ci: checks markdown for bad links

.github/workflows/test_markdown.yml

@@ -0,0 +1,33 @@
+# yamllint --format github .github/workflows/test_markdown.yml
+---
+name: test_markdown
+
+on:  # yamllint disable-line rule:truthy
+  push:  # non-tagged pushes to master
+    branches:
+      - master
+    tags-ignore:
+      - '*'
+    paths:
+      - '**/*.md'
+      - ./build-bin/mlc_config.json
+  pull_request:  # pull requests targeted at the master branch.
+    branches:
+      - master
+    paths:
+      - '**/*.md'
+      - ./build-bin/mlc_config.json
+
+jobs:
+  test-markdown:
+    name: Test Markdown
+    runs-on: ubuntu-22.04  # newest available distribution, aka jellyfish
+    # skip commits made by the release plugin
+    if: "!contains(github.event.head_commit.message, 'maven-release-plugin')"
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v4
+      - name: Check Markdown links
+        uses: gaurav-nelson/github-action-markdown-link-check@v1
+        with:
+          config-file: './build-bin/mlc_config.json'

README.md

@@ -48,7 +48,7 @@ Api and all collector components.
 
 | Storage                                    | Description                 |
 |--------------------------------------------|-----------------------------|
-| [Stackdriver Trace](./storage/stackdriver) | Free cloud service provider |
+| [Stackdriver Trace](./storage-stackdriver) | Free cloud service provider |
 
 ## Server integration
 In order to integrate with zipkin-server, you need to use properties
@@ -79,7 +79,7 @@ $ STORAGE_TYPE=stackdriver STACKDRIVER_PROJECT_ID=zipkin-demo \
 If you cannot use our [Docker image](./docker/README.md), you can still integrate
 yourself by downloading a couple jars.
 
-[Here's an example](autoconfigure/storage-stackdriver#quick-start) of
+[Here's an example](module/README.md#quick-start) of
 integrating Stackdriver storage.
 
 ## Troubleshooting

build-bin/README.md

@@ -5,8 +5,15 @@ This is a Maven+Docker project, which uses standard conventions for test and dep
 The Docker image for zipkin-gcp is a layer over zipkin, including only the [../module] and
 configuration settings.
 
-[docker-compose-zipkin-gcp.xml] ensures GCP authentication works. It is not run on pull request, as
-the required secure variable is only available on master push.
+[docker-compose-zipkin-gcp.xml](docker-compose-zipkin-gcp.yml) ensures GCP authentication works.
+It is not run on pull request, as the required secure variable is only available on master push.
+
+[mlc_config.json](mlc_config.json) is run by GitHub Action, but you can also run it locally,
+assuming you installed markdown-link-check via NPM.
+
+```bash
+$ find . -name \*.md |xargs markdown-link-check -c ./build-bin/mlc_config.json
+```
 
 [//]: # (Below here should be standard for all projects)
 

build-bin/mlc_config.json

@@ -0,0 +1,10 @@
+{
+  "ignorePatterns": [
+    {
+      "pattern": "https://oss.sonatype.org/content/repositories/snapshots"
+    },
+    {
+      "pattern": "http://localhost:9411/api/v[12]/spans"
+    }
+  ]
+}

docker/README.md

@@ -33,7 +33,7 @@ In docker, the following can also be set:
 
 ### Stackdriver
 
-Stackdriver Configuration variables are detailed [here](../module/storage-stackdriver#configuration).
+Stackdriver Configuration variables are detailed [here](../module/README.md#configuration).
 
 ## Building
 

module/README.md

@@ -47,7 +47,7 @@ The Zipkin server can be further configured as described in the
 
 Configuration can be applied either through environment variables or an external Zipkin
 configuration file.  The module includes default configuration that can be used as a 
-[reference](https://github.com/openzipkin/zipkin-gcp/tree/master/autoconfigure/storage-stackdriver/src/main/resources/zipkin-server-stackdriver.yml)
+[reference](./src/main/resources/zipkin-server-gcp.yml)
 for users that prefer a file based approach.
 
 #### Environment Variables