GuidesAccess control CORSAuthenticationBrowser detection using the user agentCachingCaching FAQCompressionConditional requestsConnection management in HTTP 1.xContent negotiationContent negotiation: List of default Accept valuesCookiesCSPMessagesOverviewProtocol upgrade mechanismProxy servers and tunnelingProxy servers and tunneling: Proxy Auto-Configuration (PAC) filePublic Key PinningRange requestsRedirectionsResources and specificationsResources and URIsResponse codesServer-Side Access ControlSessionGuides: BasicsBasics of HTTPChoosing between www and non-www URLsData URIsEvolution of HTTPIdentifying resources on the WebMIME TypesMIME types: Complete list of MIME typesCSPContent-Security-PolicyContent-Security-Policy-Report-OnlyCSP: base-uriCSP: block-all-mixed-contentCSP: child-srcCSP: connect-srcCSP: default-srcCSP: font-srcCSP: form-actionCSP: frame-ancestorsCSP: frame-srcCSP: img-srcCSP: manifest-srcCSP: media-srcCSP: object-srcCSP: plugin-typesCSP: referrerCSP: report-uriCSP: require-sri-forCSP: sandboxCSP: script-srcCSP: style-srcCSP: upgrade-insecure-requestsCSP: worker-srcHeadersAcceptAccept-CharsetAccept-EncodingAccept-LanguageAccept-RangesAccess-Control-Allow-CredentialsAccess-Control-Allow-HeadersAccess-Control-Allow-MethodsAccess-Control-Allow-OriginAccess-Control-Expose-HeadersAccess-Control-Max-AgeAccess-Control-Request-HeadersAccess-Control-Request-MethodAgeAllowAuthorizationCache-ControlConnectionContent-DispositionContent-EncodingContent-LanguageContent-LengthContent-LocationContent-RangeContent-TypeCookieCookie2DateDNTETagExpectExpiresForwardedFromHeadersHostIf-MatchIf-Modified-SinceIf-None-MatchIf-RangeIf-Unmodified-SinceKeep-AliveLarge-AllocationLast-ModifiedLocationOriginPragmaProxy-AuthenticateProxy-AuthorizationPublic-Key-PinsPublic-Key-Pins-Report-OnlyRangeRefererReferrer-PolicyRetry-AfterServerSet-CookieSet-Cookie2SourceMapStrict-Transport-SecurityTETkTrailerTransfer-EncodingUpgrade-Insecure-RequestsUser-AgentUser-Agent: FirefoxVaryViaWarningWWW-AuthenticateX-Content-Type-OptionsX-DNS-Prefetch-ControlX-Forwarded-ForX-Forwarded-HostX-Forwarded-ProtoX-Frame-OptionsX-XSS-ProtectionMethodsCONNECTDELETEGETHEADMethodsOPTIONSPATCHPOSTPUTStatus100 Continue101 Switching Protocols200 OK201 Created202 Accepted203 Non-Authoritative Information204 No Content205 Reset Content206 Partial Content300 Multiple Choices301 Moved Permanently302 Found303 See Other304 Not Modified307 Temporary Redirect308 Permanent Redirect400 Bad Request401 Unauthorized403 Forbidden404 Not Found405 Method Not Allowed406 Not Acceptable407 Proxy Authentication Required408 Request Timeout409 Conflict410 Gone411 Length Required412 Precondition Failed413 Payload Too Large414 URI Too Long415 Unsupported Media Type416 Range Not Satisfiable417 Expectation Failed426 Upgrade Required428 Precondition Required429 Too Many Requests431 Request Header Fields Too Large451 Unavailable For Legal Reasons500 Internal Server Error501 Not Implemented502 Bad Gateway503 Service Unavailable504 Gateway Timeout505 HTTP Version Not Supported511 Network Authentication RequiredStatus
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Expect HTTP 请求头表明，需要通过服务器，以便正确地处理该请求符合预期。
规范中定义的唯一期望是Expect: 100-continue，服务器应该以此作为回应：
100如果标题中包含的信息足以立即获得成功，
417（期望失败），如果它不能达到预期; 或者其他任何其他 4xx 状态。
例如，如果它的Content-Length太大，服务器可能会拒绝一个请求。
没有常见的浏览器发送Expect头文件，但其他一些客户端（例如 cURL ）默认会这样做。
Header type | Request header |
|---|---|
Forbidden header name | no |
语法
目前没有指定除“100-continue”之外的其他期望。
Expect: 100-continue
指令
100-continue 通知收件人客户端将在此请求中发送消息主体100（希望大），并希望接收（继续）临时响应。
例子
大邮件正文
客户端发送带有 Expect 头的请求，并在发送消息正文之前等待服务器作出响应。
PUT /somewhere/fun HTTP/1.1Host: origin.example.com Content-Type: video/h264 Content-Length: 1234567890987Expect: 100-continue
服务器现在检查请求标题，并可能会响应100（继续）响应以指示客户端继续并发送消息正文，或者417如果无法满足任何期望，它将发送（期望失败）状态。
规范
Specification | Title |
|---|---|
RFC 7231, section 5.1.1: Expect | Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content |
浏览器兼容性
已知没有常见的浏览器发送此标头。