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moby--moby/engine/streams.go

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package engine
import (
"bytes"
"fmt"
"io"
"strings"
"sync"
"unicode"
)
type Output struct {
sync.Mutex
dests []io.Writer
tasks sync.WaitGroup
used bool
}
// Tail returns the n last lines of a buffer
// stripped out of trailing white spaces, if any.
//
// if n <= 0, returns an empty string
func Tail(buffer *bytes.Buffer, n int) string {
if n <= 0 {
return ""
}
s := strings.TrimRightFunc(buffer.String(), unicode.IsSpace)
i := len(s) - 1
for ; i >= 0 && n > 0; i-- {
if s[i] == '\n' {
n--
if n == 0 {
break
}
}
}
// when i == -1, return the whole string which is s[0:]
return s[i+1:]
}
// NewOutput returns a new Output object with no destinations attached.
// Writing to an empty Output will cause the written data to be discarded.
func NewOutput() *Output {
return &Output{}
}
// Return true if something was written on this output
func (o *Output) Used() bool {
o.Lock()
defer o.Unlock()
return o.used
}
// Add attaches a new destination to the Output. Any data subsequently written
// to the output will be written to the new destination in addition to all the others.
// This method is thread-safe.
func (o *Output) Add(dst io.Writer) {
o.Lock()
defer o.Unlock()
o.dests = append(o.dests, dst)
}
// Set closes and remove existing destination and then attaches a new destination to
// the Output. Any data subsequently written to the output will be written to the new
// destination in addition to all the others. This method is thread-safe.
func (o *Output) Set(dst io.Writer) {
o.Close()
o.Lock()
defer o.Unlock()
o.dests = []io.Writer{dst}
}
// AddPipe creates an in-memory pipe with io.Pipe(), adds its writing end as a destination,
// and returns its reading end for consumption by the caller.
// This is a rough equivalent similar to Cmd.StdoutPipe() in the standard os/exec package.
// This method is thread-safe.
func (o *Output) AddPipe() (io.Reader, error) {
r, w := io.Pipe()
o.Add(w)
return r, nil
}
// Write writes the same data to all registered destinations.
// This method is thread-safe.
func (o *Output) Write(p []byte) (n int, err error) {
o.Lock()
defer o.Unlock()
o.used = true
var firstErr error
for _, dst := range o.dests {
_, err := dst.Write(p)
if err != nil && firstErr == nil {
firstErr = err
}
}
return len(p), firstErr
}
// Close unregisters all destinations and waits for all background
// AddTail and AddString tasks to complete.
// The Close method of each destination is called if it exists.
func (o *Output) Close() error {
o.Lock()
defer o.Unlock()
var firstErr error
for _, dst := range o.dests {
if closer, ok := dst.(io.Closer); ok {
err := closer.Close()
if err != nil && firstErr == nil {
firstErr = err
}
}
}
o.tasks.Wait()
o.dests = nil
return firstErr
}
type Input struct {
src io.Reader
sync.Mutex
}
// NewInput returns a new Input object with no source attached.
// Reading to an empty Input will return io.EOF.
func NewInput() *Input {
return &Input{}
}
// Read reads from the input in a thread-safe way.
func (i *Input) Read(p []byte) (n int, err error) {
i.Mutex.Lock()
defer i.Mutex.Unlock()
if i.src == nil {
return 0, io.EOF
}
return i.src.Read(p)
}
// Closes the src
// Not thread safe on purpose
func (i *Input) Close() error {
if i.src != nil {
if closer, ok := i.src.(io.Closer); ok {
return closer.Close()
}
}
return nil
}
// Add attaches a new source to the input.
// Add can only be called once per input. Subsequent calls will
// return an error.
func (i *Input) Add(src io.Reader) error {
i.Mutex.Lock()
defer i.Mutex.Unlock()
if i.src != nil {
return fmt.Errorf("Maximum number of sources reached: 1")
}
i.src = src
return nil
}
// AddEnv starts a new goroutine which will decode all subsequent data
// as a stream of json-encoded objects, and point `dst` to the last
// decoded object.
// The result `env` can be queried using the type-neutral Env interface.
// It is not safe to query `env` until the Output is closed.
func (o *Output) AddEnv() (dst *Env, err error) {
src, err := o.AddPipe()
if err != nil {
return nil, err
}
dst = &Env{}
o.tasks.Add(1)
go func() {
defer o.tasks.Done()
decoder := NewDecoder(src)
for {
env, err := decoder.Decode()
if err != nil {
return
}
*dst = *env
}
}()
return dst, nil
}