HEAD and OPTIONS methods in Rest API - Step-by-Step Execution

Concept Flow - HEAD and OPTIONS methods

Client sends OPTIONS request

↓

Server responds with allowed methods

↓

Client sends HEAD request

↓

Server responds with headers only

↓

Client processes headers without body

The client first asks the server which methods are allowed using OPTIONS, then requests headers only with HEAD, receiving no body.

Execution Sample

Rest API

OPTIONS /resource HTTP/1.1
Host: example.com

HEAD /resource HTTP/1.1
Host: example.com

Client sends OPTIONS to check allowed methods, then HEAD to get headers without body.

Execution Table

Step	Request Method	Request Target	Server Action	Response Content	Notes
1	OPTIONS	/resource	Check allowed methods for /resource	Headers with Allow: GET, POST, HEAD, OPTIONS	Client learns allowed methods
2	HEAD	/resource	Retrieve headers for /resource	Headers only, no body	Client gets metadata without content
3	-	-	-	-	No body sent in HEAD response

💡 HEAD response ends after headers; OPTIONS response ends after allowed methods headers.

Variable Tracker

Variable	Start	After OPTIONS	After HEAD	Final
Request Method	None	OPTIONS	HEAD	HEAD
Response Headers	None	Allow: GET, POST, HEAD, OPTIONS	Resource headers only	Resource headers only
Response Body	None	None	None	None

Key Moments - 2 Insights

Why does the HEAD response have no body even though the resource exists?

Because HEAD returns only headers without the body, as shown in execution_table step 2 and 3.

What information does the OPTIONS method provide to the client?

OPTIONS returns the allowed HTTP methods for the resource in the Allow header, as seen in execution_table step 1.

Visual Quiz - 3 Questions

Look at the execution_table, what does the server send back in response to the OPTIONS request?

A Only status code 200 OK

B Full resource body

C Headers listing allowed methods

D No response

💡 Hint

Check execution_table row 1 under Response Content

At which step does the server send headers without a body?

A Step 1

B Step 2

C Step 3

D No step sends headers only

💡 Hint

Look at execution_table rows 2 and 3 for Response Content

If the client wants to know if POST is allowed, which method should it use according to the execution flow?

A OPTIONS

B HEAD

C GET

D PUT

💡 Hint

Refer to concept_flow and execution_table step 1 about allowed methods

Concept Snapshot

HEAD and OPTIONS methods:
- OPTIONS asks server which methods are allowed
- Server responds with Allow header listing methods
- HEAD requests headers only, no body
- Useful for checking resource metadata or capabilities
- HEAD response matches GET headers but no content

Full Transcript

This visual execution shows how the HEAD and OPTIONS HTTP methods work. First, the client sends an OPTIONS request to the server asking which HTTP methods are allowed on a resource. The server responds with headers including an Allow header listing methods like GET, POST, HEAD, OPTIONS. Next, the client sends a HEAD request to get only the headers of the resource without the body. The server responds with headers but no content body. This helps clients check resource metadata or capabilities without downloading the full content. The execution table traces each step, showing request method, server action, and response content. The variable tracker shows how request method and response headers change. Key moments clarify why HEAD has no body and what OPTIONS returns. The quiz tests understanding of these steps. The snapshot summarizes the key points for quick review.

Practice

1. What is the primary purpose of the HEAD method in REST APIs?

easy

A. To create a new resource on the server

B. To delete a resource from the server

C. To update a resource partially

D. To retrieve only the headers of a resource without the body

Solution

1. Step 1: Understand the HEAD method role

   The HEAD method requests headers only, not the full content.

2. Step 2: Compare with other methods

   Unlike GET, it does not return the body, only metadata.

3. Final Answer:

   To retrieve only the headers of a resource without the body -> Option D

4. Quick Check:

   HEAD returns headers only [OK]

Hint: HEAD fetches headers only, no content body [OK]

Common Mistakes:

• Confusing HEAD with GET which returns full content
• Thinking HEAD modifies data on server
• Assuming HEAD returns body content

2. Which of the following is the correct syntax to send an OPTIONS request using curl?

easy

A. curl -X POST https://api.example.com/resource

B. curl -X HEAD https://api.example.com/resource

C. curl -X OPTIONS https://api.example.com/resource

D. curl --get https://api.example.com/resource

Solution

1. Step 1: Identify the method flag in curl

   The -X option specifies the HTTP method to use.

2. Step 2: Match the method to the question

   To send an OPTIONS request, use -X OPTIONS.

3. Final Answer:

   curl -X OPTIONS https://api.example.com/resource -> Option C

4. Quick Check:

   curl -X OPTIONS sends OPTIONS request [OK]

Hint: Use curl -X OPTIONS to send OPTIONS request [OK]

Common Mistakes:

• Using -X HEAD instead of OPTIONS
• Using --get which sends GET request
• Using POST method incorrectly

3. Given the following HTTP response headers from an OPTIONS request:

Allow: GET, POST, OPTIONS, HEAD

What does this header tell the client?

medium

A. The server supports only GET and POST methods

B. The server supports GET, POST, OPTIONS, and HEAD methods on this resource

C. The server denies all methods except OPTIONS

D. The server supports DELETE and PUT methods

Solution

1. Step 1: Read the Allow header

   The Allow header lists HTTP methods the server supports for the resource.

2. Step 2: Interpret the methods listed

   It shows GET, POST, OPTIONS, and HEAD are allowed methods.

3. Final Answer:

   The server supports GET, POST, OPTIONS, and HEAD methods on this resource -> Option B

4. Quick Check:

   Allow header lists supported methods [OK]

Hint: Allow header shows all supported methods [OK]

Common Mistakes:

• Ignoring OPTIONS and HEAD in the list
• Assuming only GET and POST are allowed
• Confusing Allow header with authentication

4. You wrote this code to handle HEAD requests in your REST API server:

if request.method == 'HEAD':
    return get_resource()

But clients receive the full content body. What is the problem?

medium

A. The code returns full content instead of headers only

B. The method name should be lowercase 'head'

C. HEAD requests must be redirected to GET method

D. The server must respond with status 201 for HEAD

Solution

1. Step 1: Analyze the code behavior

   The code calls get_resource() which returns full content including body.

2. Step 2: Understand HEAD response requirements

   HEAD must return headers only, no body content.

3. Final Answer:

   The code returns full content instead of headers only -> Option A

4. Quick Check:

   HEAD returns headers only, not full body [OK]

Hint: HEAD must not return body, only headers [OK]

Common Mistakes:

• Returning full content for HEAD requests
• Using wrong method name case
• Confusing HEAD with GET behavior

5. You want to optimize your REST API by using HEAD and OPTIONS methods. Which approach best improves client efficiency?

hard

A. Use HEAD to check resource existence and OPTIONS to discover allowed methods before sending requests

B. Use OPTIONS to fetch full resource data and HEAD to update resources

C. Use HEAD to delete resources and OPTIONS to create new ones

D. Ignore HEAD and OPTIONS and always use GET and POST

Solution

1. Step 1: Understand HEAD usage

   HEAD checks if a resource exists by fetching headers without body, saving bandwidth.

2. Step 2: Understand OPTIONS usage

   OPTIONS tells clients which HTTP methods are allowed, helping avoid invalid requests.

3. Step 3: Combine for efficiency

   Using both before heavy requests reduces unnecessary data transfer and errors.

4. Final Answer:

   Use HEAD to check resource existence and OPTIONS to discover allowed methods before sending requests -> Option A

5. Quick Check:

   HEAD checks headers, OPTIONS lists methods [OK]

Hint: HEAD checks existence, OPTIONS lists allowed methods [OK]

Common Mistakes:

• Using OPTIONS to fetch full data (wrong)
• Using HEAD to modify resources (wrong)
• Ignoring these methods and wasting bandwidth