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GCP API Gateway Spec Generator

This is a simple tool that:

• Takes a Swagger 2.0 spec file
• Takes a configuration file
• Generates a new Swagger 2.0 spec file with API Gateway specific properties
• Optionally (recommended), strips responses from the original spec file, and replaces them with generic 200 responses.
  • Complicated responses are a constant source of errors when deploying to the API Gateway, and in most use cases are not necessary.

The generator does not handle converting API specs (i.e., OpenAPI 3.0 to Swagger 2.0). It is assumed that you have a Swagger 2.0 spec file. If you have an API spec file in a different format, it is recommended to use api-spec-converter or another tool to convert it to Swagger 2.0.

The main use case of this tool is an intermediate step in the deployment of an API to Google Cloud Platform's API Gateway. As Google still uses the old Swagger 2.0 spec, and has additional fields that can be added/removed, this tool helps to automate the process of generating a spec file that is compatible with the API Gateway. A common use case for this tool would be on a CI pipeline:

1. Autogenerate spec for your API
2. Convert spec to Swagger 2.0
3. Generate API Gateway spec file
4. Deploy to API Gateway

Installation

Ensure you have Composer installed and available in your PATH, as well as PHP 8.0 or later.

Note for PHP 8.0: every symfony/yaml version installable on PHP 8.0 carries known (low-severity) security advisories — the 6.x line was only patched in 6.4, which requires PHP 8.1. Composer ≥ 2.9 therefore blocks resolution on PHP 8.0 by default; you would need to opt out via config.audit.block-insecure: false (at your own risk). On PHP 8.1+ this does not apply.

Local

Run the following command in your project root:

After installing, you can now run the tool using: ./vendor/bin/gcp-api-gateway-spec generate from your project root.

Global

Run the following command anywhere in your terminal:

After installing, the tool will now be in your composer installation's bin directory at <composer-home>/vendor/bin/gcp-api-gateway-spec.

You can view the path to your composer's home directory by running composer -n config --global home.

You can alias the path to the tool or add the composer vendor/bin directory to your PATH in your .zshrc or .bashrc for easier access.

Usage

Requirements

• Swagger 2.0 YAML spec file, passed as the first argument to generate
  • If you are working with an OpenAPI 3.0 spec file, I recommend using api-spec-converter to create a Swagger 2.0 spec file.
• Configuration file (see Configuration)

Command

Output path resolution

• Absolute path (e.g. --output=/tmp/specs/api-gateway.yaml): used as-is. Missing directories are created.
• Relative path (e.g. --output=build/api-gateway.yaml): resolved against the current working directory.
• Directory (existing): the file is written inside it as generator-output.yaml.
• Omitted: writes generator-output.yaml in the current working directory.

Examples

Absolute path with filename:

With --preserve-responses and a relative output to cwd:

Configuration

Values in the config file take precedence over the corresponding values in the input spec (info, basePath, produces, consumes, securityDefinitions, x-google-backend). Take a look at the example config for a practical example.

For each operation, the effective spec starts from path-defaults, with same-named keys replaced wholesale by the matching path-overrides.<path>.<method> entry; the operation from the input spec is then merged in recursively, winning per key (and per index for lists). Note this means an override such as security: [] cannot remove a security list the input spec itself defines — the input's entries win index-wise. It does work for the common case where security comes from path-defaults.

Normalization

Besides merging the config, the generator applies a few normalizations so that the output passes the API Gateway's Swagger 2.0 validation:

• Responses are replaced with a generic 200 response unless --preserve-responses is passed. Empty responses maps are replaced with the generic response as well.
• Path parameters that appear in a path template (e.g. /pets/{petId}) but are not declared on the operation are added as required string parameters.
• Nullable types are rewritten: type: "null" becomes type: string with x-nullable: true. A type list collapses to its first non-"null" entry (so type: [string, "null"] becomes type: string with x-nullable: true, and a multi-type list like type: [string, integer] becomes type: string). Properties literally named type, and map-valued type keys inside free-form data (examples, default, enum values, x- extensions), are left untouched.
• Unsupported JSON Schema keywords are removed: additionalItems, patternProperties, dependencies, propertyNames, contains, const, if, then, else.
• Empty schemas (e.g. nickname: {}, common in specs converted with api-spec-converter) are kept as empty objects instead of degrading to [], which the API Gateway validator rejects. Empty sequences such as security: [] are unaffected.

Development

Generated output is byte-compared against golden files in tests/fixtures/cases/*/expected.yaml and validated against the official Swagger 2.0 JSON schema — the same validation gcloud api-gateway api-configs create performs. After an intentional output change, regenerate goldens with UPDATE_GOLDENS=1 vendor/bin/phpunit.

Disclaimer

This tool is not officially supported by Google Cloud Platform or the API Gateway team.

This tool is provided as-is and without warranties of any kind. Luke Davis is not responsible for any security issues, vulnerabilities, or other problems that may arise from the use of this tool.

Users are responsible for ensuring the security and suitability of this tool for their specific needs and use cases. Use at your own risk.