Reva create error when upload empty file when TUS is enabled

[JarCz]

I tried to upload empty file to Reva when TUS is enabled.
It’s necessary because JupyterLab try to upload empty file when create new file.

Riva version: commit 55bfeb6
Default config from: examples/ocmd/ocmd-server-1.toml

Step to reproduce:

touch zero.txt
echo "Test" > non_zero.txt
./reva --insecure login basic

Creates an error:

./reva --insecure upload ./zero.txt /home/zero.txt
Local file size: 0 bytes
Data server: http://localhost:19001/data/da4b3114-672d-4bf7-9495-484e41816973
Allowed checksums: [type:RESOURCE_CHECKSUM_TYPE_MD5 priority:100  type:RESOURCE_CHECKSUM_TYPE_UNSET priority:1000 ]
Checksum selected: RESOURCE_CHECKSUM_TYPE_MD5
Local XS: RESOURCE_CHECKSUM_TYPE_MD5:d41d8cd98f00b204e9800998ecf8427e
 0 B / ? [------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------=] 0s
error: code=CODE_NOT_FOUND msg="file not found" support_trace="ec271773afd25787ea2b3b5ca7d6d688"

It’s works:

./reva --insecure upload ./non_zero.txt /home/non_zero.txt
Local file size: 5 bytes
Data server: http://localhost:19001/data/5e159493-7bf0-4aed-8f6f-b27ead52ad7f
Allowed checksums: [type:RESOURCE_CHECKSUM_TYPE_MD5 priority:100  type:RESOURCE_CHECKSUM_TYPE_UNSET priority:1000 ]
Checksum selected: RESOURCE_CHECKSUM_TYPE_MD5
Local XS: RESOURCE_CHECKSUM_TYPE_MD5:2205e48de5f93c784733ffcca841d2b5
 5 B / 5 B [=====================================================================================================================================================================================================================] 100.00% 0s
File uploaded: 123e4567-e89b-12d3-a456-426655440000:fileid-einstein%2Fnon_zero.txt 5 /home/non_zero.txt

[ishank011]

For zero size files, this condition fails and so UploadChunk is never called. I'll add a condition to handle this specific case.