Theory

This section describes how SERP providers work, before we get into writing the code itself.

Q&A

What is a SERP provider?

According to SERP providers:

SERP (search engine results page) providers allow Gugal to search the web using different search engines, and can be used to search data on the device (e.g. contacts, files, messages).

And from a technical standpoint?

From a technical standpoint SERP providers are Kotlin classes implementing the SerpProvider interface.

SERP providers identify themselves to the app internally using UUIDs and to the user using ProviderInfo objects.

Any other classes I need to know about?

SERP providers send results back to the app using Result objects. If an error occured doing a web search, they can return certain error responses instead.

What about the license?

SERP providers are considered parts of Gugal, which is licensed under GPLv3.

Web search using proprietary search engines is allowed. Usage of proprietary libraries to perform search is discouraged to keep Gugal fully free (as in freedom) and open-source, and it's preferred if there are alternatives that can be called using free libraries or parts of Android (e.g. if a web search engine offering a proprietary search library also has a search API that is affordable, call the API using standard web requests). But, if you must use a proprietary library, please also add a way to disable it when building the app (like adding a separate nonfree flavor).

The lifecycle of a SERP provider

This part describes the interactions between Gugal and a SERP provider.

When Gugal is started for the first time

1. Gugal shows a setup wizard page describing what it is.
2. After the user skips the page, Gugal shows a list of SERP providers defined in Global.allSerpProviders, getting data from the providers' ProviderInfo. The user should then select a SERP provider and tap Next.
3. Gugal shows the SERP provider's ConfigComposable in a setup page, letting the user configure any settings that might be required for searching. If ProviderInfo.requiresSetup is false on the provider this step is skipped.
4. Finally, Gugal shows the last setup page with a few tips.

When Gugal is started subsequently

1. The app loads encrypted preferences and loads the picked SERP provider.
2. The app calls getSensitiveCredentialNames(). The provider should return an array of keys for it's sensitive credentials (but not the credentials themselves!)
3. Gugal loads the credentials from encrypted preferences using the keys from the array.
4. The app calls useSensitiveCredentials() with a map where the keys are the ones from step 2 and the values are the corresponding credentials. The provider should save them in variables, as Gugal won't provide them in the current session anymore.

When the user makes a search

1. Gugal calls search() with the query the user typed in and functions for setting the result and error.
2. The provider performs a web search for the provided query and the credentials. If the provider implements web search using the Volley library it can return a web request, which will be performed by the app. Otherwise the provider should return null.
3. The app performs the web request if one was returned by the provider. If an error occured doing a web search, the provider should call the setError function with an appropriate error response.
4. When the search is finished the provider should add the results as Result objects to a mutable list and provide it to Gugal with the setResults function. The list will be shown by the app.

Go to the next chapter to start developing your own SERP provider.