Safe methods vs unsafe methods in Rest API - Quick Revision & Key Differences

Recall & Review

beginner

What are safe methods in REST APIs?

Safe methods are HTTP methods that do not change the server's state. They are used only to retrieve data without causing side effects. Examples include GET and HEAD.

beginner

Give examples of unsafe methods in REST APIs.

Unsafe methods are HTTP methods that can change the server's state or data. Examples include POST, PUT, DELETE, and PATCH.

intermediate

Why are safe methods considered 'safe'?

Because they do not modify data on the server, so calling them multiple times has no side effects. They are read-only.

intermediate

What does it mean for a method to be idempotent?

An idempotent method means that making the same request multiple times results in the same server state as making it once. Examples: GET, PUT, DELETE.

beginner

Is POST a safe or unsafe method? Why?

POST is an unsafe method because it usually creates or modifies data on the server, changing its state.

Which HTTP method is considered safe?

A GET

B POST

C DELETE

D PUT

GET is a safe method because it only retrieves data without changing server state.

Which method is NOT idempotent?

A PUT

B DELETE

C POST

D GET

POST is not idempotent because multiple identical POST requests can create multiple resources.

What does an unsafe method do?

A Modifies server data

B Only reads data

C Is always idempotent

D Never changes server state

Unsafe methods modify server data or state.

Which method is both safe and idempotent?

A POST

B GET

C PATCH

D POST and PUT

GET is safe and idempotent because it only reads data and does not change server state.

Which HTTP method is typically used to delete a resource?

A GET

B POST

C HEAD

D DELETE

DELETE is used to remove resources and is an unsafe method.

Explain the difference between safe and unsafe HTTP methods in REST APIs.

Think about whether the method changes data or just reads it.

Describe what idempotency means for HTTP methods and give examples.

Consider what happens if you repeat the same request many times.

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