Lithic Kotlin API Library

The Lithic Kotlin SDK provides convenient access to the Lithic REST API from applications written in Kotlin.

The Lithic Kotlin SDK is similar to the Lithic Java SDK but with minor differences that make it more ergonomic for use in Kotlin, such as nullable values instead of Optional, Sequence instead of Stream, and suspend functions instead of CompletableFuture.

The REST API documentation can be found on docs.lithic.com. KDocs are available on javadoc.io.

Installation

Gradle

implementation("com.lithic.api:lithic-kotlin:0.90.0")

Maven

<dependency>
  <groupId>com.lithic.api</groupId>
  <artifactId>lithic-kotlin</artifactId>
  <version>0.90.0</version>
</dependency>

Requirements

This library requires Java 8 or later.

Usage

import com.lithic.api.client.LithicClient
import com.lithic.api.client.okhttp.LithicOkHttpClient
import com.lithic.api.models.Card
import com.lithic.api.models.CardCreateParams

// Configures using the `LITHIC_API_KEY`, `LITHIC_WEBHOOK_SECRET` and `LITHIC_BASE_URL` environment variables
val client: LithicClient = LithicOkHttpClient.fromEnv()

val params: CardCreateParams = CardCreateParams.builder()
    .type(CardCreateParams.Type.SINGLE_USE)
    .build()
val card: Card = client.cards().create(params)

Client configuration

Configure the client using environment variables:

import com.lithic.api.client.LithicClient
import com.lithic.api.client.okhttp.LithicOkHttpClient

// Configures using the `LITHIC_API_KEY`, `LITHIC_WEBHOOK_SECRET` and `LITHIC_BASE_URL` environment variables
val client: LithicClient = LithicOkHttpClient.fromEnv()

Or manually:

import com.lithic.api.client.LithicClient
import com.lithic.api.client.okhttp.LithicOkHttpClient

val client: LithicClient = LithicOkHttpClient.builder()
    .apiKey("My Lithic API Key")
    .build()

Or using a combination of the two approaches:

import com.lithic.api.client.LithicClient
import com.lithic.api.client.okhttp.LithicOkHttpClient

val client: LithicClient = LithicOkHttpClient.builder()
    // Configures using the `LITHIC_API_KEY`, `LITHIC_WEBHOOK_SECRET` and `LITHIC_BASE_URL` environment variables
    .fromEnv()
    .apiKey("My Lithic API Key")
    .build()

See this table for the available options:

Setter	Environment variable	Required	Default value
apiKey	LITHIC_API_KEY	true	-
webhookSecret	LITHIC_WEBHOOK_SECRET	false	-
baseUrl	LITHIC_BASE_URL	true	"https://api.lithic.com"

Tip

Don't create more than one client in the same application. Each client has a connection pool and thread pools, which are more efficient to share between requests.

Requests and responses

To send a request to the Lithic API, build an instance of some Params class and pass it to the corresponding client method. When the response is received, it will be deserialized into an instance of a Kotlin class.

For example, client.cards().create(...) should be called with an instance of CardCreateParams, and it will return an instance of Card.

Immutability

Each class in the SDK has an associated builder or factory method for constructing it.

Each class is immutable once constructed. If the class has an associated builder, then it has a toBuilder() method, which can be used to convert it back to a builder for making a modified copy.

Because each class is immutable, builder modification will never affect already built class instances.

Asynchronous execution

The default client is synchronous. To switch to asynchronous execution, call the async() method:

import com.lithic.api.client.LithicClient
import com.lithic.api.client.okhttp.LithicOkHttpClient
import com.lithic.api.models.Card
import com.lithic.api.models.CardCreateParams

// Configures using the `LITHIC_API_KEY`, `LITHIC_WEBHOOK_SECRET` and `LITHIC_BASE_URL` environment variables
val client: LithicClient = LithicOkHttpClient.fromEnv()

val params: CardCreateParams = CardCreateParams.builder()
    .type(CardCreateParams.Type.SINGLE_USE)
    .build()
val card: Card = client.async().cards().create(params)

Or create an asynchronous client from the beginning:

import com.lithic.api.client.LithicClientAsync
import com.lithic.api.client.okhttp.LithicOkHttpClientAsync
import com.lithic.api.models.Card
import com.lithic.api.models.CardCreateParams

// Configures using the `LITHIC_API_KEY`, `LITHIC_WEBHOOK_SECRET` and `LITHIC_BASE_URL` environment variables
val client: LithicClientAsync = LithicOkHttpClientAsync.fromEnv()

val params: CardCreateParams = CardCreateParams.builder()
    .type(CardCreateParams.Type.SINGLE_USE)
    .build()
val card: Card = client.cards().create(params)

The asynchronous client supports the same options as the synchronous one, except most methods are suspending.

Raw responses

The SDK defines methods that deserialize responses into instances of Kotlin classes. However, these methods don't provide access to the response headers, status code, or the raw response body.

To access this data, prefix any HTTP method call on a client or service with withRawResponse():

import com.lithic.api.core.http.Headers
import com.lithic.api.core.http.HttpResponseFor
import com.lithic.api.models.Card
import com.lithic.api.models.CardCreateParams

val params: CardCreateParams = CardCreateParams.builder()
    .type(CardCreateParams.Type.SINGLE_USE)
    .build()
val card: HttpResponseFor<Card> = client.cards().withRawResponse().create(params)

val statusCode: Int = card.statusCode()
val headers: Headers = card.headers()

You can still deserialize the response into an instance of a Kotlin class if needed:

import com.lithic.api.models.Card

val parsedCard: Card = card.parse()

Error handling

The SDK throws custom unchecked exception types:

• LithicServiceException: Base class for HTTP errors. See this table for which exception subclass is thrown for each HTTP status code:

  Status	Exception
  400	BadRequestException
  401	UnauthorizedException
  403	PermissionDeniedException
  404	NotFoundException
  422	UnprocessableEntityException
  429	RateLimitException
  5xx	InternalServerException
  others	UnexpectedStatusCodeException

• LithicIoException: I/O networking errors.

• LithicInvalidDataException: Failure to interpret successfully parsed data. For example, when accessing a property that's supposed to be required, but the API unexpectedly omitted it from the response.

• LithicException: Base class for all exceptions. Most errors will result in one of the previously mentioned ones, but completely generic errors may be thrown using the base class.

Pagination

The SDK defines methods that return a paginated lists of results. It provides convenient ways to access the results either one page at a time or item-by-item across all pages.

Auto-pagination

To iterate through all results across all pages, use the autoPager() method, which automatically fetches more pages as needed.

When using the synchronous client, the method returns a Sequence

import com.lithic.api.models.CardListPage

val page: CardListPage = client.cards().list()
page.autoPager()
    .take(50)
    .forEach { card -> println(card) }

When using the asynchronous client, the method returns a Flow:

import com.lithic.api.models.CardListPageAsync

val page: CardListPageAsync = client.async().cards().list()
page.autoPager()
    .take(50)
    .forEach { card -> println(card) }

Manual pagination

To access individual page items and manually request the next page, use the items(), hasNextPage(), and nextPage() methods:

import com.lithic.api.models.CardListPage
import com.lithic.api.models.NonPciCard

val page: CardListPage = client.cards().list()
while (true) {
    for (card in page.items()) {
        println(card)
    }

    if (!page.hasNextPage()) {
        break
    }

    page = page.nextPage()
}

Logging

The SDK uses the standard OkHttp logging interceptor.

Enable logging by setting the LITHIC_LOG environment variable to info:

$ export LITHIC_LOG=info

Or to debug for more verbose logging:

$ export LITHIC_LOG=debug

Webhook Verification

We provide helper methods for verifying that a webhook request came from Lithic, and not a malicious third party.

You can use lithic.webhooks().verifySignature(body, headers, secret?) or lithic.webhooks().unwrap(body, headers, secret?), both of which will raise an error if the signature is invalid.

Note that the "body" parameter must be the raw JSON string sent from the server (do not parse it first). The .unwrap() method can parse this JSON for you.

Jackson

The SDK depends on Jackson for JSON serialization/deserialization. It is compatible with version 2.13.4 or higher, but depends on version 2.18.2 by default.

The SDK throws an exception if it detects an incompatible Jackson version at runtime (e.g. if the default version was overridden in your Maven or Gradle config).

If the SDK threw an exception, but you're certain the version is compatible, then disable the version check using the checkJacksonVersionCompatibility on LithicOkHttpClient or LithicOkHttpClientAsync.

Caution

We make no guarantee that the SDK works correctly when the Jackson version check is disabled.

Network options

Retries

The SDK automatically retries 2 times by default, with a short exponential backoff.

Only the following error types are retried:

• Connection errors (for example, due to a network connectivity problem)
• 408 Request Timeout
• 409 Conflict
• 429 Rate Limit
• 5xx Internal

The API may also explicitly instruct the SDK to retry or not retry a response.

To set a custom number of retries, configure the client using the maxRetries method:

import com.lithic.api.client.LithicClient
import com.lithic.api.client.okhttp.LithicOkHttpClient

val client: LithicClient = LithicOkHttpClient.builder()
    .fromEnv()
    .maxRetries(4)
    .build()

Timeouts

Requests time out after 1 minute by default.

To set a custom timeout, configure the method call using the timeout method:

import com.lithic.api.models.Card

val card: Card = client.cards().create(
  params, RequestOptions.builder().timeout(Duration.ofSeconds(30)).build()
)

Or configure the default for all method calls at the client level:

import com.lithic.api.client.LithicClient
import com.lithic.api.client.okhttp.LithicOkHttpClient
import java.time.Duration

val client: LithicClient = LithicOkHttpClient.builder()
    .fromEnv()
    .timeout(Duration.ofSeconds(30))
    .build()

Proxies

To route requests through a proxy, configure the client using the proxy method:

import com.lithic.api.client.LithicClient
import com.lithic.api.client.okhttp.LithicOkHttpClient
import java.net.InetSocketAddress
import java.net.Proxy

val client: LithicClient = LithicOkHttpClient.builder()
    .fromEnv()
    .proxy(Proxy(
      Proxy.Type.HTTP, InetSocketAddress(
        "https://example.com", 8080
      )
    ))
    .build()

Environments

The SDK sends requests to the production by default. To send requests to a different environment, configure the client like so:

import com.lithic.api.client.LithicClient
import com.lithic.api.client.okhttp.LithicOkHttpClient

val client: LithicClient = LithicOkHttpClient.builder()
    .fromEnv()
    .sandbox()
    .build()

Custom HTTP client

The SDK consists of three artifacts:

• lithic-kotlin-core
  • Contains core SDK logic
  • Does not depend on OkHttp
  • Exposes LithicClient, LithicClientAsync, LithicClientImpl, and LithicClientAsyncImpl, all of which can work with any HTTP client
• lithic-kotlin-client-okhttp
  • Depends on OkHttp
  • Exposes LithicOkHttpClient and LithicOkHttpClientAsync, which provide a way to construct LithicClientImpl and LithicClientAsyncImpl, respectively, using OkHttp
• lithic-kotlin
  • Depends on and exposes the APIs of both lithic-kotlin-core and lithic-kotlin-client-okhttp
  • Does not have its own logic

This structure allows replacing the SDK's default HTTP client without pulling in unnecessary dependencies.

Customized OkHttpClient

Tip

Try the available network options before replacing the default client.

To use a customized OkHttpClient:

1. Replace your lithic-kotlin dependency with lithic-kotlin-core
2. Copy lithic-kotlin-client-okhttp's OkHttpClient class into your code and customize it
3. Construct LithicClientImpl or LithicClientAsyncImpl, similarly to LithicOkHttpClient or LithicOkHttpClientAsync, using your customized client

Completely custom HTTP client

To use a completely custom HTTP client:

1. Replace your lithic-kotlin dependency with lithic-kotlin-core
2. Write a class that implements the HttpClient interface
3. Construct LithicClientImpl or LithicClientAsyncImpl, similarly to LithicOkHttpClient or LithicOkHttpClientAsync, using your new client class

Undocumented API functionality

The SDK is typed for convenient usage of the documented API. However, it also supports working with undocumented or not yet supported parts of the API.

Parameters

To set undocumented parameters, call the putAdditionalHeader, putAdditionalQueryParam, or putAdditionalBodyProperty methods on any Params class:

import com.lithic.api.core.JsonValue
import com.lithic.api.models.CardCreateParams

val params: CardCreateParams = CardCreateParams.builder()
    .putAdditionalHeader("Secret-Header", "42")
    .putAdditionalQueryParam("secret_query_param", "42")
    .putAdditionalBodyProperty("secretProperty", JsonValue.from("42"))
    .build()

These can be accessed on the built object later using the _additionalHeaders(), _additionalQueryParams(), and _additionalBodyProperties() methods.

To set a documented parameter or property to an undocumented or not yet supported value, pass a JsonValue object to its setter:

import com.lithic.api.core.JsonValue
import com.lithic.api.models.CardCreateParams

val params: CardCreateParams = CardCreateParams.builder()
    .type(JsonValue.from(42))
    .build()

The most straightforward way to create a JsonValue is using its from(...) method:

import com.lithic.api.core.JsonValue

// Create primitive JSON values
val nullValue: JsonValue = JsonValue.from(null)
val booleanValue: JsonValue = JsonValue.from(true)
val numberValue: JsonValue = JsonValue.from(42)
val stringValue: JsonValue = JsonValue.from("Hello World!")

// Create a JSON array value equivalent to `["Hello", "World"]`
val arrayValue: JsonValue = JsonValue.from(listOf(
  "Hello", "World"
))

// Create a JSON object value equivalent to `{ "a": 1, "b": 2 }`
val objectValue: JsonValue = JsonValue.from(mapOf(
  "a" to 1, "b" to 2
))

// Create an arbitrarily nested JSON equivalent to:
// {
//   "a": [1, 2],
//   "b": [3, 4]
// }
val complexValue: JsonValue = JsonValue.from(mapOf(
  "a" to listOf(
    1, 2
  ), "b" to listOf(
    3, 4
  )
))

Normally a Builder class's build method will throw IllegalStateException if any required parameter or property is unset.

To forcibly omit a required parameter or property, pass JsonMissing:

import com.lithic.api.core.JsonMissing
import com.lithic.api.models.CardCreateParams

val params: CardCreateParams = CardCreateParams.builder()
    .type(JsonMissing.of())
    .build()

Response properties

To access undocumented response properties, call the _additionalProperties() method:

import com.lithic.api.core.JsonBoolean
import com.lithic.api.core.JsonNull
import com.lithic.api.core.JsonNumber
import com.lithic.api.core.JsonValue

val additionalProperties: Map<String, JsonValue> = client.cards().create(params)._additionalProperties()
val secretPropertyValue: JsonValue = additionalProperties.get("secretProperty")

val result = when (secretPropertyValue) {
    is JsonNull -> "It's null!"
    is JsonBoolean -> "It's a boolean!"
    is JsonNumber -> "It's a number!"
    // Other types include `JsonMissing`, `JsonString`, `JsonArray`, and `JsonObject`
    else -> "It's something else!"
}

To access a property's raw JSON value, which may be undocumented, call its _ prefixed method:

import com.lithic.api.core.JsonField
import com.lithic.api.models.CardCreateParams

val type: JsonField<CardCreateParams.Type> = client.cards().create(params)._type()

if (type.isMissing()) {
  // The property is absent from the JSON response
} else if (type.isNull()) {
  // The property was set to literal null
} else {
  // Check if value was provided as a string
  // Other methods include `asNumber()`, `asBoolean()`, etc.
  val jsonString: String? = type.asString();

  // Try to deserialize into a custom type
  val myObject: MyClass = type.asUnknown()!!.convert(MyClass::class.java)
}

Response validation

In rare cases, the API may return a response that doesn't match the expected type. For example, the SDK may expect a property to contain a String, but the API could return something else.

By default, the SDK will not throw an exception in this case. It will throw LithicInvalidDataException only if you directly access the property.

If you would prefer to check that the response is completely well-typed upfront, then either call validate():

import com.lithic.api.models.Card

val card: Card = client.cards().create(params).validate()

Or configure the method call to validate the response using the responseValidation method:

import com.lithic.api.models.Card

val card: Card = client.cards().create(
  params, RequestOptions.builder().responseValidation(true).build()
)

Or configure the default for all method calls at the client level:

import com.lithic.api.client.LithicClient
import com.lithic.api.client.okhttp.LithicOkHttpClient

val client: LithicClient = LithicOkHttpClient.builder()
    .fromEnv()
    .responseValidation(true)
    .build()

FAQ

Why don't you use plain enum classes?

Kotlin enum classes are not trivially forwards compatible. Using them in the SDK could cause runtime exceptions if the API is updated to respond with a new enum value.

Why do you represent fields using JsonField<T> instead of just plain T?

Using JsonField<T> enables a few features:

• Allowing usage of undocumented API functionality
• Lazily validating the API response against the expected shape
• Representing absent vs explicitly null values

Why don't you use data classes?

It is not backwards compatible to add new fields to a data class and we don't want to introduce a breaking change every time we add a field to a class.

Why don't you use checked exceptions?

Checked exceptions are widely considered a mistake in the Java programming language. In fact, they were omitted from Kotlin for this reason.

Checked exceptions:

• Are verbose to handle
• Encourage error handling at the wrong level of abstraction, where nothing can be done about the error
• Are tedious to propagate due to the function coloring problem
• Don't play well with lambdas (also due to the function coloring problem)

Semantic versioning

This package generally follows SemVer conventions, though certain backwards-incompatible changes may be released as minor versions:

1. Changes to library internals which are technically public but not intended or documented for external use. (Please open a GitHub issue to let us know if you are relying on such internals.)
2. Changes that we do not expect to impact the vast majority of users in practice.

We take backwards-compatibility seriously and work hard to ensure you can rely on a smooth upgrade experience.

We are keen for your feedback; please open an issue with questions, bugs, or suggestions.