From eb5d58799445b06ffad9f5f164b3579e79fdd314 Mon Sep 17 00:00:00 2001
From: Pierre-Olivier Mercier <nemunaire@nemunai.re>
Date: Thu, 4 Feb 2021 00:50:39 +0100
Subject: [PATCH] Implement read and checksum

---
 main.go | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 65 insertions(+), 2 deletions(-)

diff --git a/main.go b/main.go
index 7e7fb97..2d290c8 100644
--- a/main.go
+++ b/main.go
@@ -1,24 +1,85 @@
 package main
 
 import (
+	"bytes"
 	"flag"
+	"io"
 	"log"
 	"os"
 	"os/signal"
 	"syscall"
 	"time"
+	"unicode"
 
 	"github.com/tarm/serial"
 )
 
-func readSerial(s *serial.Port, interval *time.Duration) {
+func readSerial(s *serial.Port, c chan []byte) {
+	var unread bytes.Buffer
+	buf := make([]byte, 128)
 
+	for {
+		n, err := s.Read(buf)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		unread.Write(buf[:n])
+
+		for {
+			line, err := unread.ReadBytes('\n')
+			if err == io.EOF {
+				if _, err = unread.Write(line); err != nil {
+					log.Println(err)
+				}
+				break
+			} else if err != nil {
+				log.Println(err)
+				break
+			}
+
+			c <- bytes.TrimRightFunc(line, func(r rune) bool {
+				return unicode.IsSpace(r) || unicode.IsControl(r)
+			})
+		}
+	}
+}
+
+func computeChecksum(area []byte) (checksum byte) {
+	for _, c := range area {
+		checksum += c
+	}
+
+	checksum = (checksum & 0x3F) + 0x20
+
+	return
+}
+
+func treatLines(c chan []byte) {
+	for {
+		line := <-c
+
+		if len(line) <= 1 {
+			continue
+		}
+
+		if computeChecksum(line[:len(line)-1]) != line[len(line)-1] {
+			log.Printf("BAD checksum on %s: calculated: %c\n", line, computeChecksum(line[:len(line)-1]))
+			continue
+		}
+
+		fields := bytes.Fields(line)
+
+		log.Println(fields)
+	}
 }
 
 func main() {
 	var interval = flag.Duration("interval", 5*time.Second, "Minimum time between releve")
 	flag.Parse()
 
+	log.Println(interval)
+
 	if len(flag.Args()) < 1 {
 		log.Println("missing required argument: serial device (eg. /dev/ttyUSB0)")
 		return
@@ -37,7 +98,9 @@ func main() {
 		log.Fatal(err)
 	}
 
-	go readSerial(s, interval)
+	c := make(chan []byte)
+	go readSerial(s, c)
+	go treatLines(c)
 
 	interrupt := make(chan os.Signal, 1)
 	signal.Notify(interrupt, os.Interrupt, syscall.SIGTERM)