Error response format in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this JSON error response?

Given this error response from an API, what is the value of the message field?

Rest API

{
  "error": {
    "code": 404,
    "message": "Resource not found",
    "details": "The requested item does not exist."
  }
}

A "404"

B "Resource not found"

C "The requested item does not exist."

D "error"

💡 Hint

Look inside the error object for the message key.

The message field inside the error object contains the string "Resource not found" which describes the error.

🧠 Conceptual

intermediate

Which HTTP status code is best for a validation error?

You want to send an error response when user input is invalid. Which HTTP status code should you use?

A 200 OK

B 404 Not Found

C 500 Internal Server Error

D 400 Bad Request

💡 Hint

Think about which code means the client sent bad data.

400 Bad Request means the server cannot process the request because of client error, such as invalid input.

🔧 Debug

advanced

What error does this JSON error response cause?

This API error response is sent as a string. What problem will the client face?

Rest API

"{ 'error': { 'code': 401, 'message': 'Unauthorized access' } }"

A SyntaxError due to single quotes in JSON string

B ValueError because code is not a string

C TypeError because of missing error key

D No error, valid JSON string

💡 Hint

JSON requires double quotes for keys and strings.

JSON must use double quotes for keys and string values. Single quotes cause a syntax error when parsing.

🚀 Application

advanced

How many fields are in this error response?

Count the total number of keys in this JSON error response object.

Rest API

{
  "error": {
    "code": 403,
    "message": "Forbidden",
    "details": {
      "reason": "User lacks permission",
      "timestamp": "2024-06-01T12:00:00Z"
    }
  },
  "requestId": "abc123"
}

A 5

B 3

C 6

D 4

💡 Hint

Count all keys at all levels inside the JSON object.

The keys are: error, requestId, and inside error: code, message, details. Inside details: reason, timestamp. Total keys are 5 at top two levels (error, requestId, code, message, details). Nested keys inside details are not counted as separate top-level keys.

❓ Predict Output

expert

Which option produces this error response JSON string?

You want to produce this exact JSON string as an error response: {"error":{"code":500,"message":"Internal Server Error"}}

A json.dumps({'error': {'code': 500, 'message': 'Internal Server Error'}, 'extra': None})

B json.dumps({'error': {'code': '500', 'message': 'Internal Server Error'}})

C json.dumps({'error': {'code': 500, 'message': 'Internal Server Error'}})

D json.dumps({'error': {'code': 500, 'msg': 'Internal Server Error'}})

💡 Hint

Check the exact keys and value types in the JSON string.

Option C matches the exact keys and value types. Option C uses code as string, which changes the output. Option C adds an extra key. Option C uses 'msg' instead of 'message'.

Practice

1. What is the main purpose of an error response format in a REST API?

easy

A. To speed up the API response time

B. To clearly communicate what went wrong during a request

C. To encrypt the data sent to the client

D. To store user information securely

Solution

1. Step 1: Understand the role of error responses

   Error responses tell the client what problem happened when processing their request.

2. Step 2: Identify the main goal

   The main goal is to communicate the error clearly so the client can handle it properly.

3. Final Answer:

   To clearly communicate what went wrong during a request -> Option B

4. Quick Check:

   Error response purpose = clear communication [OK]

Hint: Error responses explain problems clearly to clients [OK]

Common Mistakes:

• Thinking error responses speed up API
• Confusing error format with encryption
• Assuming error responses store data

2. Which of the following is a correct JSON structure for a simple error response in a REST API?

easy

A. {"error": {"code": 404, "message": "Not Found"}}

B. {"status": 200, "message": "Success"}

C. {"data": {"id": 1, "name": "Item"}}

D. {"error_code": "404", "error_msg": "Not Found"}

Solution

1. Step 1: Identify standard error response keys

   Common keys include "error", "code", and "message" to describe the problem.

2. Step 2: Check each option

   {"error": {"code": 404, "message": "Not Found"}} uses "error" with "code" and "message" correctly in JSON format.

3. Final Answer:

   {"error": {"code": 404, "message": "Not Found"}} -> Option A

4. Quick Check:

   Standard error keys = code and message [OK]

Hint: Look for 'error', 'code', and 'message' keys in JSON [OK]

Common Mistakes:

• Confusing success response with error
• Using wrong key names like error_code
• Missing nested error object

3. Given this error response JSON:

{"error": {"code": 401, "message": "Unauthorized"}}

What HTTP status code should the API return?

medium

A. 401

B. 500

C. 404

D. 200

Solution

1. Step 1: Match error code to HTTP status

   The error code 401 means "Unauthorized", which is an HTTP status code for authentication failure.

2. Step 2: Confirm correct HTTP status

   The API should return HTTP status 401 to match the error code in the response body.

3. Final Answer:

   401 -> Option A

4. Quick Check:

   Error code 401 = HTTP status 401 [OK]

Hint: Match error code with HTTP status code [OK]

Common Mistakes:

• Returning 200 for error responses
• Confusing 401 with 404
• Using 500 for client errors

4. You receive this error response from an API:

{"error": {"code": "403", "message": "Forbidden"}}

But your client expects the code as an integer. What is the best fix?

medium

A. Change the message to "Access Denied"

B. Remove the code field entirely

C. Change the code value to an integer 403 in the response

D. Wrap the code in quotes to make it a string

Solution

1. Step 1: Identify data type mismatch

   The code is a string "403" but the client expects an integer 403.

2. Step 2: Fix the data type in the response

   Change the code value from a string to an integer to match client expectations.

3. Final Answer:

   Change the code value to an integer 403 in the response -> Option C

4. Quick Check:

   Match data types for code field [OK]

Hint: Ensure error code data type matches client expectation [OK]

Common Mistakes:

• Removing important error fields
• Changing message instead of code type
• Leaving code as string when integer needed

5. You want to design an error response format that includes an error code, a message, and optional details for debugging. Which JSON structure below best fits this need?

hard

A. {"error": "Bad Request", "code": 400}

B. {"status": "error", "code": 400, "msg": "Bad Request"}

C. {"error_code": 400, "error_message": "Bad Request"}

D. {"error": {"code": 400, "message": "Bad Request", "details": "Missing 'id' parameter"}}

Solution

1. Step 1: Check required fields in each option

   We need code, message, and optional details inside a clear error object.

2. Step 2: Evaluate each JSON structure

   {"error": {"code": 400, "message": "Bad Request", "details": "Missing 'id' parameter"}} includes all three: code, message, and details nested inside "error".

3. Final Answer:

   {"error": {"code": 400, "message": "Bad Request", "details": "Missing 'id' parameter"}} -> Option D

4. Quick Check:

   Include code, message, and details in error object [OK]

Hint: Include optional details inside error object for clarity [OK]

Common Mistakes:

• Omitting details field
• Using inconsistent key names
• Not nesting error info properly