diff --git a/ext/twitter/main.go b/ext/twitter/main.go
index 205bb6e..5b6d921 100644
--- a/ext/twitter/main.go
+++ b/ext/twitter/main.go
@@ -173,17 +173,22 @@ func GetTweetAPI(
 	if resp.StatusCode != http.StatusOK {
 		return nil, fmt.Errorf("invalid response code: %s", resp.Status)
 	}
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read body: %w", err)
+	}
 
 	var apiResponse APIResponse
-	decoder := sonic.ConfigFastest.NewDecoder(resp.Body)
-	err = decoder.Decode(&apiResponse)
+	err = sonic.ConfigFastest.Unmarshal(body, &apiResponse)
 	if err != nil {
 		return nil, fmt.Errorf("failed to parse response: %w", err)
 	}
+
 	result := apiResponse.Data.TweetResult.Result
 	if result == nil {
 		return nil, errors.New("failed to get tweet result")
 	}
+
 	var tweet *Tweet
 	if result.Tweet != nil {
 		tweet = result.Tweet
diff --git a/util/download.go b/util/download.go
index e66d789..0149904 100644
--- a/util/download.go
+++ b/util/download.go
@@ -55,7 +55,6 @@ func DownloadFile(
 		case <-ctx.Done():
 			return "", ctx.Err()
 		default:
-			// create the download directory if it doesn't exist
 			if err := EnsureDownloadDir(config.DownloadDir); err != nil {
 				return "", err
 			}
@@ -184,26 +183,35 @@ func downloadInMemory(
 		return nil, fmt.Errorf("file too large for in-memory download: %d bytes", resp.ContentLength)
 	}
 
-	var bufPool = sync.Pool{
-		New: func() any {
-			return bytes.NewBuffer(make([]byte, 0, 1024*1024))
-		},
-	}
-
-	buf := bufPool.Get().(*bytes.Buffer)
-	buf.Reset()
-	defer bufPool.Put(buf)
-
+	// allocate a single buffer with the
+	// correct size upfront to prevent reallocations
+	var data []byte
 	if resp.ContentLength > 0 {
-		buf.Grow(int(resp.ContentLength))
+		data = make([]byte, 0, resp.ContentLength)
+	} else {
+		// 64KB initial capacity
+		data = make([]byte, 0, 64*1024)
 	}
 
-	_, err = io.Copy(buf, resp.Body)
-	if err != nil {
-		return nil, fmt.Errorf("failed to read response body: %w", err)
+	// use a limited reader to prevent
+	// exceeding memory limits even if content-length is wrong
+	limitedReader := io.LimitReader(resp.Body, int64(config.MaxInMemory))
+
+	buf := make([]byte, 32*1024) // 32KB buffer
+	for {
+		n, err := limitedReader.Read(buf)
+		if n > 0 {
+			data = append(data, buf[:n]...)
+		}
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return nil, fmt.Errorf("failed to read response body: %w", err)
+		}
 	}
 
-	return buf.Bytes(), nil
+	return data, nil
 }
 
 func EnsureDownloadDir(dir string) error {
@@ -252,12 +260,15 @@ func runChunkedDownload(
 		}
 	}
 
-	chunks := createChunks(fileSize, config.ChunkSize)
+	numChunks := 1
+	if fileSize > 0 {
+		numChunks = int(math.Ceil(float64(fileSize) / float64(config.ChunkSize)))
+	}
 
 	semaphore := make(chan struct{}, config.Concurrency)
 	var wg sync.WaitGroup
 
-	errChan := make(chan error, len(chunks))
+	errChan := make(chan error, numChunks)
 	var downloadErr error
 	var errOnce sync.Once
 
@@ -267,12 +278,22 @@ func runChunkedDownload(
 	downloadCtx, cancelDownload := context.WithCancel(ctx)
 	defer cancelDownload()
 
-	for idx, chunk := range chunks {
+	// use a mutex to synchronize file access
+	var fileMutex sync.Mutex
+
+	for i := range numChunks {
 		wg.Add(1)
 
-		go func(idx int, chunk [2]int) {
+		go func(chunkIndex int) {
 			defer wg.Done()
 
+			// calculate chunk bounds
+			start := chunkIndex * config.ChunkSize
+			end := start + config.ChunkSize - 1
+			if end >= fileSize && fileSize > 0 {
+				end = fileSize - 1
+			}
+
 			// respect concurrency limit
 			select {
 			case semaphore <- struct{}{}:
@@ -281,36 +302,31 @@ func runChunkedDownload(
 				return
 			}
 
-			chunkData, err := downloadChunkWithRetry(downloadCtx, fileURL, chunk, config)
+			err := downloadChunkToFile(
+				downloadCtx, fileURL,
+				file, start, end,
+				config, &fileMutex,
+			)
 			if err != nil {
 				errOnce.Do(func() {
-					downloadErr = fmt.Errorf("chunk %d: %w", idx, err)
+					downloadErr = fmt.Errorf("chunk %d: %w", chunkIndex, err)
 					cancelDownload() // cancel all other downloads
 					errChan <- downloadErr
 				})
 				return
 			}
 
-			if err := writeChunkToFile(file, chunkData, chunk[0]); err != nil {
-				errOnce.Do(func() {
-					downloadErr = fmt.Errorf("failed to write chunk %d: %w", idx, err)
-					cancelDownload()
-					errChan <- downloadErr
-				})
-				return
-			}
-
 			// update progress
-			chunkSize := chunk[1] - chunk[0] + 1
+			chunkSize := end - start + 1
 			completedChunks.Add(1)
 			completedBytes.Add(int64(chunkSize))
-			progress := float64(completedBytes.Load()) / float64(fileSize)
-
-			// report progress if handler exists
-			if config.ProgressUpdater != nil {
-				config.ProgressUpdater(progress)
+			if fileSize > 0 {
+				progress := float64(completedBytes.Load()) / float64(fileSize)
+				if config.ProgressUpdater != nil {
+					config.ProgressUpdater(progress)
+				}
 			}
-		}(idx, chunk)
+		}(i)
 	}
 
 	done := make(chan struct{})
@@ -352,7 +368,11 @@ func runChunkedDownload(
 	return nil
 }
 
-func getFileSize(ctx context.Context, fileURL string, timeout time.Duration) (int, error) {
+func getFileSize(
+	ctx context.Context,
+	fileURL string,
+	timeout time.Duration,
+) (int, error) {
 	reqCtx, cancel := context.WithTimeout(ctx, timeout)
 	defer cancel()
 
@@ -374,12 +394,15 @@ func getFileSize(ctx context.Context, fileURL string, timeout time.Duration) (in
 	return int(resp.ContentLength), nil
 }
 
-func downloadChunkWithRetry(
+func downloadChunkToFile(
 	ctx context.Context,
 	fileURL string,
-	chunk [2]int,
+	file *os.File,
+	start int,
+	end int,
 	config *models.DownloadConfig,
-) ([]byte, error) {
+	fileMutex *sync.Mutex,
+) error {
 	var lastErr error
 
 	for attempt := 0; attempt <= config.RetryAttempts; attempt++ {
@@ -387,20 +410,72 @@ func downloadChunkWithRetry(
 			// wait before retry
 			select {
 			case <-ctx.Done():
-				return nil, ctx.Err()
+				return ctx.Err()
 			case <-time.After(config.RetryDelay):
 			}
 		}
 
-		data, err := downloadChunk(ctx, fileURL, chunk, config.Timeout)
+		err := downloadAndWriteChunk(
+			ctx, fileURL, file,
+			start, end, config.Timeout,
+			fileMutex,
+		)
 		if err == nil {
-			return data, nil
+			return nil
 		}
 
 		lastErr = err
 	}
 
-	return nil, fmt.Errorf("all %d attempts failed: %w", config.RetryAttempts+1, lastErr)
+	return fmt.Errorf("all %d attempts failed: %w", config.RetryAttempts+1, lastErr)
+}
+
+func downloadAndWriteChunk(
+	ctx context.Context,
+	fileURL string,
+	file *os.File,
+	start int,
+	end int,
+	timeout time.Duration,
+	fileMutex *sync.Mutex,
+) error {
+	reqCtx, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+
+	req, err := http.NewRequestWithContext(reqCtx, http.MethodGet, fileURL, nil)
+	if err != nil {
+		return fmt.Errorf("failed to create request: %w", err)
+	}
+
+	req.Header.Add("Range", fmt.Sprintf("bytes=%d-%d", start, end))
+
+	resp, err := downloadHTTPSession.Do(req)
+	if err != nil {
+		return fmt.Errorf("download failed: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusPartialContent && resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("unexpected status code: %d", resp.StatusCode)
+	}
+
+	// use a fixed-size buffer for
+	// copying to avoid large allocations (32KB)
+	buf := make([]byte, 32*1024)
+
+	fileMutex.Lock()
+	defer fileMutex.Unlock()
+
+	if _, err := file.Seek(int64(start), io.SeekStart); err != nil {
+		return fmt.Errorf("failed to seek file: %w", err)
+	}
+
+	_, err = io.CopyBuffer(file, resp.Body, buf)
+	if err != nil {
+		return fmt.Errorf("failed to write chunk data: %w", err)
+	}
+
+	return nil
 }
 
 func downloadFile(
@@ -421,85 +496,28 @@ func downloadFile(
 		return "", fmt.Errorf("failed to download file: %w", err)
 	}
 	defer resp.Body.Close()
+
 	if resp.StatusCode != http.StatusOK {
 		return "", fmt.Errorf("unexpected status code: %d", resp.StatusCode)
 	}
+
 	file, err := os.Create(filePath)
 	if err != nil {
 		return "", fmt.Errorf("failed to create file: %w", err)
 	}
 	defer file.Close()
-	_, err = io.Copy(file, resp.Body)
+
+	// use a fixed-size buffer for
+	// copying to avoid large allocations (32KB)
+	buf := make([]byte, 32*1024)
+	_, err = io.CopyBuffer(file, resp.Body, buf)
 	if err != nil {
 		return "", fmt.Errorf("failed to write file: %w", err)
 	}
+
 	return filePath, nil
 }
 
-func downloadChunk(
-	ctx context.Context,
-	fileURL string,
-	chunk [2]int,
-	timeout time.Duration,
-) ([]byte, error) {
-	reqCtx, cancel := context.WithTimeout(ctx, timeout)
-	defer cancel()
-
-	req, err := http.NewRequestWithContext(reqCtx, http.MethodGet, fileURL, nil)
-	if err != nil {
-		return nil, fmt.Errorf("failed to create request: %w", err)
-	}
-	req.Header.Add("Range", fmt.Sprintf("bytes=%d-%d", chunk[0], chunk[1]))
-
-	resp, err := downloadHTTPSession.Do(req)
-	if err != nil {
-		return nil, fmt.Errorf("download failed: %w", err)
-	}
-	defer resp.Body.Close()
-
-	if resp.StatusCode != http.StatusPartialContent && resp.StatusCode != http.StatusOK {
-		return nil, fmt.Errorf("unexpected status code: %d", resp.StatusCode)
-	}
-
-	var buf bytes.Buffer
-	if resp.ContentLength > 0 {
-		buf.Grow(int(resp.ContentLength))
-	} else {
-		buf.Grow(chunk[1] - chunk[0] + 1)
-	}
-	_, err = io.Copy(&buf, resp.Body)
-	if err != nil {
-		return nil, fmt.Errorf("failed to read chunk data: %w", err)
-	}
-
-	return buf.Bytes(), nil
-}
-
-func writeChunkToFile(file *os.File, data []byte, offset int) error {
-	_, err := file.WriteAt(data, int64(offset))
-	return err
-}
-
-func createChunks(fileSize int, chunkSize int) [][2]int {
-	if fileSize <= 0 {
-		return [][2]int{{0, 0}}
-	}
-
-	numChunks := int(math.Ceil(float64(fileSize) / float64(chunkSize)))
-	chunks := make([][2]int, numChunks)
-
-	for i := range chunks {
-		start := i * chunkSize
-		end := start + chunkSize - 1
-		if end >= fileSize {
-			end = fileSize - 1
-		}
-		chunks[i] = [2]int{start, end}
-	}
-
-	return chunks
-}
-
 func downloadSegments(
 	ctx context.Context,
 	path string,