server.go

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"math/rand"
	"net/http"
	"strconv"
	"time"
)

func main() {
	dataReadChan := make(chan map[string]StampedReading) // Channel to handle data readings
	dataBuffer := make(map[string][]StampedReading)      // Map to store readings in until they are sent

	go dataReadLoop(dataReadChan)                    // Start our async read loop
	dataSendTick := time.NewTicker(time.Second * 10) // Ticker to send data

	// Non-blocking channel reads
	for {
		select {

		case reading := <-dataReadChan:
			// We got a data packet
			fmt.Printf("New reading: %v\n", reading)

			// Put our reading in the map
			for metric, value := range reading {
				if record, found := dataBuffer[metric]; !found {
					dataBuffer[metric] = []StampedReading{value}
				} else {
					dataBuffer[metric] = append(record, value)
				}
			}

		case <-dataSendTick.C:
			// Time to send some data
			if len(dataBuffer) > 0 { // Only send if we have data
				if err := sendData(dataBuffer); err != nil { // Something went wrong
					fmt.Printf("Error sending data: %v\n", err)
				} else { // Data sent, clear the map
					dataBuffer = make(map[string][]StampedReading)
				}
			} else { // There was no data to send
				fmt.Println("Got data send signal but buffer is empty")
				// TODO: manage the map so that it doesn't run out of memory and kill everything if we don't send data
			}

		}
	}
}

func dataReadLoop(x chan map[string]StampedReading) {
	for {
		// Send our read packets down the channel
		// TODO: error handling
		x <- readData()
		time.Sleep(time.Second)
	}
}

func readData() map[string]StampedReading {
	// TODO: modbus
	return map[string]StampedReading{
		"oil.temp": {
			Timestamp: int(time.Now().Unix()),
			Value:     rand.Intn(150),
		},
		"fuel.temp": {
			Timestamp: int(time.Now().Unix()),
			Value:     rand.Intn(150),
		},
	}
}

func sendData(data map[string][]StampedReading) error {

	url := "http://localhost:8081/data"
	jsonStr, err := json.Marshal(data)
	if err != nil {
		fmt.Printf("Error marshalling data: %v\n", err)
		return err
	}

	fmt.Printf("Sending json: %v\n", string(jsonStr))

	req, err := http.NewRequest("POST", url, bytes.NewBuffer(jsonStr))
	fillHeader(req)

	client := &http.Client{}
	resp, err := client.Do(req)
	if err != nil {
		return err
	}

	defer func() {
		if err := resp.Body.Close(); err != nil {
			fmt.Printf("Error: %v", err)
		}
	}()

	fmt.Println("response Status:", resp.Status)
	if resp.StatusCode != 200 {
		fmt.Printf("Received a non-200 response: %v\n", resp.StatusCode)
	}

	return nil
}

func fillHeader(req *http.Request) { // Sets the uuid and timestamp for a request
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("uuid", "0000001bcd3f")	// TODO: get this from somewhere
	req.Header.Set("time", strconv.FormatInt(time.Now().Unix(), 10))
}