net/http: builtin slash-suffix redirect does not persist the raw (encoded) url

[WestleyK]

Go version

go version go1.22.6 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/westley/.cache/go-build'
GOENV='/home/westley/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/westley/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/westley/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.6'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build4141769775=/tmp/go-build -gno-record-gcc-switches'

What did you do?

https://go.dev/play/p/dw5wFNBPzix (go 1.23, sometimes the playground time outs, just rerun it)

The default/builtin slash-suffix redirector does not persist the raw url, specifically a url encoded url.

What did you see happen?

Got:

• Request: /api/resource%2fsubdir/info returns <a href="/api/resource/subdir/info/">Moved Permanently</a>.

Returns a url which is invalid, and does not match the original path.

What did you expect to see?

Expected:

• Request: /api/resource%2fsubdir/info should return <a href="/api/resource%2fsubdir/info/">Moved Permanently</a>.

Which persists the url encoded url.

[gabyhelp]

Related Issues

• net/http: `http.StripPrefix` causing incorrect `Location` header and HTML page in 301 response #69485 (closed)
• net/http: redirect with 308 rather than 301 #60769
• net/http/httputil: ReverseProxy appends trailing slash to url with empty path #50337
• net/http: 301 instead of 404 for unmatched requests #65624 (closed)
• net/http/httputil: SingleHostReverseProxy escaped paths are decoded #35908 (closed)
• net/http: infinite redirect on path variable followed by trailing slash #67657 (closed)
• net/http: DefaultServeMux incorrectly redirect (301) to path if path includes `%2F%2F` #21955 (closed)
• net/http: StripPrefix does not preserve url path #24366 (closed)
• net/url: resolvePath should not collapse leading slashes in the path component #21158 (closed)
• net/http: ServeMux forcibly cleans double forward slash in URLs even when behaving as a gateway #42244 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[cagedmantis]

cc/ @neild

[seankhliao]

I'm inclined to say it's a won't fix...
If your application is sensitive to / in the paths, then adding a trailing slash isn't necessarily correct.

[runxiyu]

@seankhliao Perhaps at least update the documentation to reflect this? The documentation clearly says "existing percent encodings will not be changed" which is, as of now, patently false.

[gopherbot]

Change https://go.dev/cl/720821 mentions this issue: net/http: preserve original path encoding in redirects

[runxiyu]

@seankhliao Thanks! Though this doesn't seem to solve the other part of #76313 (double slashes are collapsed into one)

[seankhliao]

I consider that working as intended, see #42244

[runxiyu]

@seankhliao Thanks; that seems to be a reasonable interpretation (although I might consider sending a patch to document it better when I can)