admin: Make `Etag` a header, not a trailer (#6208)

* Making eTags a header not a trailer * Checked the write * Fixed typo * Corrected comment * Added sync Pool * Changed control flow of buffer reset / putting and changed error code * Switched from interface{} to any in bufferPool

Hayder committed Apr 11, 2024 at 17:19 UTC 4a0492f3e178c8ab970234b27702c76fedffec5f

1 file changed +21 -6

admin.go

+21 -6

@@ -954,17 +954,28 @@ func makeEtag(path string, hash hash.Hash) string {

954 return fmt.Sprintf(`"%s %x"`, path, hash.Sum(nil))

955 }

956

957 +// This buffer pool is used to keep buffers for

958 +// reading the config file during eTag header generation

959 +var bufferPool = sync.Pool{

960 + New: func() any {

961 + return new(bytes.Buffer)

962 + },

963 +}

964 +

965 func handleConfig(w http.ResponseWriter, r *http.Request) error {

966 switch r.Method {

967 case http.MethodGet:

968 w.Header().Set("Content-Type", "application/json")

961 - // Set the ETag as a trailer header.

962 - // The alternative is to write the config to a buffer, and

963 - // then hash that.

964 - w.Header().Set("Trailer", "ETag")

965 -

969 hash := etagHasher()

967 - configWriter := io.MultiWriter(w, hash)

970 +

971 + // Read the config into a buffer instead of writing directly to

972 + // the response writer, as we want to set the ETag as the header,

973 + // not the trailer.

974 + buf := bufferPool.Get().(*bytes.Buffer)

975 + buf.Reset()

976 + defer bufferPool.Put(buf)

977 +

978 + configWriter := io.MultiWriter(buf, hash)

979 err := readConfig(r.URL.Path, configWriter)

980 if err != nil {

981 return APIError{HTTPStatus: http.StatusBadRequest, Err: err}

@@ -973,6 +984,10 @@ func handleConfig(w http.ResponseWriter, r *http.Request) error {

984 // we could consider setting up a sync.Pool for the summed

985 // hashes to reduce GC pressure.

986 w.Header().Set("Etag", makeEtag(r.URL.Path, hash))

987 + _, err = w.Write(buf.Bytes())

988 + if err != nil {

989 + return APIError{HTTPStatus: http.StatusInternalServerError, Err: err}

990 + }

991

992 return nil

993