/
adapter.go
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/
adapter.go
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// Package awswebsocketadapter can be used to run an AWS Lambda function integration for a
// websocket-type API Gateway, locally.
//
// It implements http.Handler to handle websocket connections and invokes the provided AWS Lambda
// handler function for any CONNECT, DISCONNECT or MESSAGE events.
//
// It also implements the apigatewaymanagementapiiface.ApiGatewayManagementApiAPI client interface,
// so it can be used to write messages back to a client.
package awswebsocketadapter
import (
"context"
"crypto/rand"
"encoding/base64"
"fmt"
"io"
"log"
"net/http"
"sync"
"time"
"github.com/aws/aws-lambda-go/events"
"github.com/aws/aws-sdk-go/aws"
"github.com/aws/aws-sdk-go/aws/request"
"github.com/aws/aws-sdk-go/service/apigatewaymanagementapi"
"github.com/gorilla/websocket"
)
type LambdaHandler func(context.Context, events.APIGatewayWebsocketProxyRequest) (events.APIGatewayProxyResponse, error)
// Adapter is an implementation of an API Gateway Websocket API that invokes an AWS Lambda
// function in-memory. It is a handler that upgrades requests to websockets and invokes an AWS
// Lambda handler on each message. It also provides API Gateway Management APIs for writing back to
// connections.
type Adapter struct {
LambdaHandler LambdaHandler
upgrader websocket.Upgrader
writersMu sync.Mutex
writers map[string]io.Writer
}
// ServeHTTP upgrades the request from HTTP to WS and then continues to send and receive websocket
// messages over the connection.
func (a *Adapter) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// Upgrade the HTTP request to WS.
ws, err := a.upgrader.Upgrade(w, r, nil)
if err != nil {
log.Print("upgrade:", err)
return
}
defer ws.Close()
// Generate a random connection ID.
var connIDSrc [8]byte
if _, err := rand.Read(connIDSrc[:]); err != nil {
log.Print("generate connection ID:", err)
return
}
connID := base64.StdEncoding.EncodeToString(connIDSrc[:])
// Invoke CONNECT handler.
if err := a.invokeHandler(connID, "CONNECT", "", r.Header); err != nil {
log.Println("handler:", err)
return
}
defer func() {
// Invoke DISCONNECT handler.
if err := a.invokeHandler(connID, "DISCONNECT", "", r.Header); err != nil {
log.Println("handler:", err)
}
}()
// Register a hook for writing back to the connection, indexed by its connection ID.
a.writersMu.Lock()
if a.writers == nil {
a.writers = make(map[string]io.Writer)
}
a.writers[connID] = &wsTextWriter{ws: ws}
a.writersMu.Unlock()
defer func() {
a.writersMu.Lock()
delete(a.writers, connID)
a.writersMu.Unlock()
}()
// Read from the connection as long as it stays open.
for {
// Read the next message.
mt, message, err := ws.ReadMessage()
if err != nil {
log.Println("read:", err)
break
}
// API Gateway Websockets only support text message types.
if mt != websocket.TextMessage {
log.Println("unsupported message type:", mt)
break
}
// Invoke the Lambda handler
if err := a.invokeHandler(connID, "MESSAGE", string(message), r.Header); err != nil {
log.Println("handler:", err)
if err := writeError(ws); err != nil {
log.Println("write:", err)
break
}
}
}
}
func (a *Adapter) invokeHandler(connID, eventType, body string, header http.Header) error {
ctx, cancel := context.WithTimeout(context.Background(), time.Second*30)
defer cancel()
res, err := a.LambdaHandler(ctx, events.APIGatewayWebsocketProxyRequest{
RequestContext: events.APIGatewayWebsocketProxyRequestContext{
ConnectionID: connID,
EventType: eventType,
},
MultiValueHeaders: header,
Body: body,
})
if err != nil {
return err
}
if res.StatusCode != http.StatusOK {
return fmt.Errorf("status code: %d", res.StatusCode)
}
return nil
}
func writeError(ws *websocket.Conn) error {
return ws.WriteMessage(websocket.TextMessage, []byte(`{"message": "Internal server error"}`))
}
func (a *Adapter) DeleteConnection(_ *apigatewaymanagementapi.DeleteConnectionInput) (*apigatewaymanagementapi.DeleteConnectionOutput, error) {
panic("not implemented")
}
func (a *Adapter) DeleteConnectionWithContext(_ aws.Context, _ *apigatewaymanagementapi.DeleteConnectionInput, _ ...request.Option) (*apigatewaymanagementapi.DeleteConnectionOutput, error) {
panic("not implemented")
}
func (a *Adapter) DeleteConnectionRequest(_ *apigatewaymanagementapi.DeleteConnectionInput) (*request.Request, *apigatewaymanagementapi.DeleteConnectionOutput) {
panic("not implemented")
}
func (a *Adapter) GetConnection(_ *apigatewaymanagementapi.GetConnectionInput) (*apigatewaymanagementapi.GetConnectionOutput, error) {
panic("not implemented")
}
func (a *Adapter) GetConnectionWithContext(_ aws.Context, _ *apigatewaymanagementapi.GetConnectionInput, _ ...request.Option) (*apigatewaymanagementapi.GetConnectionOutput, error) {
panic("not implemented")
}
func (a *Adapter) GetConnectionRequest(_ *apigatewaymanagementapi.GetConnectionInput) (*request.Request, *apigatewaymanagementapi.GetConnectionOutput) {
panic("not implemented")
}
func (a *Adapter) PostToConnection(input *apigatewaymanagementapi.PostToConnectionInput) (*apigatewaymanagementapi.PostToConnectionOutput, error) {
return a.PostToConnectionWithContext(context.Background(), input)
}
func (a *Adapter) PostToConnectionWithContext(_ aws.Context, input *apigatewaymanagementapi.PostToConnectionInput, _ ...request.Option) (*apigatewaymanagementapi.PostToConnectionOutput, error) {
var writer io.Writer
a.writersMu.Lock()
if a.writers != nil {
writer = a.writers[*input.ConnectionId]
}
a.writersMu.Unlock()
if writer == nil {
return nil, &apigatewaymanagementapi.GoneException{}
}
_, err := writer.Write(input.Data)
return &apigatewaymanagementapi.PostToConnectionOutput{}, err
}
func (a *Adapter) PostToConnectionRequest(_ *apigatewaymanagementapi.PostToConnectionInput) (*request.Request, *apigatewaymanagementapi.PostToConnectionOutput) {
panic("not implemented")
}
type wsTextWriter struct {
ws *websocket.Conn
}
func (w *wsTextWriter) Write(p []byte) (n int, err error) {
return len(p), w.ws.WriteMessage(websocket.TextMessage, p)
}