ktor-patterns

Ktor Client Patterns

Modern HTTP client for Kotlin.

Dependencies

val ktor = "3.5.2"   // current 3.x — verify latest at ktor.io/docs/releases
dependencies {
    implementation("io.ktor:ktor-client-core:$ktor")
    implementation("io.ktor:ktor-client-okhttp:$ktor")
    implementation("io.ktor:ktor-client-content-negotiation:$ktor")
    implementation("io.ktor:ktor-serialization-kotlinx-json:$ktor")
    implementation("io.ktor:ktor-client-logging:$ktor")   // Logger.ANDROID + Logging plugin
    implementation("io.ktor:ktor-client-auth:$ktor")       // bearer-token Auth plugin
}

Client Setup

val httpClient = HttpClient(OkHttp) {
    // JSON serialization
    install(ContentNegotiation) {
        json(Json {
            ignoreUnknownKeys = true
            isLenient = true
            prettyPrint = false
        })
    }
    
    // Timeouts
    install(HttpTimeout) {
        requestTimeoutMillis = 30_000
        connectTimeoutMillis = 10_000
        socketTimeoutMillis = 30_000
    }
    
    // Logging (debug only)
    install(Logging) {
        logger = Logger.ANDROID   // import io.ktor.client.plugins.logging.ANDROID — writes to Logcat when no
                                  // SLF4J provider is on the classpath (falls back to Logger.DEFAULT if one is),
                                  // and splits messages past Android's 4068-char log limit.
                                  // Logger.DEFAULT alone is SLF4J-only and silently no-ops on Android.
        level = if (BuildConfig.DEBUG) LogLevel.BODY else LogLevel.NONE
        sanitizeHeader { it == HttpHeaders.Authorization }   // don't log bearer tokens
    }
    
    // Default request config
    defaultRequest {
        url("https://api.example.com")
        contentType(ContentType.Application.Json)
    }
    
    // Auth
    install(Auth) {
        bearer {
            loadTokens {
                BearerTokens(tokenStorage.accessToken, tokenStorage.refreshToken)
            }
            refreshTokens {
                val tokens: TokenResponse = client.post("auth/refresh") {
                    markAsRefreshTokenRequest()                       // don't recurse into Auth
                    setBody(RefreshRequest(oldTokens?.refreshToken.orEmpty()))
                }.body()                                              // read the body exactly once
                tokenStorage.save(tokens)
                BearerTokens(tokens.accessToken, tokens.refreshToken)
            }
        }
    }
}