Development History of the HTTP Protocol#

The Hypertext Transfer Protocol (HTTP) is an application layer protocol used for transmitting hypertext documents. It is designed for communication between web browsers and web servers. Up to now, all versions of the HTTP protocol can be divided into HTTP 0.9, HTTP 1.0, HTTP 1.1, HTTP 2.0, and HTTP 3.0. Among them, the widely used version is HTTP 1.1, which is currently advancing towards HTTP 2.0 and the future HTTP 3.0 version.

HTTP 0.9#

HTTP 0.9, also known as the single-line protocol, originally did not have a version number. Later, its version number was designated as 0.9 to distinguish it from later versions. HTTP 0.9 is extremely simple, with requests consisting of a single-line command starting with the only available GET method, followed by the path of the target resource. The response content of HTTP 0.9 does not contain HTTP headers, which means that only HTML files can be transmitted, and other types of files cannot be transmitted. There are also no status codes or error codes. When an exception occurs, a special HTML file containing a description of the problem will be returned in the response.

Characteristics#

• It only has a single request line, without HTTP request headers and bodies.
• The server does not return header information, only data information.
• The returned file content is transmitted as an ASCII character stream because they are in HTML format, so using ASCII bytecode for transmission is most appropriate.

HTTP 1.0#

HTTP 1.0 was designed for extensibility to meet the needs of transmitting various types of files and to allow deeper communication between clients and servers. HTTP 1.0 introduced request and response headers, both of which are stored in a Key-Value form. When sending an HTTP request, request header information will be included, and when the server returns data, it will first return response header information.

Characteristics#

• The protocol version information is sent with each request, i.e., HTTP 1.0 is appended to the GET line.
• Introducing request headers, when making a request, the client will inform the server through HTTP request headers what type of file it expects the server to return, in what form it should be compressed, what language the file should be provided in, and the specific encoding of the file.
• Introducing response headers, the server prepares data based on the information in the request headers and informs the client through the information in the response headers of the format in which the data is returned. If an unsupported format is encountered, only the supported format by the server can be returned, which will be reflected in the response headers. In other words, the browser ultimately interprets the data based on the information in the response headers.
• Introducing status codes, status codes are sent at the beginning of the response to allow the browser to understand whether the request was successful or not and adjust its behavior accordingly.
• Introducing a caching mechanism through status codes and If-Modified-Since, Expires, and other controls for updating or using local caches.
• Introducing the Content-Type header, allowing HTTP to transmit documents other than pure text HTML files.

HTTP 1.1#

HTTP 1.1 is a standardized protocol that eliminates a significant amount of ambiguity and introduces multiple improvements.

Characteristics#

• Cache handling: HTTP 1.1 introduced additional caching control strategies, such as Entity tag, If-Unmodified-Since, If-Match, If-None-Match, and more cache headers for control.
• Bandwidth optimization and use of network connections: HTTP 1.1 introduced the range in the request header, allowing only a part of a resource to be requested, resulting in a 206 status code. This allows developers to freely choose to fully utilize bandwidth and connections, and implement breakpoint resumable downloads using Range and Content-Range.
• Error notification management: HTTP 1.1 introduced 24 new error status codes.
• Addition of the Host request header, allowing different domain names to be hosted on the same IP address server.
• Support for persistent connections: HTTP 1.1 supports persistent connections, enabling multiple HTTP requests and responses to be transmitted on a single TCP connection, reducing the overhead and delays of establishing and closing connections. In HTTP 1.1, Connection: keep-alive is enabled by default, and browsers typically allow up to 6 persistent connections to the same domain.
• Introduction of pipelining technology: allowing the second request to be sent before the first response is fully sent to improve the head-of-line blocking problem, although the responses are still returned in the order of the requests.
• Support for chunked responses: using Transfer-Encoding: chunked for chunked responses, allowing response data to be divided into multiple parts. Releasing the buffer as early as possible on the server side can achieve faster response speeds.

HTTP 2.0#

HTTP 2.0 offers better performance. As web pages become increasingly complex, even evolving into standalone applications, and with the increase in media playback and the growth of interactive script sizes, more data is being transmitted through HTTP requests. As a result, HTTP 2.0 has made significant optimizations for network efficiency.

Features#

• Binary framing: HTTP 2.0 is a binary protocol rather than a text protocol. It divides all transmitted information into smaller messages and frames, encoding them in binary format.
• Multiplexing: Parallel requests can be processed in the same connection. All access under the same domain goes through the same TCP connection. HTTP messages are broken down into independent frames, and the server reassembles them based on identifiers and headers, eliminating the sequencing and blocking constraints in HTTP 1.1.
• Header compression: Headers in a series of requests are often similar, so this feature removes the cost of duplicating and transmitting redundant data.
• Server push: Servers can proactively push resources to clients without the need for an explicit client request.

HTTP 3.0#

HTTP 3.0 is currently in the drafting and testing phase. It is a brand-new HTTP protocol for the future. Operating on top of the QUIC protocol, HTTP 3.0 achieves reliable transmission over UDP, balancing transmission speed and reliability, and optimizing them. Using UDP helps avoid the head-of-line blocking problem of TCP and speeds up network transmission. However, it still requires mechanisms for reliable transmission. HTTP 3.0 is not an extension of HTTP 2.0; it will be an entirely new protocol.

Daily Question#

References#