HTTP

HTTP Versions

With WWW becoming popular, the need for supporting differnt file formats grows:
- Need to support different resource format
- Information of the resource's encoding and type must be included for client side to handle properly
Response header are introduced

Text-based framing
HTTP/1.0 build and close the connection on every request, which is resource consuming nad increases response time
- Connection is kept opened unless closed explicitly
- Often has a connection amount limitation to avoid resource exhaustion on the server (e.g Chrome limits 6 connection per domain)
Introduces Host header to support multiple host sharing a same IP
Introduces Content-Length header to support streaming data
Introduce cookie mechanism
Improved caching headers such as: ETag, If-Unmodified-Since, If-Match, If-None-Match
More request methods
TCP connection issues:
- Each connection has the head-of-line (HOF) blocking issue
- TCP has a slow start issue
- Connections might race of bandwith, causing critical resource to take longer time to response

Binary-based framing
Tries to solve TCP connection issue in HTTP/1.1 by introduces multiplexing mechanism:
- Requests/responses are break down to frames with id (stream id) using binar framing technique, such that receiver can receive packets in any order and reconstruct the content.
- Priority can be given to requests
Introduces header compression using HPack
Allows servers to proactively send resources to the client, reducing latency and improving perceived page load times.
Enhances security with encrypted connection
Partially addresses the head-of-line blocking (HOLB) issue by using multiplexing, but HOLB still exists at the transport layer (TCP).

Introduces QUIC based on UDP to implement multiplexing and reliable connection.
Based on TLS1.3
Allow solves multiple issue in previous versions, still faces challenges such as:
- UDP support in routers are less optimized
- Device support
- Requires more memory
- Risks such as DDos attack