feat: initial implementation

Author: jeronimoalbi

.gitignore

@@ -0,0 +1 @@
+build

Makefile

@@ -0,0 +1,17 @@
+.PHONY: tailws
+all: build
+
+build: tailws
+
+install: install_tailws
+
+tailws:
+	@echo "Building tail-ws"
+	go build -o build/tail-ws ./cmd/tail-ws
+
+install_tailws:
+	@echo "Installing tail-ws"
+	go install ./cmd/tail-ws
+
+clean:
+	rm -rf build

README.md

@@ -1,4 +1,31 @@
-Broadcaster for appended file lines
-===================================
+WebSocket broadcaster for appended file lines
+=============================================
 
+[![Go Report Card](https://goreportcard.com/badge/github.com/jeronimoalbi/tail-ws)](https://goreportcard.com/report/github.com/jeronimoalbi/tail-ws)
 [![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](https://opensource.org/licenses/MIT)
+
+Installation
+------------
+
+Install the binary by running:
+
+```
+go install github.com/jeronimoalbi/tail-ws/cmd/tail-ws@latest
+```
+
+or alternatively:
+
+```
+make install
+```
+
+Run
+---
+
+To start broadcasting appended lines run:
+
+```
+tail-ws FILE
+```
+
+New lines are broadcasted by default from the address `ws://127.0.0.1:8080`.

broadcast/connections.go

@@ -0,0 +1,65 @@
+package broadcast
+
+import (
+	"sync"
+
+	"github.com/gorilla/websocket"
+)
+
+// NewConnections create a new Websocket connections registry.
+func NewConnections() *Connections {
+	return &Connections{
+		registry: make(map[*websocket.Conn]struct{}),
+	}
+}
+
+// Connections keeps track of active Websocket connections.
+type Connections struct {
+	mu       sync.RWMutex
+	registry map[*websocket.Conn]struct{}
+}
+
+// IsEmpty checks if there are registered connections.
+func (c *Connections) IsEmpty() bool {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+
+	return len(c.registry) == 0
+}
+
+// Add adds a new Websocket connection to the registry.
+func (c *Connections) Add(ws *websocket.Conn) {
+	c.mu.Lock()
+	c.registry[ws] = struct{}{}
+	c.mu.Unlock()
+}
+
+// Delete removes a Websocket connection from the registry.
+// Connections are closed after being removed.
+func (c *Connections) Delete(ws *websocket.Conn) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	delete(c.registry, ws)
+	return ws.Close()
+}
+
+// Close closes all connections.
+func (c *Connections) Close() {
+	c.Iter(func(ws *websocket.Conn) bool {
+		ws.Close()
+		return true
+	})
+}
+
+// Iter allows iterating the current connections.
+// Iteration stops when when false is returned.
+func (c *Connections) Iter(fn func(*websocket.Conn) bool) {
+	c.mu.RLock()
+	for ws := range c.registry {
+		if !fn(ws) {
+			return
+		}
+	}
+	c.mu.RUnlock()
+}

broadcast/server.go

@@ -0,0 +1,214 @@
+package broadcast
+
+import (
+	"bufio"
+	"context"
+	"errors"
+	"log"
+	"net"
+	"net/http"
+	"time"
+
+	"github.com/gorilla/websocket"
+	"golang.org/x/sync/errgroup"
+
+	"github.com/jeronimoalbi/tail-ws/watch"
+)
+
+var (
+	// DefaultAddr defines the default Websocket server address.
+	DefaultAddr = "127.0.0.1:8080"
+
+	maxMessageSize int64 = 1024
+	pingPeriod           = (pongWait * 9) / 10
+	pongWait             = 60 * time.Second
+	writeWait            = 8 * time.Second
+)
+
+// Option configures transaction broadcast servers.
+type Option func(*Server)
+
+// Address sets the server address.
+func Address(addr string) Option {
+	return func(s *Server) {
+		s.addr = addr
+	}
+}
+
+// Origin sets the allowed origin for incoming requests.
+func Origin(origin string) Option {
+	return func(s *Server) {
+		s.origin = origin
+	}
+}
+
+// Secure enables secure Websockets (WSS).
+func Secure(certFile, keyFile string) Option {
+	return func(s *Server) {
+		s.certFile = certFile
+		s.keyFile = keyFile
+	}
+}
+
+// NewServer creates a new transactions broadcast server.
+func NewServer(options ...Option) *Server {
+	s := Server{
+		addr:        DefaultAddr,
+		connections: NewConnections(),
+	}
+
+	for _, apply := range options {
+		apply(&s)
+	}
+
+	s.upgrader.CheckOrigin = func(r *http.Request) bool {
+		if s.origin != "" {
+			return s.origin == r.Header.Get("Origin")
+		}
+		return true
+	}
+
+	return &s
+}
+
+// Server handles Websocket connections and broadcasts new transactions.
+// It watches the transactions head file and when new transactions are indexed
+// it pushes the new entries to the connected clients.
+type Server struct {
+	addr, origin, certFile, keyFile string
+	reader                          watch.Reader
+	connections                     *Connections
+	upgrader                        websocket.Upgrader
+}
+
+// HandleWS is an HTTP handler that upgrades incoming connections to WS or WSS.
+func (s *Server) HandleWS(w http.ResponseWriter, r *http.Request) {
+	// TODO: Add authentication support
+	log.Printf("connection stablished with %s", r.RemoteAddr)
+
+	ws, err := s.upgrader.Upgrade(w, r, nil)
+	if err != nil {
+		// Upgrade already returns the error to the client on failure
+		log.Printf("connection from %s failed: %v", r.RemoteAddr, err)
+		return
+	}
+
+	ws.SetReadLimit(maxMessageSize)
+
+	// Prepare keep alive protocol for the new connection
+	ws.SetReadDeadline(time.Now().Add(pongWait))
+	ws.SetPongHandler(func(string) error {
+		ws.SetReadDeadline(time.Now().Add(pongWait))
+		return nil
+	})
+
+	// Launch a gopher to keep connection alive
+	ctx, cancel := context.WithCancel(context.Background())
+
+	go func() {
+		ticker := time.NewTicker(pingPeriod)
+		defer ticker.Stop()
+
+		for {
+			select {
+			case <-ticker.C:
+				err := ws.WriteControl(websocket.PingMessage, []byte{}, time.Now().Add(writeWait))
+				if err != nil {
+					log.Printf("error sending ping: %v", err)
+					ws.Close()
+				}
+			case <-ctx.Done():
+				return
+			}
+		}
+	}()
+
+	// Make sure to cleanup connection when closed
+	ws.SetCloseHandler(func(int, string) error {
+		log.Printf("closing connextion %s", ws.RemoteAddr())
+		cancel()
+		return s.connections.Delete(ws)
+	})
+
+	s.connections.Add(ws)
+}
+
+// Start starts a new HTTP server to listen for incoming WS or WSS connections.
+func (s *Server) Start(ctx context.Context) error {
+	g, ctx := errgroup.WithContext(ctx)
+	server := &http.Server{
+		Addr:    s.addr,
+		Handler: http.HandlerFunc(s.HandleWS),
+		BaseContext: func(l net.Listener) context.Context {
+			return ctx
+		},
+	}
+
+	g.Go(func() error {
+		<-ctx.Done()
+		s.connections.Close()
+		return server.Close()
+	})
+
+	g.Go(func() error {
+		var err error
+		if s.certFile != "" && s.keyFile != "" {
+			log.Printf("listening for connections -> wss://%s", s.addr)
+			err = server.ListenAndServeTLS(s.certFile, s.keyFile)
+		} else {
+			log.Printf("listening for connections -> ws://%s", s.addr)
+			err = server.ListenAndServe()
+		}
+
+		if errors.Is(err, http.ErrServerClosed) {
+			return nil
+		}
+		return err
+	})
+
+	return g.Wait()
+}
+
+// Watch starts watching a transaction head file and broadcasts
+// the newly indexed transactions to all connected peers.
+func (s *Server) Watch(ctx context.Context, name string) error {
+	r := watch.NewReader(watch.SeekEnd())
+	g, ctx := errgroup.WithContext(ctx)
+
+	g.Go(func() error {
+		scanner := bufio.NewScanner(r)
+		for scanner.Scan() {
+			s.broadcast(scanner.Bytes())
+		}
+
+		return scanner.Err()
+	})
+
+	g.Go(func() error {
+		defer r.Close()
+
+		for {
+			// Keep watching when the file is ovewritten
+			if err := r.Watch(ctx, name); err != watch.ErrFileOverwritten {
+				return err
+			}
+		}
+	})
+
+	return g.Wait()
+}
+
+func (s Server) broadcast(tx []byte) {
+	s.connections.Iter(func(ws *websocket.Conn) bool {
+		go func() {
+			ws.SetWriteDeadline(time.Now().Add(writeWait))
+
+			if err := ws.WriteMessage(websocket.BinaryMessage, tx); err != nil {
+				log.Printf("tx broadcast failed: %v", err)
+				ws.Close()
+			}
+		}()
+
+		return true
+	})
+}