HTTP Methods - GET, POST, PUT, PATCH, DELETE & Idempotency

▶

Steps

setup

Client prepares GET request

The client constructs an HTTP GET request packet to retrieve data from the server.

💡 This step shows how a simple GET request is formed before sending, establishing the starting point of communication.

Line:

request = HTTPRequest(method='GET', url='/resource')

💡 Understanding the initial request setup is crucial to follow the packet flow.

traverse

Client sends GET request to server

The client sends the GET request packet to the server over the network.

💡 This step shows the packet leaving the client and traveling to the server, illustrating the request flow.

Line:

network.send(request_packet)

💡 Packet transmission is the core of client-server communication.

processing

Server receives and processes GET request

The server receives the GET request and begins processing it to retrieve the requested resource.

💡 This step highlights the server's role in handling incoming requests.

Line:

response = server.handle_request(request)

💡 Server processing is where the request method determines the action taken.

traverse

Server sends response to GET request

The server sends back the requested resource in an HTTP response packet to the client.

💡 This step completes the GET request cycle by returning data to the client.

Line:

network.send(response_packet)

💡 Response packets carry requested data back to the client.

processing

Client receives response to GET request

The client receives the server's response and processes the returned data.

💡 This step shows the client completing the GET request cycle by handling the response.

Line:

client.process_response(response_packet)

💡 Client processes data after successful GET response.

setup

Client prepares POST request

The client constructs an HTTP POST request to submit new data to the server.

💡 POST differs from GET by sending data to the server, so this step shows the request setup.

Line:

request = HTTPRequest(method='POST', url='/resource', body='new data')

💡 POST requests modify server state and are not idempotent.

traverse

Client sends POST request to server

The client sends the POST request packet containing new data to the server.

💡 This step shows data submission from client to server.

Line:

network.send(request_packet)

💡 POST requests change server state and are not idempotent, so each request matters.

processing

Server receives and processes POST request

The server receives the POST request and updates its state with the new data.

💡 This step shows how POST modifies server resources.

Line:

response = server.handle_request(request)

💡 POST is not idempotent; repeated requests create multiple changes.

traverse

Server sends response to POST request

The server sends a confirmation response back to the client after processing the POST request.

💡 This step confirms the server has accepted and processed the POST data.

Line:

network.send(response_packet)

💡 Server responses confirm request success or failure.

processing

Client receives response to POST request

The client receives the server's confirmation and processes the POST response.

💡 This step completes the POST request cycle by acknowledging server acceptance.

Line:

client.process_response(response_packet)

💡 Client confirms that POST data was successfully stored.

setup

Client prepares PUT request

The client constructs an HTTP PUT request to update an existing resource on the server.

💡 PUT replaces the resource entirely and is idempotent, so this step shows the update request setup.

Line:

request = HTTPRequest(method='PUT', url='/resource', body='updated data')

💡 PUT requests overwrite resources and repeated identical requests have the same effect.

traverse

Client sends PUT request to server

The client sends the PUT request packet to update the resource on the server.

💡 This step shows the update request traveling to the server.

Line:

network.send(request_packet)

💡 PUT requests are idempotent; sending the same request multiple times results in the same server state.

processing

Server receives and processes PUT request

The server receives the PUT request and replaces the existing resource with the new data.

💡 This step shows how PUT updates resources idempotently.

Line:

response = server.handle_request(request)

💡 PUT ensures the resource state is consistent after repeated identical requests.

traverse

Server sends response to PUT request

The server sends a confirmation response back to the client after processing the PUT request.

💡 This step confirms the server has updated the resource.

Line:

network.send(response_packet)

💡 Server responses confirm successful resource replacement.

processing

Client receives response to PUT request

The client receives the server's confirmation and processes the PUT response.

💡 This step completes the PUT request cycle by acknowledging server acceptance.

Line:

client.process_response(response_packet)

💡 Client confirms that the resource was successfully updated.

setup

Client prepares DELETE request

The client constructs an HTTP DELETE request to remove a resource from the server.

💡 DELETE requests remove resources and are idempotent; this step shows the request setup.

Line:

request = HTTPRequest(method='DELETE', url='/resource')

💡 DELETE requests remove resources and repeated identical requests have the same effect.

traverse

Client sends DELETE request to server

The client sends the DELETE request packet to remove the resource on the server.

💡 This step shows the delete request traveling to the server.

Line:

network.send(request_packet)

💡 DELETE requests are idempotent; repeated deletes have the same effect as one.

processing

Server receives and processes DELETE request

The server receives the DELETE request and removes the specified resource.

💡 This step shows how DELETE removes resources idempotently.

Line:

response = server.handle_request(request)

💡 DELETE ensures resource removal; repeated deletes do not cause errors.

traverse

Server sends response to DELETE request

The server sends a confirmation response back to the client after processing the DELETE request.

💡 This step confirms the server has deleted the resource.

Line:

network.send(response_packet)

💡 Server responses confirm successful resource deletion.

processing

Client receives response to DELETE request

The client receives the server's confirmation and processes the DELETE response.

💡 This step completes the DELETE request cycle by acknowledging server acceptance.

Line:

client.process_response(response_packet)

💡 Client confirms that the resource was successfully deleted.

class HTTPRequest:
    def __init__(self, method, url, body=None):
        self.method = method  # STEP 1,6,11,16
        self.url = url
        self.body = body

class Network:
    def send(self, packet):
        pass  # STEP 2,7,12,17

class Server:
    def handle_request(self, request):
        if request.method == 'GET':
            # STEP 3
            return '200 OK', 'resource data'
        elif request.method == 'POST':
            # STEP 8
            return '201 Created', None
        elif request.method == 'PUT':
            # STEP 13
            return '200 OK', None
        elif request.method == 'DELETE':
            # STEP 18
            return '200 OK', None

class Client:
    def process_response(self, response):
        pass  # STEP 5,10,15,20

# Example usage:
client = Client()
server = Server()
network = Network()

# Steps 1-5: GET
request = HTTPRequest('GET', '/resource')  # STEP 1
network.send(request)  # STEP 2
response = server.handle_request(request)  # STEP 3
network.send(response)  # STEP 4
client.process_response(response)  # STEP 5

# Steps 6-10: POST
request = HTTPRequest('POST', '/resource', 'new data')  # STEP 6
network.send(request)  # STEP 7
response = server.handle_request(request)  # STEP 8
network.send(response)  # STEP 9
client.process_response(response)  # STEP 10

# Steps 11-15: PUT
request = HTTPRequest('PUT', '/resource', 'updated data')  # STEP 11
network.send(request)  # STEP 12
response = server.handle_request(request)  # STEP 13
network.send(response)  # STEP 14
client.process_response(response)  # STEP 15

# Steps 16-20: DELETE
request = HTTPRequest('DELETE', '/resource')  # STEP 16
network.send(request)  # STEP 17
response = server.handle_request(request)  # STEP 18
network.send(response)  # STEP 19
client.process_response(response)  # STEP 20

📊

HTTP Methods - GET, POST, PUT, PATCH, DELETE & Idempotency - Watch the Algorithm Execute, Step by Step

Watching each HTTP method's request and response flow helps you understand the fundamental differences and the concept of idempotency in HTTP.

Client prepares GET request packet.

Hop: 0

Client

Server

src→192.168.1.2:12345

dst→192.168.1.10:80

data→GET /resource HTTP/1.1

Packet is in transit from client to server.

Hop: 1

Client

Server

📦Packet

↗ fromclient

↘ toserver

📄 payloadGET /resource HTTP/1.1

🔌 protocolHTTP

🚩 flags

src→192.168.1.2:12345

dst→192.168.1.10:80

data→GET /resource HTTP/1.1

GET: client→server (request)

Server is processing GET request.

Hop: 1

Client

Server

src→192.168.1.2:12345

dst→192.168.1.10:80

data→GET /resource HTTP/1.1

GET: client→server (request)

Server sends response packet to client.

Hop: 2

Client

Server

📦Packet

↗ fromserver

↘ toclient

📄 payloadHTTP/1.1 200 OK Content: resource data

🔌 protocolHTTP

🚩 flags

src→192.168.1.10:80

dst→192.168.1.2:12345

data→HTTP/1.1 200 OK Content: resource data

GET: client→server (request)

200 OK: server→client (response)

Client processes response data.

Hop: 2

Client

Server

src→192.168.1.10:80

dst→192.168.1.2:12345

data→HTTP/1.1 200 OK Content: resource data

GET: client→server (request)

200 OK: server→client (response)

Client prepares POST request packet.

Hop: 0

Client

Server

src→192.168.1.2:12345

dst→192.168.1.10:80

data→POST /resource HTTP/1.1 Body: new data

GET: client→server (request)

200 OK: server→client (response)

POST request packet is in transit.

Hop: 1

Client

Server

📦Packet

↗ fromclient

↘ toserver

📄 payloadPOST /resource HTTP/1.1 Body: new data

🔌 protocolHTTP

🚩 flags

src→192.168.1.2:12345

dst→192.168.1.10:80

data→POST /resource HTTP/1.1 Body: new data

GET: client→server (request)

200 OK: server→client (response)

POST: client→server (request)

Server processes POST request and updates resource.

Hop: 1

Client

Server

src→192.168.1.2:12345

dst→192.168.1.10:80

data→POST /resource HTTP/1.1 Body: new data

GET: client→server (request)

200 OK: server→client (response)

POST: client→server (request)

Server sends POST response to client.

Hop: 2

Client

Server

📦Packet

↗ fromserver

↘ toclient

📄 payloadHTTP/1.1 201 Created

🔌 protocolHTTP

🚩 flags

src→192.168.1.10:80

dst→192.168.1.2:12345

data→HTTP/1.1 201 Created

200 OK: server→client (response)

POST: client→server (request)

201 Created: server→client (response)

Client processes POST response.

Hop: 2

Client

Server

src→192.168.1.10:80

dst→192.168.1.2:12345

data→HTTP/1.1 201 Created

200 OK: server→client (response)

POST: client→server (request)

201 Created: server→client (response)

Client prepares PUT request packet.

Hop: 0

Client

Server

src→192.168.1.2:12345

dst→192.168.1.10:80

data→PUT /resource HTTP/1.1 Body: updated data

200 OK: server→client (response)

POST: client→server (request)

201 Created: server→client (response)

PUT request packet is in transit.

Hop: 1

Client

Server

📦Packet

↗ fromclient

↘ toserver

📄 payloadPUT /resource HTTP/1.1 Body: updated data

🔌 protocolHTTP

🚩 flags

src→192.168.1.2:12345

dst→192.168.1.10:80

data→PUT /resource HTTP/1.1 Body: updated data

POST: client→server (request)

201 Created: server→client (response)

PUT: client→server (request)

Server processes PUT request and updates resource.

Hop: 1

Client

Server

src→192.168.1.2:12345

dst→192.168.1.10:80

data→PUT /resource HTTP/1.1 Body: updated data

POST: client→server (request)

201 Created: server→client (response)

PUT: client→server (request)

Server sends PUT response to client.

Hop: 2

Client

Server

📦Packet

↗ fromserver

↘ toclient

📄 payloadHTTP/1.1 200 OK

🔌 protocolHTTP

🚩 flags

src→192.168.1.10:80

dst→192.168.1.2:12345

data→HTTP/1.1 200 OK

201 Created: server→client (response)

PUT: client→server (request)

200 OK: server→client (response)

Client processes PUT response.

Hop: 2

Client

Server

src→192.168.1.10:80

dst→192.168.1.2:12345

data→HTTP/1.1 200 OK

201 Created: server→client (response)

PUT: client→server (request)

200 OK: server→client (response)

Client prepares DELETE request packet.

Hop: 0

Client

Server

src→192.168.1.2:12345

dst→192.168.1.10:80

data→DELETE /resource HTTP/1.1

201 Created: server→client (response)

PUT: client→server (request)

200 OK: server→client (response)

DELETE request packet is in transit.

Hop: 1

Client

Server

📦Packet

↗ fromclient

↘ toserver

📄 payloadDELETE /resource HTTP/1.1

🔌 protocolHTTP

🚩 flags

src→192.168.1.2:12345

dst→192.168.1.10:80

data→DELETE /resource HTTP/1.1

PUT: client→server (request)

200 OK: server→client (response)

DELETE: client→server (request)

Server processes DELETE request and removes resource.

Hop: 1

Client

Server

src→192.168.1.2:12345

dst→192.168.1.10:80

data→DELETE /resource HTTP/1.1

PUT: client→server (request)

200 OK: server→client (response)

DELETE: client→server (request)

Server sends DELETE response to client.

Hop: 2

Client

Server

📦Packet

↗ fromserver

↘ toclient

📄 payloadHTTP/1.1 200 OK

🔌 protocolHTTP

🚩 flags

src→192.168.1.10:80

dst→192.168.1.2:12345

data→HTTP/1.1 200 OK

200 OK: server→client (response)

DELETE: client→server (request)

200 OK: server→client (response)

Client processes DELETE response.

Hop: 2

Client

Server

src→192.168.1.10:80

dst→192.168.1.2:12345

data→HTTP/1.1 200 OK

200 OK: server→client (response)

DELETE: client→server (request)

200 OK: server→client (response)

Key Takeaways

✓ HTTP methods differ in how they affect server state and idempotency.

Reading code alone doesn't clearly show how repeated requests behave differently; watching packet flows clarifies this.

✓ GET requests retrieve data without side effects, while POST requests submit data and are not idempotent.

Visualizing the request and response packets helps understand why POST can cause multiple changes if repeated.

✓ PUT and DELETE methods are idempotent, meaning repeated identical requests result in the same server state.

Seeing the packet flow and server processing steps highlights the idempotency concept concretely.

Practice

1. In which scenario is the TCP sequence number most critical for ensuring reliable data transfer?

easy

A. When the receiver needs to reorder out-of-sequence packets before delivering data to the application

B. When the sender wants to detect duplicate acknowledgments to trigger fast retransmission

C. When the receiver uses it to calculate the retransmission timeout (RTO)

D. When the sender uses it to encrypt the data payload for security

Solution

1. Step 1: Understand the role of TCP sequence numbers in packet ordering

   TCP sequence numbers uniquely identify bytes in the data stream, allowing the receiver to reorder packets that arrive out of order.

2. Step 2: Analyze each option

   When the receiver needs to reorder out-of-sequence packets before delivering data to the application is correct because reordering depends on sequence numbers. When the sender wants to detect duplicate acknowledgments to trigger fast retransmission relates to ACKs, not sequence numbers directly. When the receiver uses it to calculate the retransmission timeout (RTO) is incorrect because RTO calculation uses RTT estimates, not sequence numbers. When the sender uses it to encrypt the data payload for security is unrelated to sequence numbers.

3. Final Answer:

   Option A -> Option A

4. Quick Check:

   Sequence numbers enable ordering, not encryption or RTO calculation.

Hint: Sequence numbers order bytes; ACKs confirm receipt.

Common Mistakes:

• Confusing sequence numbers with ACK numbers
• Thinking sequence numbers affect RTO calculation
• Assuming sequence numbers relate to encryption

2. Trace the sequence of events when a TCP sender receives three duplicate ACKs for the same sequence number. What happens next?

easy

A. The sender ignores duplicate ACKs and continues sending new data segments

B. The sender waits for the retransmission timeout (RTO) before retransmitting the missing segment

C. The sender immediately retransmits the missing segment without waiting for RTO expiration

D. The sender resets the connection due to suspected network failure

Solution

1. Step 1: Understand duplicate ACKs in TCP

   Three duplicate ACKs indicate packet loss but that the network is still delivering packets, triggering fast retransmission.

2. Step 2: Analyze sender's response

   Upon receiving three duplicate ACKs, the sender retransmits the missing segment immediately without waiting for RTO.

3. Step 3: Evaluate options

   The sender ignores duplicate ACKs and continues sending new data segments is incorrect because the sender does not ignore duplicate ACKs. The sender waits for the retransmission timeout (RTO) before retransmitting the missing segment is incorrect because RTO wait is bypassed. The sender immediately retransmits the missing segment without waiting for RTO expiration correctly describes the fast retransmit behavior. The sender resets the connection due to suspected network failure is an extreme reaction not triggered by duplicate ACKs.

4. Final Answer:

   Option C -> Option C

5. Quick Check:

   Fast retransmit improves performance by avoiding RTO delays.

Hint: 3 duplicate ACKs -> fast retransmit, no RTO wait.

Common Mistakes:

• Confusing fast retransmit with waiting for RTO
• Ignoring duplicate ACKs as noise
• Assuming connection reset on packet loss

3. If a load balancer using IP Hash algorithm encounters clients behind a NAT (Network Address Translation) device, what is a potential challenge and how can it be mitigated?

hard

A. Clients behind NAT have different IPs, causing inconsistent routing; mitigation is to disable IP Hash and use Round Robin

B. Multiple clients share the same public IP, causing all their requests to be routed to the same server; mitigation involves using additional session identifiers beyond IP

C. NAT devices block IP Hash algorithms; mitigation is to switch to Least Connections

D. IP Hash cannot detect unhealthy servers behind NAT; mitigation is to increase health check frequency

Solution

1. Step 1: Understand NAT impact on IP Hash

   NAT causes multiple clients to share a single public IP address.

2. Step 2: Effect on IP Hash routing

   Since IP Hash uses client IP, all clients behind the same NAT get routed to the same backend server, potentially causing load imbalance.

3. Step 3: Mitigation strategies

   Using additional session identifiers (cookies, tokens) can differentiate clients beyond IP, improving distribution.

4. Step 4: Why other options are incorrect

   Clients behind NAT have different IPs, causing inconsistent routing; mitigation is to disable IP Hash and use Round Robin incorrectly states clients behind NAT have different IPs; they share one. NAT devices block IP Hash algorithms; mitigation is to switch to Least Connections falsely claims NAT blocks IP Hash. IP Hash cannot detect unhealthy servers behind NAT; mitigation is to increase health check frequency confuses health checks with NAT issues.

5. Final Answer:

   Option B -> Option B

6. Quick Check:

   NAT causes IP Hash collisions; use extra session info to mitigate.

Hint: NAT causes IP Hash collisions; add session IDs

Common Mistakes:

• Assuming IP Hash works perfectly behind NAT
• Thinking NAT changes client IPs individually
• Confusing NAT issues with health check problems

4. If a client crashes immediately after sending the final ACK in the TCP three-way handshake, what is the likely impact on the server's connection state?

hard

A. The server resets the connection upon detecting no ACK from the client

B. The server immediately closes the connection due to missing data

C. The server retransmits SYN-ACK packets until timeout, then closes the connection

D. The server considers the connection established and waits indefinitely for data

Solution

1. Step 1: Understand handshake completion

   After the client sends the final ACK, the server marks the connection as established.

2. Step 2: Consider client crash impact

   If the client crashes immediately after ACK, the server has no immediate way to detect this and will wait for data or timeout based on application-level timeouts.

3. Step 3: Analyze options

   The server considers the connection established and waits indefinitely for data correctly states the server waits indefinitely (or until timeout). The server immediately closes the connection due to missing data is incorrect; server does not close immediately. The server retransmits SYN-ACK packets until timeout, then closes the connection is wrong; retransmission of SYN-ACK happens before handshake completes, not after. The server resets the connection upon detecting no ACK from the client is incorrect; server does not reset connection without explicit reset packet.

4. Final Answer:

   Option D -> Option D

5. Quick Check:

   Server trusts handshake completion after final ACK, unaware of client crash.

Hint: Server trusts final ACK; client crash after means server waits for data

Common Mistakes:

• Assuming server detects client crash immediately
• Confusing retransmission behavior post-handshake
• Thinking server resets connection without RST packet

5. Suppose you need to design a protocol for a sensor network where devices send frequent small updates, but network bandwidth is very limited and packet loss is common. Which approach best balances reliability and efficiency?

hard

A. Use UDP with application-layer acknowledgments and selective retransmissions to reduce overhead

B. Use TCP to ensure all packets are received and in order, despite bandwidth overhead

C. Use UDP without any reliability mechanisms to maximize speed and minimize bandwidth

D. Use TCP but disable retransmissions to save bandwidth

Solution

1. Step 1: Understand constraints

   Limited bandwidth and frequent small updates require minimizing overhead.

2. Step 2: Analyze TCP suitability

   TCP guarantees reliability but adds overhead and retransmits all lost packets, which may be costly.

3. Step 3: Analyze UDP with app-layer reliability

   UDP avoids connection overhead; adding selective retransmissions at the application layer balances reliability and efficiency.

4. Step 4: Evaluate options

   Use UDP with application-layer acknowledgments and selective retransmissions to reduce overhead best fits the scenario. TCP is too heavy for constrained bandwidth. UDP without reliability risks losing important data. TCP cannot disable retransmissions without breaking reliability.

5. Final Answer:

   Option A -> Option A

6. Quick Check:

   Custom reliability on UDP can optimize for constrained networks.

Hint: Combine UDP speed with app-layer reliability for constrained, lossy networks.

Common Mistakes:

• Assuming TCP is always best for reliability regardless of overhead
• Thinking UDP without reliability is sufficient for sensor data
• Believing TCP retransmissions can be disabled