Dev Containers generates `dd bs=0` during GPG forwarding and skips `postCreateCommand`

[V-Subhankar-infy]

Dev Containers extension: GPG forwarding generates dd bs=0 and stops lifecycle provisioning

• VS Code Version: 1.133.0 (stable)
• Local OS Version: macOS on Apple Silicon
• Remote OS Version: Ubuntu 26.04 linux/arm64 development container
• Remote Extension/Connection Type: Dev Containers
• Dev Containers Version: 0.466.0
• Docker: Docker Desktop 4.73.0
• Insiders build: Not tested

Problem

This is a Dev Containers extension issue: its GPG-forwarding path generates an invalid dd bs=0 command, and the resulting failure prevents lifecycle provisioning from reaching postCreateCommand. I reproduced it end to end on the environment above.

The behavior was first reported at devcontainers/images#1949. That image exposes the failure through Ubuntu 26.04's dd behavior, but it does not generate the command or control the extension's lifecycle error handling, so it's not a error at the devcontainers/images.

The forwarding path emits a final remainder command even when the remainder is zero. For a zero-byte source, that produces dd ... bs=0. Command generation is not Ubuntu 26.04-specific: I instrumented dd in an Ubuntu 24.04 development container and observed:

DD: iflag=fullblock bs=8192 count=0
DD: iflag=fullblock bs=0 count=1

GNU dd on 24.04 returns a normal error with exit 1 and setup continues. uutils dd on 26.04 aborts with exit 134, after which the optional GPG-forwarding failure prevents lifecycle setup from reaching postCreateCommand.

Expected Behavior

• The forwarding path does not generate dd bs=0.
• A GPG keyring or trust-database forwarding failure is reported as a warning and does not prevent lifecycle commands from running.

Requested Changes

1. Skip the remainder transfer when the remainder is zero. For a zero-byte source, create an empty destination directly; for a nonzero size divisible by 8192, issue only the full-block transfer.
2. Catch and log GPG-forwarding failures, then continue provisioning and lifecycle commands.
3. Add regression coverage for source sizes 0, 8191, 8192, and 8193, plus a forwarding failure that must not suppress lifecycle commands.

Steps to Reproduce

1. Follow the attached, manually verified procedure exactly as written in repro.md. It contains the complete setup, Ubuntu 24.04 control, verification, and restoration steps.

Logs

The relevant container-log output from the failing run is:

Start: Run in container: # Copy .../.gnupg/pubring.gpg to /home/vscode/.gnupg/pubring.gpg
Aborted
Exit code 134
Command in container failed: # Copy .../.gnupg/pubring.gpg to /home/vscode/.gnupg/pubring.gpg
(dd iflag=fullblock bs=8192 count=0 2>/dev/null; dd iflag=fullblock bs=0 count=1 2>/dev/null) >>'/home/vscode/.gnupg/pubring.gpg'

The container attaches normally, but there is no Running the postCreateCommand log entry and the post-create sentinel file is absent.

Do let me know if you need any further information about the issue.