Rewrite HTTP server without net/http

This cuts down the binary size from 5.7MB to 3.3MB.

src/server.go

@@ -0,0 +1,112 @@
+package fzf
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"fmt"
+	"net"
+	"strconv"
+	"strings"
+)
+
+const (
+	crlf           = "\r\n"
+	httpOk         = "HTTP/1.1 200 OK" + crlf
+	httpBadRequest = "HTTP/1.1 400 Bad Request" + crlf
+)
+
+func startHttpServer(port int, channel chan []*action) {
+	if port == 0 {
+		return
+	}
+
+	listener, err := net.Listen("tcp", fmt.Sprintf(":%d", port))
+	if err != nil {
+		return
+	}
+
+	go func() {
+		for {
+			conn, err := listener.Accept()
+			if err != nil {
+				if errors.Is(err, net.ErrClosed) {
+					break
+				} else {
+					continue
+				}
+			}
+			conn.Write([]byte(handleHttpRequest(conn, channel)))
+			conn.Close()
+		}
+		listener.Close()
+	}()
+}
+
+// Here we are writing a simplistic HTTP server without using net/http
+// package to reduce the size of the binary.
+//
+// * No --listen:            2.8MB
+// * --listen with net/http: 5.7MB
+// * --listen w/o net/http:  3.3MB
+func handleHttpRequest(conn net.Conn, channel chan []*action) string {
+	line := 0
+	headerRead := false
+	contentLength := 0
+	body := ""
+	bad := func(message string) string {
+		message += "\n"
+		return httpBadRequest + fmt.Sprintf("Content-Length: %d%s", len(message), crlf+crlf+message)
+	}
+	scanner := bufio.NewScanner(conn)
+	scanner.Split(func(data []byte, atEOF bool) (int, []byte, error) {
+		found := bytes.Index(data, []byte(crlf))
+		if found >= 0 {
+			token := data[:found+len(crlf)]
+			return len(token), token, nil
+		}
+		if atEOF || len(body)+len(data) >= contentLength {
+			return 0, data, bufio.ErrFinalToken
+		}
+		return 0, nil, nil
+	})
+
+	for scanner.Scan() {
+		text := scanner.Text()
+		if line == 0 && !strings.HasPrefix(text, "POST / HTTP") {
+			return bad("invalid request method")
+		}
+		if text == crlf {
+			headerRead = true
+		}
+		if !headerRead {
+			pair := strings.SplitN(text, ":", 2)
+			if len(pair) == 2 && strings.ToLower(pair[0]) == "content-length" {
+				length, err := strconv.Atoi(strings.TrimSpace(pair[1]))
+				if err != nil {
+					return bad("invalid content length")
+				}
+				contentLength = length
+			}
+		} else if contentLength <= 0 {
+			break
+		} else {
+			body += text
+		}
+		line++
+	}
+
+	errorMessage := ""
+	actions := parseSingleActionList(strings.TrimSpace(string(body)), func(message string) {
+		errorMessage = message
+	})
+	if len(errorMessage) > 0 {
+		return bad(errorMessage)
+	}
+	if len(actions) == 0 {
+		return bad("no action specified")
+	}
+
+	channel <- actions
+	return httpOk
+}

src/terminal.go

@@ -3,10 +3,8 @@ package fzf
 import (
 	"bufio"
 	"fmt"
-	"io"
 	"io/ioutil"
 	"math"
-	"net/http"
 	"os"
 	"os/signal"
 	"regexp"
@@ -626,39 +624,6 @@ func NewTerminal(opts *Options, eventBox *util.EventBox) *Terminal {
 	return &t
 }
 
-func (t *Terminal) startServer() {
-	if t.listenPort == 0 {
-		return
-	}
-
-	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
-		if r.Method != "POST" {
-			w.WriteHeader(http.StatusBadRequest)
-			return
-		}
-		body, err := io.ReadAll(r.Body)
-		if err != nil {
-			w.WriteHeader(http.StatusBadRequest)
-			return
-		}
-
-		response := ""
-		actions := parseSingleActionList(string(body), func(message string) {
-			response = message
-		})
-
-		if len(response) > 0 {
-			w.WriteHeader(http.StatusBadRequest)
-			fmt.Fprintln(w, response)
-			return
-		}
-		t.serverChan <- actions
-	})
-	go func() {
-		http.ListenAndServe(fmt.Sprintf(":%d", t.listenPort), nil)
-	}()
-}
-
 func borderLines(shape tui.BorderShape) int {
 	switch shape {
 	case tui.BorderHorizontal, tui.BorderRounded, tui.BorderSharp, tui.BorderBold, tui.BorderDouble:
@@ -2535,7 +2500,7 @@ func (t *Terminal) Loop() {
 	looping := true
 	_, startEvent := t.keymap[tui.Start.AsEvent()]
 
-	t.startServer()
+	startHttpServer(t.listenPort, t.serverChan)
 	eventChan := make(chan tui.Event)
 	needBarrier := true
 	barrier := make(chan bool)