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All articles starting with H

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HTTP 417 Expectation Failed

HTTP 417 Expectation Failed is a client error status code meaning the expectation in a request's Expect header, typically 100-continue, could not be met by an inbound server.

HTTP 424 Failed Dependency

HTTP 424 Failed Dependency is a WebDAV client error status code meaning a method could not be performed because a dependent action failed, defined in RFC 4918.

HTTP 451

HTTP 451 Unavailable For Legal Reasons is an HTTP status code returned when legal demands, such as court orders or government blocklists, deny access to a resource.

HTTP 451 Unavailable For Legal Reasons

HTTP 451 Unavailable For Legal Reasons is an HTTP status code indicating a server is blocking a resource because of a legal demand, such as a court order.

HTTP 501 Not Implemented

HTTP 501 Not Implemented is an HTTP server error status code meaning the server does not support the functionality needed to fulfill the request, defined in RFC 9110.

HTTP 503 Service Unavailable

HTTP 503 Service Unavailable is an HTTP server error status code indicating temporary overload or maintenance, with an optional Retry-After header suggesting when clients should retry.

HTTP 504 Gateway Timeout

HTTP 504 Gateway Timeout is an HTTP status code defined in RFC 9110, sent when a gateway or proxy receives no timely response from an upstream server.

HTTP 505 HTTP Version Not Supported

HTTP 505 HTTP Version Not Supported is a server error status code meaning the server does not support the major HTTP version used in the request, defined in RFC 9110.

HTTP 507 Insufficient Storage

HTTP 507 Insufficient Storage is a 5xx server error status code meaning the server cannot store the representation needed to complete a request, defined by WebDAV's RFC 4918.

HTTP compression

HTTP compression is the lossless compression of HTTP message bodies such as HTML, CSS, and JavaScript, negotiated between server and client to make pages load faster.

HTTP cookie

An HTTP cookie, also called a web browser cookie, is a small piece of data a website stores in your browser to remember logins and preferences.

HTTP ETag

The HTTP ETag, or entity tag, is an HTTP response header that identifies a version of a resource, enabling efficient cache validation and preventing accidental overwrites.

HTTP flood

An HTTP flood is a Layer 7 denial-of-service attack in which a botnet sends high volumes of HTTP requests to exhaust a web server's resources and block legitimate users.

HTTP Live Streaming

HTTP Live Streaming (HLS) is an adaptive bitrate streaming protocol developed by Apple in 2009 that delivers video and audio over ordinary HTTP in short segments.

HTTP persistent connection

An HTTP persistent connection, also known as a keep-alive connection or HTTP connection reuse, stays open after a response so later requests reuse it instead of opening a new one.

HTTP query parameter semantics

HTTP query parameters are the name–value pairs after the ? in a URI; RFC 9110 makes them part of resource identification, with UTF-8 and percent-encoding per RFC 3986.

HTTP referer

The HTTP referer (Referer) is an optional HTTP request header in which a browser tells a server the address of the page containing the link clicked.

HTTP session

An HTTP session is a sequence of related requests and responses between a user agent and a web service, preserving state such as a logged-in identity.

HTTP Strict Transport Security

HTTP Strict Transport Security (HSTS) is a web security mechanism, standardized as RFC 6797 in 2012, that forces browsers to connect to a server only over HTTPS.

HTTP TRACE method

The HTTP TRACE method, defined in HTTP/1.1 in June 1999, asks the final recipient to echo the request back for diagnosis; its echo enabled the 2003 Cross-Site Tracing attack.

HTTP tunnel

An HTTP tunnel carries non-HTTP traffic, typically TCP, UDP, or IP packets, inside HTTP proxy connections via the CONNECT method, extended to UDP and IP by the MASQUE standards.

HTTP/2

HTTP/2 is the second major version of the Hypertext Transfer Protocol, standardized by the IETF in 2015. It multiplexes many exchanges over one connection using binary frames and compressed headers.

HTTP/2 server push

HTTP/2 server push is an HTTP/2 feature, defined in RFC 7540 in 2015, letting a server send anticipated resources; it was disabled by default in Chrome in 2022.

HTTP/3

HTTP/3 is the third major version of the Hypertext Transfer Protocol, standardized by the IETF in 2022 and running over the QUIC transport instead of TCP.

HTTPS

HTTPS, or Hypertext Transfer Protocol Secure, is the use of HTTP over a TLS-encrypted connection, typically on port 443, authenticating websites and protecting web traffic from eavesdropping and tampering.

HTTR

The High Temperature engineering Test Reactor (HTTR) is a 30 MW gas-cooled test reactor at JAEA's Oarai institute in Ibaraki, Japan, the only HTGR in the country.

HTX Studio

HTX Studio is a DIY science and technology YouTube channel created in 2024 by Chinese creator He Shijie of Hangzhou, known for the AirDesk build and open-source hardware.

Hu (胡) (people)

Hu (胡) was the Chinese term for the horse-riding peoples north and northwest of China, chiefly the Xiongnu, later broadened to Central Asians and Sogdians; also called Donghu, Xihu, Sanhu.

Hu Anguo

Hu Anguo (胡安国) was a Song dynasty Confucian scholar and official, 1074 to 1138, whose Chunqiu zhuan commentary on the Spring and Autumn Annals became the examination standard.

Hu Baoquan

Hu Baoquan (胡宝瑔, 1694–1763) was a Qing dynasty official who served the Qianlong Emperor as a censor, vice minister of war, and governor of four provinces.