I've been playing around with the spotify api and came to an Problem. context.Context gets used and therefore the functions just "randomly" execute. The OAuth function should check if the Code is invalid but If I don't do this with an channel the last part of the code gets executed directly without even the first/second function finishing. Because of that I made an second goroutine that checks if the channel is received and then write an response. But now I get this error http: wrote more than the declared Content-Length how can I correct the Content-Lenght? Why is context even used?
My Code:
// Wrapper: github.com/zmb3/spotify/v2
func WriteResponse(w http.ResponseWriter, h chan *spotify.Client) {
client := <-h
user, err := client.CurrentUser(context.Background())
fmt.Println(user.User.DisplayName)
if err != nil {
_, err := fmt.Fprint(w, "Couldn't get user sorry :(")
if err != nil {
return
}
}
_, err = fmt.Fprintf(w, "Logged in as %s!", user.User.DisplayName)
if err != nil {
log.Println(err)
return
}
}
func OAuth(w http.ResponseWriter, r *http.Request) {
ch := make(chan *spotify.Client)
tok, err := auth.Token(r.Context(), state, r)
if err != nil {
w.WriteHeader(503)
_, err := fmt.Fprint(w, "Couldn't get token sorry :(")
if err != nil {
return
}
}
if st := r.FormValue("state"); st != state {
http.NotFound(w,r)
log.Fatalf("State mismatch: %s != %s\n", st, state)
}
go WriteResponse(w, ch)
client := spotify.New(auth.Client(r.Context(), tok))
ch <- client
}
You forgot to return..
if err != nil {
w.WriteHeader(503)
_, err := fmt.Fprint(w, "Couldn't get token sorry :(")
if err != nil {
return
}
// here
return
}
Related
i have function:
func write() {
defer func() {
serverConn.Close()
}()
for message := range msgChan {
w, err := serverConn.NextWriter(websocket.TextMessage)
if err != nil {
return
}
bmessage, err := json.Marshal(message)
if err != nil {
return
}
_, err = w.Write(bmessage)
if err != nil {
fmt.Println(err)
}
if err := w.Close(); err != nil {
return
}
}
}
And i got
panic: concurrent write to websocket connection
I'm wondering how is this possible? in ws writes only this function, which is running in 1 instance. and second question: what is the point of using NextWriter instead of just conn.WriteMessage()? Is it possible that with a large number of messages NextWriter accumulate and can try to write at the same time?
I need to write unit test cases for Gorilla Web-socket.
var upgrader = websocket.Upgrader{} // use default options
func socketHandler(w http.ResponseWriter, r *http.Request) {
// Upgrade our raw HTTP connection to a websocket based one
conn, err := upgrader.Upgrade(w, r, nil)
if err != nil {
log.Print("Error during connection upgradation:", err)
return
}
defer conn.Close()
// The event loop
for {
messageType, message, err := conn.ReadMessage()
if err != nil {
log.Println("Error during message reading:", err)
break
}
log.Printf("Received: %s", message)
err = conn.WriteMessage(messageType, message)
if err != nil {
log.Println("Error during message writing:", err)
break
}
}
}
func home(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(w, "Index Page")
}
func main() {
http.HandleFunc("/socket", socketHandler)
http.HandleFunc("/", home)
log.Fatal(http.ListenAndServe("localhost:8080", nil))
}
I want to write the Unit Test case for socketHandler function. How should I go about it?
Spin up an httptest.Server with the websocket endpoint. Dial the server with the websocket client. Send and receive messages as needed.
Here's a simple example:
func TestWs(t *testing.T) {
s := httptest.NewServer(http.HandlerFunc(socketHandler))
defer s.Close()
wsURL := "ws" + strings.TrimPrefix(s.URL, "http")
c, _, err := websocket.DefaultDialer.Dial(wsURL, nil)
if err != nil {
t.Error(err)
}
defer c.Close()
// Write a message.
c.WriteMessage(websocket.TextMessage, []byte("hello"))
// Expect the server to echo the message back.
c.SetReadDeadline(time.Now().Add(time.Second * 2))
mt, msg, err := c.ReadMessage()
if err != nil {
t.Error(err)
}
if mt != websocket.TextMessage || string(msg) != "hello" {
t.Errorf("expected text hello, got %d: %s", mt, msg)
}
}
Run the example on the playground.
To test a client, write a server endpoint that sends as receives messages as needed for a test. Run your client code against the endpoint as above.
I wrote a connection closure function. It sends a closing frame and expects the same in response.
func TryCloseNormally(wsConn *websocket.Conn) error {
closeNormalClosure := websocket.FormatCloseMessage(websocket.CloseNormalClosure, "")
defer wsConn.Close()
if err := wsConn.WriteControl(websocket.CloseMessage, closeNormalClosure, time.Now().Add(time.Second)); err != nil {
return err
}
if err := wsConn.SetReadDeadline(time.Now().Add(time.Second)); err != nil {
return err
}
_, _, err := wsConn.ReadMessage()
if websocket.IsCloseError(err, websocket.CloseNormalClosure) {
return nil
} else {
return errors.New("Websocket doesn't send a close frame in response")
}
}
I wrote a test for this function.
func TestTryCloseNormally(t *testing.T) {
done := make(chan struct{})
exit := make(chan struct{})
ctx := context.Background()
ln, err := net.Listen("tcp", "localhost:")
require.Nil(t, err)
handler := HandlerFunc(func(conn *websocket.Conn) {
for {
_, _, err := conn.ReadMessage()
if err != nil {
require.True(t, websocket.IsCloseError(err, websocket.CloseNormalClosure), err.Error())
return
}
}
})
s, err := makeServer(ctx, handler)
require.Nil(t, err)
go func() {
require.Nil(t, s.Run(ctx, exit, ln))
close(done)
}()
wsConn, _, err := websocket.DefaultDialer.Dial(addr+strconv.Itoa(ln.Addr().(*net.TCPAddr).Port), nil) //nolint:bodyclose
require.Nil(t, err)
require.Nil(t, wsConn.WriteMessage(websocket.BinaryMessage, []byte{'o', 'k'}))
require.Nil(t, TryCloseNormally(wsConn))
close(exit)
<-done
}
To my surprise, it works correctly. Readmessage() reads the closing frame. But in the test, I don't write anything.
Is this happening at the gorilla/websocket level?
Did I write the function correctly? Maybe reading the response frame also happens at the gorilla level.
The function is mostly correct.
Websocket endpoints echo close messages unless the endpoint has already send a close message on its own. See Closing Handshake in the Websocket RFC for more details.
In the normal close scenario, an application should expect to receive a close message after sending a close message.
To handle the case where the peer sent a data message before the sending the close message, read and discard data messages until an error is returned.
func TryCloseNormally(wsConn *websocket.Conn) error {
defer wsConn.Close()
closeNormalClosure := websocket.FormatCloseMessage(websocket.CloseNormalClosure, "")
if err := wsConn.WriteControl(websocket.CloseMessage, closeNormalClosure, time.Now().Add(time.Second)); err != nil {
return err
}
if err := wsConn.SetReadDeadline(time.Now().Add(time.Second)); err != nil {
return err
}
for {
_, _, err := wsConn.ReadMessage()
if websocket.IsCloseError(err, websocket.CloseNormalClosure) {
return nil
}
if err != nil {
return err
}
}
}
I am able to zip a file using logic similar to the zip writer seen here.
This results in an array of bytes ([]byte) being created within the bytes.Buffer object that is returned. I would just like to know if there is there any way I can upload this 'zipped' array of bytes to an API endpoint that expects a 'multipart/form-data' request body (without having to save it locally).
Supplementary information:
I have code that utilizes this when compressing a folder. I am able to successfully execute an HTTP POST request with the zip file to the endpoint with this logic.
However, this unfortunately saves zipped files in a user's local file system. I would like to try to avoid this :)
You can create multipart writer and write []byte zipped data into field with field name you like and file name like below.
func addZipFileToReq(zipped []byte) (*http.Request, error){
body := bytes.NewBuffer(nil)
writer := multipart.NewWriter(body)
part, err := writer.CreateFormFile(`fileField`, `filename`)
if err != nil {
return nil, err
}
_, err = part.Write(zipped)
if err != nil {
return nil, err
}
err = writer.Close()
if err != nil {
return nil, err
}
r, err := http.NewRequest(http.MethodPost, "https://example.com", body)
if err != nil {
return nil, err
}
r.Header.Set("Content-Type", writer.FormDataContentType())
return r, nil
}
If you want to stream-upload the zip, you should be able to do so with io.Pipe. The following is an incomplete and untested example to demonstrate the general idea. To make it work you'll need to modify it and potentially fix whatever bugs you encounter.
func UploadReader(r io.Reader) error {
req, err := http.NewRequest("POST", "<UPLOAD_URL>", r)
if err != nil {
return err
}
// TODO set necessary headers (content type, auth, etc)
res, err := http.DefaultClient.Do(req)
if err != nil {
return err
} else if res.StatusCode != 200 {
return errors.New("not ok")
}
return nil
}
func ZipDir(dir string, w io.Writer) error {
zw := zip.NewWriter(w)
defer zw.Close()
return filepath.Walk(dir, func(path string, fi os.FileInfo, err error) error {
if err != nil {
return err
}
if !fi.Mode().IsRegular() {
return nil
}
header, err := zip.FileInfoHeader(fi)
if err != nil {
return err
}
header.Name = path
header.Method = zip.Deflate
w, err := zw.CreateHeader(header)
if err != nil {
return err
}
f, err := os.Open(path)
if err != nil {
return err
}
defer f.Close()
if _, err := io.Copy(w, f); err != nil {
return err
}
return nil
})
}
func UploadDir(dir string) error {
r, w := io.Pipe()
ch := make(chan error)
wg := sync.WaitGroup{}
wg.Add(1)
go func() {
defer wg.Done()
defer w.Close()
if err := ZipDir(dir, w); err != nil {
ch <- err
}
}()
wg.Add(1)
go func() {
defer wg.Done()
defer r.Close()
if err := UploadReader(r); err != nil {
ch <- err
}
}()
go func() {
wg.Wait()
close(ch)
}()
return <-ch
}
I am new to Go and building web apps. An example of my handler is something like this:
func getAllPostsHandler(w http.ResponseWriter, r *http.Request) {
var posts []Post
dbSesstion := context.Get(r, "database").(*mgo.Session)
err := dbSesstion.DB(dbsett.Name).C(dbsett.Collection).Find(nil).All(&posts)
if err != nil {
log.Print("error: ", nil)
w.WriteHeader(http.StatusInternalServerError)
return
}
err = json.NewEncoder(w).Encode(posts)
if err != nil {
log.Print("error: ", nil)
w.WriteHeader(http.StatusInternalServerError)
return
}
w.WriteHeader(http.StatusOK)
}
My handlers have a lot of repeating error checking like this:
if err != nil {
log.Print("error: ", nil)
w.WriteHeader(http.StatusInternalServerError)
return
}
I want to make a function, which checks for error, print logs, write the response writer if neccessary, and return, but not only to the handler, but to stop all other response writings and return the handler itself. Is it possible to do so? I am thinking about panicing, but something tells me that its not the right way.
You can't escape outermost function from innermost but you can at least compact code a bit by inverting control flow
err := dbSesstion.DB(dbsett.Name).C(dbsett.Collection).Find(nil).All(&posts)
if err == nil {
err = json.NewEncoder(w).Encode(posts)
if err == nil {
err = somethingelse()
if err == nil {
w.WriteHeader(http.StatusOK)
return //successfully
}
}
}
log.Print("error: ", nil)
w.WriteHeader(http.StatusInternalServerError)