Android Ktor Error Handling

When building Android applications using Ktor, robust error handling is crucial for providing a smooth and reliable user experience. Ktor offers several mechanisms to gracefully manage errors that can arise during HTTP requests and responses.

Common Error Scenarios

Before diving into error handling techniques, it's helpful to understand common error scenarios you might encounter:

• Network Issues: Connection timeouts, DNS resolution failures, and no internet connectivity.
• Server Errors: HTTP status codes like 500 (Internal Server Error), 502 (Bad Gateway), 503 (Service Unavailable).
• Client Errors: HTTP status codes like 400 (Bad Request), 401 (Unauthorized), 404 (Not Found).
• Serialization/Deserialization Errors: Issues converting data to and from JSON or other formats.
• Exceptions within the Application: Runtime exceptions thrown during request processing.

Error Handling Techniques

1. Try-Catch Blocks

The most basic approach is to wrap potentially problematic code blocks within try-catch blocks. This allows you to catch specific exceptions and handle them appropriately.

try {
    val response: HttpResponse = client.get("https://example.com/api/data")
    // Process the response
} catch (e: ConnectTimeoutException) {
    // Handle connection timeout
    Log.e("Ktor", "Connection Timeout: ${e.message}")
    // Show an error message to the user
} catch (e: Exception) {
    // Handle other exceptions
    Log.e("Ktor", "An error occurred: ${e.message}")
    // Show a generic error message
}

2. Status Code Handling

Ktor provides access to the HTTP status code of the response. You can use this to check for errors and handle them accordingly.

val response: HttpResponse = client.get("https://example.com/api/data")

when (response.status) {
    HttpStatusCode.OK -> {
        // Process the successful response
    }
    HttpStatusCode.NotFound -> {
        // Handle resource not found
        Log.w("Ktor", "Resource not found")
    }
    HttpStatusCode.InternalServerError -> {
        // Handle server error
        Log.e("Ktor", "Internal Server Error")
    }
    else -> {
        // Handle other status codes
        Log.w("Ktor", "Unexpected status code: ${response.status}")
    }
}

3. Exception Handling in Response Pipeline

Ktor allows you to intercept responses using the response pipeline. You can install a feature in the client to handle exceptions during response processing.

install(ResponseObserver) {
  onResponse { response ->
    if (!response.status.isSuccess()) {
      // Log error or perform retry logic.
      Log.e("Ktor", "Request failed with status: ${response.status}")
    }
  }
}

4. Custom Exceptions

For more complex scenarios, consider defining custom exception classes to represent specific error conditions. This can improve code readability and maintainability.

5. Retry Mechanisms

For transient errors like network glitches or temporary server unavailability, implementing a retry mechanism can improve the resilience of your application. Ktor doesn't have built in retry functionality, but you can achieve retries using libraries such as kotlinx-coroutines-core's kotlinx.coroutines.delay and write logic to retry the request with a backoff strategy.

Best Practices

• Log Errors: Log detailed error information for debugging and monitoring.
• Provide User-Friendly Messages: Display informative error messages to the user. Avoid exposing technical details.
• Graceful Degradation: Design your application to gracefully handle errors and continue functioning, even if some features are unavailable.
• Test Error Handling: Thoroughly test your error handling logic to ensure it works as expected.

By implementing these error handling techniques, you can build robust and reliable Android applications using Ktor.