pre and post

content/post/creating-go-actions.md

@@ -142,7 +142,7 @@ name: 'Test Go Action'
 on: [push]
 jobs:
   use-go-action:
-    runs-on: host-docker-ubuntu20.04
+    runs-on: ubuntu-latest
     steps:
       - name: Setup Go
         uses: actions/setup-go@v3
@@ -162,3 +162,98 @@ jobs:
 After pushing the updated workflow file, you will see the result:
 
 ![use-go-action-input-and-output](/demos/creating-go-actions/use-go-action-input-and-output.png)
+
+## Pre and Post
+
+In the `action.yml` file, we set the `runs.main` to `main.go` to specify the code that the action needs to run.
+Except the `main`, You can also specify the `pre` and the `post` for an action. 
+The `pre` allows you to run some code before running the `main` and the `post` allows you to run some code at the end of the job.
+If you need more information, please read GitHub's documentation about [`pre`](https://docs.github.com/en/actions/creating-actions/metadata-syntax-for-github-actions#runspre) and [`post`](https://docs.github.com/en/actions/creating-actions/metadata-syntax-for-github-actions#runspost).
+
+Let's add the `pre` and the `post` to the action.
+Firstly, you need to create a `pre` directory and add a `pre.go` file in it:
+
+```go
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("Pre of Simple Go Action")
+}
+```
+
+Then, create the `post` directory and `post.go` file in the similar way:
+
+```go
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("Post of Simple Go Action")
+}
+```
+
+And you'll also need to update the `action.yml` file:
+
+```yml
+name: 'Simple Go Action'
+description: 'A simple Gitea action written in go'
+inputs:
+  username:
+    description: 'The username to print'
+    required: true
+outputs:
+  time:
+    description: 'The time when the action was called'
+runs:
+  using: 'go'
+  main: 'main.go'
+  pre: "pre/pre.go"
+  post: "post/post.go"
+```
+
+Now the structure of the directory should be like:
+
+```
+├── action.yml
+├── go.mod
+├── main.go
+├── post
+│   └── post.go
+└── pre
+    └── pre.go
+```
+
+Everything looks ok! But when you re-run the workflow, you may see an error: `"go": executable file not found in $PATH`.
+The reason is that the code in `pre` will be executed before calling the `setup-go` action, and the Go runtime has not yet been set up.
+In this case, you need to use an image with Go installed to run this workflow and you won't need to call the `setup-go` action since the image already has the Go runtime.
+You can use `container.image` to specify the image (replace `<image-with-go>` with an image with go installed):
+
+```yml
+name: 'Test Go Action'
+on: [push]
+jobs:
+  use-go-action:
+    runs-on: host-docker-ubuntu20.04
+    container:
+      image: <image-with-go>
+    steps:
+      - name: Use Go Action  
+        id: use-go-action
+        uses: <action-url>
+        with:
+          username: foo
+
+      - name: Print Output
+        run: echo 'output time is ${{ steps.use-go-action.outputs.time }}'
+```
+
+Then the workflow will work. You'll see the output of the `pre` in `Set up job`:
+
+![go-action-pre](/demos/creating-go-actions/go-action-pre.png)
+
+and the output of the `post` in `Complete job`:
+
+![go-action-post](/demos/creating-go-actions/go-action-post.png)