What is the difference between HTTP/1 and HTTP/2?

Main differences:

• Multiplexing. HTTP/2 allows sending and receiving multiple requests and responses over a single TCP connection simultaneously. HTTP/1.1 required a separate connection for each request/response (except when pipelining was used, which had limitations).
• Header Compression. HTTP/2 uses HPACK compression to reduce header size and the amount of data transmitted. In HTTP/1.1, headers are sent in plain text.
• Stream Prioritization. In HTTP/2, the client can specify priorities for different streams (requests/responses), enabling the server to optimize data delivery order. HTTP/1.1 does not have this mechanism.
• Server Push. HTTP/2 allows the server to send resources to the client before the client requests them, based on assumptions about their necessity for page rendering. In HTTP/1.1, the client must explicitly request each resource.
• Frame Format. HTTP/2 transmits data in binary frames, which simplifies parsing and improves efficiency compared to the text format of HTTP/1.1.

Comparison table:

Feature	HTTP/1.1	HTTP/2
Connection	One connection per request (no pipelining)	One connection for multiple streams
Multiplexing	No (or limited with pipelining)	Yes
Header Compression	No	HPACK (binary compression)
Stream Prioritization	No	Yes
Server Push	No	Yes
Data Format	Text	Binary (frames)
Head-of-Line Blocking	Present	Partially mitigated by multiplexing

Example of an HTTP/1.1 request:

GET /index.html HTTP/1.1
Host: example.com
User-Agent: curl/7.68.0
Accept: */*

Example of partial data representation in HTTP/2 (frame exchange is more complex and not shown simply):

// In HTTP/2, communication occurs at the frame level (HEADERS, DATA, etc.),
// which are binary and hidden from the application layer.
// Representing them in plain text for illustration is difficult.
// Headers are compressed and sent in HEADERS frames.
// Response body is transmitted in DATA frames.