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net/http: keep Content-Encoding in Error, add GODEBUG for ServeContent

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This reverts the changes to Error from CL 571995, and adds a
GODEBUG controlling the changes to ServeContent/ServeFile/ServeFS.

The change to remove the Content-Encoding header when serving an error
breaks middleware which sets Content-Encoding: gzip and wraps a
ResponseWriter in one which compresses the response body.

This middleware already breaks when ServeContent handles a Range request.
Correct uses of ServeContent which serve pre-compressed content with
a Content-Encoding: gzip header break if we don't remove that header
when serving errors. Therefore, we keep the change to ServeContent/
ServeFile/ServeFS, but we add the ability to disable the new behavior
by setting GODEBUG=httpservecontentkeepheaders=1.

We revert the change to Error, because users who don't want to include
a Content-Encoding header in errors can simply remove the header
themselves, or not add it in the first place.

Fixes #66343

Change-Id: Ic19a24b73624a5ac1a258ed7a8fe7d9bf86c6a38
Reviewed-on: https://go-review.googlesource.com/c/go/+/593157
Reviewed-by: Russ Cox <rsc@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Damien Neil 2024-06-17 12:30:19 -07:00
parent 2b12bbcb45
commit 879ace1434
8 changed files with 115 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
doc/godebug.md
View File

@ -200,6 +200,15 @@ This behavior is controlled by the `x509keypairleaf` setting. For Go 1.23, it
defaults to `x509keypairleaf=1`. Previous versions default to
`x509keypairleaf=0`.
Go 1.23 changed
[`net/http.ServeContent`](/pkg/net/http#ServeContent),
[`net/http.ServeFile`](/pkg/net/http#ServeFile), and
[`net/http.ServeFS`](/pkg/net/http#ServeFS) to
remove Cache-Control, Content-Encoding, Etag, and Last-Modified headers
when serving an error. This behavior is controlled by
the [`httpservecontentkeepheaders` setting](/pkg/net/http#ServeContent).
Using `httpservecontentkeepheaders=1` restores the pre-Go 1.23 behavior.
### Go 1.22
Go 1.22 adds a configurable limit to control the maximum acceptable RSA key size

17
doc/next/6-stdlib/99-minor/net/http/66343.md
View File

@ -1 +1,16 @@
[Error] now removes misleading response headers.
[ServeContent], [ServeFile], and [ServeFileFS] now remove
the `Cache-Control`, `Content-Encoding`, `Etag`, and `Last-Modified`
headers when serving an error. These headers usually apply to the
non-error content, but not to the text of errors.
Middleware which wraps a [ResponseWriter] and applies on-the-fly
encoding, such as `Content-Encoding: gzip`, will not function after
this change. The previous behavior of [ServeContent], [ServeFile],
and [ServeFileFS] may be restored by setting
`GODEBUG=httpservecontentkeepheaders=1`.
Note that middleware which changes the size of the served content
(such as by compressing it) already does not function properly when
[ServeContent] handles a Range request. On-the-fly compression
should use the `Transfer-Encoding` header instead of `Content-Encoding`.

1
src/internal/godebugs/table.go
View File

@ -36,6 +36,7 @@ var All = []Info{
{Name: "http2server", Package: "net/http"},
{Name: "httplaxcontentlength", Package: "net/http", Changed: 22, Old: "1"},
{Name: "httpmuxgo121", Package: "net/http", Changed: 22, Old: "1"},
{Name: "httpservecontentkeepheaders", Package: "net/http", Changed: 23, Old: "0"},
{Name: "installgoroot", Package: "go/build"},
{Name: "jstmpllitinterp", Package: "html/template", Opaque: true}, // bug #66217: remove Opaque
//{Name: "multipartfiles", Package: "mime/multipart"},

37
src/net/http/fs.go
View File

@ -9,6 +9,7 @@ package http
import (
"errors"
"fmt"
"internal/godebug"
"io"
"io/fs"
"mime"
@ -171,15 +172,37 @@ func dirList(w ResponseWriter, r *Request, f File) {
fmt.Fprintf(w, "</pre>\n")
}
// GODEBUG=httpservecontentkeepheaders=1 restores the pre-1.23 behavior of not deleting
// Cache-Control, Content-Encoding, Etag, or Last-Modified headers on ServeContent errors.
var httpservecontentkeepheaders = godebug.New("httpservecontentkeepheaders")
// serveError serves an error from ServeFile, ServeFileFS, and ServeContent.
// Because those can all be configured by the caller by setting headers like
// Etag, Last-Modified, and Cache-Control to send on a successful response,
// the error path needs to clear them, since they may not be meant for errors.
func serveError(w ResponseWriter, text string, code int) {
h := w.Header()
h.Del("Etag")
h.Del("Last-Modified")
h.Del("Cache-Control")
nonDefault := false
for _, k := range []string{
"Cache-Control",
"Content-Encoding",
"Etag",
"Last-Modified",
} {
if !h.has(k) {
continue
}
if httpservecontentkeepheaders.Value() == "1" {
nonDefault = true
} else {
h.Del(k)
}
}
if nonDefault {
httpservecontentkeepheaders.IncNonDefault()
}
Error(w, text, code)
}
@ -203,11 +226,17 @@ func serveError(w ResponseWriter, text string, code int) {
//
// The content's Seek method must work: ServeContent uses
// a seek to the end of the content to determine its size.
// Note that [*os.File] implements the [io.ReadSeeker] interface.
//
// If the caller has set w's ETag header formatted per RFC 7232, section 2.3,
// ServeContent uses it to handle requests using If-Match, If-None-Match, or If-Range.
//
// Note that [*os.File] implements the [io.ReadSeeker] interface.
// If an error occurs when serving the request (for example, when
// handling an invalid range request), ServeContent responds with an
// error message. By default, ServeContent strips the Cache-Control,
// Content-Encoding, ETag, and Last-Modified headers from error responses.
// The GODEBUG setting httpservecontentkeepheaders=1 causes ServeContent
// to preserve these headers.
func ServeContent(w ResponseWriter, req *Request, name string, modtime time.Time, content io.ReadSeeker) {
sizeFunc := func() (int64, error) {
size, err := content.Seek(0, io.SeekEnd)

49
src/net/http/fs_test.go
View File

@ -1223,8 +1223,20 @@ type issue12991File struct{ File }
func (issue12991File) Stat() (fs.FileInfo, error) { return nil, fs.ErrPermission }
func (issue12991File) Close() error { return nil }
func TestFileServerErrorMessages(t *testing.T) { run(t, testFileServerErrorMessages) }
func testFileServerErrorMessages(t *testing.T, mode testMode) {
func TestFileServerErrorMessages(t *testing.T) {
run(t, func(t *testing.T, mode testMode) {
t.Run("keepheaders=0", func(t *testing.T) {
testFileServerErrorMessages(t, mode, false)
})
t.Run("keepheaders=1", func(t *testing.T) {
testFileServerErrorMessages(t, mode, true)
})
}, testNotParallel)
}
func testFileServerErrorMessages(t *testing.T, mode testMode, keepHeaders bool) {
if keepHeaders {
t.Setenv("GODEBUG", "httpservecontentkeepheaders=1")
}
fs := fakeFS{
"/500": &fakeFileInfo{
err: errors.New("random error"),
@ -1254,8 +1266,12 @@ func testFileServerErrorMessages(t *testing.T, mode testMode) {
t.Errorf("GET /%d: StatusCode = %d; want %d", code, res.StatusCode, code)
}
for _, hdr := range []string{"Etag", "Last-Modified", "Cache-Control"} {
if v, ok := res.Header[hdr]; ok {
t.Errorf("GET /%d: Header[%q] = %q, want not present", code, hdr, v)
if v, got := res.Header[hdr]; got != keepHeaders {
want := "not present"
if keepHeaders {
want = "present"
}
t.Errorf("GET /%d: Header[%q] = %q, want %v", code, hdr, v, want)
}
}
}
@ -1710,6 +1726,17 @@ func testFileServerDirWithRootFile(t *testing.T, mode testMode) {
}
func TestServeContentHeadersWithError(t *testing.T) {
t.Run("keepheaders=0", func(t *testing.T) {
testServeContentHeadersWithError(t, false)
})
t.Run("keepheaders=1", func(t *testing.T) {
testServeContentHeadersWithError(t, true)
})
}
func testServeContentHeadersWithError(t *testing.T, keepHeaders bool) {
if keepHeaders {
t.Setenv("GODEBUG", "httpservecontentkeepheaders=1")
}
contents := []byte("content")
ts := newClientServerTest(t, http1Mode, HandlerFunc(func(w ResponseWriter, r *Request) {
w.Header().Set("Content-Type", "application/octet-stream")
@ -1738,6 +1765,12 @@ func TestServeContentHeadersWithError(t *testing.T) {
out, _ := io.ReadAll(res.Body)
res.Body.Close()
ifKept := func(s string) string {
if keepHeaders {
return s
}
return ""
}
if g, e := res.StatusCode, 416; g != e {
t.Errorf("got status = %d; want %d", g, e)
}
@ -1750,16 +1783,16 @@ func TestServeContentHeadersWithError(t *testing.T) {
if g, e := res.Header.Get("Content-Length"), strconv.Itoa(len(out)); g != e {
t.Errorf("got content-length = %q, want %q", g, e)
}
if g, e := res.Header.Get("Content-Encoding"), ""; g != e {
if g, e := res.Header.Get("Content-Encoding"), ifKept("gzip"); g != e {
t.Errorf("got content-encoding = %q, want %q", g, e)
}
if g, e := res.Header.Get("Etag"), ""; g != e {
if g, e := res.Header.Get("Etag"), ifKept(`"abcdefgh"`); g != e {
t.Errorf("got etag = %q, want %q", g, e)
}
if g, e := res.Header.Get("Last-Modified"), ""; g != e {
if g, e := res.Header.Get("Last-Modified"), ifKept("Wed, 21 Oct 2015 07:28:00 GMT"); g != e {
t.Errorf("got last-modified = %q, want %q", g, e)
}
if g, e := res.Header.Get("Cache-Control"), ""; g != e {
if g, e := res.Header.Get("Cache-Control"), ifKept("immutable"); g != e {
t.Errorf("got cache-control = %q, want %q", g, e)
}
if g, e := res.Header.Get("Content-Range"), "bytes */7"; g != e {

3
src/net/http/serve_test.go
View File

@ -7166,13 +7166,12 @@ func testErrorContentLength(t *testing.T, mode testMode) {
func TestError(t *testing.T) {
w := httptest.NewRecorder()
w.Header().Set("Content-Length", "1")
w.Header().Set("Content-Encoding", "ascii")
w.Header().Set("X-Content-Type-Options", "scratch and sniff")
w.Header().Set("Other", "foo")
Error(w, "oops", 432)
h := w.Header()
for _, hdr := range []string{"Content-Length", "Content-Encoding"} {
for _, hdr := range []string{"Content-Length"} {
if v, ok := h[hdr]; ok {
t.Errorf("%s: %q, want not present", hdr, v)
}

13
src/net/http/server.go
View File

@ -2226,17 +2226,22 @@ func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
// writes are done to w.
// The error message should be plain text.
//
// Error deletes the Content-Length and Content-Encoding headers,
// Error deletes the Content-Length header,
// sets Content-Type to “text/plain; charset=utf-8”,
// and sets X-Content-Type-Options to “nosniff”.
// This configures the header properly for the error message,
// in case the caller had set it up expecting a successful output.
func Error(w ResponseWriter, error string, code int) {
h := w.Header()
// We delete headers which might be valid for some other content,
// but not anymore for the error content.
// Delete the Content-Length header, which might be for some other content.
// Assuming the error string fits in the writer's buffer, we'll figure
// out the correct Content-Length for it later.
//
// We don't delete Content-Encoding, because some middleware sets
// Content-Encoding: gzip and wraps the ResponseWriter to compress on-the-fly.
// See https://go.dev/issue/66343.
h.Del("Content-Length")
h.Del("Content-Encoding")
// There might be content type already set, but we reset it to
// text/plain for the error message.

5
src/runtime/metrics/doc.go
View File

@ -267,6 +267,11 @@ Below is the full list of supported metrics, ordered lexicographically.
The number of non-default behaviors executed by the net/http
package due to a non-default GODEBUG=httpmuxgo121=... setting.
/godebug/non-default-behavior/httpservecontentkeepheaders:events
The number of non-default behaviors executed
by the net/http package due to a non-default
GODEBUG=httpservecontentkeepheaders=... setting.
/godebug/non-default-behavior/installgoroot:events
The number of non-default behaviors executed by the go/build
package due to a non-default GODEBUG=installgoroot=... setting.