telebit/mplexer/packer/encoder.go

package packer

import (
	"context"
	"errors"
	"io"
	"sync"
)

// TODO: try to be more like encoding/csv, or more like encoding/pem and encoding/json?

// Encoder converts TCP to MPLEXY-TCP
type Encoder struct {
	ctx        context.Context
	subctx     context.Context
	mux        sync.Mutex
	out        io.WriteCloser
	outErr     chan error
	bufferSize int
}

// NewEncoder returns an Encoder instance
func NewEncoder(ctx context.Context, wout io.WriteCloser) *Encoder {
	enc := &Encoder{
		ctx:        ctx,
		out:        wout,
		outErr:     make(chan error),
		bufferSize: defaultBufferSize,
	}
	return enc
}

// Run loops over a select of contexts and error channels
// to cancel and close south-side connections, if needed.
// TODO should this be pushed elsewhere to handled?
func (enc *Encoder) Run() error {
	ctx, cancel := context.WithCancel(enc.ctx)
	defer cancel()

	enc.subctx = ctx

	for {
		select {
		// TODO: do children respond to children cancelling?
		case <-enc.ctx.Done():
			// TODO
			_ = enc.out.Close()
			return errors.New("context cancelled")
		case err := <-enc.outErr:
			// if a write fails for one, it fail for all
			return err
		}
	}
}

// Start will Run() the encoder in a goroutine
func (enc *Encoder) Start() error {
	go enc.Run()
	return nil
}

// Encode adds MPLEXY headers to raw net traffic, and is intended to be used on each client connection
func (enc *Encoder) Encode(rin io.ReadCloser, src Addr) error {
	rx := make(chan []byte)
	rxErr := make(chan error)

	go func() {
		for {
			b := make([]byte, enc.bufferSize)
			//fmt.Println("loopers gonna loop")
			n, err := rin.Read(b)
			if n > 0 {
				rx <- b[:n]
			}
			if nil != err {
				rxErr <- err
				return
			}
		}
	}()

	for {
		//fmt.Println("poopers gonna poop")
		select {
		// TODO, do we actually need ctx here?
		// would it be sufficient to expect the reader to be closed by the caller instead?
		case <-enc.ctx.Done():
			// TODO: verify that closing the reader will cause the goroutine to be released
			rin.Close()
			return errors.New("cancelled by context")
		case <-enc.subctx.Done():
			rin.Close()
			return errors.New("cancelled by context")
		case b := <-rx:
			header, _, err := Encode(src, Addr{}, "", b)
			if nil != err {
				rin.Close()
				return err
			}
			_, err = enc.write(header, b)
			if nil != err {
				rin.Close()
				return err
			}
		case err := <-rxErr:
			// it can be assumed that err will close though, right?
			rin.Close()
			if io.EOF == err {
				header, _, _ := Encode(src, Addr{scheme: "end"}, "", nil)
				// ignore err, which may have already closed
				_, _ = enc.write(header, nil)
				return nil
			}
			header, _, _ := Encode(src, Addr{scheme: "error"}, "", []byte(err.Error()))
			// ignore err, which may have already closed
			_, _ = enc.write(header, nil)
			return err
		}

	}
}

func (enc *Encoder) write(h, b []byte) (int, error) {
	// mutex here so that we can get back error info
	enc.mux.Lock()
	var m int
	n, err := enc.out.Write(h)
	if nil == err && len(b) > 0 {
		m, err = enc.out.Write(b)
	}
	enc.mux.Unlock()
	if nil != err {
		enc.outErr <- err
	}
	return n + m, err
}