HTTP Protocol in Go

What it is?

HTTP is just a communication protocol over TCP. In other words, just one of the ways in which clients communicate with servers via some specially organized string.

What it is NOT?

Some fancy alien technology which requires vast knowledge of quantum physics :D. Anyone can easily implement the HTTP protocol either as a client or as a server side.

RFC (Protocol)

For HTTP to be valid and acceptable for any client/server it should have the following:

HTTP MESSAGE STRUCTURE

REQUEST/STATUS LINE\r\n
HEADER1\r\n
HEADER2\r\n
...\r\n
HEADERX\r\n
\r\n
OPTIONAL REQUEST/RESPONSE

REQUEST LINE (REQUEST)

HTTP VERB / METHOD ␣ URL/URI ␣ HTTP VERSION

GET /some/uri HTTP/1.1

STATUS LINE (RESPONSE)

HTTP VERSION ␣ STATUS CODE ␣ REASON PHRASE

HTTP/1.1 200 OK

Note: Also in order for the HTTP request/response to be valid it also need to have Content-Length header provided. In the request it equals to the length of the request body, and should be present only if request body is present. In case of response should be equal to the length of the response body if any.

Useful Links

• RFC 7230 - HTTP Spec
• RFC 7230 - Content Length
• RFC 7231 - Request Methods
• RFC 2616 - Status Codes

HTTP Verbs

Generally speaking HTTP Verbs or Methods are ways to describe how the client is going to have an effect on some resource located on the server, like GET or POST for example.

Because HTTP is just a communication protocol, nobody restricts you to use specific methods aka verbs. However, there are different verbs for different kinds of actions on resources on the server.

Here are the most widely used and known verbs:

• GET - typically used for getting resources
• POST - typically used for creating a resource or executing an action with side effects
• PATCH - typically used for partially updating resources
• PUT - typically used for fully updating resources
• DELETE - typically used for deleting resources

However, there are other verbs/methods, such as:

OPTIONS, CONNECT, TRACE, HEAD

which we will not care to use, or rarely do so.

Useful Links

• HTTP Verbs/Request Methods

HTTP Statuses

HTTP Statuses are used for the server to communicate the client the result of its request, meaning if the client made a request, it can generally know how the server responded and what's the result of his action by simply getting back a Status Code in the response.

Status Codes usually come hand in hand with Reason Phrases. So a Status Code is made up of: NUMBER ␣ REASON PHRASE, something like:

• 200 OK
• 400 Bad Request

There are many status codes, and you can even create your own Custom Status Codes, however generally speaking you should know:

• 1.X.X - Represents Informational statuses
• 2.X.X - Represents Success statuses
• 3.X.X - Represents Redirects statuses
• 4.X.X - Represents Client Error statuses
• 5.X.X - Represents Server Error statuses

Useful Links

• HTTP Statuses/Response Status Codes
• HTTP Cat

HTTP Versions

• HTTP 1 - Good old HTTP
• HTTP 2 - SPDY
• HTTP 3 - QUIC

HTTP/1.0 vs HTTP/1.1

HTTP/1.0

• connection is closed after every request/response (results in inefficiency)

HTTP/1.1

• requires Host header
• allows persistent connections (multiple request/response on the same connection)
• introduces the OPTIONS method mainly used for CORS
• has improved caching mechanism
• introduces 100 status code which lets the client know whether to proceed sending a large request body
• introduces chuncked transfer encoding
• introduces Connection header
• introduces enhanced compression support
• Much more (Generally stick with HTTP/1.1)

Useful Links

• HTTP/1.0 vs HTTP/1.1
• Differences between HTTP/1.0 & HTTP/1.1
• Evolution of HTTP

REST

Generally speaking REST is nothing, but a community effort & instruction around HTTP on how to properly structure URLs and use HTTP Verbs & Statuses. So REST is the same old HTTP used properly, with a little less freedom and at the end of the day it's a lot of debate on how to properly use it, hence it's just a recommendation which most companies follow.

HTTP Alternatives

• Web Sockets
• HTTP2/HTTP3
• gRPC
• GraphQL