Code cleanup. Use go mime type detection

Dockerfile

@@ -3,7 +3,6 @@ FROM golang:1.26-alpine AS builder
 WORKDIR /build
 
 COPY go.mod ./
-RUN go mod download
 
 COPY index.html.tmpl main.go ./
 
@@ -11,7 +10,10 @@ RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o beam .
 
 FROM alpine:latest
 
-RUN adduser -D -u 1000 beam
+RUN apk add mailcap \ # for mime types
+    && adduser -D -u 1000 beam \
+    && mkdir /uploads \
+    && chown beam /uploads
 
 USER beam
 WORKDIR /app

main.go

@@ -4,21 +4,24 @@ import (
 	"crypto/rand"
 	"encoding/json"
 	"fmt"
+	"html/template"
 	"io"
 	"log"
+	"mime"
 	"net/http"
 	"os"
 	"path/filepath"
 	"strings"
 	"time"
-	"html/template"
 )
 
 var uploadDir string
 
 const idLength = 8
 const idCharset = "abcdefghijklmnopqrstuvwxyz0123456789"
+
 var indexHTML *template.Template
+
 func main() {
 	uploadDir = os.Getenv("UPLOAD_DIR")
 	if uploadDir == "" {
@@ -60,7 +63,7 @@ func handleRequest(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if r.Method == "PUT" {
-		handleCurlUpload(w, r, start)
+		handleUpload(w, r, start)
 		return
 	}
 
@@ -69,11 +72,15 @@ func handleRequest(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if r.Method == "HEAD" {
+		return
+	}
+
 	w.WriteHeader(http.StatusMethodNotAllowed)
 	logRequest(r, 405, time.Since(start))
 }
 
-func handleCurlUpload(w http.ResponseWriter, r *http.Request, start time.Time) {
+func handleUpload(w http.ResponseWriter, r *http.Request, start time.Time) {
 	filename := strings.TrimPrefix(r.URL.Path, "/")
 	if filename == "" {
 		http.Error(w, "Filename required", http.StatusBadRequest)
@@ -192,6 +199,12 @@ func handleDownload(w http.ResponseWriter, r *http.Request, start time.Time) {
 		logRequest(r, 404, time.Since(start))
 		return
 	}
+	if !strings.HasPrefix(filePath, uploadDir) {
+		http.NotFound(w, r)
+		logRequest(r, 404, time.Since(start))
+		return
+	}
+
 	defer file.Close()
 
 	stat, err := file.Stat()
@@ -212,7 +225,7 @@ func handleDownload(w http.ResponseWriter, r *http.Request, start time.Time) {
 func generateUniqueID() (string, error) {
 	const maxRetries = 100
 
-	for i := 0; i < maxRetries; i++ {
+	for range maxRetries {
 		id := generateID()
 		targetDir := filepath.Join(uploadDir, id)
 
@@ -249,11 +262,11 @@ func getHost(r *http.Request) string {
 	// Check standard Forwarded header (RFC 7239)
 	if forwarded := r.Header.Get("Forwarded"); forwarded != "" {
 		// Parse "Forwarded: for=...; host=example.com; proto=https"
-		parts := strings.Split(forwarded, ";")
+		parts := strings.SplitSeq(forwarded, ";")
-		for _, part := range parts {
+		for part := range parts {
 			part = strings.TrimSpace(part)
-			if strings.HasPrefix(part, "host=") {
+			if host, found := strings.CutPrefix(part, "host="); found {
-				return strings.TrimPrefix(part, "host=")
+				return host
 			}
 		}
 	}
@@ -267,29 +280,23 @@ func getHost(r *http.Request) string {
 }
 
 func getProtocol(r *http.Request) string {
-	// Check X-Forwarded-Proto (common proxy header)
 	if proto := r.Header.Get("X-Forwarded-Proto"); proto != "" {
 		return proto
 	}
 
-	// Check standard Forwarded header (RFC 7239)
 	if forwarded := r.Header.Get("Forwarded"); forwarded != "" {
-		// Parse "Forwarded: for=...; proto=https; host=..."
+		parts := strings.SplitSeq(forwarded, ";")
-		parts := strings.Split(forwarded, ";")
+		for part := range parts {
-		for _, part := range parts {
 			part = strings.TrimSpace(part)
-			if strings.HasPrefix(part, "proto=") {
+			if proto, found := strings.CutPrefix(part, "proto="); found {
-				return strings.TrimPrefix(part, "proto=")
+				return proto
 			}
 		}
 	}
 
-	// Check X-Forwarded-SSL (some proxies use this)
 	if ssl := r.Header.Get("X-Forwarded-SSL"); ssl == "on" {
 		return "https"
 	}
-
-	// Check if connection is TLS
 	if r.TLS != nil {
 		return "https"
 	}
@@ -298,28 +305,10 @@ func getProtocol(r *http.Request) string {
 }
 
 func detectContentType(filename string) string {
-	ext := strings.ToLower(filepath.Ext(filename))
+	ext := filepath.Ext(filename)
-	types := map[string]string{
+	mimeType := mime.TypeByExtension(ext)
-		".txt":  "text/plain",
+	if mimeType == "" {
-		".html": "text/html",
+		return mimeType
-		".css":  "text/css",
-		".js":   "application/javascript",
-		".json": "application/json",
-		".xml":  "application/xml",
-		".pdf":  "application/pdf",
-		".zip":  "application/zip",
-		".jpg":  "image/jpeg",
-		".jpeg": "image/jpeg",
-		".png":  "image/png",
-		".gif":  "image/gif",
-		".svg":  "image/svg+xml",
-		".mp3":  "audio/mpeg",
-		".mp4":  "video/mp4",
-		".webm": "video/webm",
-	}
-
-	if ct, ok := types[ext]; ok {
-		return ct
 	}
 	return "application/octet-stream"
 }