OkHttp interceptors in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a logging interceptor to the OkHttpClient builder.

Android Kotlin

val client = OkHttpClient.Builder()
    .addInterceptor({ chain ->
        val request = chain.request()
        println("Request URL: ${request.url}")
        chain.proceed(request)
    })
    .[1]()

Drag options to blanks, or click blank then click option'

Abuild

Brun

Cexecute

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using start() or execute() instead of build()

Forgetting to call any method after adding the interceptor

The OkHttpClient.Builder requires calling build() to create the OkHttpClient instance.

2fill in blank

medium

Complete the code to create an interceptor that adds a custom header "X-Auth" with value "token123".

Android Kotlin

val interceptor = Interceptor { chain ->
    val newRequest = chain.request().newBuilder()
        .[1]("X-Auth", "token123")
        .build()
    chain.proceed(newRequest)
}

Drag options to blanks, or click blank then click option'

AsetHeader

BaddHeader

CremoveHeader

Dheader

Attempts:

3 left

💡 Hint

Common Mistakes

Using setHeader which does not exist

Using header which is a getter, not a setter

To add a header in OkHttp request builder, use addHeader().

3fill in blank

hard

Fix the error in the interceptor code to correctly log the response body as a string.

Android Kotlin

val loggingInterceptor = Interceptor { chain ->
    val response = chain.proceed(chain.request())
    val bodyString = response.body?.string() ?: ""
    println("Response: ${bodyString}")
    [1]
}

Drag options to blanks, or click blank then click option'

Aresponse.newBuilder().body(response.body).build()

Bresponse

Cresponse.newBuilder().body(ResponseBody.create(null, bodyString)).build()

Dresponse.newBuilder().body(ResponseBody.create(response.body?.contentType(), bodyString)).build()

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the original response after consuming the body causes errors

Using null content type loses the original content type

Reading response.body.string() consumes the body, so we must create a new response with a new body containing the same content.

4fill in blank

hard

Fill both blanks to create an interceptor that retries the request once if the response code is 500.

Android Kotlin

val retryInterceptor = Interceptor { chain ->
    var response = chain.proceed(chain.request())
    if (response.code == [1]) {
        response.close()
        response = chain.proceed(chain.request())
    }
    response
}

Drag options to blanks, or click blank then click option'

A500

B404

C200

D503

Attempts:

3 left

💡 Hint

Common Mistakes

Using 404 which means not found

Not closing the original response before retrying

HTTP status code 500 means server error; retrying on 500 is common.

5fill in blank

hard

Fill all three blanks to create a custom interceptor that adds a query parameter "lang" with value "en" to every request URL.

Android Kotlin

val langInterceptor = Interceptor { chain ->
    val originalRequest = chain.request()
    val originalUrl = originalRequest.url
    val newUrl = originalUrl.newBuilder()
        .[1]("lang", "en")
        .build()
    val newRequest = originalRequest.newBuilder()
        .[2](newUrl)
        .build()
    chain.[3](newRequest)
}

Drag options to blanks, or click blank then click option'

AaddQueryParameter

Burl

Cproceed

DaddHeader

Attempts:

3 left

💡 Hint

Common Mistakes

Using addHeader instead of addQueryParameter

Not updating the request URL properly

Calling chain.proceed with the original request

To add a query parameter, use addQueryParameter on the URL builder, set the new URL with url(), and proceed with the new request.

Practice

1. What is the main purpose of an OkHttp interceptor in Android Kotlin?

easy

A. To manage database transactions

B. To observe and modify network requests and responses

C. To create UI components dynamically

D. To handle user input events

Solution

1. Step 1: Understand the role of interceptors

   OkHttp interceptors allow you to watch and change network requests and responses before they are sent or after they are received.

2. Step 2: Compare with other options

   The other options relate to managing database transactions, creating UI components dynamically, and handling user input events, which are unrelated to network interception.

3. Final Answer:

   To observe and modify network requests and responses -> Option B

4. Quick Check:

   Interceptor purpose = Observe and modify network calls [OK]

Hint: Interceptors always deal with network requests/responses [OK]

Common Mistakes:

• Confusing interceptors with UI or database components
• Thinking interceptors handle user input
• Assuming interceptors manage app navigation

2. Which of the following is the correct way to implement an OkHttp interceptor in Kotlin?

easy

A. fun intercept(chain: Chain): Response {
return chain.proceed(chain.request())
}

B. class MyInterceptor : Runnable {
override fun run() {
// code
}
}

C. class MyInterceptor : Interceptor {
override fun intercept(chain: Interceptor.Chain): Response {
return chain.proceed(chain.request())
}
}

D. class MyInterceptor {
fun intercept(chain: Interceptor.Chain) {
// code
}
}

Solution

1. Step 1: Check the interface implementation

   OkHttp interceptors implement the Interceptor interface and override the intercept() method with the correct signature.

2. Step 2: Validate method signature and return type

   The intercept method must take Interceptor.Chain and return a Response object, as shown in class MyInterceptor : Interceptor { override fun intercept(chain: Interceptor.Chain): Response { return chain.proceed(chain.request()) } }.

3. Final Answer:

   Correct interceptor implementation with override and proper method signature -> Option C

4. Quick Check:

   Interceptor class implements Interceptor interface [OK]

Hint: Interceptor must override intercept(chain: Interceptor.Chain): Response [OK]

Common Mistakes:

• Not implementing Interceptor interface
• Wrong method signature or missing return type
• Using unrelated interfaces like Runnable

3. Given this interceptor code snippet, what will be the value of the "User-Agent" header in the outgoing request?

class UserAgentInterceptor : Interceptor {
  override fun intercept(chain: Interceptor.Chain): Response {
    val newRequest = chain.request().newBuilder()
      .header("User-Agent", "MyAppAgent")
      .build()
    return chain.proceed(newRequest)
  }
}

medium

A. The request will have "User-Agent" header set to "MyAppAgent"

B. The request will have no "User-Agent" header

C. The request will have "User-Agent" header set to the default OkHttp value

D. The code will cause a compile error

Solution

1. Step 1: Analyze header modification

   The interceptor creates a new request builder from the original request and sets the "User-Agent" header explicitly to "MyAppAgent".

2. Step 2: Understand header effect

   Setting the header with .header() replaces any existing "User-Agent" header with the new value.

3. Final Answer:

   "User-Agent" header is set to "MyAppAgent" in the outgoing request -> Option A

4. Quick Check:

   Header set by interceptor = "MyAppAgent" [OK]

Hint: .header() replaces existing header values [OK]

Common Mistakes:

• Assuming header is appended instead of replaced
• Thinking default headers remain unchanged
• Confusing compile errors with runtime behavior

4. Identify the error in this interceptor code snippet:

class LoggingInterceptor : Interceptor {
  override fun intercept(chain: Interceptor.Chain): Response {
    val request = chain.request()
    println("Request URL: ${request.url}")
    val response = chain.proceed(request)
    println("Response code: ${response.code}")
  }

medium

A. Missing return statement for the Response object

B. Incorrect method name; should be interceptRequest

C. Cannot use println inside intercept method

D. Request object is not created properly

Solution

1. Step 1: Check method return type

   The intercept method must return a Response object, but this code does not return anything.

2. Step 2: Verify other code parts

   Method name and usage of println are valid; request creation is correct.

3. Final Answer:

   Missing return statement for the Response object -> Option A

4. Quick Check:

   intercept() must return Response [OK]

Hint: Always return the Response from intercept() [OK]

Common Mistakes:

• Forgetting to return the response
• Renaming intercept method incorrectly
• Thinking println is disallowed in intercept

5. You want to create an OkHttp interceptor that retries a request up to 3 times if the response code is 500 (server error). Which approach correctly implements this behavior?

hard

A. Use a separate thread to retry the request after intercept() returns

B. Throw an exception inside intercept() when response code is 500 to trigger retry

C. Modify the request headers to include "Retry: 3" and proceed once

D. Override intercept() to loop up to 3 times calling chain.proceed(request) until response.code != 500 or max retries reached

Solution

1. Step 1: Understand retry logic in intercept()

   Retries must happen inside intercept() by calling chain.proceed(request) multiple times if needed.

2. Step 2: Evaluate options for retry implementation

   Override intercept() to loop up to 3 times calling chain.proceed(request) until response.code != 500 or max retries reached correctly loops and retries up to 3 times checking response code. The other options do not implement retry correctly or rely on unsupported mechanisms.

3. Final Answer:

   Loop inside intercept() to retry request up to 3 times on 500 response -> Option D

4. Quick Check:

   Retry logic = loop in intercept() calling chain.proceed() [OK]

Hint: Retries must be done inside intercept() by repeating chain.proceed() [OK]

Common Mistakes:

• Trying to retry outside intercept() method
• Assuming headers control retry automatically
• Throwing exceptions to trigger retry without handling