Fix 500 Internal Server Error on empty files. (#189)

* Fix 500 Internal Server Error on empty files.

* Fixes #187.

* Gofmt.

* Remove unnecessary set to zero.

* Fix etag on empty files. Prevent setting content type on zero-sized bodies.

Author: patrickdappollonio

internal/middlewares/etag.go

@@ -64,7 +64,7 @@ func Etag(enabled bool, maxBodySize int64) func(http.Handler) http.Handler {
 				}
 
 				// Only proceed if the response was fully buffered and status code is in the 200 range.
-				if rw.size <= rw.maxSize && rw.err == nil && rw.statusCode >= 200 && rw.statusCode < 300 {
+				if rw.size > 0 && rw.size <= rw.maxSize && rw.err == nil && rw.statusCode >= 200 && rw.statusCode < 300 {
 					// Compute the ETag.
 					etag := fmt.Sprintf("\"%x\"", hasher.Sum(nil))
 					// Set the ETag header.

internal/server/handlers.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
+	"io"
 	"net/http"
 	"os"
 	"path"
@@ -305,31 +306,35 @@ func (s *Server) serveFile(statusCode int, location string, w http.ResponseWrite
 	}
 
 	var data [512]byte
-	if _, err := f.Read(data[:]); err != nil {
+	n, err := f.Read(data[:])
+	if err != nil && !errors.Is(err, io.EOF) {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}
 
-	if contentType == "" {
-		if local := http.DetectContentType(data[:]); local != "application/octet-stream" {
+	// Only detect content type if we have content to examine
+	if contentType == "" && n > 0 {
+		if local := http.DetectContentType(data[:n]); local != "application/octet-stream" {
 			contentType = local
 		}
 	}
 
+	// Only attempt charset detection if we have content to examine
 	charset := ""
-	if utf8.Valid(data[:]) {
-		charset = "utf-8"
-	}
-
-	if charset == "" {
-		res, err := chardet.NewTextDetector().DetectBest(data[:])
-		if err == nil && res.Confidence > 50 && res.Charset != "" {
-			charset = res.Charset
+	if n > 0 && contentType != "" && !strings.HasPrefix(contentType, "application/octet-stream") {
+		if utf8.Valid(data[:n]) {
+			charset = "utf-8"
+		} else {
+			res, err := chardet.NewTextDetector().DetectBest(data[:n])
+			if err == nil && res.Confidence > 50 && res.Charset != "" {
+				charset = res.Charset
+			}
 		}
 	}
 
-	if contentType != "" && contentType != "application/octet-stream" {
-		if charset != "" {
+	if contentType != "" {
+		// Add charset for text-based content types only
+		if charset != "" && contentType != "application/octet-stream" {
 			contentType += "; charset=" + charset
 		}
 
@@ -342,6 +347,12 @@ func (s *Server) serveFile(statusCode int, location string, w http.ResponseWrite
 		w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=%q", filename))
 	}
 
+	// Reset file position to beginning after reading first bytes for content detection
+	if _, err := f.Seek(0, io.SeekStart); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
 	// Check if the caller changed the status code, if not, simply call
 	// the appropriate handler/
 	if statusCode == 0 {