init

draft3_pinroute/sentinel.go

@@ -0,0 +1,156 @@
+// =============================================================================
+// Auth: Alex Celani
+// File: sentinel.go
+// Revn: 06-26-2022  1.2
+// Func: Receive message, determine recipient, forward, get response,
+//       forward back
+//
+// TODO:
+// =============================================================================
+// 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 commenting
+// 06-23-2022: removed call to parse
+// 06-26-2022: refined a new route() function to check for destination
+//                  validity
+//
+// =============================================================================
+
+package main
+
+import (
+    "net"       // ResolveTCPAddr, DialTCP, conn.Write,Read,Close
+                // ListenTCP, listener.Accept
+    "os"        // Exit, Stderr, Stdin, Args
+    "fmt"       // Println, Fprintf
+    "strings"   // ToLower, ToUpper
+)
+
+
+// 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
+    }
+}
+
+
+// read the given message and route to the right endpoint
+func route( recv []string ) bool {
+    return recv[1] == "led"     // only option right now is led
+}
+
+
+// function to send message to third party and get response
+func send( toSend string ) string {
+    // ip:port
+    // ip doesn't exist, implies localhost
+    service := ":1202"      // capture ip address and host
+
+    // "resolve" ip & host according to TCP rules
+    tcpAddr, err := net.ResolveTCPAddr( "tcp", service )
+    check( err )    // check error
+
+    // "dial" ( establish connection ) to destination ip & port
+    // according to TCP rules
+    // laddr = nil -> local address is localhost
+    conn, err := net.DialTCP( "tcp", nil, tcpAddr )
+    check( err )    // check error
+
+    defer conn.Close()  // barring any error, still close connection
+
+    // convert user input to bytes and send over connection
+    _, err = conn.Write( []byte( toSend ) )
+    check( err )    // check error
+
+    var buf [512]byte                   // init byte array
+    // read from connection into byte array
+    // amount of bytes read stored in n
+    //n, err := conn.Read( buf[0:] )
+    n, err := conn.Read( buf[0:] )
+    check( err )    // check error
+
+    return string( buf[:n] )        // return only written bytes
+}
+
+
+// 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 )
+
+        keywords := strings.Split( recv, " " )
+
+        // parse the input in some way
+        var resp string             // declare response variable
+        if route( keywords ) {      // is destination valid?
+            resp = send( recv )     // send message and get response
+        // if user wants a list of endpoints
+        } else if keywords[1] == "list" {
+            resp = "led"            // return list of endpoints
+        }
+
+
+        fmt.Println( "node: ", resp )   // print response
+
+        // write that response back to original client
+        _, err = conn.Write( []byte( resp ) )
+        if err != nil { // erroring on write will simply leave the
+            return      // function so it can start again later
+        }
+    }
+}
+
+
+func main() {
+
+    // 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 )
+    }
+}
+