What are the differences between HTTP/1 and HTTP/2 protocols?

Main differences between HTTP/1.1 and HTTP/2:

• Multiplexing:

  • HTTP/1.1: Sequential processing of requests over one connection. Multiple TCP connections were required for parallel loading.
  • HTTP/2: Multiplexing over a single TCP connection. Allows sending multiple requests and receiving responses simultaneously without blocking each other.

• Header compression (HPACK):

  • HTTP/1.1: Headers are transmitted uncompressed, which can be redundant with many requests.
  • HTTP/2: Header compression using the HPACK algorithm. Reduces the size of transmitted data.

• Stream prioritization:

  • HTTP/1.1: No prioritization capability.
  • HTTP/2: Clients can assign priorities to different data streams, influencing their processing order on the server.

• Server Push:

  • HTTP/1.1: Clients must explicitly request each resource (CSS, JS, images).
  • HTTP/2: Server can proactively send resources it anticipates the client will need to display the page, before the client requests them.

• Binary protocol:

  • HTTP/1.1: Text-based protocol, relatively easy to read.
  • HTTP/2: Binary protocol, more efficient for parsing and transmission.

Comparison table:

Characteristic	HTTP/1.1	HTTP/2
Multiplexing	No (requires multiple TCP)	Yes (single TCP)
Header compression	No	Yes (HPACK)
Stream prioritization	No	Yes
Server push	No	Yes
Protocol format	Text	Binary
Head-of-Line blocking issue	Present (for one TCP)	Reduced thanks to multiplexing

Conceptual example of multiplexing:

// HTTP/1.1: Sequential requests
fetch('/resource1')
  .then(() => fetch('/resource2'))
  .then(() => fetch('/resource3'));

// HTTP/2: Parallel requests over one connection
// In browsers, this happens automatically for HTTP/2
// Requests can be sent almost simultaneously