feat: try to get content length with zero copy

[murasakiakari]

No description provided.

[murasakiakari]

@chripo
here is the fix for the previous issue
Thank you for your reviewing

[jkowalski]

this is probably slightly incorrect as the reader could be at a position other than zero:

I think you need to:

1. startPos, err = reader.Seek(0, io.SeekCurrent) to determine the current position
2. totalLength, err = reader.Seek(0, io.SeekEnd) to determine the length entire stream
3. reader.Seek(0, startPos) to restore the original starting position.
4. return totalLength - startPos - this is how many bytes are remaining

[jkowalski]

zero is a valid length for some transfers, this should probably return -1 to indicate the length is unknown or return additional bool

[murasakiakari]

@jkowalski
Thank you for your idea, I have made the changes on getContentLength logic, feel free to take a review

[murasakiakari]

The branch for bytes.Reader and strings.Reader are removed because they have implemented io.Seeker

[chripo]

thanks for the collaboration!
lgtm.
could you please add some tests?

[jkowalski]

I think you still need to modify c.put to ignore -1 content lengths (and not set the ContentLength field at all). You may also have to have special-case for zero-length buffer.

For the testing I would recommend trying the following case:

• reader is bytes.Buffer
• reader is bytes.NewReader()
• another reader does not support io.Seeker
• custom request that does support io.Seeker

For each implementation try different lengths:

Try the length of zero and make sure it is explicitly passed as Content-Length: 0 when length Is known and not set at all if length is unknown

Try some non-zero determinate and non-determinate lengths and make sure Content-Length is set accordingly.

bonus points if you can also try a very large stream of 1GB without a length to make sure it's never loaded into memory and streamed all the way to the server.

[murasakiakari]

Thank for your idea, I will implement it in these days