Request headers (Content-Type, Accept) in Rest API - Step-by-Step Execution

Concept Flow - Request headers (Content-Type, Accept)

Client prepares request

↓

Set headers: Content-Type, Accept

↓

Send request to server

↓

Server reads Content-Type

↓

Server processes data accordingly

↓

Server prepares response

↓

Server sets response Content-Type

↓

Client reads response based on Accept header

The client sets Content-Type to tell the server the data format sent, and Accept to tell what response formats it can handle. The server uses these headers to process and respond correctly.

Execution Sample

Rest API

POST /api/data HTTP/1.1
Content-Type: application/json
Accept: application/xml

{"name":"Alice"}

Client sends a POST request with JSON data and asks for XML response.

Execution Table

Step	Action	Header Checked/Set	Value	Effect
1	Client prepares request	Content-Type	application/json	Tells server data is JSON
2	Client prepares request	Accept	application/xml	Tells server client wants XML response
3	Client sends request	-	-	Request sent with headers and body
4	Server receives request	Content-Type	application/json	Server knows to parse JSON body
5	Server processes data	-	-	Server reads JSON data {"name":"Alice"}
6	Server prepares response	Content-Type	application/xml	Server sets response format to XML
7	Server sends response	-	-	Response sent in XML format
8	Client receives response	Accept	application/xml	Client reads XML response as requested
9	End	-	-	Request-response cycle complete

💡 Request-response cycle ends after client receives response matching Accept header

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	After Step 6	Final
Content-Type	none	application/json	application/json	application/json	application/xml	application/xml
Accept	none	none	application/xml	application/xml	application/xml	application/xml
Request Body	empty	empty	{"name":"Alice"}	{"name":"Alice"}	{"name":"Alice"}	{"name":"Alice"}
Response Body	empty	empty	empty	empty	<name>Alice</name>	<name>Alice</name>

Key Moments - 3 Insights

Why do we set Content-Type in the request?

Content-Type tells the server what format the data in the request body is, so the server knows how to read it. See execution_table step 4.

What does the Accept header do?

Accept tells the server what response formats the client can handle. The server uses this to decide the response format. See execution_table steps 2 and 6.

Can the server ignore the Accept header?

Yes, but usually it tries to honor it. If it can't provide the requested format, it may respond with an error or default format. This is implied in step 6.

Visual Quiz - 3 Questions

Look at the execution_table, what is the Content-Type header value when the server processes the request?

A application/json

B text/plain

C application/xml

D none

💡 Hint

Check step 4 in the execution_table where the server reads Content-Type

At which step does the client specify it wants an XML response?

A Step 1

B Step 3

C Step 2

D Step 6

💡 Hint

Look at when Accept header is set in the execution_table

If the client changed Accept to application/json, what would likely change in the execution_table?

A Client would send JSON body at step 1

B Server would set response Content-Type to application/json at step 6

C Server would ignore Content-Type header

D No change in response format

💡 Hint

Refer to step 6 where server sets response Content-Type based on Accept header

Concept Snapshot

Request headers Content-Type and Accept:
- Content-Type: tells server the format of data sent (e.g., application/json)
- Accept: tells server what response formats client can handle (e.g., application/xml)
- Server uses Content-Type to parse request body
- Server uses Accept to format response
- Proper headers ensure smooth data exchange in APIs

Full Transcript

In REST API communication, the client sends headers to tell the server about the data format. Content-Type header specifies the format of the data sent in the request body, such as JSON or XML. The Accept header tells the server what response formats the client can understand. The server reads Content-Type to parse the incoming data correctly and uses Accept to decide the response format. This exchange ensures both sides understand each other and data is processed properly. The execution steps show the client setting these headers, the server reading them, processing data, and responding accordingly.

Practice

1. What does the Content-Type header specify in an HTTP request?

easy

A. The format of the data being sent to the server

B. The format of the data the client wants to receive

C. The server's IP address

D. The HTTP method used in the request

Solution

1. Step 1: Understand the role of Content-Type

   The Content-Type header tells the server what format the request body data is in, such as JSON or XML.

2. Step 2: Differentiate from Accept header

   The Accept header tells the server what response format the client wants, not the data sent.

3. Final Answer:

   The format of the data being sent to the server -> Option A

4. Quick Check:

   Content-Type = request data format [OK]

Hint: Content-Type = your data format sent [OK]

Common Mistakes:

• Confusing Content-Type with Accept header
• Thinking Content-Type is about response format
• Ignoring the header completely

2. Which of the following is the correct way to set the Accept header to request JSON data in an HTTP request?

easy

A. Content-Type: application/json

B. Accept: text/html

C. Accept: application/json

D. Content-Type: text/plain

Solution

1. Step 1: Identify the Accept header usage

   The Accept header tells the server what response format the client wants, such as JSON.

2. Step 2: Match the correct MIME type for JSON

   The MIME type for JSON is application/json, so the header should be Accept: application/json.

3. Final Answer:

   Accept: application/json -> Option C

4. Quick Check:

   Accept header for JSON = application/json [OK]

Hint: Accept header = desired response format [OK]

Common Mistakes:

• Using Content-Type instead of Accept for response format
• Using wrong MIME type like text/html for JSON
• Mixing up header names

3. Given this HTTP request snippet:

POST /api/data HTTP/1.1
Host: example.com
Content-Type: application/json
Accept: application/xml

{"name": "Alice"}

What format will the server expect the request body to be, and what format will it try to respond with?

medium

A. Request body XML, response JSON

B. Request body XML, response XML

C. Request body JSON, response JSON

D. Request body JSON, response XML

Solution

1. Step 1: Analyze Content-Type header

   The Content-Type is application/json, so the server expects JSON data in the request body.

2. Step 2: Analyze Accept header

   The Accept header is application/xml, so the client wants the response in XML format.

3. Final Answer:

   Request body JSON, response XML -> Option D

4. Quick Check:

   Content-Type = JSON, Accept = XML [OK]

Hint: Content-Type = sent data, Accept = wanted response [OK]

Common Mistakes:

• Mixing up Content-Type and Accept roles
• Assuming response matches request format
• Ignoring headers and guessing defaults

4. You wrote this HTTP request:

POST /submit HTTP/1.1
Host: example.com
Content-Type: application/json
Accept: application/json

name=John&age=30

Why might the server reject this request or fail to parse the data?

medium

A. Because the HTTP method POST is not allowed

B. Because the Content-Type says JSON but the body is URL-encoded form data

C. Because Accept header is incorrect for JSON

D. Because the Host header is missing

Solution

1. Step 1: Check Content-Type and body format

   The Content-Type is application/json, but the body is name=John&age=30, which is URL-encoded form data, not JSON.

2. Step 2: Understand server parsing behavior

   The server expects JSON data but receives form data, so it may reject or fail to parse the request.

3. Final Answer:

   Because the Content-Type says JSON but the body is URL-encoded form data -> Option B

4. Quick Check:

   Content-Type must match body format [OK]

Hint: Match Content-Type with actual body format [OK]

Common Mistakes:

• Ignoring mismatch between Content-Type and body
• Assuming Accept header affects request body
• Thinking Host header is missing when it is present

5. You want to send JSON data to an API and receive a JSON response. Which headers should you set correctly in your HTTP request to ensure this communication?

hard

A. Content-Type: application/json and Accept: application/json

B. Content-Type: text/plain and Accept: application/json

C. Content-Type: application/json and Accept: text/html

D. Content-Type: application/xml and Accept: application/json

Solution

1. Step 1: Set Content-Type for request data

   Since you are sending JSON data, set Content-Type: application/json so the server knows the format of the data you send.

2. Step 2: Set Accept for response format

   To receive JSON response, set Accept: application/json to tell the server you want JSON back.

3. Final Answer:

   Content-Type: application/json and Accept: application/json -> Option A

4. Quick Check:

   Both headers set to application/json for JSON exchange [OK]

Hint: Both headers must match JSON for send and receive [OK]

Common Mistakes:

• Setting Content-Type and Accept to different formats
• Using text/plain or XML when JSON is needed
• Forgetting to set Accept header