Long-running operations (async responses) in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the HTTP status code returned for an accepted long-running operation?

Consider a REST API that starts a long-running operation and immediately returns a response. What HTTP status code should the server return to indicate the request was accepted but processing is not complete?

A 202 Accepted

B 404 Not Found

C 200 OK

D 500 Internal Server Error

💡 Hint

Think about the status code that means the request is accepted but still processing.

The 202 Accepted status code means the server has accepted the request but the processing is not finished yet. This is common for long-running operations.

❓ Predict Output

intermediate

What is the typical HTTP header used to provide the URL for checking operation status?

When a long-running operation is accepted, the server often provides a URL where the client can check the status. Which HTTP header is commonly used to provide this URL?

A Location

B Retry-After

C Content-Type

D Authorization

💡 Hint

This header tells the client where to find the resource or status.

The Location header is used to provide the URL where the client can check the status of the long-running operation.

❓ Predict Output

advanced

What is the expected JSON response when polling a long-running operation that is still in progress?

A client polls the status URL of a long-running operation. The operation is still running. What JSON response should the server return to indicate this?

Rest API

HTTP/1.1 200 OK
Content-Type: application/json

{
  "status": "InProgress"
}

A { "status": "Unknown" }

B { "status": "Failed", "error": "Timeout" }

C { "status": "Completed", "result": {...} }

D { "status": "InProgress" }

💡 Hint

The status should clearly say the operation is still running.

When the operation is still running, the server returns a JSON with "status": "InProgress" to indicate the client should keep waiting.

❓ Predict Output

advanced

What is the correct final JSON response when a long-running operation completes successfully?

After polling, the long-running operation finishes successfully. What JSON response should the server return?

Rest API

HTTP/1.1 200 OK
Content-Type: application/json

{
  "status": "Succeeded",
  "result": {
    "message": "Operation completed"
  }
}

A { "status": "Failed", "error": "Timeout" }

B { "status": "InProgress" }

C { "status": "Succeeded", "result": { "message": "Operation completed" } }

D { "status": "Cancelled" }

💡 Hint

The status should indicate success and include the result.

The server returns "status": "Succeeded" and includes the result data when the operation finishes successfully.

🧠 Conceptual

expert

Which HTTP method is best suited for starting a long-running operation that creates a resource asynchronously?

You want to design a REST API where clients start a long-running operation that creates a new resource asynchronously. Which HTTP method should you use to start this operation?

A GET

B POST

C PUT

D DELETE

💡 Hint

Think about which method is used to create resources or trigger actions.

The POST method is used to create resources or trigger operations that may take time. GET is for reading, PUT for replacing, DELETE for removing.

Practice

1. What is the main purpose of using long-running operations with async responses in REST APIs?

easy

A. To make the server process all requests instantly.

B. To let clients start a task and check its progress later without waiting.

C. To block the client until the task finishes.

D. To avoid using URLs for task status.

Solution

1. Step 1: Understand client-server interaction in async operations

   Clients start a task and receive a URL to check progress later, avoiding waiting.

2. Step 2: Identify the benefit of async responses

   This approach keeps apps responsive and user-friendly by not blocking clients.

3. Final Answer:

   To let clients start a task and check its progress later without waiting. -> Option B

4. Quick Check:

   Async responses = clients check progress later [OK]

Hint: Async means start task, check later URL [OK]

Common Mistakes:

• Thinking server processes all requests instantly
• Assuming client waits for task completion
• Ignoring the use of status URLs

2. Which HTTP status code is typically returned immediately by a REST API to indicate a long-running operation has started asynchronously?

easy

A. 200 OK

B. 404 Not Found

C. 202 Accepted

D. 500 Internal Server Error

Solution

1. Step 1: Recall HTTP status codes for async start

   202 Accepted means the request is accepted but processing is not complete yet.

2. Step 2: Compare with other codes

   200 OK means completed, 404 means missing resource, 500 means server error.

3. Final Answer:

   202 Accepted -> Option C

4. Quick Check:

   Async start = 202 Accepted [OK]

Hint: 202 means accepted but not done yet [OK]

Common Mistakes:

• Using 200 OK for async start
• Confusing 404 with async status
• Assuming 500 means task started

3. Given this REST API response after starting a long-running task:

{"status": "accepted", "status_url": "/tasks/123/status"}

What should the client do next to get the task result?

medium

A. Send a DELETE request to /tasks/123/status to cancel the task.

B. Send a POST request to /tasks/123/status to get the result.

C. Wait for the server to push the result automatically.

D. Send a GET request to /tasks/123/status to check progress.

Solution

1. Step 1: Identify the purpose of status_url

   The status_url is provided for the client to check the task progress or result.

2. Step 2: Determine correct HTTP method to check status

   GET requests are used to retrieve information, so client should GET the status URL.

3. Final Answer:

   Send a GET request to /tasks/123/status to check progress. -> Option D

4. Quick Check:

   Check progress = GET status URL [OK]

Hint: Use GET on status URL to check progress [OK]

Common Mistakes:

• Using POST instead of GET to check status
• Expecting server to push result without polling
• Using DELETE to check or cancel unintentionally

4. A developer wrote this code to start a long-running task and check its status:

response = start_task()
if response.status_code == 202:
    status_url = response.json()["status_url"]
    result = requests.post(status_url)
    print(result.json())

What is the error in this code?

medium

A. Using POST instead of GET to check the status URL.

B. Not checking if status_url exists in the response.

C. Not handling the case when status_code is not 202.

D. Printing result without parsing JSON.

Solution

1. Step 1: Review HTTP method used to check status

   The code uses POST to check status, but status URLs require GET requests.

2. Step 2: Confirm other parts of code

   Checking status_url existence and status_code handling are good practices but not the main error here.

3. Final Answer:

   Using POST instead of GET to check the status URL. -> Option A

4. Quick Check:

   Status check = GET, not POST [OK]

Hint: Status check always uses GET method [OK]

Common Mistakes:

• Using POST instead of GET for status check
• Ignoring missing status_url key
• Not handling unexpected status codes

5. You want to design a REST API endpoint for a long-running image processing task. Which approach best follows async response principles?

hard

A. Client POSTs image, server returns 202 Accepted with a status URL; client polls status URL until done.

B. Client POSTs image, server processes image immediately and returns 200 OK with result.

C. Client POSTs image, server returns 404 Not Found if task is slow.

D. Client POSTs image, server holds connection open until processing finishes.

Solution

1. Step 1: Understand async response design

   Server accepts task, returns 202 with status URL for client to poll progress.

2. Step 2: Evaluate other options

   Immediate processing (200 OK) blocks client; 404 is wrong status; holding connection open blocks client.

3. Final Answer:

   Client POSTs image, server returns 202 Accepted with a status URL; client polls status URL until done. -> Option A

4. Quick Check:

   Async design = 202 + status URL + polling [OK]

Hint: Async = 202 + status URL + client polls [OK]

Common Mistakes:

• Returning 200 OK immediately for slow tasks
• Using 404 for slow processing
• Keeping connection open until done