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image.Decode doesn't work as expect #27728

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MaeThird opened this issue Sep 18, 2018 · 2 comments
Closed

image.Decode doesn't work as expect #27728

MaeThird opened this issue Sep 18, 2018 · 2 comments
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@MaeThird
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I'm testing image.Decode with a truly PNG file with these pieces of code:

logo,err := ioutil.ReadFile(os.Args[1]) 
if err != nil{
	fmt.Println(err)
}
_ ,_ , err = image.Decode(bytes.NewReader(logo))
if err != nil {
	fmt.Println(err)
}
_,err = png.Decode(bytes.NewReader(logo))
if err != nil{
	fmt.Println(err)
}

with _,err = png.Decode(bytes.NewReader(logo)) appended the image.Decode works well,but when I commented out it like this :

logo,err := ioutil.ReadFile(os.Args[1]) 
if err != nil{
	fmt.Println(err)
}
_ ,_ , err = image.Decode(bytes.NewReader(logo))
if err != nil {
	fmt.Println(err)
}

it errors and output is "image: unknown format"
Why should this be happened ? Should I register all the decoder by hand so image.Decode can work correctly ?
@bcmills
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bcmills commented Sep 18, 2018

See https://tip.golang.org/pkg/image/:

Registration is typically automatic as a side effect of initializing that format's package so that, to decode a PNG image, it suffices to have

import _ "image/png"

in a program's main package. The _ means to import a package purely for its initialization side effects.

@bcmills bcmills closed this as completed Sep 18, 2018
@MaeThird
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@bcmills Thanks.

@golang golang locked and limited conversation to collaborators Sep 19, 2019
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@bcmills @gopherbot @MaeThird