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pam4 opened this issue Oct 27, 2019 · 6 comments
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bufio: Writer.ReadFrom ignores the stored error #35194

pam4 opened this issue Oct 27, 2019 · 6 comments
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FrozenDueToAge help wanted NeedsFix The path to resolution is known, but the work has not been done. release-blocker
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Go1.14

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@pam4
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pam4 commented Oct 27, 2019

If an error occurs writing to a Writer, no more data will be accepted and all subsequent writes, and Flush, will return the error.

type writer struct{}

func (w writer) Write(p []byte) (n int, err error) {
	return 0, errors.New("bad move")
}

func main() {
	var wr = bufio.NewWriter(writer{})
	wr.WriteString("test1") // 5 <nil>
	wr.Flush()              // bad move
	wr.ReadFrom(strings.NewReader("test2")) // 5 <nil>
	wr.Buffered() // 10
}

https://play.golang.org/p/--WBbDHbIS9

no more data will be accepted

Then I would expect ReadFrom to fail and the Buffered() count not to grow.

all subsequent writes [...] will return the error.

Isn't ReadFrom a write?

This seems unlikely to have bad consequences, but I don't think it's a valid reason for the documentation to be incorrect about corner cases.
@FiloSottile FiloSottile added help wanted NeedsFix The path to resolution is known, but the work has not been done. release-blocker labels Oct 28, 2019
@FiloSottile FiloSottile added this to the Go1.14 milestone Oct 28, 2019
@FiloSottile
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This definitely looks like a bug. It also calls the underlying ReadFrom without persisting the error.

@gopherbot
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Change https://golang.org/cl/203999 mentions this issue: bufio: fix writer ReadFrom do not set underlying error

@gopherbot
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Change https://golang.org/cl/204000 mentions this issue: bufio: returns the underlying error in ReadFrom if not nil

gopherbot pushed a commit that referenced this issue Oct 31, 2019
@cuonglm @bradfitz
bufio: save error from underlying ReadFrom
d5caea7 
Updates #35194

Change-Id: Ib854bc6250ddeb606d6ff6240179e23b98e4ac62
Reviewed-on: https://go-review.googlesource.com/c/go/+/203999
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
@tandr
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tandr commented Nov 1, 2019

Will it be backported to 1.13 and 1.12 ?

@cuonglm
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cuonglm commented Nov 1, 2019

cc @bradfitz @bcmills

@bcmills
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bcmills commented Nov 1, 2019

Will it be backported to 1.13 and 1.12 ?

If it's not a regression from 1.11 and not a security issue, then a backport seems doubtful. (Do we know whether it's a regression from 1.11?)

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