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go.blog/context: Context blog post Gorilla example has a subtle bug #8443

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gopherbot opened this issue Jul 29, 2014 · 5 comments
Closed

go.blog/context: Context blog post Gorilla example has a subtle bug #8443

gopherbot opened this issue Jul 29, 2014 · 5 comments
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@gopherbot
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http://blog.golang.org/context has an example
http://blog.golang.org/context/gorilla/gorilla.go
that does

var reqKey struct{}

    if key == &reqKey {

However, http://golang.org/ref/spec#Comparison_operators says

"Pointers to distinct zero-size variables may or may not be equal."

Which means multiple parties trying to be clever and using pointers to struct{} values
may end up colliding.
@adg
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adg commented Jul 30, 2014

Comment 1:

I seem to recall this was originally an int?

Owner changed to @Sajmani.

Status changed to Accepted.

@adg
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adg commented Jul 30, 2014

Comment 2:

Labels changed: added repo-blog.

@Sajmani
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Sajmani commented Jul 30, 2014

Comment 3:

Yes, I changed it to use the address of an empty struct var when I updated the example
to use just a single key.
The example server still works because there's only a single context key used in the
example, but this is a bug.
I will send a CL to fix the affected examples in the blog post (gorilla.go and
userip.go).
Note that the context godoc uses an int key and so is ok.

@gopherbot
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Comment 4:

CL https://golang.org/cl/121890043 mentions this issue.

@Sajmani
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Sajmani commented Jul 30, 2014

Comment 5:

This issue was closed by revision golang/blog@9cab33c.

Status changed to Fixed.

minux pushed a commit to Go-zh/blog that referenced this issue Dec 14, 2014
@Sajmani
go.blog/context: don't use the address of an empty struct as a context
9cab33c 
key, as this is not guaranteed to be unique.

Fixes golang/go#8443.

LGTM=campoy
R=adg, campoy
CC=dsymonds, golang-codereviews
https://golang.org/cl/121890043
@golang golang locked and limited conversation to collaborators Jun 25, 2016
gopherbot pushed a commit to golang/website that referenced this issue May 26, 2021
@Sajmani
[x/blog] go.blog/context: don't use the address of an empty struct as…
7b9a4c0 
… a context

key, as this is not guaranteed to be unique.

Fixes golang/go#8443.

LGTM=campoy
R=adg, campoy
CC=dsymonds, golang-codereviews
https://golang.org/cl/121890043
X-Blog-Commit: 9cab33ca8e480d9a24efdd84433601a80f9c7fb5
@rsc rsc unassigned Sajmani Jun 23, 2022
passionSeven added a commit to passionSeven/website that referenced this issue Oct 18, 2022
@passionSeven
[x/blog] go.blog/context: don't use the address of an empty struct as…
397b018 
… a context

key, as this is not guaranteed to be unique.

Fixes golang/go#8443.

LGTM=campoy
R=adg, campoy
CC=dsymonds, golang-codereviews
https://golang.org/cl/121890043
X-Blog-Commit: 9cab33ca8e480d9a24efdd84433601a80f9c7fb5
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@adg @gopherbot @Sajmani