datavow.com - Documents

1) Introduction
- 1) Purpose
- 2) Requirements
- 3) Terminology
- 4) Overall Operation
2) Notational Conventions and Generic Grammar
- 1) Augmented BNF
- 2) Basic Rules
3) Protocol Parameters
- 1) HTTP Version
- 2) Uniform Resource Identifiers
- 3) Date/Time Formats
  - 1) Full Date
  - 2) Delta Seconds
- 4) Character Sets
  - 1) Missing Charset
- 5) Content Codings
- 6) Transfer Codings
  - 1) Chunked Transfer Coding
- 7) Media Types
  - 1) Canonicalization and Text Defaults
  - 2) Multipart Types
- 8) Product Tokens
- 9) Quality Values
- 10) Language Tags
- 11) Entity Tags
- 12) Range Units
4) HTTP Message
- 1) Message Types
- 2) Message Headers
- 3) Message Body
- 4) Message Length
- 5) General Header Fields
5) Request
- 1) Request-Line
  - 1) Method
  - 2) Request-URI
- 2) The Resource Identified by a Request
- 3) Request Header Fields
6) Response
- 1) Status-Line
  - 1) Status Code and Reason Phrase
- 2) Response Header Fields
7) Entity
- 1) Entity Header Fields
- 2) Entity Body
  - 1) Type
  - 2) Entity Length
8) Connections
- 1) Persistent Connections
- 2) Message Transmission Requirements
9) Method Definitions
- 1) Safe and Idempotent Methods
  - 1) Safe Methods
  - 2) Idempotent Methods
- 2) OPTIONS
- 3) GET
- 4) HEAD
- 5) POST
- 6) PUT
- 7) DELETE
- 8) TRACE
- 9) CONNECT
10) Status Code Definitions
- 1) Informational 1xx
  - 1) Continue
  - 2) Switching Protocols
- 2) Successful 2xx
- 3) Redirection 3xx
- 4) Client Error 4xx
- 5) Server Error 5xx
11) Access Authentication
12) Content Negotiation
- 1) Server-driven Negotiation
- 2) Agent-driven Negotiation
- 3) Transparent Negotiation
13) Caching in HTTP
- 1) ..
- 2) Expiration Model
- 3) Validation Model
- 4) Response Cacheability
- 5) Constructing Responses From Caches
- 6) Caching Negotiated Responses
- 7) Shared and Non-Shared Caches
- 8) Errors or Incomplete Response Cache Behavior
- 9) Side Effects of GET and HEAD
- 10) Invalidation After Updates or Deletions
- 11) Write-Through Mandatory
- 12) Cache Replacement
- 13) History Lists
14) Header Field Definitions
- 1) Accept
- 2) Accept-Charset
- 3) Accept-Encoding
- 4) Accept-Language
- 5) Accept-Ranges
- 6) Age
- 7) Allow
- 8) Authorization
- 9) Cache-Control
  - 1) What is Cacheable
  - 2) What May be Stored by Caches
  - 3) Modifications of the Basic Expiration Mechanism
  - 4) Cache Revalidation and Reload Controls
  - 5) No-Transform Directive
  - 6) Cache Control Extensions
- 10) Connection
- 11) Content-Encoding
- 12) Content-Language
- 13) Content-Length
- 14) Content-Location
- 15) Content-MD5
- 16) Content-Range
- 17) Content-Type
- 18) Date
  - 1) Clockless Origin Server Operation
- 19) ETag
- 20) Expect
- 21) Expires
- 22) From
- 23) Host
- 24) If-Match
- 25) If-Modified-Since
- 26) If-None-Match
- 27) If-Range
- 28) If-Unmodified-Since
- 29) Last-Modified
- 30) Location
- 31) Max-Forwards
- 32) Pragma
- 33) Proxy-Authenticate
- 34) Proxy-Authorization
- 35) Range
  - 1) Byte Ranges
  - 2) Range Retrieval Requests
- 36) Referer
- 37) Retry-After
- 38) Server
- 39) TE
- 40) Trailer
- 41) Transfer-Encoding
- 42) Upgrade
- 43) User-Agent
- 44) Vary
- 45) Via
- 46) Warning
- 47) WWW-Authenticate
15) Security Considerations
- 1) Personal Information
- 2) Attacks Based On File and Path Names
- 3) DNS Spoofing
- 4) Location Headers and Spoofing
- 5) Content-Disposition Issues
- 6) Authentication Credentials and Idle Clients
- 7) Proxies and Caching
  - 1) Denial of Service Attacks on Proxies
16) Acknowledgments
17) References
18) Authors' Addresses
19) Appendices
- 1) Internet Media Type message/http and application/http
- 2) Internet Media Type multipart/byteranges
- 3) Tolerant Applications
- 4) Differences Between HTTP Entities and RFC 2045 Entities
- 5) Additional Features
  - 1) Content-Disposition
- 6) Compatibility with Previous Versions
20) Index
21) Full Copyright Statement
22) Acknowledgement

8.2.3 Use of the 100 (Continue) Status

The purpose of the 100 (Continue) status (see Section 10.1.1) is to allow a client that is sending a request message with a request body to determine if the origin server is willing to accept the request (based on the request headers) before the client sends the request body. In some cases, it might either be inappropriate or highly inefficient for the client to send the body if the server will reject the message without looking at the body.

Requirements for HTTP/1.1 clients:

- If a client will wait for a 100 (Continue) response before sending the request body, it MUST send an Expect request-header field (Section 14.20) with the "100-continue" expectation.

- A client MUST NOT send an Expect request-header field (Section 14.20) with the "100-continue" expectation if it does not intend to send a request body.

Because of the presence of older implementations, the protocol allows ambiguous situations in which a client may send "Expect: 100- continue" without receiving either a 417 (Expectation Failed) status or a 100 (Continue) status. Therefore, when a client sends this header field to an origin server (possibly via a proxy) from which it has never seen a 100 (Continue) status, the client SHOULD NOT wait for an indefinite period before sending the request body.

Requirements for HTTP/1.1 origin servers:

- Upon receiving a request which includes an Expect request-header field with the "100-continue" expectation, an origin server MUST either respond with 100 (Continue) status and continue to read from the input stream, or respond with a final status code. The origin server MUST NOT wait for the request body before sending the 100 (Continue) response. If it responds with a final status code, it MAY close the transport connection or it MAY continue to read and discard the rest of the request. It MUST NOT perform the requested method if it returns a final status code.

- An origin server SHOULD NOT send a 100 (Continue) response if the request message does not include an Expect request-header field with the "100-continue" expectation, and MUST NOT send a 100 (Continue) response if such a request comes from an HTTP/1.0 (or earlier) client. There is an exception to this rule: for compatibility with RFC 2068, a server MAY send a 100 (Continue) status in response to an HTTP/1.1 PUT or POST request that does not include an Expect request-header field with the "100- continue" expectation. This exception, the purpose of which is to minimize any client processing delays associated with an undeclared wait for 100 (Continue) status, applies only to HTTP/1.1 requests, and not to requests with any other HTTP- version value.

- An origin server MAY omit a 100 (Continue) response if it has already received some or all of the request body for the corresponding request.

- An origin server that sends a 100 (Continue) response MUST ultimately send a final status code, once the request body is received and processed, unless it terminates the transport connection prematurely.

- If an origin server receives a request that does not include an Expect request-header field with the "100-continue" expectation, the request includes a request body, and the server responds with a final status code before reading the entire request body from the transport connection, then the server SHOULD NOT close the transport connection until it has read the entire request, or until the client closes the connection. Otherwise, the client might not reliably receive the response message. However, this requirement is not be construed as preventing a server from defending itself against denial-of-service attacks, or from badly broken client implementations.

Requirements for HTTP/1.1 proxies:

- If a proxy receives a request that includes an Expect request- header field with the "100-continue" expectation, and the proxy either knows that the next-hop server complies with HTTP/1.1 or higher, or does not know the HTTP version of the next-hop server, it MUST forward the request, including the Expect header field.

- If the proxy knows that the version of the next-hop server is HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST respond with a 417 (Expectation Failed) status.

- Proxies SHOULD maintain a cache recording the HTTP version numbers received from recently-referenced next-hop servers.

- A proxy MUST NOT forward a 100 (Continue) response if the request message was received from an HTTP/1.0 (or earlier) client and did not include an Expect request-header field with the "100-continue" expectation. This requirement overrides the general rule for forwarding of 1xx responses (see Section 10.1).