Merge pull request #13 from cherti/socketactivation

socket-activate printer

Makefile

@@ -24,14 +24,15 @@ install: printer.arm
 	ssh -o AddKeysToAgent=yes root@$(host) systemctl stop printer || true
 	scp printer.arm root@$(host):
 	scp printer.service root@$(host):/etc/systemd/system
+	scp printer.socket root@$(host):/etc/systemd/system
 	ssh root@$(host) systemctl daemon-reload
-	ssh root@$(host) systemctl enable printer
-	ssh root@$(host) systemctl restart printer
+	ssh root@$(host) systemctl enable printer.socket
+	ssh root@$(host) systemctl restart printer.socket
 
 .PHONY: release
 release: printer.arm printer.x86
 	rm -f release.zip
-	zip release.zip printer.arm printer.x86 printer.service -r
+	zip release.zip printer.arm printer.x86 printer.service printer.socket -r
 
 .PHONY: install_config
 install_config:

README.md

@@ -48,7 +48,7 @@ No authentication, so keep WiFi off while not in use.
 
 Virtually all network printers accept raw Postscript/PDF data on TCP port 9100 via the Appsocket/HP Jetdirect protocol.  Sometimes this data is preceded by a few plaintext lines telling the printer information such as the print job name and print settings.
 
-This script simply listens on TCP 9100 and waits for a PDF header, then begins saving data to a pdf file (while also creating the accompanying .metadata file).  The output filename is extracted from the print job name line, if it exists.
+This setup simply listens on TCP 9100 and upon data sent waits for a PDF header, then begins saving data to a pdf file (while also creating the accompanying .metadata file) and then exits again, waiting for the next connection on the port to repeat the procedure.  The output filename is extracted from the print job name line, if it exists.
 
 ## Testing on host
 

install.sh

@@ -1,9 +1,11 @@
 systemctl stop printer.service || true
+systemctl stop printer.socket || true
 mkdir -p /home/root/bin
 cd /home/root/bin
 wget -O release.zip http://github.com/evidlo/remarkable_printer/releases/latest/download/release.zip
 unzip -o release.zip
 mv printer.service /etc/systemd/system
+mv printer.socket /etc/systemd/system
 systemctl daemon-reload
-systemctl enable --now printer.service
+systemctl enable --now printer.socket
 rm printer.x86 release.zip

main.go

@@ -4,22 +4,24 @@
 package main
 
 import (
+	"bufio"
+	"flag"
 	"fmt"
+	"io"
 	"net"
 	"os"
 	"os/exec"
-	"bufio"
+	"strconv"
 	"strings"
-	"io"
-	"flag"
-	"github.com/google/uuid"
 	"time"
+
+	"github.com/google/uuid"
 )
 
 var (
-	CONN_HOST = "0.0.0.0"
-	CONN_PORT = "9100"
-	LOG_LEVEL = "error"
+	CONN_HOST   = "0.0.0.0"
+	CONN_PORT   = "9100"
+	LOG_LEVEL   = "error"
 	XOCHITL_DIR = "/home/root/.local/share/remarkable/xochitl/"
 )
 
@@ -39,11 +41,7 @@ const METADATA_TEMPLATE = `{
 }
 `
 
-const CONTENT_TEMPLATE = `{
-    "fileType": "pdf"
-}
-`
-
+const CONTENT_TEMPLATE = "{}"
 
 func main() {
 
@@ -68,14 +66,14 @@ func main() {
 	// ----- Listen for connections -----
 
 	// Listen for incoming connections.
-	l, err := net.Listen("tcp", *CONN_HOST + ":" + *CONN_PORT)
-	check(err)
-	defer l.Close()
 
-	// Close the listener when the application closes.
-	fmt.Println("Listening on " + *CONN_HOST + ":" + *CONN_PORT)
-	for {
-		// Listen for an incoming connection.
+	var l net.Listener
+	var err error
+	var isSocketActivated = os.Getenv("LISTEN_PID") == strconv.Itoa(os.Getpid())
+	if isSocketActivated {
+		l, err = net.FileListener(os.NewFile(3, "systemd-socket"))
+		fmt.Println("Listening on systemd-socket")
+
 		conn, err := l.Accept()
 		if err != nil {
 			fmt.Println("Error accepting: ", err.Error())
@@ -83,24 +81,33 @@ func main() {
 		}
 		handleRequest(conn)
 
-		// Restart xochitl
 		if *restart {
-			services := []string{"xochitl", "remux", "tarnish", "draft"}
-			for _, service := range services {
-				_, exitcode := exec.Command("systemctl", "is-active", service).CombinedOutput()
-				if exitcode == nil {
-					debug("Restarting " + service)
-					stdout, err := exec.Command("systemctl", "restart", service).CombinedOutput()
-					if err != nil {
-						fmt.Println(service + " restart failed with message:", string(stdout))
-					}
-				}
-			}
+			restartUISoftware()
 		}
 
-	}
-}
+	} else {
+		l, err = net.Listen("tcp", *CONN_HOST+":"+*CONN_PORT)
+		fmt.Println("Listening on " + *CONN_HOST + ":" + *CONN_PORT)
 
+		for {
+			// Listen for an incoming connection.
+			conn, err := l.Accept()
+			if err != nil {
+				fmt.Println("Error accepting: ", err.Error())
+				os.Exit(1)
+			}
+			handleRequest(conn)
+
+			if *restart {
+				restartUISoftware()
+			}
+
+		}
+	}
+	check(err)
+	defer l.Close() // Close the listener when the application closes.
+
+}
 
 func debug(msg ...string) {
 	if LOG_LEVEL == "debug" {
@@ -118,7 +125,6 @@ func check(e error) {
 	}
 }
 
-
 // Handles incoming requests.
 func handleRequest(conn net.Conn) {
 	u, _ := uuid.NewRandom()
@@ -191,3 +197,18 @@ func handleRequest(conn net.Conn) {
 
 	conn.Close()
 }
+
+// Restarts xochitl or other UI software
+func restartUISoftware() {
+	services := []string{"xochitl", "remux", "tarnish", "draft"}
+	for _, service := range services {
+		_, exitcode := exec.Command("systemctl", "is-active", service).CombinedOutput()
+		if exitcode == nil {
+			debug("Restarting " + service)
+			stdout, err := exec.Command("systemctl", "restart", service).CombinedOutput()
+			if err != nil {
+				fmt.Println(service+" restart failed with message:", string(stdout))
+			}
+		}
+	}
+}

printer.service

@@ -1,9 +1,6 @@
 [Unit]
 Description=Native printing to reMarkable
+Requires=printer.socket
 
 [Service]
 ExecStart=/home/root/bin/printer.arm -restart -debug
-Restart=always
-
-[Install]
-WantedBy=multi-user.target

printer.socket

@@ -0,0 +1,9 @@
+[Unit]
+Description=Socket for native printing to reMarkable
+After=multi-user.target
+
+[Socket]
+ListenStream=0.0.0.0:9100
+
+[Install]
+WantedBy=multi-user.target