This file describes steps and files needed when adding a new API to Chrome. Before you start coding your new API, though, make sure you follow the process described at: http://www.chromium.org/developers/design-documents/extensions/proposed-changes/apis-under-development

Two approaches are available for writing your API specification. The original approach relies on JSON specification files. The more recent and simpler system uses Web IDL files, but does not yet support all the features of the JSON files. Discuss with a member of the extensions team (aa@chromium.org) before you decide which approach is better suited to your API.

The following steps suppose you're writing an experimental API called "Foo".

---

APPROACH 1: JSON FILES

1. Write your API specification. Create "chrome/common/extensions/api/experimental_foo.json". For inspiration look at the "app" API. Include descriptions fields to generate the documentation.

2. Add your API specification to extensions_api_resources.grd. Add an "<include ...>" line with your JSON specification file to "chrome/common/extensions_api_resources.grd".

3. Add your API specification to api.gyp. Add "experimental_foo.json" to the "json_schema_files" section in "chrome/common/extensions/api/api.gyp".

4. Write the API function handlers. Create foo_api.cc and foo_api.h under "chrome/browser/extensions/api/foo". You should use the JSON Schema Compiler. Look at the "permissions_api.cc" for details on how to do that.

5. Register function handlers. In "chrome/browser/extensions/extension_function_registry.cc" include foo_api.h and instantiate a RegisterFunction for each function you created in (3).

---

APPROACH 2: IDL FILES

1. Write your API specification. Create "chrome/common/extensions/api/experimental_foo.idl". For inspiration look at "alarms.idl". Include comments, they will be used to automatically generate the documentation.

2. Add your API specification to api.gyp. Add "experimental_foo.idl" to the "idl_schema_files" section in "chrome/common/extensions/api/api.gyp".

3. Write the API function handlers. Create foo_api.cc and foo_api.h under "chrome/browser/extensions/api/foo". You should use the JSON Schema Compiler. Look at the "alarms_api.cc" for details on how to do that.

4-5) Nothing to do! Function handlers are automatically registered for you.

---

STEPS COMMON TO BOTH APPROACHES

6. Write support classes for your API If your API needs any support classes add them to "chrome/browser/extensions/api/foo". Some old APIs added their support classes directly to chrome/browser/extensions. Don't do that.

7. Update the project with your new files. The files you created in (3) and (5) should be added to "chrome/chrome_browser_extensions.gypi".

---

GENERATING DOCUMENTATION

8. Build the project. (Only required if you used IDL files.) If you used IDL files, you need to build the project once in order for the documentation to be properly generated. Do this now. (This is required in order to generate the JSON file used to generate documentation.)

9. Add your JSON file to the documentation controller Open "chrome/common/extensions/docs/js/api_page_generator.js" and add a line referring to "../api/experimental_foo.json". Do this even if you used the IDL approach as this JSON file has been generated in (7).

10. Write the static HTML page. Write a small snippet of static HTML describing your API in "chrome/common/extensions/docs/static/experimental.foo.html". For the moment, just include the following in this file, adjusting it to describe your API:

The current methods allow applications to...

11. Build the documentation. You will need to build DumpRenderTree once before you can build the documentation. Once this is done, from "chrome/common/extensions/docs" run "build/build.py". For more information on building documentation see README.txt in "chrome/common/extensions/docs".

---

WRITING TESTS

12. Write a unit test for your API. Create "chrome/browser/extensions/api/foo/foo_api_unittest.cc" and test each of your API methods. See "alarms_api_unittest.cc" for details. Once done add your .cc to "chrome/chrome_tests.gypi".