init

draft2_pin/sentinel.go

@@ -0,0 +1,119 @@
+// =============================================================================
+// Auth: Alex Celani
+// File: sentinel.go
+// Revn: 06-22-2022  1.0
+// Func: Receive message, play with it, send to a third place, receive
+//       response, send off to first place
+//
+// TODO: comment
+// =============================================================================
+// CHANGE LOG
+// -----------------------------------------------------------------------------
+// 05-04-2022: init
+// 05-05-2022: commented
+// 05-10-2022: added argument 'n' to alter() for halving purposes
+//             changed passed value to alter()/forward() a slice
+// 06-20-2022: changed name to reflect first draft of sentinel.go
+//*06-22-2022: bug fixing and comments
+//
+// =============================================================================
+
+package main
+
+import (
+    "net"       // ResolveTCPAddr, DialTCP, conn.Write,Read,Close
+                // ListenTCP, listener.Accept
+    "os"        // Exit, Stderr, Stdin, Args
+    "fmt"       // Println, Fprintf
+    "github.com/stianeikeland/go-rpio"      // talk to RasPi pins
+)
+
+
+// quick error checking
+func check( err error ){
+    // if user checks an error, it better be nil
+    if err != nil {
+        // put error in string, print to stderr
+        fmt.Fprintf( os.Stderr, "Fatal error: %s", err.Error() )
+        os.Exit( 1 )        // quit
+    }
+}
+
+
+// function to handle incoming connections
+func handleClient( conn net.Conn ) {
+    defer conn.Close()  // barring any error, still close connection
+
+    var buf [512]byte   // declare large byte array, store messages
+
+    // iterate forever to always read over connection
+    for {
+        // read n bytes from connection into buffer
+        n, err := conn.Read( buf[0:] )
+        if err != nil { // erroring on read will simply leave the 
+            return      // function so it can start again later
+        }
+
+        // instantiate receipt variable
+        var recv string = string( buf[:n] )
+
+        // print recv'd message
+        // string() only works on byte SLICES so [:] is required
+        fmt.Println( "recv: ", recv )
+
+        // toggle pin on successful receipt
+        pin.Toggle()
+
+    }
+}
+
+
+// declare pin
+var (
+	// Use mcu pin 10, corresponds to physical pin 19 on the pi
+	pin = rpio.Pin(10)
+)
+
+
+func main() {
+
+	// Open and map memory to access gpio, check for errors
+    // inline open gpio pin and check the error var
+	if err := rpio.Open(); err != nil {
+        // on error, print error and exit
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	// Unmap gpio memory when done
+	defer rpio.Close()
+
+	// Set pin to output mode
+	pin.Output()
+
+    // ip:port
+    // ip doesn't exist, implies localhost
+    service := ":1201"      // capture ip address and host
+
+    // "resolve" ip & host according to TCP rules
+    tcpAddr, err := net.ResolveTCPAddr( "tcp", service )
+    check( err )    // check error
+
+    // bind and "listen" to ip and port, according to tcp rules
+    listener, err := net.ListenTCP( "tcp", tcpAddr )
+    check( err )    // check error
+
+    // iterate forever
+    // TODO i mean i can totally make this more user friendly
+    for {
+        // accept a connection that makes its way to bound port
+        conn, err := listener.Accept()
+        if err != nil {     // if connection fails...
+            continue        // don't quit program, not fatal error
+        }
+
+        // asynchronous function to handle connection to client
+        go handleClient( conn )
+    }
+}
+