refactor: internals

Signed-off-by: skidoodle <contact@albert.lol>

Dockerfile

@@ -1,4 +1,4 @@
-FROM --platform=$BUILDPLATFORM golang:1.25.5 AS builder
+FROM --platform=$BUILDPLATFORM golang:1.25.6 AS builder
 
 WORKDIR /app
 

go.mod

@@ -1,3 +1,3 @@
 module github.com/skidoodle/safebin
 
-go 1.25.5
+go 1.25.6

internal/app/config.go

@@ -21,36 +21,54 @@ type App struct {
 	Logger *slog.Logger
 }
 
-func LoadConfig() Config {
-	h := getEnv("SAFEBIN_HOST", "0.0.0.0")
-	p := getEnvInt("SAFEBIN_PORT", 8080)
-	s := getEnv("SAFEBIN_STORAGE", "./storage")
-	mDefault := int64(getEnvInt("SAFEBIN_MAX_MB", 512))
+const (
+	defaultHost = "0.0.0.0"
+	defaultPort  = 8080
+	defaultStorage = "./storage"
+	defaultMaxMB = 512
+)
 
-	var m int64
-	flag.StringVar(&h, "h", h, "Bind address")
-	flag.IntVar(&p, "p", p, "Port")
-	flag.StringVar(&s, "s", s, "Storage directory")
-	flag.Int64Var(&m, "m", mDefault, "Max file size in MB")
+func LoadConfig() Config {
+	hostEnv := getEnv("SAFEBIN_HOST", defaultHost)
+	portEnv := getEnvInt("SAFEBIN_PORT", defaultPort)
+	storageEnv := getEnv("SAFEBIN_STORAGE", defaultStorage)
+	maxMBEnv := int64(getEnvInt("SAFEBIN_MAX_MB", defaultMaxMB))
+
+	var host string
+	var port int
+	var storage string
+	var maxMB int64
+
+	flag.StringVar(&host, "h", hostEnv, "Bind address")
+	flag.IntVar(&port, "p", portEnv, "Port")
+	flag.StringVar(&storage, "s", storageEnv, "Storage directory")
+	flag.Int64Var(&maxMB, "m", maxMBEnv, "Max file size in MB")
 	flag.Parse()
 
-	return Config{Addr: fmt.Sprintf("%s:%d", h, p), StorageDir: s, MaxMB: m}
-}
-
-func getEnv(k, f string) string {
-	if v, ok := os.LookupEnv(k); ok {
-		return v
+	return Config{
+		Addr:       fmt.Sprintf("%s:%d", host, port),
+		StorageDir: storage,
+		MaxMB:      maxMB,
 	}
-	return f
 }
 
-func getEnvInt(k string, f int) int {
-	if v, ok := os.LookupEnv(k); ok {
-		if i, err := strconv.Atoi(v); err == nil {
+func getEnv(key, fallback string) string {
+	if value, ok := os.LookupEnv(key); ok {
+		return value
+	}
+
+	return fallback
+}
+
+func getEnvInt(key string, fallback int) int {
+	if value, ok := os.LookupEnv(key); ok {
+		i, err := strconv.Atoi(value)
+		if err == nil {
 			return i
 		}
 	}
-	return f
+
+	return fallback
 }
 
 func ParseTemplates() *template.Template {

internal/app/handlers.go

@@ -2,6 +2,7 @@ package app
 
 import (
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"io"
 	"mime"
@@ -14,187 +15,268 @@ import (
 	"github.com/skidoodle/safebin/internal/crypto"
 )
 
+const (
+	uploadChunkSize    = 8 << 20
+	maxRequestOverhead = 10 << 20
+	permUserRWX        = 0o700
+	slugLength         = 22
+	keyLength          = 16
+	megaByte           = 1 << 20
+	chunkSafetyMargin  = 2
+)
+
 var reUploadID = regexp.MustCompile(`^[a-zA-Z0-9]{10,50}$`)
 
-func (app *App) HandleHome(w http.ResponseWriter, r *http.Request) {
-	err := app.Tmpl.ExecuteTemplate(w, "base", map[string]any{
+func (app *App) HandleHome(writer http.ResponseWriter, request *http.Request) {
+	err := app.Tmpl.ExecuteTemplate(writer, "base", map[string]any{
 		"MaxMB": app.Conf.MaxMB,
-		"Host":  r.Host,
+		"Host":  request.Host,
 	})
+
 	if err != nil {
 		app.Logger.Error("Template error", "err", err)
 	}
 }
 
-func (app *App) HandleUpload(w http.ResponseWriter, r *http.Request) {
-	limit := (app.Conf.MaxMB << 20) + (1 << 20)
-	r.Body = http.MaxBytesReader(w, r.Body, limit)
+func (app *App) HandleUpload(writer http.ResponseWriter, request *http.Request) {
+	limit := (app.Conf.MaxMB * megaByte) + megaByte
+	request.Body = http.MaxBytesReader(writer, request.Body, limit)
+
+	file, header, err := request.FormFile("file")
 
-	file, header, err := r.FormFile("file")
 	if err != nil {
 		if err.Error() == "http: request body too large" {
-			app.SendError(w, r, http.StatusRequestEntityTooLarge)
+			app.SendError(writer, request, http.StatusRequestEntityTooLarge)
 			return
 		}
-		app.SendError(w, r, http.StatusBadRequest)
+
+		app.SendError(writer, request, http.StatusBadRequest)
+
 		return
 	}
-	defer file.Close()
 
-	tmpPath := filepath.Join(app.Conf.StorageDir, "tmp", fmt.Sprintf("up_%d", os.Getpid()))
-	tmp, err := os.Create(tmpPath)
+	defer func() {
+		if closeErr := file.Close(); closeErr != nil {
+			app.Logger.Error("Failed to close upload file", "err", closeErr)
+		}
+	}()
+
+	tmp, err := os.CreateTemp(filepath.Join(app.Conf.StorageDir, "tmp"), "up_*")
+
 	if err != nil {
 		app.Logger.Error("Failed to create temp file", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
+		app.SendError(writer, request, http.StatusInternalServerError)
+
 		return
 	}
-	defer os.Remove(tmpPath)
-	defer tmp.Close()
+
+	tmpPath := tmp.Name()
+
+	defer func() {
+		if removeErr := os.Remove(tmpPath); removeErr != nil && !os.IsNotExist(removeErr) {
+			app.Logger.Error("Failed to remove temp file", "err", removeErr)
+		}
+	}()
+
+	defer func() {
+		if closeErr := tmp.Close(); closeErr != nil {
+			app.Logger.Error("Failed to close temp file", "err", closeErr)
+		}
+	}()
 
 	if _, err := io.Copy(tmp, file); err != nil {
 		app.Logger.Error("Failed to write temp file", "err", err)
-		app.SendError(w, r, http.StatusRequestEntityTooLarge)
+		app.SendError(writer, request, http.StatusRequestEntityTooLarge)
+
 		return
 	}
 
-	app.FinalizeFile(w, r, tmp, header.Filename)
+	app.FinalizeFile(writer, request, tmp, header.Filename)
 }
 
-func (app *App) HandleChunk(w http.ResponseWriter, r *http.Request) {
-	r.Body = http.MaxBytesReader(w, r.Body, 10<<20)
+func (app *App) HandleChunk(writer http.ResponseWriter, request *http.Request) {
+	request.Body = http.MaxBytesReader(writer, request.Body, maxRequestOverhead)
 
-	uid := r.FormValue("upload_id")
-	idx, err := strconv.Atoi(r.FormValue("index"))
+	uid := request.FormValue("upload_id")
+
+	idx, err := strconv.Atoi(request.FormValue("index"))
 	if err != nil {
-		app.SendError(w, r, http.StatusBadRequest)
+		app.SendError(writer, request, http.StatusBadRequest)
 		return
 	}
 
-	const chunkSize = 8 << 20
-	maxChunks := int((app.Conf.MaxMB<<20)/chunkSize) + 2
+	maxChunks := int((app.Conf.MaxMB*megaByte)/uploadChunkSize) + chunkSafetyMargin
 
 	if !reUploadID.MatchString(uid) || idx > maxChunks || idx < 0 {
-		app.SendError(w, r, http.StatusBadRequest)
+		app.SendError(writer, request, http.StatusBadRequest)
 		return
 	}
 
-	file, _, err := r.FormFile("chunk")
+	file, _, err := request.FormFile("chunk")
+
 	if err != nil {
 		if err.Error() == "http: request body too large" {
-			app.SendError(w, r, http.StatusRequestEntityTooLarge)
+			app.SendError(writer, request, http.StatusRequestEntityTooLarge)
 			return
 		}
-		app.SendError(w, r, http.StatusBadRequest)
+
+		app.SendError(writer, request, http.StatusBadRequest)
+
 		return
 	}
-	defer file.Close()
 
+	defer func() {
+		if closeErr := file.Close(); closeErr != nil {
+			app.Logger.Error("Failed to close chunk file", "err", closeErr)
+		}
+	}()
+
+	if err := app.saveChunk(uid, idx, file); err != nil {
+		app.Logger.Error("Failed to save chunk", "err", err)
+		app.SendError(writer, request, http.StatusInternalServerError)
+	}
+}
+
+func (app *App) saveChunk(uid string, idx int, src io.Reader) error {
 	dir := filepath.Join(app.Conf.StorageDir, "tmp", uid)
-	if err := os.MkdirAll(dir, 0700); err != nil {
-		app.Logger.Error("Failed to create chunk dir", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
-		return
+
+	if err := os.MkdirAll(dir, permUserRWX); err != nil {
+		return fmt.Errorf("create chunk dir: %w", err)
 	}
 
 	dest, err := os.Create(filepath.Join(dir, strconv.Itoa(idx)))
 	if err != nil {
-		app.Logger.Error("Failed to create chunk file", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
+		return fmt.Errorf("create chunk file: %w", err)
+	}
+
+	defer func() {
+		if closeErr := dest.Close(); closeErr != nil {
+			app.Logger.Error("Failed to close chunk dest", "err", closeErr)
+		}
+	}()
+
+	if _, err := io.Copy(dest, src); err != nil {
+		return fmt.Errorf("copy chunk: %w", err)
+	}
+
+	return nil
+}
+
+func (app *App) HandleFinish(writer http.ResponseWriter, request *http.Request) {
+	uid := request.FormValue("upload_id")
+
+	total, err := strconv.Atoi(request.FormValue("total"))
+	if err != nil {
+		app.SendError(writer, request, http.StatusBadRequest)
 		return
 	}
-	defer dest.Close()
 
-	if _, err := io.Copy(dest, file); err != nil {
-		app.Logger.Error("Failed to save chunk", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
+	maxChunks := int((app.Conf.MaxMB*megaByte)/uploadChunkSize) + chunkSafetyMargin
+
+	if !reUploadID.MatchString(uid) || total > maxChunks || total <= 0 {
+		app.SendError(writer, request, http.StatusBadRequest)
 		return
 	}
+
+	mergedPath, err := app.mergeChunks(uid, total)
+
+	if err != nil {
+		app.Logger.Error("Merge failed", "err", err)
+
+		if errors.Is(err, io.ErrShortWrite) {
+			app.SendError(writer, request, http.StatusRequestEntityTooLarge)
+		} else {
+			app.SendError(writer, request, http.StatusInternalServerError)
+		}
+
+		return
+	}
+
+	defer func() {
+		if removeErr := os.Remove(mergedPath); removeErr != nil && !os.IsNotExist(removeErr) {
+			app.Logger.Error("Failed to remove merged file", "err", removeErr)
+		}
+	}()
+
+	mergedRead, err := os.Open(mergedPath)
+
+	if err != nil {
+		app.Logger.Error("Failed to open merged file", "err", err)
+		app.SendError(writer, request, http.StatusInternalServerError)
+
+		return
+	}
+
+	defer func() {
+		if closeErr := mergedRead.Close(); closeErr != nil {
+			app.Logger.Error("Failed to close merged reader", "err", closeErr)
+		}
+	}()
+
+	app.FinalizeFile(writer, request, mergedRead, request.FormValue("filename"))
+
+	if err := os.RemoveAll(filepath.Join(app.Conf.StorageDir, "tmp", uid)); err != nil {
+		app.Logger.Error("Failed to remove chunk dir", "err", err)
+	}
 }
 
-func (app *App) HandleFinish(w http.ResponseWriter, r *http.Request) {
-	uid := r.FormValue("upload_id")
-	total, err := strconv.Atoi(r.FormValue("total"))
-	if err != nil {
-		app.SendError(w, r, http.StatusBadRequest)
-		return
-	}
-
-	const chunkSize = 8 << 20
-	maxChunks := int((app.Conf.MaxMB<<20)/chunkSize) + 2
-
-	if !reUploadID.MatchString(uid) || total > maxChunks || total <= 0 {
-		app.SendError(w, r, http.StatusBadRequest)
-		return
-	}
-
+func (app *App) mergeChunks(uid string, total int) (string, error) {
 	tmpPath := filepath.Join(app.Conf.StorageDir, "tmp", "m_"+uid)
+
 	merged, err := os.Create(tmpPath)
 	if err != nil {
-		app.Logger.Error("Failed to create merge file", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
-		return
+		return "", fmt.Errorf("create merge file: %w", err)
 	}
-	defer os.Remove(tmpPath)
-	defer merged.Close()
 
-	limit := app.Conf.MaxMB << 20
+	defer func() {
+		if closeErr := merged.Close(); closeErr != nil {
+			app.Logger.Error("Failed to close merged file", "err", closeErr)
+		}
+	}()
+
+	limit := app.Conf.MaxMB * megaByte
 	var written int64
 
 	for i := range total {
 		partPath := filepath.Join(app.Conf.StorageDir, "tmp", uid, strconv.Itoa(i))
+
 		part, err := os.Open(partPath)
 		if err != nil {
-			app.Logger.Error("Missing chunk during merge", "uid", uid, "index", i, "err", err)
-			app.SendError(w, r, http.StatusBadRequest)
-			return
+			return "", fmt.Errorf("open chunk %d: %w", i, err)
 		}
 
 		n, err := io.Copy(merged, part)
-		part.Close()
+
+		if closeErr := part.Close(); closeErr != nil {
+			app.Logger.Error("Failed to close chunk part", "err", closeErr)
+		}
+
 		if err != nil {
-			app.Logger.Error("Failed to append chunk", "err", err)
-			app.SendError(w, r, http.StatusInternalServerError)
-			return
+			return "", fmt.Errorf("append chunk %d: %w", i, err)
 		}
 
 		written += n
 		if written > limit {
-			app.SendError(w, r, http.StatusRequestEntityTooLarge)
-			return
+			return "", io.ErrShortWrite
 		}
 	}
 
-	if err := merged.Close(); err != nil {
-		app.Logger.Error("Failed to close merged file", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
-		return
-	}
-
-	mergedRead, err := os.Open(tmpPath)
-	if err != nil {
-		app.Logger.Error("Failed to open merged file", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
-		return
-	}
-	defer mergedRead.Close()
-
-	app.FinalizeFile(w, r, mergedRead, r.FormValue("filename"))
-	os.RemoveAll(filepath.Join(app.Conf.StorageDir, "tmp", uid))
+	return tmpPath, nil
 }
 
-func (app *App) HandleGetFile(w http.ResponseWriter, r *http.Request) {
-	slug := r.PathValue("slug")
-	if len(slug) < 22 {
-		app.SendError(w, r, http.StatusBadRequest)
+func (app *App) HandleGetFile(writer http.ResponseWriter, request *http.Request) {
+	slug := request.PathValue("slug")
+	if len(slug) < slugLength {
+		app.SendError(writer, request, http.StatusBadRequest)
 		return
 	}
 
-	keyBase64 := slug[:22]
-	ext := slug[22:]
+	keyBase64 := slug[:slugLength]
+	ext := slug[slugLength:]
 
 	key, err := base64.RawURLEncoding.DecodeString(keyBase64)
-	if err != nil || len(key) != 16 {
-		app.SendError(w, r, http.StatusUnauthorized)
+	if err != nil || len(key) != keyLength {
+		app.SendError(writer, request, http.StatusUnauthorized)
 		return
 	}
 
@@ -203,105 +285,133 @@ func (app *App) HandleGetFile(w http.ResponseWriter, r *http.Request) {
 
 	info, err := os.Stat(path)
 	if err != nil {
-		app.SendError(w, r, http.StatusNotFound)
+		app.SendError(writer, request, http.StatusNotFound)
 		return
 	}
 
-	f, err := os.Open(path)
+	file, err := os.Open(path)
+
 	if err != nil {
 		app.Logger.Error("Failed to open file", "path", path, "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
+		app.SendError(writer, request, http.StatusInternalServerError)
+
 		return
 	}
-	defer f.Close()
+
+	defer func() {
+		if closeErr := file.Close(); closeErr != nil {
+			app.Logger.Error("Failed to close file", "err", closeErr)
+		}
+	}()
 
 	streamer, err := crypto.NewGCMStreamer(key)
+
 	if err != nil {
 		app.Logger.Error("Failed to create crypto streamer", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
+		app.SendError(writer, request, http.StatusInternalServerError)
+
 		return
 	}
 
-	decryptor := crypto.NewDecryptor(f, streamer.AEAD, info.Size())
+	decryptor := crypto.NewDecryptor(file, streamer.AEAD, info.Size())
 
 	contentType := mime.TypeByExtension(ext)
 	if contentType == "" {
 		contentType = "application/octet-stream"
 	}
 
-	w.Header().Set("Content-Type", contentType)
-	w.Header().Set("Content-Security-Policy", "default-src 'none'; img-src 'self' data:; media-src 'self' data:; style-src 'unsafe-inline'; sandbox allow-forms allow-scripts allow-downloads allow-same-origin")
-	w.Header().Set("X-Content-Type-Options", "nosniff")
-	w.Header().Set("Content-Disposition", fmt.Sprintf("inline; filename=%q", slug))
+	csp := "default-src 'none'; img-src 'self' data:; media-src 'self' data:; " +
+		"style-src 'unsafe-inline'; sandbox allow-forms allow-scripts allow-downloads allow-same-origin"
 
-	http.ServeContent(w, r, slug, info.ModTime(), decryptor)
+	writer.Header().Set("Content-Type", contentType)
+	writer.Header().Set("Content-Security-Policy", csp)
+	writer.Header().Set("X-Content-Type-Options", "nosniff")
+	writer.Header().Set("Content-Disposition", fmt.Sprintf("inline; filename=%q", slug))
+
+	http.ServeContent(writer, request, slug, info.ModTime(), decryptor)
 }
 
-func (app *App) FinalizeFile(w http.ResponseWriter, r *http.Request, src *os.File, filename string) {
+func (app *App) FinalizeFile(writer http.ResponseWriter, request *http.Request, src *os.File, filename string) {
 	if _, err := src.Seek(0, 0); err != nil {
 		app.Logger.Error("Seek failed", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
+		app.SendError(writer, request, http.StatusInternalServerError)
+
 		return
 	}
 
 	key, err := crypto.DeriveKey(src)
+
 	if err != nil {
 		app.Logger.Error("Key derivation failed", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
+		app.SendError(writer, request, http.StatusInternalServerError)
+
 		return
 	}
 
 	ext := filepath.Ext(filename)
 	id := crypto.GetID(key, ext)
-
-	if _, err := src.Seek(0, 0); err != nil {
-		app.Logger.Error("Seek failed", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
-		return
-	}
-
 	finalPath := filepath.Join(app.Conf.StorageDir, id)
 
 	if _, err := os.Stat(finalPath); err == nil {
-		app.RespondWithLink(w, r, key, filename)
+		app.RespondWithLink(writer, request, key, filename)
 		return
 	}
 
-	out, err := os.Create(finalPath + ".tmp")
-	if err != nil {
-		app.Logger.Error("Failed to create final file", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
+	if _, err := src.Seek(0, 0); err != nil {
+		app.Logger.Error("Seek failed", "err", err)
+		app.SendError(writer, request, http.StatusInternalServerError)
+
 		return
 	}
+
+	if err := app.encryptAndSave(src, key, finalPath); err != nil {
+		app.Logger.Error("Encryption failed", "err", err)
+		app.SendError(writer, request, http.StatusInternalServerError)
+
+		return
+	}
+
+	app.RespondWithLink(writer, request, key, filename)
+}
+
+func (app *App) encryptAndSave(src io.Reader, key []byte, finalPath string) error {
+	out, err := os.Create(finalPath + ".tmp")
+	if err != nil {
+		return fmt.Errorf("create final file: %w", err)
+	}
+
+	var closed bool
+
 	defer func() {
-		out.Close()
-		os.Remove(finalPath + ".tmp")
+		if !closed {
+			if closeErr := out.Close(); closeErr != nil {
+				app.Logger.Error("Failed to close final file", "err", closeErr)
+			}
+		}
+
+		if removeErr := os.Remove(finalPath + ".tmp"); removeErr != nil && !os.IsNotExist(removeErr) {
+			app.Logger.Error("Failed to remove temp final file", "err", removeErr)
+		}
 	}()
 
 	streamer, err := crypto.NewGCMStreamer(key)
 	if err != nil {
-		app.Logger.Error("Failed to create streamer", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
-		return
+		return fmt.Errorf("create streamer: %w", err)
 	}
 
 	if err := streamer.EncryptStream(out, src); err != nil {
-		app.Logger.Error("Encryption failed", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
-		return
+		return fmt.Errorf("encrypt stream: %w", err)
 	}
 
 	if err := out.Close(); err != nil {
-		app.Logger.Error("Failed to close final file", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
-		return
+		return fmt.Errorf("close final file: %w", err)
 	}
 
+	closed = true
+
 	if err := os.Rename(finalPath+".tmp", finalPath); err != nil {
-		app.Logger.Error("Failed to rename final file", "err", err)
-		app.SendError(w, r, http.StatusInternalServerError)
-		return
+		return fmt.Errorf("rename final file: %w", err)
 	}
 
-	app.RespondWithLink(w, r, key, filename)
+	return nil
 }

internal/app/server.go

@@ -9,22 +9,25 @@ import (
 
 func (app *App) Routes() *http.ServeMux {
 	mux := http.NewServeMux()
-	fs := http.FileServer(http.Dir("./web/static"))
-	mux.Handle("GET /static/", http.StripPrefix("/static/", fs))
+	fileServer := http.FileServer(http.Dir("./web/static"))
+
+	mux.Handle("GET /static/", http.StripPrefix("/static/", fileServer))
 	mux.HandleFunc("GET /{$}", app.HandleHome)
 	mux.HandleFunc("POST /{$}", app.HandleUpload)
 	mux.HandleFunc("POST /upload/chunk", app.HandleChunk)
 	mux.HandleFunc("POST /upload/finish", app.HandleFinish)
 	mux.HandleFunc("GET /{slug}", app.HandleGetFile)
+
 	return mux
 }
 
-func (app *App) RespondWithLink(w http.ResponseWriter, r *http.Request, key []byte, originalName string) {
+func (app *App) RespondWithLink(writer http.ResponseWriter, request *http.Request, key []byte, originalName string) {
 	keySlug := base64.RawURLEncoding.EncodeToString(key)
 	ext := filepath.Ext(originalName)
-	link := fmt.Sprintf("%s/%s%s", r.Host, keySlug, ext)
-	if r.Header.Get("X-Requested-With") == "XMLHttpRequest" {
-		fmt.Fprintf(w, `
+	link := fmt.Sprintf("%s/%s%s", request.Host, keySlug, ext)
+
+	if request.Header.Get("X-Requested-With") == "XMLHttpRequest" {
+		html := `
 			<div class="result-container">
 				<div class="dim result-label">Upload Complete:</div>
 				<div class="copy-box">
@@ -34,27 +37,44 @@ func (app *App) RespondWithLink(w http.ResponseWriter, r *http.Request, key []by
 				<div class="reset-wrapper">
 					<button class="reset-btn" onclick="resetUI()">Upload another</button>
 				</div>
-			</div>`, link)
+			</div>`
+
+		if _, err := fmt.Fprintf(writer, html, link); err != nil {
+			app.Logger.Error("Failed to write response", "err", err)
+		}
+
 		return
 	}
+
 	scheme := "https"
-	if r.TLS == nil {
+
+	if request.TLS == nil {
 		scheme = "http"
 	}
-	fmt.Fprintf(w, "%s://%s\n", scheme, link)
+
+	if _, err := fmt.Fprintf(writer, "%s://%s\n", scheme, link); err != nil {
+		app.Logger.Error("Failed to write response", "err", err)
+	}
 }
 
-func (app *App) SendError(w http.ResponseWriter, r *http.Request, code int) {
-	if r.Header.Get("X-Requested-With") == "XMLHttpRequest" {
-		w.WriteHeader(code)
-		fmt.Fprintf(w, `
+func (app *App) SendError(writer http.ResponseWriter, request *http.Request, code int) {
+	if request.Header.Get("X-Requested-With") == "XMLHttpRequest" {
+		writer.WriteHeader(code)
+
+		html := `
 			<div class="result-container">
 				<div class="error-text">Error %d</div>
 				<div class="reset-wrapper">
 					<button class="reset-btn" onclick="resetUI()">Try again</button>
 				</div>
-			</div>`, code)
+			</div>`
+
+		if _, err := fmt.Fprintf(writer, html, code); err != nil {
+			app.Logger.Error("Failed to write error response", "err", err)
+		}
+
 		return
 	}
-	http.Error(w, http.StatusText(code), code)
+
+	http.Error(writer, http.StatusText(code), code)
 }

internal/app/storage.go

@@ -8,43 +8,82 @@ import (
 	"time"
 )
 
+const (
+	cleanupInterval = 1 * time.Hour
+	tempExpiry      = 4 * time.Hour
+	minRetention    = 24 * time.Hour
+	maxRetention    = 365 * 24 * time.Hour
+	bytesInMB       = 1 << 20
+)
+
 func (app *App) StartCleanupTask(ctx context.Context) {
-	ticker := time.NewTicker(1 * time.Hour)
+	ticker := time.NewTicker(cleanupInterval)
+
 	for {
 		select {
 		case <-ctx.Done():
+			ticker.Stop()
 			return
 		case <-ticker.C:
-			app.CleanDir(app.Conf.StorageDir, false)
-			app.CleanDir(filepath.Join(app.Conf.StorageDir, "tmp"), true)
+			app.CleanStorage(app.Conf.StorageDir)
+			app.CleanTemp(filepath.Join(app.Conf.StorageDir, "tmp"))
 		}
 	}
 }
 
-func (app *App) CleanDir(path string, isTmp bool) {
-	entries, _ := os.ReadDir(path)
+func (app *App) CleanStorage(path string) {
+	entries, err := os.ReadDir(path)
+	if err != nil {
+		app.Logger.Error("Failed to read storage dir", "err", err)
+		return
+	}
+
 	for _, entry := range entries {
-		info, _ := entry.Info()
-		expiry := 4 * time.Hour
-		if !isTmp {
-			expiry = CalculateRetention(info.Size(), app.Conf.MaxMB)
+		info, err := entry.Info()
+		if err != nil {
+			continue
 		}
 
+		expiry := CalculateRetention(info.Size(), app.Conf.MaxMB)
+
 		if time.Since(info.ModTime()) > expiry {
-			os.RemoveAll(filepath.Join(path, entry.Name()))
+			if err := os.RemoveAll(filepath.Join(path, entry.Name())); err != nil {
+				app.Logger.Error("Failed to remove expired file", "path", entry.Name(), "err", err)
+			}
 		}
 	}
 }
 
-func CalculateRetention(fileSize int64, maxMB int64) time.Duration {
-	const (
-		minAge = 24 * time.Hour
-		maxAge = 365 * 24 * time.Hour
-	)
-	ratio := math.Max(0, math.Min(1, float64(fileSize)/float64(maxMB<<20)))
-	retention := float64(maxAge) * math.Pow(1.0-ratio, 3)
-	if retention < float64(minAge) {
-		return minAge
+func (app *App) CleanTemp(path string) {
+	entries, err := os.ReadDir(path)
+	if err != nil {
+		app.Logger.Error("Failed to read temp dir", "err", err)
+		return
 	}
+
+	for _, entry := range entries {
+		info, err := entry.Info()
+		if err != nil {
+			continue
+		}
+
+		if time.Since(info.ModTime()) > tempExpiry {
+			if err := os.RemoveAll(filepath.Join(path, entry.Name())); err != nil {
+				app.Logger.Error("Failed to remove expired temp file", "path", entry.Name(), "err", err)
+			}
+		}
+	}
+}
+
+func CalculateRetention(fileSize, maxMB int64) time.Duration {
+	ratio := math.Max(0, math.Min(1, float64(fileSize)/float64(maxMB*bytesInMB)))
+
+	invRatio := 1.0 - ratio
+	retention := float64(maxRetention) * (invRatio * invRatio * invRatio)
+
+	if retention < float64(minRetention) {
+		return minRetention
+	}
+
 	return time.Duration(retention)
 }

internal/crypto/crypto.go

@@ -6,27 +6,34 @@ import (
 	"crypto/sha256"
 	"encoding/base64"
 	"encoding/binary"
+	"errors"
+	"fmt"
 	"io"
 )
 
 const (
 	GCMChunkSize = 64 * 1024
 	NonceSize    = 12
+	KeySize      = 16
+	IDSize       = 9
 )
 
-func DeriveKey(r io.Reader) ([]byte, error) {
-	h := sha256.New()
-	if _, err := io.Copy(h, r); err != nil {
-		return nil, err
+func DeriveKey(reader io.Reader) ([]byte, error) {
+	hasher := sha256.New()
+
+	if _, err := io.Copy(hasher, reader); err != nil {
+		return nil, fmt.Errorf("failed to copy to hasher: %w", err)
 	}
-	return h.Sum(nil)[:16], nil
+
+	return hasher.Sum(nil)[:KeySize], nil
 }
 
 func GetID(key []byte, ext string) string {
-	h := sha256.New()
-	h.Write(key)
-	h.Write([]byte(ext))
-	return base64.RawURLEncoding.EncodeToString(h.Sum(nil)[:9])
+	hasher := sha256.New()
+	hasher.Write(key)
+	hasher.Write([]byte(ext))
+
+	return base64.RawURLEncoding.EncodeToString(hasher.Sum(nil)[:IDSize])
 }
 
 type GCMStreamer struct {
@@ -34,37 +41,46 @@ type GCMStreamer struct {
 }
 
 func NewGCMStreamer(key []byte) (*GCMStreamer, error) {
-	b, err := aes.NewCipher(key)
+	block, err := aes.NewCipher(key)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to create cipher: %w", err)
 	}
-	g, err := cipher.NewGCM(b)
+
+	gcm, err := cipher.NewGCM(block)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to create GCM: %w", err)
 	}
-	return &GCMStreamer{AEAD: g}, nil
+
+	return &GCMStreamer{AEAD: gcm}, nil
 }
 
 func (g *GCMStreamer) EncryptStream(dst io.Writer, src io.Reader) error {
 	buf := make([]byte, GCMChunkSize)
-	var chunkIdx uint64 = 0
+	var chunkIdx uint64
+
 	for {
-		n, err := io.ReadFull(src, buf)
-		if n > 0 {
+		bytesRead, err := io.ReadFull(src, buf)
+		if bytesRead > 0 {
 			nonce := make([]byte, NonceSize)
 			binary.BigEndian.PutUint64(nonce[4:], chunkIdx)
-			ciphertext := g.AEAD.Seal(nil, nonce, buf[:n], nil)
+
+			ciphertext := g.AEAD.Seal(nil, nonce, buf[:bytesRead], nil)
+
 			if _, werr := dst.Write(ciphertext); werr != nil {
-				return werr
+				return fmt.Errorf("failed to write ciphertext: %w", werr)
 			}
+
 			chunkIdx++
 		}
-		if err == io.EOF || err == io.ErrUnexpectedEOF {
+
+		if errors.Is(err, io.EOF) || errors.Is(err, io.ErrUnexpectedEOF) {
 			break
 		}
+
 		if err != nil {
-			return err
+			return fmt.Errorf("failed to read source: %w", err)
 		}
 	}
+
 	return nil
 }

internal/crypto/reader.go

@@ -4,34 +4,41 @@ import (
 	"crypto/cipher"
 	"encoding/binary"
 	"errors"
+	"fmt"
 	"io"
 )
 
+var ErrInvalidWhence = errors.New("invalid whence")
+var ErrNegativeBias = errors.New("negative bias")
+
 type Decryptor struct {
-	rs     io.ReadSeeker
-	aead   cipher.AEAD
-	size   int64
-	offset int64
+	readSeeker io.ReadSeeker
+	aead       cipher.AEAD
+	size       int64
+	offset     int64
 }
 
-func NewDecryptor(rs io.ReadSeeker, aead cipher.AEAD, encryptedSize int64) *Decryptor {
+func NewDecryptor(readSeeker io.ReadSeeker, aead cipher.AEAD, encryptedSize int64) *Decryptor {
 	overhead := int64(aead.Overhead())
-	fullBlocks := encryptedSize / (GCMChunkSize + overhead)
-	remainder := encryptedSize % (GCMChunkSize + overhead)
+	chunkWithOverhead := int64(GCMChunkSize) + overhead
 
-	plainSize := (fullBlocks * GCMChunkSize)
+	fullBlocks := encryptedSize / chunkWithOverhead
+	remainder := encryptedSize % chunkWithOverhead
+
+	plainSize := fullBlocks * GCMChunkSize
 	if remainder > overhead {
 		plainSize += (remainder - overhead)
 	}
 
 	return &Decryptor{
-		rs:   rs,
-		aead: aead,
-		size: plainSize,
+		readSeeker: readSeeker,
+		aead:       aead,
+		size:       plainSize,
+		offset:     0,
 	}
 }
 
-func (d *Decryptor) Read(p []byte) (int, error) {
+func (d *Decryptor) Read(buf []byte) (int, error) {
 	if d.offset >= d.size {
 		return 0, io.EOF
 	}
@@ -40,25 +47,29 @@ func (d *Decryptor) Read(p []byte) (int, error) {
 	overhang := d.offset % GCMChunkSize
 
 	overhead := int64(d.aead.Overhead())
-	actualChunkSize := int64(GCMChunkSize + overhead)
+	actualChunkSize := int64(GCMChunkSize) + overhead
 
-	_, err := d.rs.Seek(chunkIdx*actualChunkSize, io.SeekStart)
+	_, err := d.readSeeker.Seek(chunkIdx*actualChunkSize, io.SeekStart)
 	if err != nil {
-		return 0, err
+		return 0, fmt.Errorf("failed to seek: %w", err)
 	}
 
 	encrypted := make([]byte, actualChunkSize)
-	n, err := io.ReadFull(d.rs, encrypted)
-	if err != nil && err != io.ErrUnexpectedEOF {
-		return 0, err
+
+	bytesRead, err := io.ReadFull(d.readSeeker, encrypted)
+	if err != nil && !errors.Is(err, io.ErrUnexpectedEOF) {
+		return 0, fmt.Errorf("failed to read encrypted data: %w", err)
 	}
 
 	nonce := make([]byte, NonceSize)
+	if chunkIdx < 0 {
+		return 0, fmt.Errorf("invalid chunk index")
+	}
 	binary.BigEndian.PutUint64(nonce[4:], uint64(chunkIdx))
 
-	plaintext, err := d.aead.Open(nil, nonce, encrypted[:n], nil)
+	plaintext, err := d.aead.Open(nil, nonce, encrypted[:bytesRead], nil)
 	if err != nil {
-		return 0, err
+		return 0, fmt.Errorf("failed to decrypt: %w", err)
 	}
 
 	if overhang >= int64(len(plaintext)) {
@@ -66,7 +77,7 @@ func (d *Decryptor) Read(p []byte) (int, error) {
 	}
 
 	available := plaintext[overhang:]
-	nCopied := copy(p, available)
+	nCopied := copy(buf, available)
 	d.offset += int64(nCopied)
 
 	return nCopied, nil
@@ -74,6 +85,7 @@ func (d *Decryptor) Read(p []byte) (int, error) {
 
 func (d *Decryptor) Seek(offset int64, whence int) (int64, error) {
 	var abs int64
+
 	switch whence {
 	case io.SeekStart:
 		abs = offset
@@ -82,11 +94,14 @@ func (d *Decryptor) Seek(offset int64, whence int) (int64, error) {
 	case io.SeekEnd:
 		abs = d.size + offset
 	default:
-		return 0, errors.New("invalid whence")
+		return 0, ErrInvalidWhence
 	}
+
 	if abs < 0 {
-		return 0, errors.New("negative bias")
+		return 0, ErrNegativeBias
 	}
+
 	d.offset = abs
+
 	return abs, nil
 }

main.go

@@ -2,27 +2,39 @@ package main
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"log/slog"
 	"net/http"
 	"os"
 	"os/signal"
+	"path/filepath"
 	"syscall"
 	"time"
 
 	"github.com/skidoodle/safebin/internal/app"
 )
 
+const (
+	permUserRWX     = 0o700
+	serverTimeout   = 10 * time.Minute
+	shutdownTimeout = 10 * time.Second
+)
+
 func main() {
 	cfg := app.LoadConfig()
-	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{Level: slog.LevelDebug}))
+	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
+		Level:     slog.LevelDebug,
+		AddSource: true,
+	}))
 
 	logger.Info("Initializing Safebin Server",
 		"storage_dir", cfg.StorageDir,
 		"max_file_size", fmt.Sprintf("%dMB", cfg.MaxMB),
 	)
 
-	if err := os.MkdirAll(fmt.Sprintf("%s/tmp", cfg.StorageDir), 0700); err != nil {
+	tmpDir := filepath.Join(cfg.StorageDir, "tmp")
+	if err := os.MkdirAll(tmpDir, permUserRWX); err != nil {
 		logger.Error("Failed to initialize storage directory", "err", err)
 		os.Exit(1)
 	}
@@ -41,13 +53,15 @@ func main() {
 	srv := &http.Server{
 		Addr:         cfg.Addr,
 		Handler:      application.Routes(),
-		ReadTimeout:  10 * time.Minute,
-		WriteTimeout: 10 * time.Minute,
+		ReadTimeout:  serverTimeout,
+		WriteTimeout: serverTimeout,
+		IdleTimeout:  serverTimeout,
 	}
 
 	go func() {
 		application.Logger.Info("Server is ready and listening", "addr", cfg.Addr)
-		if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+
+		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
 			application.Logger.Error("Server failed to start", "err", err)
 			os.Exit(1)
 		}
@@ -56,10 +70,12 @@ func main() {
 	<-ctx.Done()
 	application.Logger.Info("Shutting down gracefully...")
 
-	shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	shutdownCtx, cancel := context.WithTimeout(context.Background(), shutdownTimeout)
 	defer cancel()
+
 	if err := srv.Shutdown(shutdownCtx); err != nil {
 		application.Logger.Error("Forced shutdown", "err", err)
 	}
+
 	application.Logger.Info("Server stopped")
 }