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1. Introduction

The Hypertext Transfer Protocol (HTTP) is a stateless application-level request/response protocol that uses extensible semantics and self-descriptive messages for flexible interaction with network-based hypertext information systems. HTTP/1.1 is defined by:

  • This document
  • "HTTP Semantics" [HTTP]
  • "HTTP Caching" [CACHING]

This document specifies how HTTP semantics are conveyed using the HTTP/1.1 message syntax, framing, and connection management mechanisms. Its goal is to define the complete set of requirements for HTTP/1.1 message parsers and message-forwarding intermediaries.

This document obsoletes the portions of RFC 7230 related to HTTP/1.1 messaging and connection management, with the changes being summarized in Appendix C.3. The other parts of RFC 7230 are obsoleted by "HTTP Semantics" [HTTP].

1.1. Requirements Notation​

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

Conformance criteria and considerations regarding error handling are defined in Section 2 of [HTTP].

1.2. Syntax Notation​

This specification uses the Augmented Backus-Naur Form (ABNF) notation of [RFC5234], extended with the notation for case-sensitivity in strings defined in [RFC7405].

It also uses a list extension, defined in Section 5.6.1 of [HTTP], that allows for compact definition of comma-separated lists using a "#" operator (similar to how the "*" operator indicates repetition). Appendix A shows the collected grammar with all list operators expanded to standard ABNF notation.

As a convention, ABNF rule names prefixed with "obs-" denote obsolete grammar rules that appear for historical reasons.

The following core rules are included by reference, as defined in [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any visible [USASCII] character).

The rules below are defined in [HTTP]:

BWS           = `<BWS, see [HTTP], Section 5.6.3>`
OWS           = `<OWS, see [HTTP], Section 5.6.3>`
RWS           = `<RWS, see [HTTP], Section 5.6.3>`
absolute-path = `<absolute-path, see [HTTP], Section 4.1>`
field-name    = `<field-name, see [HTTP], Section 5.1>`
field-value   = `<field-value, see [HTTP], Section 5.5>`
obs-text      = `<obs-text, see [HTTP], Section 5.6.4>`
quoted-string = `<quoted-string, see [HTTP], Section 5.6.4>`
token         = `<token, see [HTTP], Section 5.6.2>`
transfer-coding =
                `<transfer-coding, see [HTTP], Section 10.1.4>`

The rules below are defined in [URI]:

absolute-URI  = `<absolute-URI, see [URI], Section 4.3>`
authority     = `<authority, see [URI], Section 3.2>`
uri-host      = `<host, see [URI], Section 3.2.2>`
port          = `<port, see [URI], Section 3.2.3>`
query         = `<query, see [URI], Section 3.4>`
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