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websocket_server.go
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websocket_server.go
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// Copyright © 2023 Ory Corp
// SPDX-License-Identifier: Apache-2.0
package watcherx
import (
"context"
"fmt"
"net"
"net/http"
"net/url"
"strings"
"sync"
"github.com/gorilla/websocket"
"github.com/ory/herodot"
)
type (
eventChannelSlice struct {
sync.Mutex
cs []EventChannel
}
websocketWatcher struct {
wsWriteLock sync.Mutex
wsReadLock sync.Mutex
wsClientChannels eventChannelSlice
}
)
const (
messageSendNow = "send values now"
messageSendNowDone = "done sending %d values"
)
func WatchAndServeWS(ctx context.Context, u *url.URL, writer herodot.Writer) (http.HandlerFunc, error) {
c := make(EventChannel)
watcher, err := Watch(ctx, u, c)
if err != nil {
return nil, err
}
w := &websocketWatcher{
wsClientChannels: eventChannelSlice{},
}
go w.broadcaster(ctx, c)
return w.serveWS(ctx, writer, watcher), nil
}
func (ww *websocketWatcher) broadcaster(ctx context.Context, c EventChannel) {
for {
select {
case <-ctx.Done():
return
case e := <-c:
ww.wsClientChannels.Lock()
for _, cc := range ww.wsClientChannels.cs {
cc <- e
}
ww.wsClientChannels.Unlock()
}
}
}
func (ww *websocketWatcher) readWebsocket(ws *websocket.Conn, c chan<- struct{}, watcher Watcher) {
for {
// blocking call to ReadMessage that waits for a close message
ww.wsReadLock.Lock()
_, msg, err := ws.ReadMessage()
ww.wsReadLock.Unlock()
switch errTyped := err.(type) {
case nil:
if string(msg) == messageSendNow {
done, err := watcher.DispatchNow()
if err != nil {
// we cant do much about this error
ww.wsWriteLock.Lock()
_ = ws.WriteJSON(&ErrorEvent{
error: err,
source: "",
})
ww.wsWriteLock.Unlock()
}
go func() {
eventsSend := <-done
ww.wsWriteLock.Lock()
defer ww.wsWriteLock.Unlock()
// we cant do much about this error
_ = ws.WriteMessage(websocket.TextMessage, []byte(fmt.Sprintf(messageSendNowDone, eventsSend)))
}()
}
case *websocket.CloseError:
if errTyped.Code == websocket.CloseNormalClosure {
close(c)
return
}
case *net.OpError:
if errTyped.Op == "read" && strings.Contains(errTyped.Err.Error(), "closed") {
// the context got canceled and therefore the connection closed
close(c)
return
}
default:
// some other unexpected error, best we can do is return
return
}
}
}
func (ww *websocketWatcher) serveWS(ctx context.Context, writer herodot.Writer, watcher Watcher) func(w http.ResponseWriter, r *http.Request) {
return func(w http.ResponseWriter, r *http.Request) {
ws, err := (&websocket.Upgrader{
ReadBufferSize: 256, // the only message we expect is the close message
WriteBufferSize: 1024,
}).Upgrade(w, r, nil)
if err != nil {
writer.WriteError(w, r, err)
return
}
// make channel and register it at broadcaster
c := make(EventChannel)
ww.wsClientChannels.Lock()
ww.wsClientChannels.cs = append(ww.wsClientChannels.cs, c)
ww.wsClientChannels.Unlock()
wsClosed := make(chan struct{})
go ww.readWebsocket(ws, wsClosed, watcher)
defer func() {
// attempt to close the websocket
// ignore errors as we are closing everything anyway
ww.wsWriteLock.Lock()
_ = ws.WriteMessage(websocket.CloseMessage, websocket.FormatCloseMessage(websocket.CloseNormalClosure, "server context canceled"))
ww.wsWriteLock.Unlock()
_ = ws.Close()
ww.wsClientChannels.Lock()
for i, cc := range ww.wsClientChannels.cs {
if c == cc {
ww.wsClientChannels.cs[i] = ww.wsClientChannels.cs[len(ww.wsClientChannels.cs)-1]
ww.wsClientChannels.cs[len(ww.wsClientChannels.cs)-1] = nil
ww.wsClientChannels.cs = ww.wsClientChannels.cs[:len(ww.wsClientChannels.cs)-1]
}
}
ww.wsClientChannels.Unlock()
close(c)
}()
for {
select {
case <-ctx.Done():
return
case <-wsClosed:
return
case e, ok := <-c:
if !ok {
return
}
ww.wsWriteLock.Lock()
err := ws.WriteJSON(e)
ww.wsWriteLock.Unlock()
if err != nil {
return
}
}
}
}
}