update-dl-url.yml

---

# This workflow allows on-call operators to safely switch the value of the `dl`
# key in `config.json` during an outage, to ensure people can continue building
# projects with `cargo`.
#
# The workflow can be invoked through GitHub's UI.
#
# To add new options change `on.workflow_dispatch.inputs.url.options` to
# include your new option, and then add the related environment variable in
# the `env` section.

name: Update download URL
on:
  workflow_dispatch:
    inputs:
      url:
        description: Switch downloads to
        required: true
        type: choice
        options:
          # The format of this is "${id}:${description}". Each option
          # corresponds to the environment variable `URL_${id}`.
          - "api: API on Heroku (default)"
          - "cdn: CloudFront CDN"
          - "s3_primary: S3 bucket in us-west-1"
          - "s3_fallback: S3 bucket in eu-west-1"

env:
  URL_api: "https://crates.io/api/v1/crates"
  URL_cdn: "https://static.crates.io/crates/{crate}/{crate}-{version}.crate"
  URL_s3_primary: "https://crates-io.s3-us-west-1.amazonaws.com/crates/{crate}/{crate}-{version}.crate"
  URL_s3_fallback: "https://crates-io-fallback.s3-eu-west-1.amazonaws.com/crates/{crate}/{crate}-{version}.crate"

permissions:
  contents: write

jobs:
  switch:
    # The option the user selected is included in the job name to permanently
    # log it, as those options are not otherwise logged and including it in the
    # build log would result in it being deleted after 90 days.
    name: Switch to ${{ github.event.inputs.url }}

    runs-on: ubuntu-latest
    steps:
      - name: Clone the source code
        uses: actions/checkout@v2

      - name: Switch the download endpoint
        run: |
          set -euo pipefail

          # Dynamically fetch the URL based on the choice the user made. The
          # first line calculates the environment variable name by
          # concatenating "URL_" and the part of the input before ":". Then the
          # second line fetches the value of the variable with that name.
          var_name="URL_$(echo "${{ github.event.inputs.url }}" | sed "s/:.*//")"
          url="${!var_name}"

          # Use `jq` to update the `dl` field of the configuration file while
          # preserving the rest of the contents.
          jq --arg url "${url}" '.dl = $url' config.json > updated-config.json

          # The GitHub API is used instead of `git commit`/`git push` to sign
          # the commit with GitHub's key. The sha of the previous `config.json`
          # is provided to make sure we don't override concurrent changes.
          curl \
            --fail \
            -X PUT \
            -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" \
            -d "{
              \"message\": \"Switching download endpoint\",
              \"content\": \"$(base64 -w0 updated-config.json)\",
              \"sha\": \"$(git hash-object config.json)\"
            }" \
            https://api.github.com/repos/${{ github.repository }}/contents/config.json