fix: update docker event format to use template syntax

[kiitosu]

Summary

This PR fixes the issue where LocalStack container state in the VSCode extension stays in starting or stopping and never transitions to running or stopped.

my environment

VSCode: Version: 1.104.1
LocalStack Toolkit: 1.2.3
macOS (Apple M1 Pro): Sequoia 15.7
docker: 20.10.21, build baeda1f82a

Problem

• In my environment, LocalStack state was stuck at starting / stopping.
• Checking Docker directly (docker ps) showed that the container itself had already reached running / stopped.
• However, the extension did not detect the state transition correctly.

Investigation

When inspecting Docker events:

docker events --filter container=localstack-main \
  --filter event=start --filter event=stop --filter event=kill \
  --filter event=die --filter event=restart \
  --format json

→ No events were captured.

But with:

docker events --filter container=localstack-main \
  --filter event=start --filter event=stop --filter event=kill \
  --filter event=die --filter event=restart \
  --format '{{json .}}'

→ Events were captured correctly (start, stop, die, etc.).

This difference in formatting prevented the extension from correctly updating the container state.

Fix

• Use --format '{{json .}}' when capturing Docker events.
• With this change, the extension correctly updates container state from starting → running and stopping → stopped.

Verification

• Built the extension locally with make vsix.
• Installed the generated .vsix file in VSCode.
• Verified that LocalStack state now transitions properly between running and stopped.

[skyrpex]

@kiitosu thanks for the contribution!

Aren't --output json and --format '{{json .}}' equivalent? I can't see any differences in the output for both of them 🤔.

Edit: I use Docker version 28.4.0, build d8eb465 though. Maybe the behavior changed in newer versions than Docker 20.10.21, build baeda1f82a. Will check it out.

Edit 2: Asked AI about it. This is the response:

• The ‎--format '{{json .}}' syntax has been supported for several years (since Docker 17.06).
• The shorthand ‎--format json (without the Go template) is a newer addition and only works in recent Docker CLI versions (23.0 and later, released in early 2023).

[kiitosu]

@skyrpex
Thank you for your reply!
You were right — the issue was caused by my old Docker version.

[anisaoshafi]

Thanks @kiitosu for the quick feedback and raising this issue 🐛

Since this does impact users that are stuck on older docker versions, we'll find some time to tackle it properly.