Can ORAS attach a file directly to a docker TAR archive?

[Atharex]

As the title says... is this possible?

I know one can extract the tar archive and run oras attach on the extracted folder, but I'd like to avoid this extra step if possible.

Especially because other commands like oras manifest fetch or oras resolve can work directly on the TAR archives.

[Wwwsylvia]

Hi @Atharex, unfortunately, this feature is not supported for now. The current implementation allows read-only access to the OCI Layout in a tarball.

Running oras attach on a tar archive is a write operation, while oras manifest fetch and oras resolve are read operations.

[Atharex]

Ok, that is unfortunate. Is there a proper way to do the modifications, without messing up the final TAR archive?
Been trying to do this myself and I get an error, which leads me to believe an un-tar and re-tar operations do not work properly

1. prepare the OCI directory

TAG=<the-chosen-tag>
tar xvf local.tar -C extracting_folder

2. attach an artifact with oras

oras attach --oci-layout extracting_folder:$TAG \
                 --artifact-type 'my-favorite-artifact/type' \
                 ./artifact.json:application/json

3. repackage the modified OCI image folder
   tar cvf modified_local.tar -C extracting_folder .

4. test the results

oras discover --oci-layout modified_local.tar:$TAG
Error: invalid OCI Image Layout: failed to open OCI layout file:  oci-layout: file does not exist

The error is weirdly misleading, because the oci-layout file is definitely inside the archive.

[Wwwsylvia]

Interesting, this could be a code defect. It might be because the file path inside the tar is nested and ORAS failed to recognize it.
Were you able to do read operations on the original tar local.tar?
For example, oras repo tags --oci-layout local.tar? Could you run tar -tf local.tar and share the path structure?

[Atharex]

Yes, I am able to perform read operations on local.tar

oras discover --oci-layout local.tar:$TAG
local.tar@sha256:7e3b87ef0305b2734e28a5167505d67ee07ef7e9abd9b2a22a3af587a87047e0

oras repo tags --oci-layout local.tar:$TAG
WARN[0000] [Experimental] querying tags associated to sha256:7e3b87ef0305b2734e28a5167505d67ee07ef7e9abd9b2a22a3af587a87047e0, it may take a while... 
$TAG

And on the modified_local.tar, I get an error with this command:

oras repo tags --oci-layout modified_local.tar:$TAG 
Error: invalid OCI Image Layout: failed to open OCI layout file:  oci-layout: file does not exist

Running tar -tf on both files gives me this:

tar -tf local.tar 
blobs/
blobs/sha256/
blobs/sha256/1bd70f80990f7476d7e49358341e36e75e1d35e1c086aea137066b0a8ffaabdb
blobs/sha256/2641af8aae2ffd04482f279a21b42efb998d9b3749f148a8702ae0fa3cc8ebe9
blobs/sha256/3c9a20db4bdb148f9288d39bd7f5a77e74a0215d80657414da618c1cecabffde
blobs/sha256/47e549d92058c6be6788e0a58015139799b80f4dfce7f15b652fc1e1e9173f3c
blobs/sha256/4f4fb700ef54461cfa02571ae0db9a0dc1e0cdb5577484a6d75e68dc38e8acc1
blobs/sha256/63e80638f63862663c24c5add6bc2061c36630999dd82ed1dd6930eefb40321b
blobs/sha256/6c0706c7fd54fc41b413f8afc8fc0a16ef3533304662d8c76dde77550daa6ce5
blobs/sha256/7e3b87ef0305b2734e28a5167505d67ee07ef7e9abd9b2a22a3af587a87047e0
blobs/sha256/8bdfa8f36fb2a96b290e2a9d34417d0d75bb336dda841b02fcfe7c71ed8e82ac
blobs/sha256/aea846b98069d2b6e8f724516dc240bb64d8c1442bff11a4214285b332752e17
blobs/sha256/b10317b39372a42769eae7f844cfb40847472f5ebc6512949ef79d4ed4b2ce5f
blobs/sha256/b330ae2d2adaa388d4550a8eefd9c2ed0408e71fbe88d1024923c07e4d159534
blobs/sha256/e8a12bb7d8bb7ed656f75d7704f0e71fa87ecacce976771b5ec3e2c33f0af4ef
index.json
manifest.json
oci-layout

tar -tf modified_local.tar 
./
./ingest/
./oci-layout
./blobs/
./manifest.json
./index.json
./blobs/sha256/
./blobs/sha256/47e549d92058c6be6788e0a58015139799b80f4dfce7f15b652fc1e1e9173f3c
./blobs/sha256/aea846b98069d2b6e8f724516dc240bb64d8c1442bff11a4214285b332752e17
./blobs/sha256/e8a12bb7d8bb7ed656f75d7704f0e71fa87ecacce976771b5ec3e2c33f0af4ef
./blobs/sha256/b330ae2d2adaa388d4550a8eefd9c2ed0408e71fbe88d1024923c07e4d159534
./blobs/sha256/8bdfa8f36fb2a96b290e2a9d34417d0d75bb336dda841b02fcfe7c71ed8e82ac
./blobs/sha256/6c0706c7fd54fc41b413f8afc8fc0a16ef3533304662d8c76dde77550daa6ce5
./blobs/sha256/2641af8aae2ffd04482f279a21b42efb998d9b3749f148a8702ae0fa3cc8ebe9
./blobs/sha256/44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a
./blobs/sha256/1bd70f80990f7476d7e49358341e36e75e1d35e1c086aea137066b0a8ffaabdb
./blobs/sha256/4f4fb700ef54461cfa02571ae0db9a0dc1e0cdb5577484a6d75e68dc38e8acc1
./blobs/sha256/63e80638f63862663c24c5add6bc2061c36630999dd82ed1dd6930eefb40321b
./blobs/sha256/b10317b39372a42769eae7f844cfb40847472f5ebc6512949ef79d4ed4b2ce5f
./blobs/sha256/3c9a20db4bdb148f9288d39bd7f5a77e74a0215d80657414da618c1cecabffde
./blobs/sha256/6c371231fb54e10d0664c39c6987da28b54ca0ae4d4b24ca5b2c39cd66d4f5d9
./blobs/sha256/6bffa3eeff0dabf4d524b76ff2a40e5fe81288e433e0fa1282d9ab6b3e1400fd
./blobs/sha256/7e3b87ef0305b2734e28a5167505d67ee07ef7e9abd9b2a22a3af587a87047e0

[Wwwsylvia]

It turns out that ORAS does not recognize ./xxx path in the tar archive, it's a bug. Would you mind helping to open a bug issue on the oras-go repo?

[Atharex]

Yes, I've opened one with a reference to this discussion: oras-project/oras-go#851