net/http: document that Etags in ServeContent must be RFC 7232 compliant #18054
Description
Change f386274 (CL/32014) caused a regression in the behavior of http.ServeContent such that explicitly setting the Etag no longer caused the server to return status 304 when the Etags match.
func Test(t *testing.T) {
fs := http.FileServer(http.Dir("/tmp"))
h := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// Delete if-modified-since header so that ETags can be used instead of the standard cache policy.
r.Header.Del("If-Modified-Since")
// Set ETag to to uniquely identify the unchanged static asset.
w.Header().Set("Etag", "6")
fs.ServeHTTP(w, r)
})
ts := httptest.NewServer(h)
// Ensure /tmp/test.txt exists.
if err := ioutil.WriteFile("/tmp/test.txt", nil, 0664); err != nil {
t.Fatal(err)
}
var c http.Client
req, err := http.NewRequest("GET", ts.URL+"/test.txt", nil)
if err != nil {
t.Fatal(err)
}
req.Header.Add("If-None-Match", "6") // Same Etag as above
resp, err := c.Do(req)
if err != nil {
t.Fatal(err)
}
if resp.StatusCode != 304 {
t.Error()
}
}I believe this is a regression because the documentation for ServeContent explicitly says:
If the caller has set w's ETag header, ServeContent uses it to handle requests using If-Range and If-None-Match.
\cc @bradfitz