Add support for docker load

.buildkite/pipeline.yml

@@ -2,7 +2,10 @@ steps:
   - label: ":shell: Shellcheck"
     plugins:
       - shellcheck#v1.3.0:
-          files: hooks/**
+          files:
+            - hooks/**
+            - commands/**
+            - lib/**
 
   - label: ":sparkles:"
     plugins:
@@ -25,4 +28,4 @@ steps:
       - ${BUILDKITE_PULL_REQUEST_REPO:-$BUILDKITE_REPO}#${BUILDKITE_COMMIT}:
           image: ubuntu:22.04
     soft_fail:
-      - exit_status: 3
+      - exit_status: 3

README.md

@@ -6,6 +6,8 @@ Also see the [Docker Compose Buildkite Plugin](https://github.com/buildkite-plug
 
 ## Example
 
+### `run`
+
 The following pipeline will build a binary in the dist directory using [golang Docker image](https://hub.docker.com/_/golang/) and then uploaded as an artifact.
 
 ```yml
@@ -113,6 +115,24 @@ steps:
           mount-checkout: false
 ```
 
+### `load`
+
+If the image that you want to run is not in a registry the `load` property can be used to load an image from a tar file.
+
+This can be useful if a previous step builds an image and uploads it as an artifact. The below example shows how a artifact can be downloaded and then passed to the `load` property to load the image which can then be referred to in the `image` property to start a container and run a command as explained above.
+
+```yml
+steps:
+  - command: "npm start"
+    plugins:
+      - artifacts#v1.9.0:
+          download: "node-7-image.tar.gz"
+      - docker#v5.8.0:
+          load: "node-7-image.tar.gz"
+          image: "node:7"
+```
+
+
 ### 🚨 Warning
 
 You need to be careful when/if [running the BuildKite agent itself in docker](https://buildkite.com/docs/agent/v3/docker) that, itself, runs pipelines that use this plugin. Make sure to read all the documentation on the matter, specially the caveats and warnings listed.
@@ -229,6 +249,10 @@ Whether or not to leave the container after the run, or immediately remove it wi
 
 Default: `false`
 
+### `load` (optional, string)
+
+Specify a file to load a docker image from. If omitted no load will be done.
+
 ### `mount-checkout` (optional, boolean)
 
 Whether to automatically mount the current working directory which contains your checked out codebase. Mounts onto `/workdir`, unless `workdir` is set, in which case that will be used.

commands/load.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+set -euo pipefail
+
+arg="${BUILDKITE_PLUGIN_DOCKER_LOAD:-}"
+
+if [[ -z "$arg" ]]; then
+  echo "Error: load has to be given a path to the file that should be loaded"
+  exit 1
+fi
+
+# Don't convert paths on gitbash on windows, as that can mangle user paths and cmd options.
+# See https://github.com/buildkite-plugins/docker-buildkite-plugin/issues/81 for more information.
+( if is_windows ; then export MSYS_NO_PATHCONV=1; fi && docker load -i "${arg}" )