Repository: opensearch-project/opensearch-go (go)
Issue: [BUG] Error http: ContentLength=401 with Body length 0
### What is the bug?
I'm getting lots of these errors when indexing documents into a data stream:
`http: ContentLength=401 with Body length 0`

### How can one reproduce the bug?
Here's my code:
```go
func (logger *MyLogger) SendLogEvent(event *MyLogEvent) error {
	// Marshal the struct
	s, err := json.Marshal(event)
	if err != nil {
		return WrapError("failed to marshal log event", err)
	}
	// Do the request
	req, err := opensearchapi.IndexReq{
		Index: logger.logsIndexName,
		Body: bytes.NewReader(s),
	}.GetRequest()
	if err != nil {
		return WrapError("failed to create OpenSearch index request", err)
	}
	resp, err := logger.client.Perform(req)
	// Make sure to close the body so the connection can be reused
	if resp != nil && resp.Body != nil {
		defer resp.Body.Close()
	}
	if resp == nil {
		return err
	}
	if err != nil || resp.StatusCode != 201 {
		// Log the error
		return errors.New("failed to log event, statuscode " + resp.Status)
	}
	// Still read the body so the connection can be reused
	io.Copy(io.Discard, resp.Body)
	// Success
	return nil
}
```

### What is the expected behavior?
No error.

### What is your host/environment?
Debian 12 and Linux Mint 21.3
opensearch-go v4.0.0

### Do you have any screenshots?

### Do you have any additional context?

Pull request description: Fix empty request body on retries with compression enabled
### Description
Make the transport use a new reader for each retry when gzip compression is enabled.
Also be more explicit about doing so for non-compressed requests.
Test included.

### Issues Resolved
Closes #541.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check [here](https://github.com/opensearch-project/OpenSearch/blob/main/CONTRIBUTING.md#developer-certificate-of-origin).


Patch:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 60d3579..9f648ee 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,8 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 ### Fixed
 
+- Fixes empty request body on retry with compression enabled ([#543](https://github.com/opensearch-project/opensearch-go/pull/543))
+
 ### Security
 
 ### Dependencies
diff --git a/opensearchtransport/opensearchtransport.go b/opensearchtransport/opensearchtransport.go
index ac8ad05..c93b2cd 100644
--- a/opensearchtransport/opensearchtransport.go
+++ b/opensearchtransport/opensearchtransport.go
@@ -245,7 +245,9 @@ func (c *Client) Perform(req *http.Request) (*http.Response, error) {
 			}
 
 			req.GetBody = func() (io.ReadCloser, error) {
-				return io.NopCloser(buf), nil
+				// We have to return a new reader each time so that retries don't read from an already-consumed body.
+				reader := bytes.NewReader(buf.Bytes())
+				return io.NopCloser(reader), nil
 			}
 			//nolint:errcheck // error is always nil
 			req.Body, _ = req.GetBody()
@@ -258,8 +260,9 @@ func (c *Client) Perform(req *http.Request) (*http.Response, error) {
 				//nolint:errcheck // ignored as this is only for logging
 				buf.ReadFrom(req.Body)
 				req.GetBody = func() (io.ReadCloser, error) {
-					r := buf
-					return io.NopCloser(&r), nil
+					// Return a new reader each time
+					reader := bytes.NewReader(buf.Bytes())
+					return io.NopCloser(reader), nil
 				}
 				//nolint:errcheck // error is always nil
 				req.Body, _ = req.GetBody()


Test patch:
diff --git a/opensearchtransport/opensearchtransport_internal_test.go b/opensearchtransport/opensearchtransport_internal_test.go
index fbe1f26..6daaeba 100644
--- a/opensearchtransport/opensearchtransport_internal_test.go
+++ b/opensearchtransport/opensearchtransport_internal_test.go
@@ -689,6 +689,47 @@ func TestTransportPerformRetries(t *testing.T) {
 		}
 	})
 
+	t.Run("Reset request body during retry with request body compression", func(t *testing.T) {
+		var bodies []string
+		u, _ := url.Parse("https://foo.com/bar")
+		tp, _ := New(
+			Config{
+				URLs:                []*url.URL{u},
+				CompressRequestBody: true,
+				Transport: &mockTransp{
+					RoundTripFunc: func(req *http.Request) (*http.Response, error) {
+						body, err := io.ReadAll(req.Body)
+						if err != nil {
+							panic(err)
+						}
+						bodies = append(bodies, string(body))
+						return &http.Response{Status: "MOCK", StatusCode: http.StatusBadGateway}, nil
+					},
+				},
+			},
+		)
+
+		foobar := "FOOBAR"
+		foobarGzipped := "\x1f\x8b\b\x00\x00\x00\x00\x00\x00\xffr\xf3\xf7wr\f\x02\x04\x00\x00\xff\xff\x13\xd8\x0en\x06\x00\x00\x00"
+
+		req, _ := http.NewRequest(http.MethodPost, "/abc", strings.NewReader(foobar))
+		//nolint:bodyclose // Mock response does not have a body to close
+		res, err := tp.Perform(req)
+		if err != nil {
+			t.Fatalf("Unexpected error: %s", err)
+		}
+		_ = res
+
+		if n := len(bodies); n != 4 {
+			t.Fatalf("expected 4 requests, got %d", n)
+		}
+		for i, body := range bodies {
+			if body != foobarGzipped {
+				t.Fatalf("request %d body: expected %q, got %q", i, foobarGzipped, body)
+			}
+		}
+	})
+
 	t.Run("Don't retry request on regular error", func(t *testing.T) {
 		var i int