(&self) -> Result<(), ShellError>;

    /// Get the sequence for generating new [`StreamId`](nu_plugin_protocol::StreamId)s.
    fn stream_id_sequence(&self) -> &Sequence;

    /// Get the [`StreamManagerHandle`] for doing stream operations.
    fn stream_manager_handle(&self) -> &StreamManagerHandle;

    /// Prepare [`PipelineData`] to be written. This is called by `init_write_pipeline_data()` as
    /// a hook so that values that need special handling can be taken care of.
    fn prepare_pipeline_data(
        &self,
        data: PipelineData,
        context: &Self::DataContext,
    ) -> Result<PipelineData, ShellError>;

    /// Initialize a write for [`PipelineData`]. This returns two parts: the header, which can be
    /// embedded in the particular message that references the stream, and a writer, which will
    /// write out all of the data in the pipeline when `.write()` is called.
    ///
    /// Note that not all [`PipelineData`] starts a stream. You should call `write()` anyway, as
    /// it will automatically handle this case.
    ///
    /// This method is provided for implementors to use.
    fn init_write_pipeline_data(
        &self,
        data: PipelineData,
        context: &Self::DataContext,
    ) -> Result<(PipelineDataHeader, PipelineDataWriter<Self>), ShellError> {
        // Allocate a stream id and a writer
        let new_stream = |high_pressure_mark: i32| {
            // Get a free stream id
            let id = self.stream_id_sequence().next()?;
            // Create the writer
            let writer =
                self.stream_manager_handle()
                    .write_stream(id, self.clone(), high_pressure_mark)?;
            Ok::<_, ShellError>((id, writer))
        };
        match self.prepare_pipeline_data(data, context)? {
            PipelineData::Value(value, metadata) => Ok((
                PipelineDataHeader::Value(value, metadata),
                PipelineDataWriter::None,
            )),
            PipelineData::Empty => Ok((PipelineDataHeader::Empty, PipelineDataWriter::None)),
            PipelineData::ListStream(stream, metadata) => {
                let (id, writer) = new_stream(LIST_STREAM_HIGH_PRESSURE)?;
                Ok((
                    PipelineDataHeader::ListStream(ListStreamInfo {
                        id,
                        span: stream.span(),
                        metadata,
                    }),
                    PipelineDataWriter::ListStream(writer, stream),
                ))
            }
            PipelineData::ByteStream(stream, metadata) => {
                let span = stream.span();
                let type_ = stream.type_();
                if let Some(reader) = stream.reader() {
                    let (id, writer) = new_stream(RAW_STREAM_HIGH_PRESSURE)?;
                    let header = PipelineDataHeader::ByteStream(ByteStreamInfo {
                        id,
                        span,
                        type_,
                        metadata,
                    });
                    Ok((header, PipelineDataWriter::ByteStream(writer, reader)))
                } else {
                    Ok((PipelineDataHeader::Empty, PipelineDataWriter::None))
                }
            }
        }
    }
}

impl<T> WriteStreamMessage for T
where
    T: Interface,
{
    fn write_stream_message(&mut self, msg: StreamMessage) -> Result<(), ShellError> {
        self.write(msg.into())
    }

    fn flush(&mut self) -> Result<(), ShellError> {
        <Self as Interface>::flush(self)
    }
}

/// Completes the write operation for a [`PipelineData`]. You must call
/// [`PipelineDataWriter::write()`] to write all of the data contained within the streams.
#[derive(Default)]
#[must_use]
pub enum PipelineDataWriter<W: WriteStreamMessage> {
    #[default]
    None,
    ListStream(StreamWriter<W>, ListStream),
    ByteStream(StreamWriter<W>, Reader),
}

impl<W> PipelineDataWriter<W>
where
    W: WriteStreamMessage + Send + 'static,
{
    /// Write all of the data in each of the streams. This method waits for completion.
    pub fn write(self) -> Result<(), ShellError> {
        match self {
            // If no stream was contained in the PipelineData, do nothing.
            PipelineDataWriter::None => Ok(()),
            // Write a list stream.
            PipelineDataWriter::ListStream(mut writer, stream) => {
                writer.write_all(stream)?;
                Ok(())
            }
            // Write a byte stream.
            PipelineDataWriter::ByteStream(mut writer, mut reader) => {
                let span = reader.span();
                let buf = &mut [0; 8192];
                writer.write_all(std::iter::from_fn(move || match reader.read(buf) {
                    Ok(0) => None,
                    Ok(len) => Some(Ok(buf[..len].to_vec())),
                    Err(err) => Some(Err(ShellError::from(IoError::new(err.kind(), span, None)))),
                }))?;
                Ok(())
            }
        }
    }

    /// Write all of the data in each of the streams. This method returns immediately; any necessary
    /// write will happen in the background. If a thread was spawned, its handle is returned.
    pub fn write_background(
        self,
    ) -> Result<Option<thread::JoinHandle<Result<(), ShellError>>>, ShellError> {
        match self {
            PipelineDataWriter::None => Ok(None),
            _ => Ok(Some(
                thread::Builder::new()
                    .name("plugin stream background writer".into())
                    .spawn(move || {
                        let result = self.write();
                        if let Err(ref err) = result {
                            // Assume that the background thread error probably won't be handled and log it
                            // here just in case.
                            log::warn!("Error while writing pipeline in background: {err}");
                        }
                        result
                    })
                    .map_err(|err| {
                        IoError::new_internal(
                            err.kind(),
                            "Could not spawn plugin stream background writer",
                            nu_protocol::location!(),
                        )
                    })?,
            )),
        }
    }
}