Safe methods vs unsafe methods in Rest API - Performance Comparison

Time Complexity: Safe methods vs unsafe methods

O(n)

Understanding Time Complexity

We want to understand how the time it takes to handle safe and unsafe REST API methods changes as the number of requests grows.

How does the server's work increase when processing these different methods?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

// Example REST API handler
function handleRequest(request) {
  if (request.method === 'GET' || request.method === 'HEAD') {
    return readData(request);
  } else {
    return modifyData(request);
  }
}

function readData(request) {
  // Reads data from database
}

function modifyData(request) {
  // Updates database and triggers side effects
}
    

This code handles safe methods (GET, HEAD) by reading data and unsafe methods by modifying data.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Reading or modifying data per request.
• How many times: Once per request, but modifyData may trigger extra operations like database writes or side effects.

How Execution Grows With Input

As the number of requests increases, the server does more work for each request.

Input Size (n)	Approx. Operations
10	10 reads or writes
100	100 reads or writes
1000	1000 reads or writes

Pattern observation: The work grows directly with the number of requests, whether safe or unsafe.

Final Time Complexity

Time Complexity: O(n)

This means the time to handle requests grows linearly with how many requests come in.

Common Mistake

[X] Wrong: "Safe methods like GET take no time or less time than unsafe methods."

[OK] Correct: Both safe and unsafe methods require processing; unsafe methods may do more work, but safe methods still take time to read and respond.

Interview Connect

Understanding how different REST methods affect server work helps you explain API performance and design choices clearly in interviews.

Self-Check

"What if modifyData triggered multiple database writes per request? How would the time complexity change?"

Practice

1. Which HTTP method is considered safe because it only retrieves data without changing anything?

easy

A. DELETE

B. POST

C. PUT

D. GET

Solution

1. Step 1: Understand safe methods

   Safe methods do not change data on the server; they only read or retrieve data.

2. Step 2: Identify the safe method among options

   GET is the method used to request data without modifying it, making it safe.

3. Final Answer:

   GET -> Option D

4. Quick Check:

   Safe method = GET [OK]

Hint: Safe methods only read data, GET is the common safe method [OK]

Common Mistakes:

• Confusing POST as safe
• Thinking PUT is safe
• Assuming DELETE is safe

2. Which of the following is the correct syntax to send data to a server to create a new resource?

easy

A. POST /resource HTTP/1.1

B. GET /resource HTTP/1.1

C. DELETE /resource HTTP/1.1

D. PUT /resource HTTP/1.1

Solution

1. Step 1: Identify method for creating resources

   POST is used to send data to the server to create new resources.

2. Step 2: Check syntax correctness

   POST /resource HTTP/1.1 is the correct syntax to send data for creation.

3. Final Answer:

   POST /resource HTTP/1.1 -> Option A

4. Quick Check:

   Creating resource = POST [OK]

Hint: POST is for sending data to create, syntax includes POST and resource path [OK]

Common Mistakes:

• Using GET to send data
• Confusing DELETE with POST
• Using PUT for creation without context

3. What will be the result of this HTTP request method usage?

PUT /items/123 HTTP/1.1
Content-Type: application/json

{"name": "New Item"}

Choose the correct description.

medium

A. It retrieves the item with ID 123 without changes.

B. It updates or replaces the item with ID 123 with new data.

C. It deletes the item with ID 123 from the server.

D. It creates a new item without specifying an ID.

Solution

1. Step 1: Understand the PUT method purpose

   PUT is used to update or replace an existing resource at a specific URL.

2. Step 2: Analyze the request details

   The request targets /items/123 with JSON data, meaning it updates item 123.

3. Final Answer:

   It updates or replaces the item with ID 123 with new data. -> Option B

4. Quick Check:

   PUT updates resource = C [OK]

Hint: PUT replaces or updates resource at given URL [OK]

Common Mistakes:

• Thinking PUT retrieves data
• Confusing PUT with DELETE
• Assuming PUT creates without ID

4. Identify the error in this HTTP request if the goal is to safely retrieve data:

POST /users HTTP/1.1
Host: example.com

medium

A. The HTTP version is incorrect; it should be HTTP/2.0.

B. The Host header is missing, causing a syntax error.

C. POST is unsafe and changes data; GET should be used to retrieve data.

D. POST cannot be used with /users endpoint.

Solution

1. Step 1: Understand the goal and method used

   The goal is to safely retrieve data, but POST is used which changes data.

2. Step 2: Identify correct method for safe retrieval

   GET is the safe method to retrieve data without side effects.

3. Final Answer:

   POST is unsafe and changes data; GET should be used to retrieve data. -> Option C

4. Quick Check:

   Safe retrieval = GET, not POST [OK]

Hint: Use GET to retrieve data safely, not POST [OK]

Common Mistakes:

• Ignoring method safety
• Thinking Host header is missing
• Confusing HTTP versions

5. You want to design an API endpoint that allows clients to delete a user account safely. Which HTTP method should you use, and why?

hard

A. DELETE, because it explicitly removes the resource on the server.

B. POST, because it can send data and create resources.

C. GET, because it is safe and does not change data.

D. PUT, because it updates existing resources.

Solution

1. Step 1: Identify the action needed

   The goal is to remove (delete) a user account from the server.

2. Step 2: Choose the correct HTTP method for deletion

   DELETE is the method designed to remove resources safely and clearly.

3. Final Answer:

   DELETE, because it explicitly removes the resource on the server. -> Option A

4. Quick Check:

   Deleting resource = DELETE method [OK]

Hint: Use DELETE to remove resources explicitly and safely [OK]

Common Mistakes:

• Using GET for deletion
• Confusing POST with DELETE
• Using PUT instead of DELETE