network-retrofit

name	network-retrofit
description	Trigger: API & Networking. Implementing Retrofit services, Moshi adapters, DTO mapping, and synchronous execution patterns.

Networking with Retrofit & Moshi

Retrofit Service Definition

Use Retrofit 2 interfaces for all network calls. Group related endpoints.

interface UsersService {
    @GET("Users/{userId}")
    suspend fun getUser(@Path("userId") userId: String): UserDTO
}

Synchronous Execution Pattern

While we use suspend functions, the underlying implementation often uses a custom extension to handle Retrofit Call objects synchronously within a coroutine context for better error handling.

executeOrThrow Extension

private fun <T> Call<T>.executeOrThrow(): T {
    val response = execute()
    if (response.isSuccessful) {
        return response.body() ?: throw IOException("Response was null")
    }
    throw IOException("Request failed with code ${response.code()} and message ${response.message()}")
}

Moshi JSON Mapping

Standard for JSON parsing. Use @Json for explicit mapping.

@JsonClass(generateAdapter = true)
data class UserDTO(
    @Json(name = "Name") val name: String,
    @Json(name = "Id") val id: String
)

Custom Moshi Adapters

For non-standard types like LocalDateTime.

class LocalDateTimeAdapter {
    @FromJson
    fun fromJson(json: String): LocalDateTime = LocalDateTime.parse(json)

    @ToJson
    fun toJson(value: LocalDateTime): String = value.toString()
}

Domain Mapping

Decouple the application from API schemas by mapping DTOs to domain models immediately.

class UserRepository(private val service: UsersService) {
    suspend fun getUser(id: String): User = withContext(Dispatchers.IO) {
        val dto = service.getUser(id)
        dto.toDomain()
    }
}