init

draft1_route/node.go

@@ -0,0 +1,130 @@
+// =============================================================================
+// Auth: Alex Celani
+// File: node.go
+// Revn: 06-22-2022  1.0
+// Func: receive data as an endpoint, send response back to middleman
+//
+// TODO:
+// =============================================================================
+// CHANGE LOG
+// -----------------------------------------------------------------------------
+// 05-04-2022: init
+// 05-09-2022: began commenting
+// 05-10-2022: finished commenting
+//             added alter() and forward()
+//             made passed value to alter()/forward() a slice
+//             changed refs to recv byte array to slice of n bytes
+// 06-20-2022: changed name to reflect first draft of node.go
+//*06-22-2022: bug squashing and commenting
+//
+// =============================================================================
+
+package main
+
+import (
+    "net"       // ResolveTCPAddr, conn.Write,Read,Close
+                // ListenTCP, listener.Accept
+    "os"        // Args, Stderr, Exit
+    "fmt"       // Fprintf, Println
+    "strings"   // ToLower
+)
+
+
+// quick error checking
+func check( err error ) {
+    // if user checks an error, it better be nil
+    if err != nil {
+        // put error in string, print in stderr
+        fmt.Fprintf( os.Stderr, "Fatal error: %s", err.Error() )
+        os.Exit( 2 )        // quit
+    }
+}
+
+
+// parse incoming message, keep only second word
+func parse( recv string ) string {
+    // split message over spaces
+    keywords := strings.Split( recv, " " )
+    return keywords[1]      // return the second word
+}
+
+
+// function to handle incoming connections
+func handleClient( conn net.Conn ) {
+    defer conn.Close()  // barring any error, still close connection
+
+    // init map of fields to their values
+    reply := map[string]string{ "soc" : "30",
+                                "batt" : "30",
+                                "temp" : "65",
+                                "humid" : "35",
+                                "sun" : "10",
+                                "list" : "soc batt temp humid sun list" }
+
+    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
+        }
+
+        // print recv'd message
+        // string() only works on byte SLICES so [:] is required
+        fmt.Println( "recv: ", string( buf[:n] ) )
+
+        // send input to parse
+        recv := parse( string( buf[:n] ) )
+        fmt.Println( "parse: ", recv )      // print
+
+        // declare variables to grab values from field map
+        var resp string
+        var prs bool
+        // get values from map, prs is false if key (recv) DNE in map
+        resp, prs = reply[recv]
+        if !prs {                           // if key was not present
+            resp = "field does not exist"   // response is DNE
+        }
+        fmt.Println( "answer: ", 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
+        }
+
+        fmt.Println( "sent: ", resp )   // print response
+    }
+}
+
+
+func main() {
+
+    // 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
+
+    // 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 )
+    }
+}
+