131 lines
4.2 KiB
Go
131 lines
4.2 KiB
Go
// =============================================================================
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// Auth: Alex Celani
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// File: node.go
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// Revn: 06-22-2022 1.0
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// Func: receive data as an endpoint, send response back to middleman
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//
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// TODO:
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// =============================================================================
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// CHANGE LOG
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// -----------------------------------------------------------------------------
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// 05-04-2022: init
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// 05-09-2022: began commenting
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// 05-10-2022: finished commenting
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// added alter() and forward()
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// made passed value to alter()/forward() a slice
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// changed refs to recv byte array to slice of n bytes
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// 06-20-2022: changed name to reflect first draft of node.go
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//*06-22-2022: bug squashing and commenting
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//
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// =============================================================================
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package main
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import (
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"net" // ResolveTCPAddr, conn.Write,Read,Close
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// ListenTCP, listener.Accept
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"os" // Args, Stderr, Exit
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"fmt" // Fprintf, Println
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"strings" // ToLower
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)
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// quick error checking
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func check( err error ) {
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// if user checks an error, it better be nil
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if err != nil {
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// put error in string, print in stderr
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fmt.Fprintf( os.Stderr, "Fatal error: %s", err.Error() )
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os.Exit( 2 ) // quit
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}
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}
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// parse incoming message, keep only second word
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func parse( recv string ) string {
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// split message over spaces
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keywords := strings.Split( recv, " " )
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return keywords[1] // return the second word
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}
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// function to handle incoming connections
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func handleClient( conn net.Conn ) {
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defer conn.Close() // barring any error, still close connection
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// init map of fields to their values
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reply := map[string]string{ "soc" : "30",
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"batt" : "30",
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"temp" : "65",
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"humid" : "35",
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"sun" : "10",
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"list" : "soc batt temp humid sun list" }
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var buf [512]byte // declare large byte array, store messages
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// iterate forever to always read over connection
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for {
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// read n bytes from connection into buffer
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n, err := conn.Read( buf[0:] )
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if err != nil { // erroring on read will simply leave the
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return // function so it can start again later
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}
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// print recv'd message
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// string() only works on byte SLICES so [:] is required
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fmt.Println( "recv: ", string( buf[:n] ) )
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// send input to parse
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recv := parse( string( buf[:n] ) )
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fmt.Println( "parse: ", recv ) // print
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// declare variables to grab values from field map
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var resp string
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var prs bool
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// get values from map, prs is false if key (recv) DNE in map
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resp, prs = reply[recv]
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if !prs { // if key was not present
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resp = "field does not exist" // response is DNE
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}
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fmt.Println( "answer: ", resp ) // print response
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// write that response back to original client
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_, err = conn.Write( []byte( resp ) )
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if err != nil { // erroring on write will simply leave the
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return // function so it can start again later
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}
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fmt.Println( "sent: ", resp ) // print response
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}
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}
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func main() {
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// ip:port
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// ip doesn't exist, implies localhost
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service := ":1202" // capture ip address and host
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// "resolve" ip & host according to TCP rules
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tcpAddr, err := net.ResolveTCPAddr( "tcp", service )
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check( err ) // check error
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// bind and "listen" to ip and port, according to tcp rules
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listener, err := net.ListenTCP( "tcp", tcpAddr )
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check( err ) // check error
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// iterate forever
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// TODO i mean i can totally make this more user friendly
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for {
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// accept a connection that makes its way to bound port
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conn, err := listener.Accept()
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if err != nil { // if connection fails...
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continue // don't quit program, not fatal error
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}
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// asynchronous function to handle connection to client
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go handleClient( conn )
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}
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}
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