fix: check if configPath is empty before writing to Annotations

[wangxiaoxuan273]

This pr adds empty string check before writing configPath to Annotations, so that if a config only specifies the type but not name, oras cli should not fetch the content of this config.

Part of issue #415
Signed-off-by: wangxiaoxuan273 wangxiaoxuan119@gmail.com

[qweeah]

LGTM

[shizhMSFT]

What if a config is named but configPath is empty? In that case, we should download it, shouldn’t we?

[shizhMSFT]

LGTM

[lizMSFT]

LGTM

[codecov-commenter]

Codecov Report

Merging #509 (9421414) into main (a6a360e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #509   +/-   ##
=======================================
  Coverage   72.68%   72.68%           
=======================================
  Files           9        9           
  Lines         388      388           
=======================================
  Hits          282      282           
  Misses         85       85           
  Partials       21       21           

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[qweeah]

Below command should download demo.config, foo and bar:

oras pull localhost:5000/oras:test

Manifest content of localhost:5000/oras:test:

{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.manifest.v1+json",
  "config": {
    "mediaType": "application/vnd.unknown.config.v1+json",
    "digest": "sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a",
    "size": 2,
    "annotations": {
      "org.opencontainers.image.title": "demo.config"
    }
  },
  "layers": [
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar",
      "digest": "sha256:b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c",
      "size": 4
      "annotations": {
        "org.opencontainers.image.title": "foo"
      }
    },
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar",
      "digest": "sha256:7d865e959b2466918c9863afca942d0fb89d7c9ac0c99bafc3749504ded97730",
      "size": 4,
      "annotations": {
        "org.opencontainers.image.title": "bar"
      }
    }
  ]
}