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Aries Cloud Agent-Python (ACA-Py) - OpenAPI Code Generation Considerations

ACA-Py provides an OpenAPI-documented REST interface for administering the agent's internal state and initiating communication with connected agents.

The running agent provides a Swagger User Interface that can be browsed and used to test various scenarios manually (see the Admin API Readme for details). However, it is often desirable to produce native language interfaces rather than coding Controllers using HTTP primitives. This is possible using several public code generation (codegen) tools. This page provides some suggestions based on experience with these tools when trying to generate Typescript wrappers. The information should be useful to those trying to generate other languages. Updates to this page based on experience are encouraged.

ACA-Py, OpenAPI Raw Output Characteristics

ACA-Py uses aiohttp_apispec tags in code to produce the OpenAPI spec file at runtime dependent on what features have been loaded. How these tags are created is documented in the API Standard Behavior section of the Admin API Readme. The OpenAPI spec is available in raw, unformatted form from a running ACA-Py instance using a route of http://<acapy host and port>/api/docs/swagger.json or from the browser Swagger User Interface directly.

The ACA-Py Admin API evolves across releases. To track these changes and ensure conformance with the OpenAPI specification, we provide a tool located at scripts/generate-open-api-spec. This tool starts ACA-Py, retrieves the swagger.json file, and runs codegen tools to generate specifications in both Swagger and OpenAPI formats with json language output. The output of this tool enables comparison with the checked-in open-api/swagger.json and open-api/openapi.json, and also serves as a useful resource for identifying any non-conformance to the OpenAPI specification. At the moment, validation is turned off via the open-api/openAPIJSON.config file, so warning messages are printed for non-conformance, but the json is still output. Most of the warnings reported by generate-open-api-spec relate to missing operationId fields which results in manufactured method names being created by codegen tools. At the moment, aiohttp_apispec does not support adding operationId annotations via tags.

The generate-open-api-spec tool was initially created to help identify issues with method parameters not being sorted, resulting in somewhat random ordering each time a codegen operation was performed. This is relevant for languages which do not have support for named parameters such as Javascript. It is recommended that the generate-open-api-spec is run prior to each release, and the resulting open-api/openapi.json file checked in to allow tracking of API changes over time. At the moment, this process is not automated as part of the release pipeline.

Generating Language Wrappers for ACA-Py

There are inevitably differences around best practice for method naming based on coding language and organization standards.

Best practice for generating ACA-Py language wrappers is to obtain the raw OpenAPI file from a configured/running ACA-Py instance and then post-process it with a merge utility to match routes and insert desired operationId fields. This allows the greatest flexibility in conforming to external naming requirements.

Two major open-source code generation tools are Swagger and OpenAPI Tools. Which of these to use can be very dependent on language support required and preference for the style of code generated.

The OpenAPI Tools was found to offer some nice features when generating Typescript. It creates separate files for each class and allows the use of a .openapi-generator-ignore file to override generation if there is a spec file issue that needs to be maintained manually.

If generating code for languages that do not support named parameters, it is recommended to specify the useSingleRequestParameter or equivalent in your code generator of choice. The reason is that, as mentioned previously, there have been instances where parameters were not sorted when output into the raw ACA-Py API spec file, and this approach helps remove that risk.

Another suggestion for code generation is to keep the modelPropertyNaming set to original when generating code. Although it is tempting to try and enable marshalling into standard naming formats such as camelCase, the reality is that the models represent what is sent on the wire and documented in the Aries Protocol RFCS. It has proven handy to be able to see code references correspond directly with protocol RFCs when debugging. It will also correspond directly with what the model shows when looking at the ACA-Py Swagger UI in a browser if you need to try something out manually before coding. One final point is that on occasions, it has been discovered that the code generation tools don't always get the marshalling correct in all circumstances when changing model name format.

Existing Language Wrappers for ACA-Py

Python

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Java