Skip to content

Instantly share code, notes, and snippets.

@ismasan
Last active January 14, 2024 18:51
Show Gist options
  • Save ismasan/d03d602b8e4e37862547e9a6f0391dc9 to your computer and use it in GitHub Desktop.
Save ismasan/d03d602b8e4e37862547e9a6f0391dc9 to your computer and use it in GitHub Desktop.
Write backend HTTP response to http.ResponseWriter and File
// fileResponseWriter wraps an http.ResponseWriter and a File
// passing it to an http.Handler's ServeHTTP
// will write to both the file and the response.
type fileResponseWriter struct {
file io.Writer
resp http.ResponseWriter
multi io.Writer
}
func newFileResponseWriter(file io.Writer, resp http.ResponseWriter) http.ResponseWriter {
multi := io.MultiWriter(file, resp)
return &fileResponseWriter{
file: file,
resp: resp,
multi: multi,
}
}
// implement http.ResponseWriter
// https://golang.org/pkg/net/http/#ResponseWriter
func (w *fileResponseWriter) Header() http.Header {
return w.resp.Header()
}
func (w *fileResponseWriter) Write(b []byte) (int, error) {
return w.multi.Write(b)
}
func (w *fileResponseWriter) WriteHeader(i int) {
w.resp.WriteHeader(i)
}
// Example http handler middleware.
// proxies to backend app,
// and then caches the response in file named after request PATH
type RequestCacher struct {
app http.Handler
cacheDir string
}
func NewRequestCacher(app http.Handler, cacheDir string) http.Handler {
handler := &RequestCacher{
app: app,
cacheDir: cacheDir,
}
return handler
}
func (h *RequestCacher) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
var writer http.ResponseWriter
writer = rw
path := filepath.Join(h.cacheDir, req.URL.Path)
dir := filepath.Dir(path)
// Make sure the cache dir exists
err := os.MkdirAll(dir, 0764)
if err != nil {
log.Println("mkdir", err)
h.app.ServeHTTP(writer, req)
return
}
// create file to cache response into.
file, err := os.Create(path)
defer file.Close()
if err != nil {
log.Println("create file", err)
h.app.ServeHTTP(writer, req)
return
}
// wrap file and original response writer
writer = newFileResponseWriter(file, rw)
// backend app will write to both
// file and http response
h.app.ServeHTTP(writer, req)
log.Println("cached", path)
}
// USAGE
//
// app := &SomeHTTPHandler{}
// app = NewRequestCacher(app, "/path/to/cache/dir")
// log.Fatal(http.ListenAndServe("localhost:4000", app))
@nea
Copy link

nea commented Apr 6, 2020

Awesome, thx!

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment