lineageos-ota-server/main.go

package main

import (
	"crypto/sha256"
	"encoding/json"
	"fmt"
	"io"
	"io/fs"
	"log"
	"net/http"
	"os"
	"strings"
	"sync"
)

// Information for a LineageOS ROM available for download
type LineageOSROM struct {
	Datetime int    `json:"datetime"`
	Filename string `json:"filename"`
	ID       string `json:"id"`
	Romtype  string `json:"romtype"`
	Size     int    `json:"size"`
	URL      string `json:"url"`
	Version  string `json:"version"`
}

// The HTTP response JSON should be a JSON array of lineageOSROMS available for download
type HTTPResponseJSON struct {
	Response []LineageOSROM `json:"response"`
}

type ROMCache struct {
	ROMs   []LineageOSROM
	Cached map[string]bool // to quickly lookup if a file is already cached
	sync.Mutex
}

var (
	romCache ROMCache
)

// Preload cached list of files and hashes
func init() {
	romCache = ROMCache{}
	romCache.Cached = make(map[string]bool)
	go updateROMCache("public")
}

// HTTP Routing
func main() {

	//Public static files
	http.Handle("/public/", http.StripPrefix("/public/", http.FileServer(http.Dir("public"))))

	// ROM list
	http.HandleFunc("/", lineageOSROMListHandler)

	log.Print("Service listening on :8080")
	log.Fatal(http.ListenAndServe(":8080", nil))

}

// Reads the ROM files on the filesystem and populates a slice of linageOSROMs
func updateROMCache(romDirectory string) {

	f, err := os.Open(romDirectory)
	if err != nil {
		log.Printf("failed to open ROM directory: %v", err)
		return
	}
	files, err := f.ReadDir(0)
	if err != nil {
		log.Printf("failed to read files in directory: %v", err)
		return
	}

	for i, v := range files {

		// skip directories
		if v.Type().IsDir() {
			continue
		}

		// skip non .zip files
		if !strings.HasSuffix(v.Name(), ".zip") {
			continue
		}

		// skip already cached files
		romCache.Lock()
		if _, ok := romCache.Cached[v.Name()]; ok {
			romCache.Unlock()
			continue
		}
		romCache.Unlock()

		// Parse filename and skip files that can't be parsed
		splitName := strings.Split(v.Name(), "-")
		if len(splitName) != 5 {
			continue
		}
		go func(v fs.DirEntry) {
			fInfo, err := v.Info()
			if err != nil {
				log.Printf("failed to get file info '%s': %v", v.Name(), err)
				return
			}

			fileHash, err := hashFile(fmt.Sprintf("%s/%s", romDirectory, v.Name()))
			if err != nil {
				log.Printf("ingore zip file '%s', failed to get sha256 hash: %v", v.Name(), err)
				return
			}

			lineageOSROM := LineageOSROM{
				Datetime: int(fInfo.ModTime().Unix()),
				Filename: v.Name(),
				ID:       fileHash,
				Romtype:  "nightly",
				Size:     int(fInfo.Size()),
				URL:      fmt.Sprintf("https://lineageos-ota.deadbeef.codes/public/%s", v.Name()),
				Version:  splitName[1],
			}

			romCache.Lock()
			if _, ok := romCache.Cached[v.Name()]; ok { // it's possible another goroutine was already working to cache the file, so we check at the end
				romCache.Unlock()
				return
			}
			romCache.ROMs = append(romCache.ROMs, lineageOSROM)
			romCache.Cached[v.Name()] = true
			romCache.Unlock()
		}(files[i])
	}
}

// http - GET /
// Writes JSON response for the updater app to know what versions are available to download
func lineageOSROMListHandler(w http.ResponseWriter, r *http.Request) {
	romCache.Lock()
	lineageOSROMs := romCache.ROMs
	romCache.Unlock()

	httpResponseJSON := &HTTPResponseJSON{Response: lineageOSROMs}

	b, err := json.Marshal(httpResponseJSON)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		log.Printf("failed to marshal lineageOSROMs to json: %v", err)
		return
	}

	w.Write(b)

	go updateROMCache("public")
}

func hashFile(filename string) (string, error) {
	f, err := os.Open(filename)
	if err != nil {
		return "", fmt.Errorf("failed to open file '%s': %v: ", filename, err)
	}
	defer f.Close()

	h := sha256.New()
	if _, err := io.Copy(h, f); err != nil {
		return "", fmt.Errorf("failed to copy data from file to hash function: %v", err)
	}

	return fmt.Sprintf("%x", h.Sum(nil)), nil
}