Ktor Integration

Mockcat provides two Ktor plugins:

• MockcatKtorIntercept — intercepts requests and returns saved mock responses
• MockcatKtorHttpLogging — captures HTTP traffic to the Mockcat log store

Both are standard Ktor client plugins installed with install(...).

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Dependencies

app/build.gradle.kts

debugImplementation("com.mockcat:mockcat-intercept-ktor:0.1.0")
debugImplementation("com.mockcat:mockcat-logger-ktor:0.1.0")
releaseImplementation("com.mockcat:mockcat-noop-android:0.1.0")

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Basic setup

Android

On Android, use the convenience helpers that automatically wire the process-wide stores:

import com.mockcat.intercept.ktor.installMockcatKtorIntercept
import com.mockcat.logger.ktor.installMockcatKtorHttpLogging
import io.ktor.client.HttpClient
import io.ktor.client.engine.okhttp.OkHttp

val client = HttpClient(OkHttp) {
    installMockcatKtorIntercept(context)
    installMockcatKtorHttpLogging(context)
    // ... other plugins
}

Using a custom store

If you manage your own MockcatStore or HttpLogWriter:

import com.mockcat.intercept.ktor.MockcatKtorIntercept
import com.mockcat.logger.ktor.MockcatKtorHttpLogging

val client = HttpClient(OkHttp) {
    install(MockcatKtorIntercept) {
        store = myStore  // Required
    }
    install(MockcatKtorHttpLogging) {
        writer = myLogWriter  // Required
    }
}

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How the intercept plugin works

The plugin hooks into client.plugin(HttpSend).intercept:

1. Checks for the X-Mockcat-Redirected header. If present, executes the request normally (prevents redirect loops).
2. Builds an HttpRequestMetadata from the HttpRequestBuilder (URL, method, all headers).
3. Calls store.resolveWithMatcher(metadata).
4. Returns one of:
5. PassThrough — delegates to execute(request), the real network call runs
6. ApplyStatic — returns a MockcatSyntheticCall with a MockcatStaticHttpResponse containing the mock status, headers, and body bytes
7. Redirect — creates a new HttpRequestBuilder, adds the X-Mockcat-Redirected marker, executes it
8. Error — returns a synthetic call with a 598/599 error response

Synthetic responses

Ktor's HttpClientCall is abstract. Mockcat wraps mock responses in: - MockcatSyntheticCall — the call object returned to the plugin - MockcatBuiltHttpRequest — wraps the original HttpRequestData - MockcatStaticHttpResponse — provides status, headers, and body as ByteReadChannel

allowDoubleReceive is set to true on synthetic responses so response bodies can be read multiple times.

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How the logging plugin works

The logging plugin hooks into HttpSend to intercept responses after the engine executes:

1. Records request timestamp and headers at the onRequest phase.
2. After execution, reads the full response body bytes.
3. Emits a LoggedHttpCall to the HttpLogWriter.
4. Returns a cached copy of the body bytes to the caller so the original response stream is not consumed.

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Pre-built client helper

If you want OkHttp with both Mockcat plugins pre-installed as a convenience factory:

import com.mockcat.intercept.ktor.MockcatKtor

val client = MockcatKtor.createHttpClient(context) {
    // additional Ktor config here
}

This creates a Ktor HttpClient(OkHttp) with both installMockcatKtorIntercept and installMockcatKtorHttpLogging already applied.

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Launching the UI

// Mock rules editor
startActivity(MockcatUi.createLaunchIntent(context))

// HTTP log viewer
startActivity(MockcatLoggerUi.createLaunchIntent(context))

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Release builds

With releaseImplementation("com.mockcat:mockcat-noop-android:0.1.0"), MockcatKtorIntercept and MockcatKtorHttpLogging become plugins that install nothing — the client behaves as if they were never added.