Overview

The generated Java types for a protobuf message implement the Message interface. This provides handy methods like .toBuilder() for any generated type, so you can have a function that takes a Message parameter and be able to call .toBuilder() on it. So far so good!

However, there are also the .newBuilder() and .parser() static methods on the generated Message types. Since those are static methods, not instance methods, their presence can't be guaranteed by the Message interface, and thus there is no way to call those methods for any Message type (without reflection, that is). This library provides MethodHandle-based helpers to invoke those methods.

Calling newBuilder()

builderWrapper() wraps the process of invoking newBuilder() and calling build(), invoking your provided builder-using logic in between. This allows you to create generic functions like this one to parse any Message from protobuf-style JSON:

private inline fun <reified T : Message> jsonParser(): (String) -> T {
    // normal protobuf json parser
    val jsonParser = JsonFormat.parser()

    // build a String -> T function that uses the json parser
    return builderWrapper { builder, json ->
        // do whatever you like with the builder instance
        jsonParser.merge(json, builder)
    }
}

You could use that to create a json parsing function for a particular type:

// reusable json -> T function
val favColorParser: (String) -> FavoriteColor = jsonParser<FavoriteColor>()
val favColor = favColorParser("""{"color": "blue", "priority": 17}""")

In this example we use Kotlin's reified T, but it can also be written to use a Class<T>, if that's more convenient for your use case.

Calling parser()

parser() is simpler -- it just produces the Parser for the corresponding Message type.

// normal protobuf Parser, reuse as needed
val parser: Parser<FavoriteColor> = parser<FavoriteColor>()
val deserialized = parser.parseDelimitedFrom(someInputData)

Usage

Artifacts are hosted in Maven Central, available as the mavenCentral() repository in Gradle.

In your build.gradle.kts, add:

implementation("com.classpass.oss.protobuf.reflection", "protobuf-reflection", "LATEST-VERSION-HERE")

Contributing

We welcome contributions from everyone! See CONTRIBUTING.md for information on making a contribution.

Formatting

The check task will check formatting (in addition to the other normal checks), and formatKotlin will auto-format.

License headers

The check task will ensure that license headers are properly applied, and licenseFormat will apply headers for you.

License

See LICENSE for the project license.