From 54c10befb23309271fce8822be3bb64d0f119f21 Mon Sep 17 00:00:00 2001
From: Bagas Aulia Rezki <bagas@fossy.my.id>
Date: Fri, 13 Sep 2024 21:36:26 +0700
Subject: [PATCH] Add range-based partial download support

---
 handler/download/file/file.go | 99 ++++++++++++++++++++++++++++++++---
 1 file changed, 91 insertions(+), 8 deletions(-)

diff --git a/handler/download/file/file.go b/handler/download/file/file.go
index 5d9204a..5e48442 100644
--- a/handler/download/file/file.go
+++ b/handler/download/file/file.go
@@ -3,50 +3,133 @@ package downloadFileHandler
 import (
 	"fmt"
 	"github.com/fossyy/filekeeper/app"
+	"github.com/fossyy/filekeeper/types/models"
 	"io"
 	"net/http"
 	"os"
 	"path/filepath"
+	"strconv"
+	"strings"
 )
 
 func GET(w http.ResponseWriter, r *http.Request) {
 	fileID := r.PathValue("id")
 	file, err := app.Server.Database.GetFile(fileID)
 	if err != nil {
-		w.WriteHeader(http.StatusInternalServerError)
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
 		app.Server.Logger.Error(err.Error())
 		return
 	}
 
 	uploadDir := "uploads"
-
 	currentDir, _ := os.Getwd()
 	basePath := filepath.Join(currentDir, uploadDir)
 	saveFolder := filepath.Join(basePath, file.OwnerID.String(), file.ID.String())
 
 	if filepath.Dir(saveFolder) != filepath.Join(basePath, file.OwnerID.String()) {
+		http.Error(w, "Invalid Path", http.StatusInternalServerError)
 		app.Server.Logger.Error("invalid path")
-		w.WriteHeader(http.StatusInternalServerError)
 		return
 	}
 
+	rangeHeader := r.Header.Get("Range")
+	if rangeHeader != "" {
+		rangeParts := strings.Split(strings.TrimPrefix(rangeHeader, "bytes="), "-")
+		if len(rangeParts) == 2 {
+			start, err := strconv.ParseInt(rangeParts[0], 10, 64)
+			if err != nil {
+				http.Error(w, "Invalid Range", http.StatusRequestedRangeNotSatisfiable)
+				return
+			}
+			end := int64(file.Size - 1)
+			if rangeParts[1] != "" {
+				end, err = strconv.ParseInt(rangeParts[1], 10, 64)
+				if err != nil {
+					http.Error(w, "Invalid Range", http.StatusRequestedRangeNotSatisfiable)
+					return
+				}
+			}
+
+			if end >= int64(file.Size) {
+				end = int64(file.Size - 1)
+			}
+
+			w.Header().Set("Content-Range", fmt.Sprintf("bytes %d-%d/%d", start, end, file.Size))
+			w.Header().Set("Content-Length", fmt.Sprintf("%d", end-start+1))
+			w.WriteHeader(http.StatusPartialContent)
+			sendFileChunk(w, saveFolder, file, start, end)
+			return
+		}
+	}
+
 	w.Header().Set("Content-Disposition", "attachment; filename="+file.Name)
 	w.Header().Set("Content-Type", "application/octet-stream")
-	for i := 0; i <= int(file.TotalChunk)-1; i++ {
-		chunkPath := filepath.Join(saveFolder, file.Name, fmt.Sprintf("chunk_%d", i))
+	w.Header().Set("Accept-Ranges", "bytes")
+	w.Header().Set("Content-Length", fmt.Sprintf("%d", file.Size))
 
+	sendFileChunk(w, saveFolder, file, 0, int64(file.Size-1))
+}
+
+func sendFileChunk(w http.ResponseWriter, saveFolder string, file *models.File, start, end int64) {
+	chunkSize := int64(2 * 1024 * 1024)
+
+	startChunk := start / chunkSize
+	endChunk := end / chunkSize
+
+	startOffset := start % chunkSize
+	endOffset := end % chunkSize
+
+	for i := startChunk; i <= endChunk; i++ {
+		chunkPath := filepath.Join(saveFolder, file.Name, fmt.Sprintf("chunk_%d", i))
 		chunkFile, err := os.Open(chunkPath)
 		if err != nil {
 			http.Error(w, fmt.Sprintf("Error opening chunk: %v", err), http.StatusInternalServerError)
 			app.Server.Logger.Error(err.Error())
 			return
 		}
-		_, err = io.Copy(w, chunkFile)
-		chunkFile.Close()
+		defer chunkFile.Close()
+
+		var chunkStart, chunkEnd int64
+		if i == startChunk {
+			chunkStart = startOffset
+		} else {
+			chunkStart = 0
+		}
+		if i == endChunk {
+			chunkEnd = endOffset
+		} else {
+			chunkEnd = chunkSize - 1
+		}
+
+		_, err = chunkFile.Seek(chunkStart, io.SeekStart)
 		if err != nil {
-			http.Error(w, fmt.Sprintf("Error writing chunk: %v", err), http.StatusInternalServerError)
+			http.Error(w, fmt.Sprintf("Error seeking chunk: %v", err), http.StatusInternalServerError)
 			app.Server.Logger.Error(err.Error())
 			return
 		}
+
+		buffer := make([]byte, 2048)
+		toSend := chunkEnd - chunkStart + 1
+		for toSend > 0 {
+			n, err := chunkFile.Read(buffer)
+			if err != nil && err != io.EOF {
+				http.Error(w, fmt.Sprintf("Error reading chunk: %v", err), http.StatusInternalServerError)
+				app.Server.Logger.Error(err.Error())
+				return
+			}
+			if n == 0 {
+				break
+			}
+			if int64(n) > toSend {
+				n = int(toSend)
+			}
+			_, err = w.Write(buffer[:n])
+			if err != nil {
+				http.Error(w, fmt.Sprintf("Error writing chunk: %v", err), http.StatusInternalServerError)
+				app.Server.Logger.Error(err.Error())
+				return
+			}
+			toSend -= int64(n)
+		}
 	}
 }