Web Engineering and HTTP Methods Quiz

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Questions and Answers

Which HTTP methods are considered to be safe?

GET, HEAD, OPTIONS, TRACE (correct)

PUT, DELETE, TRACE, PATCH

POST, PATCH, DELETE, PUT

GET, POST, OPTIONS, TRACE

What defines an idempotent request?

The request results are always unique irrespective of the number of calls.

Multiple identical requests have the same side effects as a single request. (correct)

The request alters the state of the resource every time it is made.

It can only be executed once without changing the resource state.

Which statement is true about the HTTP methods POST and PATCH?

Both methods are non-idempotent and may alter the resource state. (correct)

Both methods are idempotent and safe.

Both methods are safe and do not require user accountability.

Both methods are used for retrieving resources.

What does the URI in a PUT request identify?

The entity enclosed within the request. Signup and view all the answers

Which of the following headers indicates the estimated age of the entity?

Age Signup and view all the answers

When should you use the GET method?

For safe interactions with the server. Signup and view all the answers

Which header field specifies whether the server can handle partial requests?

Accept-Ranges Signup and view all the answers

In the structure of an HTTP response message, what comes after the status-line?

General-header Signup and view all the answers

Which statement accurately differentiates the Web from the Internet?

The Web allows for resource retrieval, while the Internet facilitates interconnected networks. Signup and view all the answers

What role does the Transport layer play in the TCP/IP model?

It allows sources and targets to converse. Signup and view all the answers

What is a characteristic of Internet Service Providers (ISPs)?

ISPs provide direct access to end-users with a fully digital network. Signup and view all the answers

What is the primary purpose of Internet Exchange Points (IXPs)?

To facilitate peering among ISP networks. Signup and view all the answers

Which option describes the influence of the last mile on user-perceived bandwidth?

The last mile can limit user access speed to digital or analog connections. Signup and view all the answers

What is a significant challenge in computer science related to web engineering?

Cache invalidation and naming things. Signup and view all the answers

What does the Internet layer's role involve in the TCP/IP model?

It allows hosts to inject packets into various networks. Signup and view all the answers

What concept is illustrated by the phrase 'not an actual network but a collection of heterogeneous networks'?

The Internet comprises various independent network types. Signup and view all the answers

What is the primary purpose of a Uniform Resource Identifier (URI)?

To provide a universal addressing scheme for resources. Signup and view all the answers

Which of the following statements is true about URLs?

A URL can uniquely identify a resource's primary access mechanism. Signup and view all the answers

What does a URN signify about a resource?

It provides a logical address for a resource regardless of where it is stored. Signup and view all the answers

What is the default port number commonly used by the HTTP protocol?

80 Signup and view all the answers

What is meant by 'connection oriented' in the context of HTTP?

HTTP does not track the state between requests and responses. Signup and view all the answers

What are query components used for in a URI?

To provide additional parameters for accessing the resource. Signup and view all the answers

How does HTTP achieve reliability?

Through the careful structuring of messages and retransmissions. Signup and view all the answers

Which of these represents a hierarchical structure in URI schemes?

The path that indicates specific semantics. Signup and view all the answers

What is the primary function of a proxy in the HTTP protocol?

To act on behalf of an origin server and forward requests. Signup and view all the answers

Which role in HTTP acts as an intermediary that translates requests?

Gateway Signup and view all the answers

What distinguishes a tunnel from other roles in HTTP?

It simply routes messages without examining their content. Signup and view all the answers

Which HTTP role is responsible for processing requests and sending responses?

Origin Server Signup and view all the answers

In the client-server architectural pattern, why is the client also referred to as a User Agent?

It is a program that submits requests to the server. Signup and view all the answers

What is the primary benefit of caching for content providers?

Reduces network bandwidth usage Signup and view all the answers

What mechanism is essential for ensuring that cached copies remain up to date?

Cache invalidation Signup and view all the answers

How does the HTTP mechanism ensure cache consistency?

Through timestamps for expiry and validity checking Signup and view all the answers

What does semantic transparency imply in the context of HTTP?

The use of cache should not change the response from the origin server Signup and view all the answers

What does the expiry model for cache correctness define about cached responses?

Responses are called fresh until their defined lifetime is exceeded Signup and view all the answers

Which of the following is NOT an exception for serving outdated responses from the cache?

Server initiates an update process Signup and view all the answers

What is the purpose of the 'Age' response header field in caching?

To track the time a resource has been cached Signup and view all the answers

What is a challenge associated with maintaining cache consistency?

Changing resources on the origin server results in outdated cached copies Signup and view all the answers

Which of the following statements regarding the cache with zero lifetime is correct?

Responses expire immediately and are never fresh Signup and view all the answers

What can happen if the clocks of caches and origin servers are not synchronized?

Cache consistency may be compromised Signup and view all the answers

What is the primary purpose of the Date header field in response messages?

To indicate when the response was generated by the server Signup and view all the answers

Which header field takes precedence if both Expires and Cache-Control are specified?

Cache-Control Signup and view all the answers

What should a server do if it wants to prevent caching of a response that changes frequently?

Specify a past date as the expiration date Signup and view all the answers

What does the freshness period of a cached response depend on?

The difference between Expires and Date headers Signup and view all the answers

In the absence of defined expiry headers, how can caches determine the validity of a response?

By evaluating the Last-Modified header Signup and view all the answers

Which of the following statements about Expires and Cache-Control headers is false?

They are mandatory for all HTTP responses. Signup and view all the answers

What happens if a cache receives a response with Cache-Control set to no-cache?

The cache may store the response but must check with the server before using it. Signup and view all the answers

What indicates that a cached response is still fresh?

The freshness period is longer than the age of the response. Signup and view all the answers

Study Notes

Web Engineering (WBCS008-05) Set 2: Foundations of the Web

The World Wide Web is an information system to retrieve resources.
Resources are identified by Uniform Resource Locators (URLs).
Resources are connected to each other by (hyper)links.
Resources are accessible over the Internet.
Resources are mainly hypertext but also include any type of (hyper)media.

Outline

Internet in a nutshell
URIs
HTTP
- Basics
- Caching
- Authentication
- Content delivery
Web Technologies
Software Architecture on the Web
Foundations of the Web

What is the Web?

The World Wide Web is an information system for retrieving resources.
Resources are identified by Uniform Resource Locators (URLs).
Resources are connected to each other by (hyper)links.
The Web is accessible over the Internet.
Resources include any type of (hyper) media but mainly hypertext.

The Internet

The Internet is a collection of heterogeneous networks, not a single network.
It evolved organically from predecessors, including ARPANET in the late 60s/70s and CSNET/NSFNET in the early 80s.
The Internet has continued to evolve since the late 80s.

Global IP Traffic by Application Type (2017-2022)

By 2022, video accounted for 82% of global IP traffic.
Video had a 26% Compound Annual Growth Rate (CAGR) from 2017-2022.

The TCP/IP Model

Layer: Application, Transport, Internet, Link
Role: Contains all high-level protocols, allows sources and targets to converse, allows hosts to inject packets, interface between hosts and transmission links.
Protocols: HTTP, SMTP, DNS, TCP, UDP, IP, ICMP, DSL, SONET, 802.11, Ethernet

Internet Architecture in a Nutshell

Internet Service Providers (ISPs) provide connectivity.
User-perceived bandwidth is limited by the "last mile" of the network (analog or digital).
Points of Presence (POPs) are locations where customer packets enter the ISP network.
ISPs peer at Internet eXchange Points (IXPs).

URIs

Defined as references that identify abstract or physical resources.
URIs have the form <scheme>:<authority><path>[?<query>].
A URI can be a URL (locator), a URN (name), or both.

URI Schemes

URL: A subset of URIs; identifies resources by their primary access mechanism (e.g., network location).
URN: A subset of URIs; uniquely identifies a resource independent of its storage location.

HTTP in a nutshell

HTTP is a simple request/response protocol.
It relies on TCP (default port: 80).
HTTP messages consist of a header and a body.
HTTP is reliable and connection oriented.
No state is maintained between request / response pairs.
Connections can persist.
Three major versions: 1.0, 1.1, 2

Roles in HTTP

Client (or User Agent): Submits a request.
Server: Processes a request and returns a response.
Origin Server: Where a resource resides.
Proxy: Acts on behalf of an origin server. May rewrite or forward requests.
Gateway: Acts as an intermediary for another server.
Tunnel: Acts as a blind relay between two connections (e.g., through a firewall).

HTTP Connection Management

HTTP/1.0: One transaction per connection.
HTTP/1.1: Multiple transactions over a persistent connection with pipelined processing.
HTTP/2: Multiplexed requests over the same connection (highly different transport model).

Content Negotiation

Resources are available in multiple representations (variants).
Specific representation is chosen by negotiation mechanism.

Types of Content Negotiation

Server-driven: Client provides headers and server delivers "best effort" response.
Client-agent-driven: Server provides a list of variants and client chooses the best.
Transparent: No standard support in HTTP

HTTP Messages & Methods

HTTP messages have a structure consisting of request-line, headers, and a message body.
Various methods for interaction, such as GET, POST, PUT, DELETE, HEAD, OPTIONS, TRACE, CONNECT.
Specific headers provide detailed information about the request or response.

HTTP Request Messages

request = request-line (general-header | request-header | entity-header) CRLF message-body?*
request-line = method SP requestURI SP HTTP-Version CRLF

HTTP Request Message (cont.)

Method specifies action e.g. 'GET', 'POST', 'PUT', 'DELETE'
Header provides further details about the request (e.g., 'Accept', 'Host', 'If-Modified-Since', 'User-Agent')

Sample Request Headers

Host
If-Match
If-Modified-Since
User-Agent

Request URIs

Request applies to particular resource or to server itself.
Use absoluteURI if request is made to a proxy.
Use abs-path if request is to origin server.
Use authority if used by CONNECT method for tunneling.

Request Methods (supportive)

CONNECT, HEAD, OPTIONS and TRACE.
CONNECT: used for tunneling
HEAD: no body but header to validate caching
OPTIONS: to get properties of a server
TRACE: to see response headers

Request Methods (main)

DELETE, GET, POST, PUT, PATCH

Request Properties

Safe Requests: Non-state-altering (e.g., GET, HEAD, OPTIONS, TRACE)
Idempotent Requests: Side-effects of multiple identical requests remain the same (e.g., GET, HEAD, OPTIONS, PUT, DELETE when implemented correctly). POST, PATCH are not idempotent

PUT vs POST

PUT: Semantic relation different to POST
POST: URI in POST points to service handling entity.
PUT: URI in PUT points to the entity itself.
GET vs POST: GET typically used for safe interactions, possibly longer URIs in POST.

HTTP Response Messages

response = status-line (general-header | response-header | entity-header) CRLF message-body**
status-line = HTTP-version SP status-code SP reason-phrase CRLF

Sample Response Headers

Age
Server
Accept-Ranges
Retry-After
WWW-Authenticate

Status Codes Categories

1xx: Informational
2xx: Success
3xx: Redirection
4xx: Client Error
5xx: Server Error

HTTP Caching

Cache is storage for temporary response messages.
Improves response time by providing copies for repeat requests.
Client-cache (browser), separate caches on proxies
Topology: client, server, and separate caches on proxies

Web Proxies and Caching Pipelines

Forward proxy: External facing proxy; acts as a stand-in for origin servers (N:1 proxy to server relation).
Reverse proxy: Internal facing proxy; usual single entry point to origin servers with load balancing and security (1:N server to proxy relation).

CDN use in practice

Using CDN involves a server that stores copies of resources and delivers them to clients.

CDN Benefits

Reduced latency (less hops).
Scalability to demand.
Increased reliability.
Separation from data transfer.
Security against DDoS attacks.

Source Material

Andrew Tanenbaum and David Wetherall, Computer Networks, 5th edition
Mozilla Developer Network

Self-evaluation Questions

Acronyms (ISP, POP, IXP) purpose
Definitions and relations between URI, URL, URN
Proxy, gateway, and tunnel differences
Conditions for safe/idempotent HTTP requests
PUT vs POST Differences
Proxy types and functions
Benefits of caching
Semantic transparency in HTTP
How server stops proxy/client from caching response
Cache freshness, no Expires header
Basic Authentication
How CDNs work and benefits

Next Lecture: REST

Appendix: A Short History of the Internet

ARPANET (distributed switching system for US DoD)
ARPANET successors (CSNET/NSFNET, ANSNET)
TCP/IP model (invented and adopted to deal with internetwork communication)

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Description

Test your knowledge on web engineering concepts and HTTP methods with this quiz. Explore the definitions of safe HTTP methods, idempotent requests, and the structure of HTTP response messages. Additionally, learn about the roles of different layers in the TCP/IP model and the characteristics of Internet Service Providers.