Change-Id: I5473071f672f8352fbd3352e158d5be12823b58a
Reviewed-on: https://go-review.googlesource.com/25017
Run-TryBot: Chris Broadfoot <cbro@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Because,

* The CGI spec defines that incoming request header "Foo: Bar" maps to
  environment variable HTTP_FOO == "Bar". (see RFC 3875 4.1.18)

* The HTTP_PROXY environment variable is conventionally used to configure
  the HTTP proxy for HTTP clients (and is respected by default for
  Go's net/http.Client and Transport)

That means Go programs running in a CGI environment (as a child
process under a CGI host) are vulnerable to an incoming request
containing "Proxy: attacker.com:1234", setting HTTP_PROXY, and
changing where Go by default proxies all outbound HTTP requests.

This is CVE-2016-5386, aka https://httpoxy.org/

Fixes #16405

Change-Id: I6f68ade85421b4807785799f6d98a8b077e871f0
Reviewed-on: https://go-review.googlesource.com/25010
Run-TryBot: Chris Broadfoot <cbro@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Chris Broadfoot <cbro@golang.org>
Reviewed-on: https://go-review.googlesource.com/25013

In the beta version of the macOS Sierra (10.12) release, the
gettimeofday system call changed on x86. Previously it always returned
the time in the AX/DX registers. Now, if AX is returned as 0, it means
that the system call has stored the values into the memory pointed to by
the first argument, just as the libc gettimeofday function does. The
libc function handles both cases, and we need to do so as well.

Fixes #16272.

Change-Id: Ibe5ad50a2c5b125e92b5a4e787db4b5179f6b723
Reviewed-on: https://go-review.googlesource.com/24812Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-on: https://go-review.googlesource.com/24755Reviewed-by: Chris Broadfoot <cbro@golang.org>

Change-Id: Ifbf1c13ce740428add68d68133c7f10876bad404
Reviewed-on: https://go-review.googlesource.com/24816
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

The shrinkstack code locks all the channels a goroutine is waiting for,
but didn't handle the case of the same channel appearing in the list
multiple times. This led to a deadlock. The channels are sorted so it's
easy to avoid locking the same channel twice.

Fixes #16286.

Change-Id: Ie514805d0532f61c942e85af5b7b8ac405e2ff65
Reviewed-on: https://go-review.googlesource.com/24815
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

Fixes #16273

Change-Id: I443e1f254fd683c4ff61beadae89c1c45ff5d972
Reviewed-on: https://go-review.googlesource.com/24744Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Quentin Smith <quentin@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

The test was checking for 1 of 2 possible error values. But based on
goroutine scheduling and the randomness of select statement receive
cases, it was possible for a 3rd type of error to be returned.

This modifies the code (not the test) to make that third type of error
actually the second type of error, which is a nicer error message.

The test is no longer flaky. The flake was very reproducible with a
5ms sleep before the select at the end of Transport.getConn.

Thanks to Github user @jaredborner for debugging.

Fixes #16049

Change-Id: I0d2a036c9555a8d2618b07bab01f28558d2b0b2c
Reviewed-on: https://go-review.googlesource.com/24748Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: I0c76e8deae49c1149647de421503c5175028b948
Reviewed-on: https://go-review.googlesource.com/24781
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Document explicitly which functions Clean the result rather than
documenting it in the package comment.

Updates #10122.
Fixes #16111.

Change-Id: Ia589c7ee3936c9a6a758725ac7f143054d53e41e
Reviewed-on: https://go-review.googlesource.com/24747
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

This new comment can be used to declare that the uintptr arguments to a
function may be converted from pointers, and that those pointers should
be considered to escape. This is used for the Call methods in
dll_windows.go that take uintptr arguments, because they call Syscall.

We can't treat these functions as we do syscall.Syscall, because unlike
Syscall they may cause the stack to grow. For Syscall we can assume that
stack arguments can remain on the stack, but for these functions we need
them to escape.

Fixes #16035.

Change-Id: Ia0e5b4068c04f8d303d95ab9ea394939f1f57454
Reviewed-on: https://go-review.googlesource.com/24551Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fixes #8833

Change-Id: I4523a1de112ed02371504e27882659bce8028a45
Reviewed-on: https://go-review.googlesource.com/24745Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fixes #16258.

Docs for Encode and EncodeValue do not mention that
nil pointers are not permitted hence we panic,
because Gobs encode values yet nil pointers have no value
to encode. It moves a comment that was internal to EncodeValue
to the top level to make it clearer to users what to expect
when they pass in nil pointers.
Supplements test TestTopLevelNilPointer.

Change-Id: Ie54f609fde4b791605960e088456047eb9aa8738
Reviewed-on: https://go-review.googlesource.com/24740Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Don't issue a copylock warning about a result type; the function may
return a composite literal with a zero value, which is OK.

Don't issue a copylock warning about a function call on the RHS, or an
indirection of a function call; the function may return a composite
literal with a zero value, which is OK.

Updates #16227.

Change-Id: I94f0e066bbfbca5d4f8ba96106210083e36694a2
Reviewed-on: https://go-review.googlesource.com/24711Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

Updates #13372.

Change-Id: If383c14af14839a303425ba7b80b97e35ca9b698
Reviewed-on: https://go-review.googlesource.com/24750
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

The original intent of the code was to allow both with and without .git
suffix for now to allow a transition period. The noVCSSuffix check was a
copy pasta error.

Fixes #15979.

Change-Id: I3d39aba8d026b40fc445244d6d01d8bc1979d1e4
Reviewed-on: https://go-review.googlesource.com/24645Reviewed-by: Ian Lance Taylor <iant@golang.org>

If we don't mark them as needzero, we have a live pointer variable
containing possible garbage, which will baffle the GC.

Fixes #16249.

Change-Id: I7c423ceaca199ddd46fc2c23e5965e7973f07584
Reviewed-on: https://go-review.googlesource.com/24715
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Fixes #16243.

Change-Id: I207d1e8aa48abe453a23c709ccf4f8e07368595b
Reviewed-on: https://go-review.googlesource.com/24648
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

The frontend may emit node with line number missing. In this case,
use the parent line number. Instead of changing every call site of
pushLine, do it in pushLine itself.

Fixes #16214.

Change-Id: I80390550b56e4d690fc770b01ff725b892ffd6dc
Reviewed-on: https://go-review.googlesource.com/24641Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Updates x/net/http2 to git rev b400c2e for https://golang.org/cl/24214,
"http2: add additional blacklisted ciphersuites"

Both TLS_RSA_WITH_AES_128_GCM_SHA256 & TLS_RSA_WITH_AES_256_GCM_SHA384
are now blacklisted, per http://httpwg.org/specs/rfc7540.html#BadCipherSuites

Change-Id: I8b9a7f4dc3c152d0675e196523ddd36111744984
Reviewed-on: https://go-review.googlesource.com/24684Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

+ test.

Fixes #16230

Change-Id: Idac995437146a9df9e73f094d2a31abc25b1fa62
Reviewed-on: https://go-review.googlesource.com/24681Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

We had ~30 one way, and these four new occurrences the other way.

Updates #11626

Change-Id: Ic6403dc4905874916ae292ff739d33482ed8e5bf
Reviewed-on: https://go-review.googlesource.com/24683Reviewed-by: Rob Pike <r@golang.org>

Fixes #16230

Change-Id: Ibb10234a6c3ab8bd0cfd93c2ebe8cfa66f80f6b0
Reviewed-on: https://go-review.googlesource.com/24682Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Ctz is a hot-spot in the Go 1.7 memory manager. In SSA it's
implemented as an intrinsic that compiles to a few instructions, but
on the old backend (all architectures other than amd64), it's
implemented as a fairly complex Go function. As a result, switching to
bitmap-based allocation was a significant hit to allocation-heavy
workloads like BinaryTree17 on non-SSA platforms.

For unknown reasons, this hit 386 particularly hard. We can regain a
lot of the lost performance by implementing Ctz in assembly on the
386. This isn't as good as an intrinsic, since it still generates a
function call and prevents useful inlining, but it's much better than
the pure Go implementation:

name                      old time/op    new time/op    delta
BinaryTree17-12              3.59s ± 1%     3.06s ± 1%  -14.74%  (p=0.000 n=19+20)
Fannkuch11-12                3.72s ± 1%     3.64s ± 1%   -2.09%  (p=0.000 n=17+19)
FmtFprintfEmpty-12          52.3ns ± 3%    52.3ns ± 3%     ~     (p=0.829 n=20+19)
FmtFprintfString-12          156ns ± 1%     148ns ± 3%   -5.20%  (p=0.000 n=18+19)
FmtFprintfInt-12             137ns ± 1%     136ns ± 1%   -0.56%  (p=0.000 n=19+13)
FmtFprintfIntInt-12          227ns ± 2%     225ns ± 2%   -0.93%  (p=0.000 n=19+17)
FmtFprintfPrefixedInt-12     210ns ± 1%     208ns ± 1%   -0.91%  (p=0.000 n=19+17)
FmtFprintfFloat-12           375ns ± 1%     371ns ± 1%   -1.06%  (p=0.000 n=19+18)
FmtManyArgs-12               995ns ± 2%     978ns ± 1%   -1.63%  (p=0.000 n=17+17)
GobDecode-12                9.33ms ± 1%    9.19ms ± 0%   -1.59%  (p=0.000 n=20+17)
GobEncode-12                7.73ms ± 1%    7.73ms ± 1%     ~     (p=0.771 n=19+20)
Gzip-12                      375ms ± 1%     374ms ± 1%     ~     (p=0.141 n=20+18)
Gunzip-12                   61.8ms ± 1%    61.8ms ± 1%     ~     (p=0.602 n=20+20)
HTTPClientServer-12         87.7µs ± 2%    86.9µs ± 3%   -0.87%  (p=0.024 n=19+20)
JSONEncode-12               20.2ms ± 1%    20.4ms ± 0%   +0.53%  (p=0.000 n=18+19)
JSONDecode-12               65.3ms ± 0%    65.4ms ± 1%     ~     (p=0.385 n=16+19)
Mandelbrot200-12            4.11ms ± 1%    4.12ms ± 0%   +0.29%  (p=0.020 n=19+19)
GoParse-12                  3.75ms ± 1%    3.61ms ± 2%   -3.90%  (p=0.000 n=20+20)
RegexpMatchEasy0_32-12       104ns ± 0%     103ns ± 0%   -0.96%  (p=0.000 n=13+16)
RegexpMatchEasy0_1K-12       805ns ± 1%     803ns ± 1%     ~     (p=0.189 n=18+18)
RegexpMatchEasy1_32-12       111ns ± 0%     111ns ± 3%     ~     (p=1.000 n=14+19)
RegexpMatchEasy1_1K-12      1.00µs ± 1%    1.00µs ± 1%   +0.50%  (p=0.003 n=19+19)
RegexpMatchMedium_32-12      133ns ± 2%     133ns ± 2%     ~     (p=0.218 n=20+20)
RegexpMatchMedium_1K-12     41.2µs ± 1%    42.2µs ± 1%   +2.52%  (p=0.000 n=18+16)
RegexpMatchHard_32-12       2.35µs ± 1%    2.38µs ± 1%   +1.53%  (p=0.000 n=18+18)
RegexpMatchHard_1K-12       70.9µs ± 2%    72.0µs ± 1%   +1.42%  (p=0.000 n=19+17)
Revcomp-12                   1.06s ± 0%     1.05s ± 0%   -1.36%  (p=0.000 n=20+18)
Template-12                 86.2ms ± 1%    84.6ms ± 0%   -1.89%  (p=0.000 n=20+18)
TimeParse-12                 425ns ± 2%     428ns ± 1%   +0.77%  (p=0.000 n=18+19)
TimeFormat-12                517ns ± 1%     519ns ± 1%   +0.43%  (p=0.001 n=20+19)
[Geo mean]                  74.3µs         73.5µs        -1.05%

Prior to this commit, BinaryTree17-12 on 386 was 33% slower than at
the go1.6 tag. With this commit, it's 13% slower.

On arm and arm64, BinaryTree17-12 is only ~5% slower than it was at
go1.6. It may be worth implementing Ctz for them as well.

I consider this change low risk, since the functions it replaces are
simple, very well specified, and well tested.

For #16117.

Change-Id: Ic39d851d5aca91330134596effd2dab9689ba066
Reviewed-on: https://go-review.googlesource.com/24640Reviewed-by: Rick Hudson <rlh@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Previously we started checking for context cancelation in Wait, but
that meant that when using StdoutPipe context cancelation never took
effect.

Fixes #16222.

Change-Id: I89cd26d3499a6080bf1a07718ce38d825561899e
Reviewed-on: https://go-review.googlesource.com/24650Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This should fix the report at #16224, and also fixes running the test as
root on my Ubuntu Trusty system.

Fixes #16224.

Change-Id: I4e3b5527aa63366afb33a7e30efab088d34fb302
Reviewed-on: https://go-review.googlesource.com/24670
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Updates x/net/http2 to git rev 8e573f40 for https://golang.org/cl/24600,
"http2: merge multiple GOAWAY frames' contents into error message"

Fixes #14627 (more)

Change-Id: I5231607c2c9e0d854ad6199ded43c59e59f62f52
Reviewed-on: https://go-review.googlesource.com/24612
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

There was only one use of "HTTP/1.n" compared to "HTTP/1.x":

h2_bundle.go://   "Just as in HTTP/1.x, header field names are strings of ASCII
httputil/dump.go:// DumpRequest returns the given request in its HTTP/1.x wire
httputil/dump.go:// intact. HTTP/2 requests are dumped in HTTP/1.x form, not in their
response.go:// Write writes r to w in the HTTP/1.x server response format,
server.go:      // Request.Body. For HTTP/1.x requests, handlers should read any
server.go:// The default HTTP/1.x and HTTP/2 ResponseWriter implementations
server.go:// The default ResponseWriter for HTTP/1.x connections supports
server.go:// http1ServerSupportsRequest reports whether Go's HTTP/1.x server
server.go:      // about HTTP/1.x Handlers concurrently reading and writing, like
server.go:      // HTTP/1.x from here on.
transport.go:   return fmt.Errorf("net/http: HTTP/1.x transport connection broken: %v", err)

Be consistent.

Change-Id: I93c4c873e500f51af2b4762055e22f5487a625ac
Reviewed-on: https://go-review.googlesource.com/24610Reviewed-by: Andrew Gerrand <adg@golang.org>

Change-Id: I2b7a81cb809d109f10d5f0db957c614f466d6bfd
Reviewed-on: https://go-review.googlesource.com/24582Reviewed-by: Adam Langley <agl@golang.org>

I believe it's necessary to use a buffer size smaller than 64KB because
(at least some versions of) Window using a TCP receive window less than
64KB. Currently the client and server use buffer sizes of 16KB and 32KB,
respectively (the server uses io.Copy, which defaults to 32KB internally).
Since the server has been using 32KB, it should be safe for the client to
do so as well.

Fixes #15899

Change-Id: I36d44b29f2a5022c03fc086213d3c1adf153e983
Reviewed-on: https://go-review.googlesource.com/24581Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The assembly is broken: it does `MOVQ g(R12), R14` expecting that
R12 contains tls address, but it does not do get_tls(R12) before.
This magically works on linux: `MOVQ g(R12), R14` is compiled to
`mov %fs:0xfffffffffffffff8,%r14` which does not use R12.
But it crashes on windows.

Add explicit `get_tls(R12)`.

Fixes #16206

Change-Id: Ic1f21a6fef2473bcf9147de6646929781c9c1e98
Reviewed-on: https://go-review.googlesource.com/24590Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

When the blocked field was first introduced back in
https://golang.org/cl/61250043 the scheduler trace code incorrectly used
m->blocked instead of mp->blocked.  That has carried through the
conversion to Go.  This CL fixes it.

Change-Id: Id81907b625221895aa5c85b9853f7c185efd8f4b
Reviewed-on: https://go-review.googlesource.com/24571Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

If creating a new thread fails with EAGAIN, point the user at ulimit.

Fixes #15476.

Change-Id: Ib36519614b5c72776ea7f218a0c62df1dd91a8ea
Reviewed-on: https://go-review.googlesource.com/24570
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Updates x/net/http2 to git rev ef2e00e88 for https://golang.org/cl/24560,
"http2: make Transport return server's GOAWAY error back to the user"

Fixes #14627

Change-Id: I2bb123a3041e168db7c9446beef4ee47638f17ee
Reviewed-on: https://go-review.googlesource.com/24561Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Prior to this change package "foo" had to be installed in order to check
example names in "foo_test" package.

However by the time "foo_test" package is checked a parsed "foo" package
has been already constructed. Use it to check example names.

Also change TestDivergentPackagesExamples test to pass directory of the
package to the vet tool as it is the most common way to invoke it. This
requires changes to errchk to add support for grabbing source files from
a directory.

Fixes #16189

Change-Id: Ief103d07b024822282b86c24250835cc591793e8
Reviewed-on: https://go-review.googlesource.com/24488Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

TestPendingConnsAfterErr only cared that things didn't deadlock, so 5
seconds is a sufficient timer. We don't need 100 milliseconds.

I was able to reproduce with a tiny (5 nanosecond) timeout value,
instead of 100 milliseconds. In the process of testing with -race and
a high -count= value, I noticed several data races and panics
(sendings on a closed channel) which are also fixed in this change.

Fixes #15684

Change-Id: Ib4605fcc0f296e658cb948352ed642b801cb578c
Reviewed-on: https://go-review.googlesource.com/24550Reviewed-by: Marko Tiikkaja <marko@joh.to>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

Fixes #16165

Change-Id: Ic90e5873e0c8ee044f09543177192dcae1dcdbed
Reviewed-on: https://go-review.googlesource.com/24531
Run-TryBot: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Change-Id: I47bd98509663d75b0d4dedbdb778e803d90053cf
Reviewed-on: https://go-review.googlesource.com/24216Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Don't configure HTTP/2 in http.Server.Serve(net.Listener) if the
Server's TLSConfig is set and doesn't include the "h2" NextProto
value. This avoids mutating a *tls.Config already in use if
previously passed to tls.NewListener.

Also document this. (it's come up a few times now)

Fixes #15908

Change-Id: I283eed82fdb29a791f80d801aadd9f75db244de0
Reviewed-on: https://go-review.googlesource.com/24508Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Fixes #16201

Change-Id: I38c17859db78c2868905da24217e0ad47739c320
Reviewed-on: https://go-review.googlesource.com/24541
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Updates #16124

Change-Id: Ib58f2bb37fd1559efc512a2e3cba976f09b939a0
Reviewed-on: https://go-review.googlesource.com/24520Reviewed-by: Andrew Gerrand <adg@golang.org>