Http4k Development

http4k

http4k is a lightweight Kotlin HTTP toolkit built on the "Server as a Function" principle, where HttpHandler is (Request) -> Response. Everything — servers, clients, routing, testing — composes through this function type.

Dependency Detection

Before loading references, detect which http4k modules the user's project depends on:

1. Read build.gradle.kts, build.gradle, or pom.xml in the project root (and subproject build files)
2. Look for dependencies matching org.http4k:http4k-*
3. Only load reference files from references/ that match detected modules
4. Always load references/core.md — it covers the foundation used by all other modules

If no build file is found, ask the user which modules they use.

Loading References

For each detected dependency org.http4k:http4k-{module}, load references/{module}.md if it exists. For example, http4k-server-undertow maps to references/server-undertow.md.

http4k-connect API Call Style

http4k-connect modules use extension functions on client interfaces, not the invoke() operator directly. Actions are called as camelCase methods on the client:

// CORRECT — extension function style
val buckets = s3.listBuckets().successValue()
s3Bucket.putObject(key, body).successValue()
dynamo.createTable(table, keySchema).successValue()
sqs.sendMessage(queueUrl, "Hello").successValue()

// WRONG — do NOT use the invoke operator with action classes
val buckets = s3(ListBuckets()).successValue()        // ✗
sqs(SendMessage(queueUrl, "Hello")).successValue()     // ✗

All connect actions return Result<T, RemoteFailure> monads.