Add container copy/cp command for host-container file transfer

[simone-panico]

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Motivation and Context

Adds the container copy (aliased as cp) command to copy files between a running container and the local filesystem.

I saw #1023 and the feedback from @dcantah — the previous attempt relied on tar being installed inside the container.
This implementation takes the recommended approach:
file transfers go through the guest agent via the existing copyIn/copyOut methods on the core Containerization, with no dependency on container tooling.

Testing

• Tested locally
• Added/updated tests
• Added/updated docs

[JaewonHur]

Related to #232

[JaewonHur]

Why UInt64 here?

[simone-panico]

Because the set Method in XPCMessage.swift expects a UInt64

[simone-panico]

Do you want to handle it differently? I looked at the code again and couldn't find a better option

[JaewonHur]

⏺ CopyOut/CopyIn Scenarios: Current vs Docker Behavior

Scenario 1: src without /, dst without / (src must exist)

• File, Directory → Non-existing:

  • Docker (desired): save as dst
  • Current: File is saved as dst, Directory is not supported.

• File → File

  • Docker (desired): replace dst
  • Current: replace dst

• Directory → File

  • Docker (desired): error
  • Current: Directory is not supported

• File, Directory → Directory

  • Docker (desired): save under dst
  • Current: File returns error, Directory is not supported.

Scenario 2: src without /, dst with / (dst must be a directory if existing)

• File → Non-existing:

  • Docker (desired): error no such directory
  • Current: dst is created and src file is saved under dst.

• Directory → Non-existing:

  • Docker (desired): save as dst
  • Current: Directory is not supported.

• File, Directory → Directory

  • Docker (desired): save under dst
  • Current: File is saved under dst. Directory is not supported.

Scenario 3: src with /, dst without / (src must be an existing directory)

• Directory → Non-existing:

  • Docker (desired): save as dst
  • Current: Directory is not supported.

• Directory → File

  • Docker (desired): error
  • Current: Directory is not supported.

• Directory → Directory

  • Docker (desired): save under dst
  • Current: Directory is not supported.

Scenario 4: src with /, dst with / (src must be an existing directory & dst must be a directory if existing)

• Directory → Non-existing:

  • Docker (desired): save as dst
  • Current: Directory is not supported.

• Directory → Directory

  • Docker (desired): save under dst
  • Current: Directory is not supported.

[JaewonHur]

Hi @simone-panico
Above I summarized the desired behavior and current behavior.

The bold italic phrases are what is different from desired behavior (i.e., docker) now, and can be addressed.

Below is general comments.

1. Copying directory is not supported yet, we need to handle it later.
2. If dst/, it would be better to check in command line if dst is directory if it exists.

[JaewonHur]

Hi @simone-panico
Could you try this PR with apple/containerization#474, which supports copying directories.

You may need to build this project with local containerization (BUILDING.md), and wire up SandboxService.

[dcantah]

@JaewonHur the change above does not allow copying directories. It adds a tar reader/writer that will be used to support this, but it's not in the change itself.

[simone-panico]

If you’re interested, I could try to create a Directory Copier within containerization. It would also be a great challenge for me

[simone-panico]

@JaewonHur @dcantah, I created apple/containerization#543 for clarity.

As soon as apple/containerization#474 is merged I think I could start with implementing the directory copying. What do you think?

[JaewonHur]

Hi @simone-panico, sorry for the delay!

We have an internal discussion how to better support container cp, and want to pause this for now. We will definitely revisit this PR once every thing becomes clear! Thanks!