Implement continuous Python Daemon

5 files changed, 177 insertions, 81 deletions

diff --git a/python/birdscan/__main__.py b/python/birdscan/__main__.py
index 71ba294..862ec1b 100644
--- a/python/birdscan/__main__.py
+++ b/python/birdscan/__main__.py
@@ -10,25 +10,58 @@ This is the main executable of the birdscan package.
 
 import sys
 import time
+import socket
+import argparse
 
 
 def main():
     """Main function of this module"""
 
-    if len(sys.argv) == 2:  # check if argument is given (--debug)
-        time.sleep(1)
-        sys.stdout.write("ok\n")
-    else:
+    # parse command line args
+    parser = argparse.ArgumentParser()
+    parser.add_argument("-d", "--debug", action="store_true", help="For use in development environment")
+    parser.add_argument("-s", "--socket", default="/dev/null", type=str, help="Unix domain socket path for IPC")
+    args = parser.parse_args()
+
+    # prepare camera if on production system
+    if not args.debug:
         from picamera import PiCamera
         camera = PiCamera()
         camera.resolution = "3280x2464"
         camera.start_preview()
-        # Camera warm-up time
-        time.sleep(2)
-        camera.capture("/var/lib/birdscan/{}.jpg".format(
-            time.strftime("%Y-%m-%d_%H-%M-%S", time.localtime()))
-        )
-        sys.stdout.write("ok\n")
+    time.sleep(2)  # camera warm-up time
+
+    # connect to IPC socket
+    sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+    sock.connect(args.socket)
+    sock.send("picamera\n".encode())  # register this service
+
+    # main loop for Python background service
+    while True:
+        cmd = read_line(sock)
+        if cmd == "single_picture":
+            if args.debug:
+                time.sleep(1)
+                sock.send("single_picture_taken\n".encode())
+            else:
+                camera.capture("/var/lib/birdscan/{}.jpg".format(
+                    time.strftime("%Y-%m-%d_%H-%M-%S", time.localtime()))
+                )
+                sock.send("single_picture_taken\n".encode())
+        elif cmd == "":
+            pass
+        else:
+            sock.send("unknown_command\n".encode())
+
+def read_line(socket):
+    data = b""
+    while True:
+        byte = socket.recv(1)
+        if byte == b"\n":
+            break
+        else:
+            data += byte
+    return data.decode()
 
 
 if __name__ == "__main__":
diff --git a/src/camera.go b/src/camera.go
index 519cc65..fe1140e 100644
--- a/src/camera.go
+++ b/src/camera.go
@@ -2,14 +2,6 @@
 
 package main
 
-import (
-	"log"
-	"os/exec"
-	"os"
-	"path/filepath"
-	"bufio"
-)
-
 type Camera struct {
 	statemachine Machine
 }
@@ -44,63 +36,10 @@ func NewCamera() Camera {
 
 func runCameraHooks(last string, next string, m *Machine) {
 	if last == "idle" && next == "single_picture" {
-		go singlePicture(m)
+		ipc.WriteLineTo("picamera", "single_picture\n")
 	}
 }
 
-func singlePicture(m *Machine) {
-
-	// create command
-	var cmd *exec.Cmd
-	if !config.Flag.Debug {
-		cmd = exec.Command("/usr/bin/python3", "/usr/lib/python3.9/site-packages/birdscan/")
-	} else {  // debug mode
-		pwd,err := os.Getwd()
-		if err != nil {
-			log.Fatal(err)
-		}
-		repoDir := filepath.Dir(pwd)
-		log.Printf("Repository path is assumed to be = '%s'", repoDir)
-		pythonPackage := repoDir + "/python/birdscan"
-		cmd = exec.Command("/usr/bin/python3", pythonPackage, "--debug")
-	}
-
-	// connect stdout of python process
-	stdout,err := cmd.StdoutPipe()
-	if err != nil {
-		log.Print(err)
-	}
-	defer stdout.Close()
-
-	// run command
-	err = cmd.Start()
-	if err != nil {
-		log.Print(err)
-	}
-
-	scanner := bufio.NewScanner(stdout)
-	for scanner.Scan() {
-		text := scanner.Text()
-		log.Printf("Python returned '%s'", text)
-		if text == "ok" {
-			break
-		}
-	}
-
-	err = cmd.Wait()  // wait until command execution and io is complete
-	if err != nil {
-		log.Print(err)
-	}
-
-	// process result
-	m.SendEvent("single_picture_taken")
-}
-
 func (cam *Camera) run() {
 	cam.statemachine.Run()
 }
-
-// read until '\n'
-func readLine(buff *[]byte, ) {
-
-}
diff --git a/src/main.go b/src/main.go
index 3218df9..dcb201e 100644
--- a/src/main.go
+++ b/src/main.go
@@ -4,11 +4,19 @@ package main
 
 import (
 	"log"
+	"os"
+	"os/signal"
+	"syscall"
 )
 
 var (
 	config RuntimeConfig
 	camera Camera
+	ipc IpcServer
+)
+
+const (
+	IPC_SOCKET = "/tmp/birdscan.sock"  // FIXME
 )
 
 func main() {
@@ -19,13 +27,27 @@ func main() {
 	// parse flags and read config
 	config = GetRuntimeConfig()
 
-	// create camera
-	camera = NewCamera()
-
-	// start goroutines
-	server := NewWebServer()
-	go server.run()  // http server / user interface
-
-	// run camera
+	// create services
+	camera = NewCamera()   // main service
+	ipc = NewIpcServer()   // inter process communication
+	web := NewWebServer()  // web frontend
+
+	// allow graceful exit
+	var listener = make(chan os.Signal)
+	signal.Notify(listener, syscall.SIGTERM)
+	signal.Notify(listener, syscall.SIGINT)
+	go func() {
+		signal := <-listener
+		log.Printf("Got signal '%+v'", signal)
+		ipc.Cleanup()
+		os.Exit(0)
+	}()
+
+	// start secondary services
+	go ipc.Run(IPC_SOCKET)
+	go PicameraSubprocess(IPC_SOCKET)  // subprocess to use Python picamera
+	go web.run()
+
+	// start main service
 	camera.run()
 }
diff --git a/src/subprocess.go b/src/subprocess.go
new file mode 100644
index 0000000..d16d4fe
--- /dev/null
+++ b/src/subprocess.go
@@ -0,0 +1,102 @@
+// vim: shiftwidth=4 tabstop=4 noexpandtab
+
+package main
+
+import (
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"net"
+	"net/textproto"
+	"bufio"
+)
+
+type IpcServer struct {
+	connections map[string]net.Conn
+	listener net.Listener
+}
+
+func NewIpcServer() IpcServer {
+	return IpcServer{
+		connections: make(map[string]net.Conn),
+	}
+}
+
+func (ipc *IpcServer) Run(ipcSocket string) {
+	log.Println("Running IPC server")
+	var err error
+	ipc.listener,err = net.Listen("unix", ipcSocket)
+	if err != nil {
+		log.Fatal(err)
+	}
+	for {
+		connection,err := ipc.listener.Accept()
+		if err != nil {
+			log.Print(err)
+		}
+		bufioreader := bufio.NewReader(connection)
+		tpreader := textproto.NewReader(bufioreader)
+		line,err := tpreader.ReadLine()
+		log.Printf("IPC: '%s'", line)
+		ipc.connections[line] = connection
+		go ipc.HandleConnection(line)
+	}
+}
+
+func (ipc *IpcServer) HandleConnection(connection string) {
+	for {
+		msg := ipc.ReadLineFrom(connection)
+		if msg != "" {
+			log.Printf("Got IPC message '%s' from '%s'", msg, connection)
+			if connection == "picamera" {
+				camera.statemachine.SendEvent(msg)
+			}
+		}
+	}
+}
+
+func (ipc *IpcServer) WriteLineTo(connection string, line string) {
+	conn := ipc.connections[connection]
+	_,err := conn.Write([]byte(line))
+	if err != nil {
+		log.Print(err)
+	}
+}
+
+func (ipc *IpcServer) ReadLineFrom(connection string) string {
+	conn := ipc.connections[connection]
+	bufioreader := bufio.NewReader(conn)
+	tpreader := textproto.NewReader(bufioreader)
+	line,_ := tpreader.ReadLine()
+	return line
+}
+
+func (ipc *IpcServer) Cleanup() {
+	log.Println("Releasing IPC socket ...")
+	for _,connection := range ipc.connections {
+		connection.Close()
+	}
+	ipc.listener.Close()
+}
+
+func PicameraSubprocess(ipcSocket string) {
+	var cmd *exec.Cmd
+	if config.Flag.Debug {
+		pwd,err := os.Getwd()
+		if err != nil {
+			log.Fatal(err)
+		}
+		repoDir := filepath.Dir(pwd)
+		pythonPackage := repoDir + "/python/birdscan"
+		cmd = exec.Command("python3", pythonPackage, "--debug", "-s", ipcSocket)
+	} else {
+		cmd = exec.Command("python3", "/usr/lib/python3.9/site-packages/birdscan/", "-s", ipcSocket)
+	}
+	log.Println("Starting picamera service")
+	err := cmd.Run()
+	log.Println("picamera service terminated!")
+	if err != nil {
+		log.Print(err)
+	}
+}
diff --git a/src/web.go b/src/web.go
index f7c7b49..8375a89 100644
--- a/src/web.go
+++ b/src/web.go
@@ -43,7 +43,7 @@ func (server *WebServer) run() {
 	router.Post("/api/reboot", rebootHandler)
 	router.Post("/api/poweroff", poweroffHandler)
 
-	log.Println("Binding to 'http://" + server.config.BindAddress + ":" + server.config.BindPort + "'")
+	log.Println("Web service binding to 'http://" + server.config.BindAddress + ":" + server.config.BindPort + "'")
 	log.Fatal(http.ListenAndServe(server.config.BindAddress + ":" + server.config.BindPort, router))
 }