How can I manually configure *resty.Request.RawRequest.ContentLength?

[BoneAsh]

go 1.23.6
resty v3

I tested it using the net/http package, and when I send an HTTP request with the body as an io.Reader type, setting the Content-Length in the header does not work. I need to set req.ContentLength directly.

util.MyReader is a custom struct that implements the io.Reader interface, specifically the Read(p []byte) (n int, err error) method.

req, err := http.NewRequest("PUT", url, &util.MyReader{Data: []byte{0x00, 0x00}})
if err != nil {
	panic(err)
}

req.ContentLength = 2 // it works
#req.Header.Set("Content-Length", "2")  // it does not work

resp, err := client.Do(req)
if err != nil {
	panic(err)
}
defer resp.Body.Close()
body, err := io.ReadAll(resp.Body)
if err != nil {
	panic(err)
}

[BoneAsh]

Typically, net/http will also automatically set req.ContentLength, but this is limited to when the body type is *bytes.Buffer, *bytes.Reader, or *strings.Reader.
net/http/request.go#L923

if body != nil {
switch v := body.(type) {
case *bytes.Buffer:
	req.ContentLength = int64(v.Len())
	buf := v.Bytes()
	req.GetBody = func() (io.ReadCloser, error) {
		r := bytes.NewReader(buf)
		return io.NopCloser(r), nil
	}
case *bytes.Reader:
	req.ContentLength = int64(v.Len())
	snapshot := *v
	req.GetBody = func() (io.ReadCloser, error) {
		r := snapshot
		return io.NopCloser(&r), nil
	}
case *strings.Reader:
	req.ContentLength = int64(v.Len())
	snapshot := *v
	req.GetBody = func() (io.ReadCloser, error) {
		r := snapshot
		return io.NopCloser(&r), nil
	}
default:
	// This is where we'd set it to -1 (at least
	// if body != NoBody) to mean unknown, but
	// that broke people during the Go 1.8 testing
	// period. People depend on it being 0 I
	// guess. Maybe retry later. See Issue 18117.
}
// For client requests, Request.ContentLength of 0
// means either actually 0, or unknown. The only way
// to explicitly say that the ContentLength is zero is
// to set the Body to nil. But turns out too much code
// depends on NewRequest returning a non-nil Body,
// so we use a well-known ReadCloser variable instead
// and have the http package also treat that sentinel
// variable to mean explicitly zero.
if req.GetBody != nil && req.ContentLength == 0 {
	req.Body = NoBody
	req.GetBody = func() (io.ReadCloser, error) { return NoBody, nil }
}

[jeevatkm]

@BoneAsh Thanks for trying out v3 and sharing your feedback.

Typically, net/http will also automatically set req.ContentLength, but this is limited to when the body type is *bytes.Buffer, *bytes.Reader, or *strings.Reader.

This is true for Resty v3

---

Regarding the Content-Length value, I will validate the resty v3 and get back to you.

[jeevatkm]

@BoneAsh, I’ve identified the root cause. It’s a side effect of removing the v2 flow. I’ll add the new content-length flow for explicit setting of a value. Once ready, you could try the branch before I create a PR.

[jeevatkm]

@BoneAsh The implementation is available in this branch set-content-length. Can you try it out with various approaches and share your feedback on content length?

[BoneAsh]

@BoneAsh The implementation is available in this branch set-content-length. Can you try it out with various approaches and share your feedback on content length?

ok, I will try it out.

[BoneAsh]

This issue has been fixed. I used the Resty library to call the PUT method to upload file slices to MinIO, and the body uses my own implementation of *io.Reader. The Content-Length value is already set in the headers. Thank you very much! You can merge this modification into the main branch of version 3. @jeevatkm

[jeevatkm]

@BoneAsh Thanks for the feedback. I need to do some final touches before the PR creation.