server.go

package main

import (
	"bytes"
	"crypto/tls"
	"crypto/x509"
	"encoding/json"
	"errors"
	"fmt"
	"io/ioutil"
	"math/rand"
	"net/http"
	"strconv"
	"time"
)

type gatewayClient struct {
	client *http.Client
}

func main() {
	rootCAs := x509.NewCertPool()                // Initialize a cert pool
	rootCert, _ := ioutil.ReadFile("rootCA.pem") // Read our root CA cert

	if ok := rootCAs.AppendCertsFromPEM(rootCert); !ok {
		fmt.Printf("Error adding gateway cert")
	}

	config := &tls.Config{RootCAs: rootCAs,} // Trust our root CA

	tr := &http.Transport{TLSClientConfig: config,}
	client := gatewayClient{&http.Client{Transport: tr}}

	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 * dataSendPeriod)   // Ticker to send data
	heartbeatTick := time.NewTicker(time.Second * heartbeatPeriod) // Ticker to send heartbeats

	if err := client.sendHeartbeat(); err != nil {
		fmt.Printf("Error sending startup heartbeat: %v\n", err)
	}

	// 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 := client.sendData(dataBuffer); err != nil { // Something went wrong
					fmt.Printf("Error sending data: %v\n", err)
				} else { // Data sent, clear the map
					fmt.Println("Sent data")
					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
			}

		case <-heartbeatTick.C:
			// Send a heartbeat
			if err := client.sendHeartbeat(); err != nil {
				fmt.Printf("Error sending heartbeat: %v\n", err)
			} else {
				fmt.Println("Sent heartbeat")
			}
		}
	}
}

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 (client *gatewayClient) sendData(data map[string][]StampedReading) error {

	jsonStr, err := json.Marshal(data) // Dump our data map into a json string
	if err != nil {
		return err
	}

	req, err := http.NewRequest("POST", dataEndpoint, bytes.NewBuffer(jsonStr)) // Create our request
	if err != nil {
		return err
	}

	fillHeader(req) // Get id and timestamp

	resp, err := client.client.Do(req) // Do the request
	if err != nil {
		return err
	}

	defer func() {
		if err := resp.Body.Close(); err != nil { // Honestly not sure what this is for
			fmt.Printf("Error: %v\n", err)
		}
	}()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 { // Make sure it was successful
		return errors.New(fmt.Sprintf("Received a non-200 response: %v\n", resp.StatusCode))
	}

	return nil
}

func (client *gatewayClient) sendHeartbeat() error {
	req, err := http.NewRequest("GET", heartbeatEndpoint, nil) // Send to heartbeat endpoint
	if err != nil {
		return err
	}

	fillHeader(req) // Get id and timestamp

	resp, err := client.client.Do(req) // Do it
	if err != nil {
		return err
	}

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

	if resp.StatusCode < 200 || resp.StatusCode >= 300 { // Make sure it was successful
		return errors.New(fmt.Sprintf("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(headerUUID, "0000001bcd3f") // TODO: get this from somewhere
	req.Header.Set(headerTimestamp, strconv.FormatInt(time.Now().Unix(), 10))
}