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https://github.com/httpwg/http-extensionsOfficial working area for the IETF HTTP Working Group (HTTPWG) to develop draft specifications for HTTP extensions. Documentation includes specifications for Cache Groups (Cache-Groups and Cache-Group-Invalidation headers) and Compression Dictionary Transport (Use-As-Dictionary, Available-Dictionary, and Dictionary-ID headers), including content encodings dcb and dcz.
The Early Hints extension introduces an informational HTTP status code designed to convey hints to a client. These hints allow the client to make preparations (such as preloading resources) while waiting for the final response to be processed.
Note: As of the current draft status, this extension is categorized as Experimental to facilitate deployment experience and gathering of real-world data.
The http-extensions repository serves as the working area for the IETF HTTP Working Group's extensions to the HTTP protocol. Developers can find the current list of specifications, including editors' drafts, document status, and associated issues, at the official HTTP extensions website.
To view the specific drafts and their current status, visit the list of specifications.
The WRAP_UP capsule is a mechanism used by HTTP proxies to signal to a client that an upcoming request stream termination is imminent.
Unlike GOAWAY (which signals connection termination), WRAP_UP is designed for scenarios where a proxy needs to terminate an individual long-lived request stream (e.g., for load balancing, maintenance, or enforcing data limits) while keeping the underlying connection active. This is particularly useful for tunneled connections like CONNECT or connect-udp, where an abrupt termination would cause truncated content and prevent the client from safely retrying requests.
Key Use Cases:
The No-Vary-Search extension allows origin servers to signal to HTTP caches (browsers, CDNs, forward proxies) that certain parts of a URL's query component do not semantically affect the response. This enables caches to reuse a stored response even if the query parameters differ, improving cache hit rates by ignoring non-semantic variations like parameter order or analytics tracking parameters.
Key use cases:
utm_source).The Expect-CT HTTP header is an experimental mechanism that allows web host operators to instruct user agents (browsers) to expect valid Signed Certificate Timestamps (SCTs) during connections.
Its primary purposes are:
The Alt-Svc (Alternative Services) extension provides a method for HTTP servers to inform clients about authoritative access to the same origin at a different network location or using a different protocol stack. This allows a client to discover multiple network or protocol endpoints for an origin that can serve content in different ways (e.g., switching from HTTP/1.1 to HTTP/2 or a different port/IP).
Key characteristics:
Alt-Svc listings are optional-to-understand. If a client encounters a parameter it does not recognize, it should ignore that specific parameter rather than discarding the entire entry.The Unencoded-Digest field is used to communicate integrity digests calculated from the unencoded representation of a message (i.e., the data after all Content-Encoding transformations have been stripped away).
This is useful when:
Repr-Digest or Content-Digest that was calculated on encoded bytes./* Example of an Unencoded-Digest field for the string "An unexceptional string\n" */
Unencoded-Digest: sha-512=:WjyMuMD9EI/v0RoJchcevbo6lF498VyE9564OgXf+98iJptoSvb1Czo9uVJu2bVU/tOv90huiMG3+YaMX1kipw==:draft-ietf-httpbis-h2-websockets specification defines a mechanism to run the WebSocket Protocol over a single stream of an existing HTTP/2 connection. This approach enables WebSockets to function on HTTP/2 servers, which can reduce operational issues for websites by consolidating traffic over a single connection.HTTP cookies allow servers to maintain state in a stateless protocol.
Set-Cookie header in an HTTP response containing name/value pairs and metadata (attributes).Cookie header field.Key behaviors:
Path and Domain attributes.Secure and HttpOnly provide additional protections.Expires attribute determines if a cookie persists across sessions.SID and sid are treated as two distinct cookies.== Server -> User Agent ==
Set-Cookie: SID=31d4d96e407aad42
== User Agent -> Server ==
Cookie: SID=31d4d96e407aad42Resumable uploads do not permit parallel requests for the same upload. A client MUST NOT perform multiple representation data transfers for the same upload resource in parallel, nor perform transfers while the creation of the same upload resource is still in progress.
To prevent race conditions, data loss, or corruption caused by network interruptions (where a client retries while a server still considers the previous request ongoing), servers should follow these guidelines:
451 is used when access to a resource is denied due to legal demands or restrictions. This status code provides a machine-readable indicator that an automated client can detect, which is useful for services like Lumen (formerly Chilling Effects) to track and report legal censorship or restricted content.Compression Dictionary Transport is an HTTP mechanism that allows clients and servers to use specific HTTP responses as external dictionaries for future requests. This enables dictionary-based compression (using schemes like Brotli or Zstandard) to reduce transmitted data size, often through delta compression.
There are two primary use cases:
app.v1.js) as a dictionary to compress a newer version (e.g., app.v2.js).