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image: make RegisterFormat safe for concurrent use

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Fixes #25884

Change-Id: I5478846ef78aecac32078ea8c3248db52f1bb534
Reviewed-on: https://go-review.googlesource.com/118755
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Tim Cooper 2018-06-13 21:19:22 -03:00 committed by Brad Fitzpatrick
parent 94f48ddb96
commit 10aeb672e0
1 changed files with 11 additions and 2 deletions
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13
src/image/format.go
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@ -8,6 +8,8 @@ import (
"bufio"
"errors"
"io"
"sync"
"sync/atomic"
)
// ErrFormat indicates that decoding encountered an unknown format.
@ -21,7 +23,10 @@ type format struct {
}
// Formats is the list of registered formats.
var formats []format
var (
formatsMu sync.Mutex
atomicFormats atomic.Value
)
// RegisterFormat registers an image format for use by Decode.
// Name is the name of the format, like "jpeg" or "png".
@ -30,7 +35,10 @@ var formats []format
// Decode is the function that decodes the encoded image.
// DecodeConfig is the function that decodes just its configuration.
func RegisterFormat(name, magic string, decode func(io.Reader) (Image, error), decodeConfig func(io.Reader) (Config, error)) {
formats = append(formats, format{name, magic, decode, decodeConfig})
formatsMu.Lock()
formats, _ := atomicFormats.Load().([]format)
atomicFormats.Store(append(formats, format{name, magic, decode, decodeConfig}))
formatsMu.Unlock()
}
// A reader is an io.Reader that can also peek ahead.
@ -62,6 +70,7 @@ func match(magic string, b []byte) bool {
// Sniff determines the format of r's data.
func sniff(r reader) format {
formats, _ := atomicFormats.Load().([]format)
for _, f := range formats {
b, err := r.Peek(len(f.magic))
if err == nil && match(f.magic, b) {