fix: buffer multipart upload body to include Content-Length header

Max Bot API requires Content-Length for file uploads, returning HTTP 406
"File size is unknown" when streaming via io.Pipe. Replaced pipe-based
streaming with in-memory buffering via bytes.Buffer.

Author: Saveliy Yudin

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## [v0.2.1] - 2026-02-15
+
+### Fixed
+- **Upload Content-Length**: `doUpload` now buffers multipart body in memory instead of streaming via `io.Pipe` — the Max Bot API requires a `Content-Length` header, which was missing with pipe-based streaming (HTTP 406: "File size is unknown")
+
 ## [v0.2.0] - 2026-02-14
 
 ### Fixed

client.go

@@ -129,24 +129,21 @@ func (c *Client) doUpload(ctx context.Context, op, uploadURL, filename string, r
 		defer cancel()
 	}
 
-	pr, pw := io.Pipe()
-	defer pr.Close() // ensure cleanup on all exit paths
-	writer := multipart.NewWriter(pw)
+	var buf bytes.Buffer
+	writer := multipart.NewWriter(&buf)
 
-	go func() {
-		part, err := writer.CreateFormFile("data", filename)
-		if err != nil {
-			pw.CloseWithError(err)
-			return
-		}
-		if _, err := io.Copy(part, reader); err != nil {
-			pw.CloseWithError(err)
-			return
-		}
-		pw.CloseWithError(writer.Close())
-	}()
+	part, err := writer.CreateFormFile("data", filename)
+	if err != nil {
+		return nil, networkError(op, fmt.Errorf("create form file: %w", err))
+	}
+	if _, err := io.Copy(part, reader); err != nil {
+		return nil, networkError(op, fmt.Errorf("copy file data: %w", err))
+	}
+	if err := writer.Close(); err != nil {
+		return nil, networkError(op, fmt.Errorf("close multipart writer: %w", err))
+	}
 
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost, uploadURL, pr)
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, uploadURL, &buf)
 	if err != nil {
 		return nil, networkError(op, fmt.Errorf("create upload request: %w", err))
 	}