feat: default http User-Agent header (#26)

internal/protocol/http/fetcher.go

@@ -428,6 +428,9 @@ func buildRequest(ctx context.Context, req *base.Request) (httpReq *http.Request
 			body = bytes.NewBufferString(extra.Body)
 		}
 	}
+	if _, ok := headers[base.HttpHeaderUserAgent]; !ok {
+		headers[base.HttpHeaderUserAgent] = []string{base.AgentName}
+	}
 
 	if ctx != nil {
 		httpReq, err = http.NewRequestWithContext(ctx, method, url.String(), body)

pkg/base/constants.go

@@ -19,6 +19,11 @@ const (
 	HttpHeaderContentLength      = "Content-Length"
 	HttpHeaderContentRange       = "Content-Range"
 	HttpHeaderContentDisposition = "Content-Disposition"
+	HttpHeaderUserAgent          = "User-Agent"
 
 	HttpHeaderRangeFormat = "bytes=%d-%d"
 )
+
+const (
+	AgentName = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/116.0.0.0 Safari/537.36"
+)