Support zero length uploads

[bluetianx]

if UploadLength is set to zero without setting IsUploadDeferLength to true, is this case reasonable in Creation of Protocol Extensions? I do not find detail about that

[Acconut]

Yes, Upload-Length can be 0. The spec only requires the header to be non-negative, so 0 is explicitly included.

The Upload-Length request and response header indicates the size of the entire upload in bytes. The value MUST be a non-negative integer.

[bluetianx]

The spec only requires the header to be non-negative

I can not find it in Creation of Protocol Extensions, but I can see it in Patch Protocol. Shall we fill it in Creation of Protocol Extensions?

[Acconut]

I can not find it in Creation of Protocol Extensions, but I can see it in Patch Protocol. Shall we fill it in Creation of Protocol Extensions?

We can add a statement to explain that zero-length uploads are explicitly allowed, yes.

[Acconut]

@bluetianx Would the changes in #197 have helped you understand this?

[bluetianx]

For sure, Thank you @Acconut