Create signal-cli-api.go

An interface for `signal-cli daemon --socket ...` to separate command responses from incoming messages.  This also solved a problem I had with using the `--tcp` option inside a LXC container, since signal-cli binds to 127.0.0.1 and I needed access from outside the container.

client-golang/signal-cli-api.go

@@ -0,0 +1,99 @@
+/**
+Accept commands on TCP socket and send to signal-cli daemon on UNIX socket.
+Immediate responses are returned via the TCP socket, and other incoming
+messages are logged to stdout.
+
+With this program running as a service, we can follow incoming messages with:
+	journalctl -fu signal-cli-api --no-tail
+**/
+
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"net"
+	"time"
+)
+
+func main() {
+	unixSocketPath := "/tmp/signal-cli/socket"
+	unixConn, err := net.Dial("unix", unixSocketPath)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer unixConn.Close()
+
+	tcpPort := "5780"
+	tcpListener, err := net.Listen("tcp", ":"+tcpPort)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer tcpListener.Close()
+
+	responses := make(chan string)
+
+	// Read messages from the UNIX socket
+	go func() {
+		scanner := bufio.NewScanner(unixConn)
+		for scanner.Scan() {
+			resp := scanner.Text()
+			if isCommandResponse(resp) {
+				responses <- resp
+			} else {
+				log.Println(resp)
+			}
+		}
+		if err := scanner.Err(); err != nil {
+			log.Println(err)
+		}
+	}()
+
+	for {
+		// Wait for TCP connection
+		tcpConn, err := tcpListener.Accept()
+		if err != nil {
+			log.Println(err)
+			continue
+		}
+
+		// Read command
+		cmd, err := bufio.NewReader(tcpConn).ReadString('\n')
+		if err != nil {
+			log.Println(err)
+			tcpConn.Close()
+			continue
+		}
+
+		// Write command to UNIX socket
+		fmt.Fprint(unixConn, cmd)
+
+		// Read responses
+		select {
+		case msg := <-responses:
+			fmt.Fprintln(tcpConn, msg)
+		case <-time.After(2 * time.Second):
+			fmt.Fprint(tcpConn, "Timed out")
+		}
+
+		// Close TCP connection
+		tcpConn.Close()
+	}
+}
+
+/** Check if signal-cli json-rpc message is a command response.
+	Command response & error formats:
+	  {"jsonrpc":"2.0","result":{...},"id":1678829060000}
+	  {"jsonrpc":"2.0","result":[...],"id":1678829060000}
+    {"jsonrpc":"2.0","error":{...},"id":1678829060000}
+	
+  Incoming message format:
+	  {"jsonrpc":"2.0","method":"receive","params":{...}}
+
+	This assumes signal-cli doesn't change jsonrpc format or version.
+	It would be more robust to parse the JSON, but shouldn't be needed.
+**/
+func isCommandResponse(resp string) bool {
+	return len(resp) >= 26 && resp[:26] != "{\"jsonrpc\":\"2.0\",\"method\":"
+}