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"` // Unix timestamp - i.e. 1685907926
	Filename string `json:"filename"` // .zip filename - i.e. lineage-20.0-20230604-UNOFFICIAL-sunfish.zip
	ID       string `json:"id"`       // A unique identifier such as a SHA256 hash of the .zip  - i.e. 603bfc02e403e5fd1bf9ed74383f1d6c9ec7fb228d03c4b37753033d79488e93
	Romtype  string `json:"romtype"`  // i.e. NIGHTLY or UNOFFICIAL
	Size     int    `json:"size"`     // size of .zip file in bytes
	URL      string `json:"url"`      // Accessible URL where client could download the .zip file
	Version  string `json:"version"`  // LineageOS version - i.e. 20.0
}

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

// Caches data about available ROMs in memory so we don't need to reference the filesystem for each request
type ROMCache struct {
	ROMs       []LineageOSROM
	Cached     map[string]bool // to quickly lookup if a file is already cached
	sync.Mutex                 // We have multiple goroutines that may be accessing this data simultaneously, so we much lock / unlock it to prevent race conditions
}

const (
	romDirectory      = "public" // directory where ROMs are available for download
	buildOutDirectory = "out"    // directory from build system containing artifacts which we can move to romDirectory
)

var ( // evil global variable
	romCache ROMCache
)

func init() {
	romCache = ROMCache{}
	romCache.Cached = make(map[string]bool)

	// Check if any new build artifacts and preload the romCache
	moveBuildArtifacts()
	go updateROMCache()
}

// HTTP Server
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() {

	log.Printf("updating ROM cache")

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

	for i, v := range files {

		isLineageROM, splitName := isLineageROMZip(v)
		if !isLineageROM {
			continue
		}

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

		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:  splitName[3], // UNOFFICIAL
				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])
	}
}

// returns true if new builds were moved
func moveBuildArtifacts() bool {

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

	var newROMs bool

	for _, v := range files {
		if isLineageROM, _ := isLineageROMZip(v); !isLineageROM { // skip files that aren't LineageOS ROMs
			continue
		}

		newROMs = true
		log.Printf("new build found - moving file %s", v.Name())
		romCache.Lock() // lock to prevent multiple concurrent goroutines moving the same file
		err := moveBuildFile(fmt.Sprintf("%s/%s", buildOutDirectory, v.Name()), fmt.Sprintf("%s/%s", romDirectory, v.Name()))
		romCache.Unlock()
		if err != nil {
			log.Printf("failed to move file '%s' from out to rom directory: %v", v.Name(), err)
			continue
		}
	}

	return newROMs
}

// false if a file is not a LineageOS ROM .zip file
// no formal validation is performed - only file naming convention is checked
// also returns a lineage ROM's filename sliced and delimited by -'s
// Example filename: lineage-20.0-20230604-UNOFFICIAL-sunfish.zip
func isLineageROMZip(v fs.DirEntry) (bool, []string) {

	// skip directories, non .zip files and files that don't begin with lineage-
	if v.Type().IsDir() || !strings.HasSuffix(v.Name(), ".zip") || !strings.HasPrefix(v.Name(), "lineage-") {
		return false, nil
	}

	splitName := strings.Split(v.Name(), "-")
	// expect 5 dashes
	return len(splitName) == 5, splitName
}

// 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) {
	go func() {
		newBuilds := moveBuildArtifacts()
		if newBuilds {
			updateROMCache()
		}
	}()

	romCache.Lock()
	httpResponseJSON := &HTTPResponseJSON{Response: romCache.ROMs}
	romCache.Unlock()

	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)
}

// Returns a sha256 hash of a file located at the path provided
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
}

// A custom "move file" function because in docker container the mounted folders are different overlay filesystems
// Instead of os.Rename, we must copy and delete
func moveBuildFile(src, dst string) error {
	sourceFileStat, err := os.Stat(src)
	if err != nil {
		return err
	}

	if !sourceFileStat.Mode().IsRegular() {
		return fmt.Errorf("%s is not a regular file", src)
	}

	source, err := os.Open(src)
	if err != nil {
		return err
	}
	defer source.Close()

	destination, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer destination.Close()
	_, err = io.Copy(destination, source)
	if err != nil {
		return fmt.Errorf("failed to copy file: %v", err)
	}

	err = os.Remove(src)
	if err != nil {
		return fmt.Errorf("failed to delete source file after copy: %v", err)
	}

	return nil
}