Firebase API API in Kotlin

Firebase API API in Kotlin

This guide shows you how to integrate the Firebase API into your Kotlin application. Firestore, Realtime Database, Auth, Storage, and Cloud Messaging.

Prerequisites

Installation

// build.gradle.kts
dependencies {
    implementation("io.ktor:ktor-client-core:2.3.0")
    implementation("io.ktor:ktor-client-cio:2.3.0")
    implementation("io.ktor:ktor-client-content-negotiation:2.3.0")
    implementation("io.ktor:ktor-serialization-kotlinx-json:2.3.0")
}

Basic Usage

import io.ktor.client.*
import io.ktor.client.engine.cio.*
import io.ktor.client.request.*
import io.ktor.client.statement.*
import kotlinx.coroutines.*

fun main() = runBlocking {
    val apiKey = System.getenv("API_KEY") ?: "YOUR_API_KEY"
    val baseUrl = "https://api.firebase.google.com"

    val client = HttpClient(CIO)
    val response: HttpResponse = client.get("$baseUrl/v1/resources") {
        header("Authorization", "Bearer $apiKey")
        header("Content-Type", "application/json")
    }

    println("Status: ${response.status}")
    println(response.bodyAsText())
    client.close()
}

Error Handling

import io.ktor.client.*
import io.ktor.client.engine.cio.*
import io.ktor.client.request.*
import io.ktor.client.statement.*
import kotlinx.coroutines.*

suspend fun callApiWithRetry(url: String, apiKey: String, maxRetries: Int = 3): HttpResponse {
    val client = HttpClient(CIO)
    var attempt = 0
    while (true) {
        val response = client.get(url) {
            header("Authorization", "Bearer $apiKey")
            header("Content-Type", "application/json")
        }
        if (response.status.value != 429 && response.status.value < 500) {
            client.close()
            return response
        }
        println("Attempt $attempt failed (HTTP ${response.status}). Waiting 60s...")
        delay(60000)
        attempt++
        if (attempt >= maxRetries) {
            client.close()
            throw RuntimeException("Max retries exceeded: ${response.status}")
        }
    }
}

fun main() = runBlocking {
    val apiKey = System.getenv("API_KEY") ?: "YOUR_API_KEY"
    val response = callApiWithRetry("https://api.firebase.google.com/v1/resources", apiKey)
    println(response.bodyAsText())
}

Advanced Usage

import io.ktor.client.*
import io.ktor.client.engine.cio.*
import io.ktor.client.request.*
import io.ktor.client.statement.*
import io.ktor.http.*
import kotlinx.coroutines.*
import kotlinx.serialization.json.*

class FirebaseClient(
    private val apiKey: String,
    private val baseUrl: String = "https://api.firebase.google.com"
) {
    private val client = HttpClient(CIO)

    suspend fun request(method: HttpMethod, path: String, body: String? = null): JsonObject {
        val url = "$baseUrl/v1$path"
        val response = client.request(url) {
            this.method = method
            header("Authorization", "Bearer $apiKey")
            header("Content-Type", "application/json")
            if (body != null) setBody(body)
        }
        if (!response.status.isSuccess()) {
            throw RuntimeException("API Error: HTTP ${response.status}")
        }
        return Json.parseToJsonElement(response.bodyAsText()).jsonObject
    }

    suspend fun listResources(limit: Int = 50): JsonObject =
        request(HttpMethod.Get, "/resources?limit=$limit")

    suspend fun createResource(data: String): JsonObject =
        request(HttpMethod.Post, "/resources", data)
}

fun main() = runBlocking {
    val client = FirebaseClient(System.getenv("API_KEY") ?: "YOUR_API_KEY")
    val resources = client.listResources()
    println("Found ${resources["data"]?.jsonArray?.size ?: 0} resources")
    client.close()
}

Best Practices

  • Store your API key in an environment variable, never in source code
  • Implement retry logic with exponential backoff for 429 and 5xx errors
  • Set reasonable timeouts (10-30 seconds) for all API calls
  • Log request IDs from response headers for debugging
  • Cache responses where appropriate to reduce API calls

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