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International standard | RFC7231 |
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Developed by | initially CERN; IETF, W3C |
Introduced | 1991; 28 years ago |
HTTP |
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Request methods |
Header fields |
Status codes |
Security access control methods |
Internet protocol suite |
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Application layer |
Transport layer |
Internet layer |
|
Link layer |
|
The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems.[1] HTTP is the foundation of data communication for the World Wide Web, where hypertext documents include hyperlinks to other resources that the user can easily access, for example by a mouse click or by tapping the screen in a web browser.
Development of HTTP was initiated by Tim Berners-Lee at CERN in 1989. Development of early HTTP Requests for Comments (RFCs) was a coordinated effort by the Internet Engineering Task Force (IETF) and the World Wide Web Consortium (W3C), with work later moving to the IETF.
HTTP/1.1 was first documented in RFC2068 in 1997. That specification was obsoleted by RFC2616 in 1999, which was likewise replaced by the RFC7230 family of RFCs in 2014.
HTTP/2 is a more efficient expression of HTTP's semantics 'on the wire', and was published in 2015; it is now supported by major web servers and browsers over Transport Layer Security (TLS) using an Application-Layer Protocol Negotiation (ALPN) extension[2] where TLS 1.2 or newer is required.[3]
HTTP/3 is the successor to HTTP/2,[4][5] using UDP instead of TCP for the underlying transport protocol. Like HTTP/2, it does not obsolete previous major versions of the protocol. HTTP/3 support was added in Cloudflare, Google Chrome, and Mozilla Firefox on 26 September 2019.[6]
- 3HTTP session
- 4HTTP authentication
- 5Message format
- 5.1Request message
- 5.1.1Request methods
- 5.2Response message
- 5.1Request message
- 7Example session
Technical overview[edit]
HTTP functions as a request–response protocol in the client–server computing model. A web browser, for example, may be the client and an application running on a computer hosting a website may be the server. The client submits an HTTP request message to the server. The server, which provides resources such as HTML files and other content, or performs other functions on behalf of the client, returns a response message to the client. The response contains completion status information about the request and may also contain requested content in its message body.
A web browser is an example of a user agent (UA). Other types of user agent include the indexing software used by search providers (web crawlers), voice browsers, mobile apps, and other software that accesses, consumes, or displays web content.
HTTP is designed to permit intermediate network elements to improve or enable communications between clients and servers. High-traffic websites often benefit from web cache servers that deliver content on behalf of upstream servers to improve response time. Web browsers cache previously accessed web resources and reuse them, when possible, to reduce network traffic. HTTP proxy servers at private network boundaries can facilitate communication for clients without a globally routable address, by relaying messages with external servers.
HTTP is an application layer protocol designed within the framework of the Internet protocol suite. Its definition presumes an underlying and reliable transport layer protocol,[7] and Transmission Control Protocol (TCP) is commonly used. However, HTTP can be adapted to use unreliable protocols such as the User Datagram Protocol (UDP), for example in HTTPU and Simple Service Discovery Protocol (SSDP).
HTTP resources are identified and located on the network by Uniform Resource Locators (URLs), using the Uniform Resource Identifiers (URI's) schemes http and https. For example, including all optional components:
URIs are encoded as hyperlinks in HTML documents, so as to form interlinked hypertext documents.
HTTP/1.1 is a revision of the original HTTP (HTTP/1.0). In HTTP/1.0 a separate connection to the same server is made for every resource request. HTTP/1.1 can reuse a connection multiple times to download images, scripts, stylesheets, etc after the page has been delivered. HTTP/1.1 communications therefore experience less latency as the establishment of TCP connections presents considerable overhead.
History[edit]
The term hypertext was coined by Ted Nelson in 1965 in the Xanadu Project, which was in turn inspired by Vannevar Bush's 1930s vision of the microfilm-based information retrieval and management 'memex' system described in his 1945 essay 'As We May Think'. Tim Berners-Lee and his team at CERN are credited with inventing the original HTTP, along with HTML and the associated technology for a web server and a text-based web browser. Berners-Lee first proposed the 'WorldWideWeb' project in 1989—now known as the World Wide Web. The first version of the protocol had only one method, namely GET, which would request a page from a server.[8] The response from the server was always an HTML page.[9]
The first documented version of HTTP was HTTP V0.9 (1991). Dave Raggett led the HTTP Working Group (HTTP WG) in 1995 and wanted to expand the protocol with extended operations, extended negotiation, richer meta-information, tied with a security protocol which became more efficient by adding additional methods and header fields.[10][11]RFC1945 officially introduced and recognized HTTP V1.0 in 1996.
The HTTP WG planned to publish new standards in December 1995[12] and the support for pre-standard HTTP/1.1 based on the then developing RFC2068 (called HTTP-NG) was rapidly adopted by the major browser developers in early 1996. By March that year, pre-standard HTTP/1.1 was supported in Arena,[13]Netscape 2.0,[13] Netscape Navigator Gold 2.01,[13]Mosaic 2.7,[citation needed]Lynx 2.5,[citation needed] and in Internet Explorer 2.0.[citation needed] End-user adoption of the new browsers was rapid. In March 1996, one web hosting company reported that over 40% of browsers in use on the Internet were HTTP 1.1 compliant.[citation needed] That same web hosting company reported that by June 1996, 65% of all browsers accessing their servers were HTTP/1.1 compliant.[14] The HTTP/1.1 standard as defined in RFC2068 was officially released in January 1997. Improvements and updates to the HTTP/1.1 standard were released under RFC2616 in June 1999.
In 2007, the HTTP Working Group was formed, in part, to revise and clarify the HTTP/1.1 specification. In June 2014, the WG released an updated six-part specification obsoleting RFC2616:
- RFC7230, HTTP/1.1: Message Syntax and Routing
- RFC7231, HTTP/1.1: Semantics and Content
- RFC7232, HTTP/1.1: Conditional Requests
- RFC7233, HTTP/1.1: Range Requests
- RFC7234, HTTP/1.1: Caching
- RFC7235, HTTP/1.1: Authentication
HTTP/2 was published as RFC7540 in May 2015.
Year | HTTP Version |
---|---|
1991 | 0.9 |
1996 | 1.0 |
1997 | 1.1 |
2015 | 2.0 |
2018 | 3.0 |
HTTP session[edit]
An HTTP session is a sequence of network request-response transactions. An HTTP client initiates a request by establishing a Transmission Control Protocol (TCP) connection to a particular port on a server (typically port 80, occasionally port 8080; see List of TCP and UDP port numbers). An HTTP server listening on that port waits for a client's request message. Upon receiving the request, the server sends back a status line, such as 'HTTP/1.1 200 OK', and a message of its own. The body of this message is typically the requested resource, although an error message or other information may also be returned.[1]
Persistent connections[edit]
In HTTP/0.9 and 1.0, the connection is closed after a single request/response pair. In HTTP/1.1 a keep-alive-mechanism was introduced, where a connection could be reused for more than one request. Such persistent connections reduce request latency perceptibly, because the client does not need to re-negotiate the TCP 3-Way-Handshake connection after the first request has been sent. Another positive side effect is that, in general, the connection becomes faster with time due to TCP's slow-start-mechanism.
Version 1.1 of the protocol also made bandwidth optimization improvements to HTTP/1.0. For example, HTTP/1.1 introduced chunked transfer encoding to allow content on persistent connections to be streamed rather than buffered. HTTP pipelining further reduces lag time, allowing clients to send multiple requests before waiting for each response. Another addition to the protocol was byte serving, where a server transmits just the portion of a resource explicitly requested by a client.
HTTP session state[edit]
HTTP is a stateless protocol. A stateless protocol does not require the HTTP server to retain information or status about each user for the duration of multiple requests. However, some web applications implement states or server side sessions using for instance HTTP cookies or hidden variables within web forms.
HTTP authentication[edit]
HTTP provides multiple authentication schemes such as basic access authentication and digest access authentication which operate via a challenge-response mechanism whereby the server identifies and issues a challenge before serving the requested content.
HTTP provides a general framework for access control and authentication, via an extensible set of challenge-response authentication schemes, which can be used by a server to challenge a client request and by a client to provide authentication information.[15]
Authentication realms[edit]
The HTTP Authentication specification also provides an arbitrary, implementation-specific construct for further dividing resources common to a given root URI. The realm value string, if present, is combined with the canonical root URI to form the protection space component of the challenge. This in effect allows the server to define separate authentication scopes under one root URI.[15]
Message format[edit]
Https Download Manager
The client sends requests to the server and the server sends responses.
Request message[edit]
The request message consists of the following:
- a request line (e.g., GET /images/logo.png HTTP/1.1, which requests a resource called
/images/logo.png
from the server.) - request header fields (e.g., Accept-Language: en).
- an empty line
- an optional message body
The request line and other header fields must each end with <CR><LF> (that is, a carriage return character followed by a line feed character). The empty line must consist of only <CR><LF> and no other whitespace.[16] In the HTTP/1.1 protocol, all header fields except Host are optional.
A request line containing only the path name is accepted by servers to maintain compatibility with HTTP clients before the HTTP/1.0 specification in RFC1945.[17]
Request methods[edit]
HTTP defines methods (sometimes referred to as verbs, but nowhere in the specification does it mention verb, nor is OPTIONS or HEAD a verb) to indicate the desired action to be performed on the identified resource. What this resource represents, whether pre-existing data or data that is generated dynamically, depends on the implementation of the server. Often, the resource corresponds to a file or the output of an executable residing on the server. The HTTP/1.0 specification[18] defined the GET, HEAD and POST methods and the HTTP/1.1 specification[19] added five new methods: OPTIONS, PUT, DELETE, TRACE and CONNECT. By being specified in these documents, their semantics are well-known and can be depended on. Any client can use any method and the server can be configured to support any combination of methods. If a method is unknown to an intermediate, it will be treated as an unsafe and non-idempotent method. There is no limit to the number of methods that can be defined and this allows for future methods to be specified without breaking existing infrastructure. For example, WebDAV defined 7 new methods and RFC5789 specified the PATCH method.
Method names are case sensitive.[20][21] This is in contrast to HTTP header field names which are case-insensitive.[22]
Summary table[edit]
HTTP method | RFC | Request has Body | Response has Body | Safe | Idempotent | Cacheable |
---|---|---|---|---|---|---|
GET | RFC7231 | Optional | Yes | Yes | Yes | Yes |
HEAD | RFC7231 | Optional | No | Yes | Yes | Yes |
POST | RFC7231 | Yes | Yes | No | No | Yes |
PUT | RFC7231 | Yes | Yes | No | Yes | No |
DELETE | RFC7231 | Optional | Yes | No | Yes | No |
CONNECT | RFC7231 | Optional | Yes | No | No | No |
OPTIONS | RFC7231 | Optional | Yes | Yes | Yes | No |
TRACE | RFC7231 | No | Yes | Yes | Yes | No |
PATCH | RFC5789 | Yes | Yes | No | No | No |
Response message[edit]
The response message consists of the following:
- a status line which includes the status code and reason message (e.g., HTTP/1.1 200 OK, which indicates that the client's request succeeded.)
- response header fields (e.g., Content-Type: text/html)
- an empty line
- an optional message body
The status line and other header fields must all end with <CR><LF>. The empty line must consist of only <CR><LF> and no other whitespace.[16] This strict requirement for <CR><LF> is relaxed somewhat within message bodies for consistent use of other system linebreaks such as <CR> or <LF> alone.[34]
Status codes[edit]
In HTTP/1.0 and since, the first line of the HTTP response is called the status line and includes a numeric status code (such as '404') and a textual reason phrase (such as 'Not Found'). The way the user agent handles the response depends primarily on the code, and secondarily on the other response header fields. Custom status codes can be used, for if the user agent encounters a code it does not recognize, it can use the first digit of the code to determine the general class of the response.[35]
The standard reason phrases are only recommendations, and can be replaced with 'local equivalents' at the web developer's discretion. If the status code indicated a problem, the user agent might display the reason phrase to the user to provide further information about the nature of the problem. The standard also allows the user agent to attempt to interpret the reason phrase, though this might be unwise since the standard explicitly specifies that status codes are machine-readable and reason phrases are human-readable. HTTP status code is primarily divided into five groups for better explanation of request and responses between client and server as named:
- Informational
1XX
- Successful
2XX
- Redirection
3XX
- Client Error
4XX
- Server Error
5XX
Encrypted connections[edit]
The most popular way of establishing an encrypted HTTP connection is HTTPS.[36] Two other methods for establishing an encrypted HTTP connection also exist: Secure Hypertext Transfer Protocol, and using the HTTP/1.1 Upgrade header to specify an upgrade to TLS. Browser support for these two is, however, nearly non-existent.[37][38][39]
Example session[edit]
Below is a sample conversation between an HTTP client and an HTTP server running on www.example.com, port 80.
Client request[edit]
A client request (consisting in this case of the request line and only one header field) is followed by a blank line, so that the request ends with a double newline, each in the form of a carriage return followed by a line feed. The 'Host' field distinguishes between various DNS names sharing a single IP address, allowing name-based virtual hosting. While optional in HTTP/1.0, it is mandatory in HTTP/1.1. (The '/' means /index.html if there is one.)
Server response[edit]
The ETag (entity tag) header field is used to determine if a cached version of the requested resource is identical to the current version of the resource on the server. Content-Type specifies the Internet media type of the data conveyed by the HTTP message, while Content-Length indicates its length in bytes. The HTTP/1.1 webserver publishes its ability to respond to requests for certain byte ranges of the document by setting the field Accept-Ranges: bytes. This is useful, if the client needs to have only certain portions[40] of a resource sent by the server, which is called byte serving. When Connection: close is sent, it means that the web server will close the TCP connection immediately after the transfer of this response.
Most of the header lines are optional. When Content-Length is missing the length is determined in other ways. Chunked transfer encoding uses a chunk size of 0 to mark the end of the content. Identity encoding without Content-Length reads content until the socket is closed.
A Content-Encoding like gzip can be used to compress the transmitted data.
Similar protocols[edit]
The Gopher protocol is a content delivery protocol that was displaced by HTTP in the early 1990s.The SPDY protocol is an alternative to HTTP developed at Google, it is superseded by the new HTTP protocol, HTTP/2.
See also[edit]
HTTP |
---|
Request methods |
Header fields |
Status codes |
Security access control methods |
- Constrained Application Protocol – a semantically similar protocol to HTTP but used UDP or UDP-like messages targeted for devices with limited processing capability; re-uses HTTP and other internet concepts like Internet media type and web linking (RFC 5988)[41]
- Curl-loader – HTTP/S loading and testing open-source software
- HTTP/2 – developed by the IETF's Hypertext Transfer Protocol (httpbis) working group[42]
- HTTP-MPLEX – A backwards compatible enhancement to HTTP to improve page and web object retrieval time in congested networks proposed by Robert Mattson
- Representational state transfer (REST)
References[edit]
- ^ abcdFielding, Roy T.; Gettys, James; Mogul, Jeffrey C.; Nielsen, Henrik Frystyk; Masinter, Larry; Leach, Paul J.; Berners-Lee, Tim (June 1999). Hypertext Transfer Protocol – HTTP/1.1. IETF. doi:10.17487/RFC2616. RFC 2616.
- ^'Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension'. IETF. July 2014. RFC7301.
- ^Belshe, M.; Peon, R.; Thomson, M. 'Hypertext Transfer Protocol Version 2, Use of TLS Features'. Retrieved 2015-02-10.
- ^Bishop, Mike (July 9, 2019). draft-ietf-quic-http-22 Hypertext Transfer Protocol Version 3 (HTTP/3) 'Hypertext Transfer Protocol Version 3 (HTTP/3)' Check
|url=
value (help). tools.ietf.org. Retrieved 2019-08-16. - ^Cimpanu, Catalin. 'HTTP-over-QUIC to be renamed HTTP/3 | ZDNet'. ZDNet. Retrieved 2018-11-19.
- ^Cimpanu, Catalin (26 September 2019). 'Cloudflare, Google Chrome, and Firefox add HTTP/3 support'. ZDNet. Retrieved 27 September 2019.
- ^'Overall Operation'. RFC 2616. p. 12. sec. 1.4. doi:10.17487/RFC2616. RFC 2616.
- ^Berners-Lee, Tim. 'HyperText Transfer Protocol'. World Wide Web Consortium. Retrieved 31 August 2010.
- ^Tim Berners-Lee. 'The Original HTTP as defined in 1991'. World Wide Web Consortium. Retrieved 24 July 2010.
- ^Raggett, Dave. 'Dave Raggett's Bio'. World Wide Web Consortium. Retrieved 11 June 2010.
- ^Raggett, Dave; Berners-Lee, Tim. 'Hypertext Transfer Protocol Working Group'. World Wide Web Consortium. Retrieved 29 September 2010.
- ^Raggett, Dave. 'HTTP WG Plans'. World Wide Web Consortium. Retrieved 29 September 2010.
- ^ abcSimon Spero. 'Progress on HTTP-NG'. World Wide Web Consortium. Retrieved 11 June 2010.
- ^'HTTP/1.1'. Webcom.com Glossary entry. Archived from the original on 2001-11-21. Retrieved 2009-05-29.
- ^ abFielding, Roy T.; Reschke, Julian F. (June 2014). Hypertext Transfer Protocol (HTTP/1.1): Authentication. IETF. doi:10.17487/RFC7235. RFC 7235.
- ^ ab'HTTP Message'. RFC 2616. p. 31. sec. 4. doi:10.17487/RFC2616. RFC 2616.
- ^'Apache Week. HTTP/1.1'. 090502 apacheweek.com
- ^Berners-Lee, Tim; Fielding, Roy T.; Nielsen, Henrik Frystyk. 'Method Definitions'. Hypertext Transfer Protocol – HTTP/1.0. IETF. pp. 30–32. sec. 8. doi:10.17487/RFC1945. RFC 1945.
- ^'Method Definitions'. RFC 2616. pp. 51–57. sec. 9. doi:10.17487/RFC2616. RFC 2616.
- ^'RFC-7210 section 3.1.1'. Tools.ietf.org. Retrieved 2019-06-26.
- ^'RFC-7231 section 4.1'. Tools.ietf.org. Retrieved 2019-06-26.
- ^'RFC-7230 section 3.2'. Tools.ietf.org. Retrieved 2019-06-26.
- ^Jacobs, Ian (2004). 'URIs, Addressability, and the use of HTTP GET and POST'. Technical Architecture Group finding. W3C. Retrieved 26 September 2010.
- ^'POST'. RFC 2616. p. 54. sec. 9.5. doi:10.17487/RFC2616. RFC 2616.
- ^'PUT'. RFC 2616. p. 55. sec. 9.6. doi:10.17487/RFC2616. RFC 2616.
- ^'CONNECT'. Hypertext Transfer Protocol – HTTP/1.1. IETF. June 1999. p. 57. sec. 9.9. doi:10.17487/RFC2616. RFC 2616. Retrieved 23 February 2014.
- ^Khare, Rohit; Lawrence, Scott (May 2000). Upgrading to TLS Within HTTP/1.1. IETF. doi:10.17487/RFC2817. RFC 2817.
- ^'Vulnerability Note VU#150227: HTTP proxy default configurations allow arbitrary TCP connections'. US-CERT. 2002-05-17. Retrieved 2007-05-10.
- ^Dusseault, Lisa; Snell, James M. (March 2010). PATCH Method for HTTP. IETF. doi:10.17487/RFC5789. RFC 5789.
- ^'Method'. RFC 2616. p. 36. sec. 5.1.1. doi:10.17487/RFC2616. RFC 2616.
- ^ abEdiger, Brad (2007-12-21). Advanced Rails: Building Industrial-Strength Web Apps in Record Time. O'Reilly Media, Inc. p. 188. ISBN978-0596519728.
A common mistake is to use GET for an action that updates a resource. [...] This problem came into the Rails public eye in 2005, when the Google Web Accelerator was released.
- ^Cantrell, Christian (2005-06-01). 'What Have We Learned From the Google Web Accelerator?'. Adobe Blogs. Adobe. Archived from the original on 2017-08-19.
- ^ ab'Cross Site Tracing'. OWASP. Retrieved 2016-06-22.
- ^'Canonicalization and Text Defaults'. RFC 2616. sec. 3.7.1. doi:10.17487/RFC2616. RFC 2616.
- ^'Status-Line'. RFC 2616. p. 39. sec. 6.1. doi:10.17487/RFC2616. RFC 2616.
- ^Canavan, John (2001). Fundamentals of Networking Security. Norwood, MA: Artech House. pp. 82–83. ISBN9781580531764.
- ^Zalewski, Michal. 'Browser Security Handbook'. Retrieved 30 April 2015.
- ^'Chromium Issue 4527: implement RFC 2817: Upgrading to TLS Within HTTP/1.1'. Retrieved 30 April 2015.
- ^'Mozilla Bug 276813 – [RFE] Support RFC 2817 / TLS Upgrade for HTTP 1.1'. Retrieved 30 April 2015.
- ^Luotonen, Ari; Franks, John (February 22, 1996). Byte Range Retrieval Extension to HTTP. IETF. I-D draft-ietf-http-range-retrieval-00.
- ^Nottingham, Mark (October 2010). Web Linking. IETF. doi:10.17487/RFC5988. RFC 5988.
- ^'Hypertext Transfer Protocol Bis (httpbis) – Charter'. IETF. 2012.
Protocol Https Download Video
External links[edit]
Wikimedia Commons has media related to Hypertext Transfer Protocol. |
- 'Change History for HTTP'. W3.org. Retrieved 2010-08-01. A detailed technical history of HTTP.
- 'Design Issues for HTTP'. W3.org. Retrieved 2010-08-01. Design Issues by Berners-Lee when he was designing the protocol.
- 'Classic HTTP Documents'. W3.org. 1998-05-14. Retrieved 2010-08-01. list of other classic documents recounting the early protocol history
Copyright 2008 Google Inc.
Overview
Protocol Buffers (a.k.a., protobuf) are Google's language-neutral,platform-neutral, extensible mechanism for serializing structured data. Youcan find protobuf's documentation on the Google Developers site.
This README file contains protobuf installation instructions. To installprotobuf, you need to install the protocol compiler (used to compile .protofiles) and the protobuf runtime for your chosen programming language.
Protocol Compiler Installation
The protocol compiler is written in C++. If you are using C++, please followthe C++ Installation Instructions to install protoc alongwith the C++ runtime.
For non-C++ users, the simplest way to install the protocol compiler is todownload a pre-built binary from our release page:
In the downloads section of each release, you can find pre-built binaries inzip packages: protoc-$VERSION-$PLATFORM.zip. It contains the protoc binaryas well as a set of standard .proto files distributed along with protobuf.
If you are looking for an old version that is not available in the releasepage, check out the maven repo here:
These pre-built binaries are only provided for released versions. If you wantto use the github master version at HEAD, or you need to modify protobuf code,or you are using C++, it's recommended to build your own protoc binary fromsource.
If you would like to build protoc binary from source, see the C++ InstallationInstructions.
Protobuf Runtime Installation
Protobuf supports several different programming languages. For each programminglanguage, you can find instructions in the corresponding source directory abouthow to install protobuf runtime for that specific language:
Language | Source | Ubuntu | MacOS | Windows |
---|---|---|---|---|
C++ (include C++ runtime and protoc) | src | |||
Java | java | |||
Python | python | |||
Objective-C | objectivec | |||
C# | csharp | |||
JavaScript | js | |||
Ruby | ruby | |||
Go | golang/protobuf | |||
PHP | php | |||
Dart | dart-lang/protobuf |
Quick Start
The best way to learn how to use protobuf is to follow the tutorials in ourdeveloper guide:
If you want to learn from code examples, take a look at the examples in theexamples directory.
Documentation
Broke Protocol Free Download
The complete documentation for Protocol Buffers is available via theweb at: