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server.go
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server.go
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package server
import (
"context"
"log"
"math/rand"
"net/http"
"net/url"
"reflect"
"strconv"
"strings"
"sync"
"time"
"github.com/gorilla/websocket"
"github.com/root-gg/wsp"
)
// Server is a Reverse HTTP Proxy over WebSocket
// This is the Server part, Clients will offer websocket connections,
// those will be pooled to transfer HTTP Request and response
type Server struct {
Config *Config
upgrader websocket.Upgrader
// In pools, keep connections with WebSocket peers.
pools []*Pool
// A RWMutex is a reader/writer mutual exclusion lock,
// and it is for exclusive control with pools operation.
//
// This is locked when reading and writing pools, the timing is when:
// 1. (rw) registering websocket clients in /register endpoint
// 2. (rw) remove empty pools which has no connections
// 3. (r) dispatching connection from available pools to clients requests
//
// And then it is released after each process is completed.
lock sync.RWMutex
done chan struct{}
// Through dispatcher channel it communicates between "server" thread and "dispatcher" thread.
// "server" thread sends the value to this channel when accepting requests in the endpoint /requests,
// and "dispatcher" thread reads this channel.
dispatcher chan *ConnectionRequest
server *http.Server
}
// ConnectionRequest is used to request a proxy connection from the dispatcher
type ConnectionRequest struct {
connection chan *Connection
}
// NewConnectionRequest creates a new connection request
func NewConnectionRequest(timeout time.Duration) (cr *ConnectionRequest) {
cr = new(ConnectionRequest)
cr.connection = make(chan *Connection)
return
}
// NewServer return a new Server instance
func NewServer(config *Config) (server *Server) {
rand.Seed(time.Now().Unix())
server = new(Server)
server.Config = config
server.upgrader = websocket.Upgrader{}
server.done = make(chan struct{})
server.dispatcher = make(chan *ConnectionRequest)
return
}
// Start Server HTTP server
func (s *Server) Start() {
go func() {
L:
for {
select {
case <-s.done:
break L
case <-time.After(5 * time.Second):
s.clean()
}
}
}()
r := http.NewServeMux()
// TODO: I want to detach the handler functon from the Server struct,
// but it is tightly coupled to the internal state of the Server.
r.HandleFunc("/register", s.Register)
r.HandleFunc("/request", s.Request)
r.HandleFunc("/status", s.status)
// Dispatch connection from available pools to clients requests
// in a separate thread from the server thread.
go s.dispatchConnections()
s.server = &http.Server{
Addr: s.Config.GetAddr(),
Handler: r,
}
go func() { log.Fatal(s.server.ListenAndServe()) }()
}
// clean removes empty Pools which has no connection.
// It is invoked every 5 sesconds and at shutdown.
func (s *Server) clean() {
s.lock.Lock()
defer s.lock.Unlock()
if len(s.pools) == 0 {
return
}
idle := 0
busy := 0
var pools []*Pool
for _, pool := range s.pools {
if pool.IsEmpty() {
log.Printf("Removing empty connection pool : %s", pool.id)
pool.Shutdown()
} else {
pools = append(pools, pool)
}
ps := pool.Size()
idle += ps.Idle
busy += ps.Busy
}
log.Printf("%d pools, %d idle, %d busy", len(pools), idle, busy)
s.pools = pools
}
// Dispatch connection from available pools to clients requests
func (s *Server) dispatchConnections() {
for {
// Runs in an infinite loop and keeps receiving the value from the `server.dispatcher` channel
// The operator <- is "receive operator", which expression blocks until a value is available.
request, ok := <-s.dispatcher
if !ok {
// The value of `ok` is false if it is a zero value generated because the channel is closed an empty.
// In this case, that means server shutdowns.
break
}
// A timeout is set for each dispatch requet.
ctx := context.Background()
ctx, cancel := context.WithTimeout(ctx, s.Config.GetTimeout())
defer cancel()
L:
for {
select {
case <-ctx.Done(): // The timeout elapses
break L
default: // Go through
}
s.lock.RLock()
if len(s.pools) == 0 {
// No connection pool available
s.lock.RUnlock()
break
}
// [1]: Select a pool which has an idle connection
// Build a select statement dynamically to handle an arbitary number of pools.
cases := make([]reflect.SelectCase, len(s.pools)+1)
for i, ch := range s.pools {
cases[i] = reflect.SelectCase{
Dir: reflect.SelectRecv,
Chan: reflect.ValueOf(ch.idle)}
}
cases[len(cases)-1] = reflect.SelectCase{
Dir: reflect.SelectDefault}
s.lock.RUnlock()
_, value, ok := reflect.Select(cases)
if !ok {
continue // a pool has been removed, try again
}
connection, _ := value.Interface().(*Connection)
// [2]: Verify that we can use this connection and take it.
if connection.Take() {
request.connection <- connection
break
}
}
close(request.connection)
}
}
func (s *Server) Request(w http.ResponseWriter, r *http.Request) {
// [1]: Receive requests to be proxied
// Parse destination URL
dstURL := r.Header.Get("X-PROXY-DESTINATION")
if dstURL == "" {
wsp.ProxyErrorf(w, "Missing X-PROXY-DESTINATION header")
return
}
URL, err := url.Parse(dstURL)
if err != nil {
wsp.ProxyErrorf(w, "Unable to parse X-PROXY-DESTINATION header")
return
}
r.URL = URL
log.Printf("[%s] %s", r.Method, r.URL.String())
if len(s.pools) == 0 {
wsp.ProxyErrorf(w, "No proxy available")
return
}
// [2]: Take an WebSocket connection available from pools for relaying received requests.
request := NewConnectionRequest(s.Config.GetTimeout())
// "Dispatcher" is running in a separate thread from the server by `go s.dispatchConnections()`.
// It waits to receive requests to dispatch connection from available pools to clients requests.
// https://github.com/hgsgtk/wsp/blob/ea4902a8e11f820268e52a6245092728efeffd7f/server/server.go#L93
//
// Notify request from handler to dispatcher through Server.dispatcher channel.
s.dispatcher <- request
// Dispatcher tries to find an available connection pool,
// and it returns the connection through Server.connection channel.
// https://github.com/hgsgtk/wsp/blob/ea4902a8e11f820268e52a6245092728efeffd7f/server/server.go#L189
//
// Here waiting for a result from dispatcher.
connection := <-request.connection
if connection == nil {
// It means that dispatcher has set `nil` which is a system error case that is
// not expected in the normal flow.
wsp.ProxyErrorf(w, "Unable to get a proxy connection")
return
}
// [3]: Send the request to the peer through the WebSocket connection.
if err := connection.proxyRequest(w, r); err != nil {
// An error occurred throw the connection away
log.Println(err)
connection.Close()
// Try to return an error to the client
// This might fail if response headers have already been sent
wsp.ProxyError(w, err)
}
}
// Request receives the WebSocket upgrade handshake request from wsp_client.
func (s *Server) Register(w http.ResponseWriter, r *http.Request) {
// 1. Upgrade a received HTTP request to a WebSocket connection
secretKey := r.Header.Get("X-SECRET-KEY")
if secretKey != s.Config.SecretKey {
wsp.ProxyErrorf(w, "Invalid X-SECRET-KEY")
return
}
ws, err := s.upgrader.Upgrade(w, r, nil)
if err != nil {
wsp.ProxyErrorf(w, "HTTP upgrade error : %v", err)
return
}
// 2. Wait a greeting message from the peer and parse it
// The first message should contains the remote Proxy name and size
_, greeting, err := ws.ReadMessage()
if err != nil {
wsp.ProxyErrorf(w, "Unable to read greeting message : %s", err)
ws.Close()
return
}
// Parse the greeting message
split := strings.Split(string(greeting), "_")
id := PoolID(split[0])
size, err := strconv.Atoi(split[1])
if err != nil {
wsp.ProxyErrorf(w, "Unable to parse greeting message : %s", err)
ws.Close()
return
}
// 3. Register the connection into server pools.
// s.lock is for exclusive control of pools operation.
s.lock.Lock()
defer s.lock.Unlock()
var pool *Pool
// There is no need to create a new pool,
// if it is already registered in current pools.
for _, p := range s.pools {
if p.id == id {
pool = p
break
}
}
if pool == nil {
pool = NewPool(s, id)
s.pools = append(s.pools, pool)
}
// update pool size
pool.size = size
// Add the WebSocket connection to the pool
pool.Register(ws)
}
func (s *Server) status(w http.ResponseWriter, r *http.Request) {
w.Write([]byte("ok"))
}
// Shutdown stop the Server
func (s *Server) Shutdown() {
close(s.done)
close(s.dispatcher)
for _, pool := range s.pools {
pool.Shutdown()
}
s.clean()
}