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Os cabeçalhos HTTP permitem que o cliente e o servidor passem informações adicionais com a solicitação ou a resposta HTTP. Um cabeçalho de solicitação é composto por seu nome case-insensitive (não diferencia letras maiúsculas e minúsculas), seguido por dois pontos ':' e pelo seu valor (sem quebras de linha). Espaços em branco antes do valor serão ignorados.
Cabeçalhos proprietários personalizados podem ser adicionados usando o prefixo 'X-', mas essa convenção foi depreciada em Junho de 2012, devido aos inconvenientes que causou quando os campos não-padronizados tornaram-se padronizados na RFC 6648; outros estão listados em um registro IANA, cujo o conteúdo original foi definido na RFC 4229. O IANA também mantém o registro das propostas de novas mensagens de cabeçalhos HTTP.
Cabeçalhos podem ser classificados de acordo com os seus contextos:
- Cabeçalho genérico: Cabeçalhos que podem ser usados tanto em solicitações quanto em respostas, porém sem relação com os dados eventualmente transmitidos no corpo da mensagem.
- Cabeçalho de solicitação: Cabeçalhos contendo mais informação sobre o recurso a ser obtido ou sobre o próprio cliente.
- Cabeçalho de resposta: Cabeçalhos contendo informação adicional sobre a solicitação, como a sua localização ou sobre o servidor.
- Cabeçalho de entidade: Cabeçalhos contendo mais informação sobre o conteúdo da entidade, como o tamanho do conteúdo ou o seu MIME-type.
Cabeçalhos também podem ser classificados de acordo com a forma que são manipulados por proxies.
- End-to-end headers
- Esses cabeçalhos devem ser transmitidos para o destinatário final da mensagem; isso é, o servidor em caso de solicitação ou o cliente caso resposta. Proxies intermediários devem reenviar cabeçalhos de end-to-end sem alterações e caches devem armazená-los.
- Hop-by-hop headers
- Esses cabeçalhos são significativos apenas para uma única conexão a nível de transporte e não devem ser reenviados por proxies ou armazenados em cache. Tais cabeçalhos são:
Connection,Keep-Alive,Proxy-Authenticate,Proxy-Authorization,TE,Trailer,Transfer-EncodingandUpgrade. Observe que apenas cabeçalhos hop-by-hop podem ser definidos utilizando o cabeçalho genéricoConnection.
A lista a seguir resume os cabeçalhos HTTP pela categoria de uso. Para uma lista alfabética, utilize o menu à esquerda.
Autenticação
WWW-Authenticate- ...
Authorization- ...
Proxy-Authenticate- ...
Proxy-Authorization- ...
Caching
Age- The time in seconds the object has been in a proxy cache.
Cache-Control- Specifies directives for caching mechanisms in both, requests and responses.
Expires- The date/time after which the response is considered stale.
Pragma- Implementation-specific header that may have various effects anywhere along the request-response chain. Used for backwards compatibility with HTTP/1.0 caches where the
Cache-Controlheader is not yet present. Warning- A general warning field containing information about possible problems.
Client hints
Accept-CH- ...
Content-DPR- ...
DPR- ...
Downlink- ...
Save-Data- ...
Viewport-Width- ...
Width- ...
-
Condicionais
Last-Modified- It is a validator, the last modification date of the resource, used to compare several versions of the same resource. It is less accurate than
ETag, but easier to calculate in some environments. Conditional requests usingIf-Modified-SinceandIf-Unmodified-Sinceuse this value to change the behavior of the request. ETag- It is a validator, a unique string identifying the version of the resource. Conditional requests using
If-MatchandIf-None-Matchuse this value to change the behavior of the request. If-Match- Makes the request conditional and applies the method only if the stored resource matches one of the given ETags.
If-None-Match- Makes the request conditional and applies the method only if the stored resource doesn't match any of the given ETags. This is used to update caches (for safe requests), or to prevent to upload a new resource when one is already existing.
If-Modified-Since- Makes the request conditional and expects the entity to be transmitted only if it has been modified after the given date. This is used to transmit data only when the cache is out of date.
If-Unmodified-Since- Makes the request conditional and expects the entity to be transmitted only if it has not been modified after the given date. This is used to ensure the coherence of a new fragment of a specific range with previous ones, or to implement an optimistic concurrency control system when modifying existing documents.
Connection management
Connection- Controls whether or not the network connection stays open after the current transaction finishes.
Keep-Alive- Controla por quanto tempo uma conexão persistente deve permanecer aberta.
Negociação de conteúdo
Accept- Informs the server about the types of data that can be sent back. It is MIME-type.
Accept-Charset- Informs the server about which character set the client is able to understand.
Accept-Encoding- Informs the server about the encoding algorithm, usually a compression algorithm, that can be used on the resource sent back.
Accept-Language- Informs the server about the language the server is expected to send back. This is a hint and is not necessarily under the full control of the user: the server should always pay attention not to override an explicit user choice (like selecting a language in a drop down list).
Controles
Expect- ...
Max-Forwards- ...
Cookies
Cookie- Contains stored HTTP cookies previously sent by the server with the
Set-Cookieheader. Set-Cookie- Send cookies from the server to the user agent.
Cookie2- Used to contain an HTTP cookie, previously sent by the server with the
Set-Cookie2header, but has been obsoleted by the specification. UseCookieinstead. Set-Cookie2- Used to send cookies from the server to the user agent, but has been obsoleted by the specification. Use
Set-Cookieinstead. -
CORS
Access-Control-Allow-Origin- Indica se a resposta pode ser compartilhada.
Access-Control-Allow-Credentials- Indicates whether or not the response to the request can be exposed when the credentials flag is true.
Access-Control-Allow-Headers- Used in response to a preflight request to indicate which HTTP headers can be used when making the actual request.
Access-Control-Allow-Methods- Specifies the method or methods allowed when accessing the resource in response to a preflight request.
Access-Control-Expose-Headers- Indicates which headers can be exposed as part of the response by listing their names.
Access-Control-Max-Age- Indicates how long the results of a preflight request can be cached.
Access-Control-Request-Headers- Used when issuing a preflight request to let the server know which HTTP headers will be used when the actual request is made.
Access-Control-Request-Method- Used when issuing a preflight request to let the server know which HTTP method will be used when the actual request is made.
Origin- Indicates where a fetch originates from.
Do Not Track
DNT- Used for expressing the user's tracking preference.
Tk- Indicates the tracking status that applied to the corresponding request.
Downloads
Content-Disposition- Is a response header if the ressource transmitted should be displayed inline (default behavior when the header is not present), or it should be handled like a download and the browser should present a 'Save As' window.
Informações do corpo da mensagem
Content-Length- indicates the size of the entity-body, in decimal number of octets, sent to the recipient.
Content-Type- Indica o tipo de mídia do recurso.
Content-Encoding- Usado para especificar o algoritmo de compressão.
Content-Language- Describes the language(s) intended for the audience, so that it allows a user to differentiate according to the users' own preferred language.
Content-Location- Indicates an alternate location for the returned data.
Roteamento de mensagens
Via- Added by proxies, both forward and reverse proxies, and can appear in the request headers and the response headers.
Redirecionamentos
Location- Indicates the URL to redirect a page to.
Contexto da requisição
From- Contains an Internet email address for a human user who controls the requesting user agent.
Host- Specifies the domain name of the server (for virtual hosting), and (optionally) the TCP port number on which the server is listening.
Referer- The address of the previous web page from which a link to the currently requested page was followed.
Referrer-Policy- Governs which referrer information sent in the
Refererheader should be included with requests made. User-Agent- Contains a characteristic string that allows the network protocol peers to identify the application type, operating system, software vendor or software version of the requesting software user agent. See also the Firefox user agent string reference.
Contexto da resposta
Allow- ...
Server- Contains information about the software used by the origin server to handle the request.
Requisições Range
Accept-Ranges- Indicates if the server supports range requests and, if so, in which unit the range can be expressed.
Range- ...
If-Range- Create a conditional range request that is only fulfilled if the etag or date given in parameter match the remote resource. Used to prevent downloading two ranges from incompatible version of the resource.
Content-Range- ...
Segurança
Content-Security-Policy(CSP)- Controls resources the user agent is allowed to load for a given page.
Content-Security-Policy-Report-Only- Allows web developers to experiment with policies by monitoring (but not enforcing) their effects. These violation reports consist of JSON documents sent via an HTTP
POSTrequest to the specified URI. Public-Key-Pins(HPKP)- Associates a specific cryptographic public key with a certain web server to decrease the risk of MITM attacks with forged certificates.
Public-Key-Pins-Report-Only- Sends reports to the report-uri specified in the header and does still allow clients to connect to the server even if the pinning is violated.
Strict-Transport-Security(HSTS)- Force communication using HTTPS instead of HTTP.
Upgrade-Insecure-Requests- Sends a signal to the server expressing the client’s preference for an encrypted and authenticated response, and that it can successfully handle the
upgrade-insecure-requestsdirective.
X-Content-Type-Options- Disables MIME sniffing and forces browser to use the type given in
Content-Type.
X-Frame-Options(XFO)- Indicates whether or not a browser should be allowed to render a page in a
<frame>,<iframe>or<object> X-XSS-Protection- Enables cross-site scripting filtering.
Server-sent events
Ping-From- ...
Ping-To- ...
Last-Event-ID- ...
Transfer coding
Transfer-Encoding- Specifies the the form of encoding used to safely transfer the entity to the user.
TE- Specifies the transfer encodings the user agent is willing to accept.
Trailer- Allows the sender to include additional fields at the end of chunked message.
WebSockets
Sec-WebSocket-Key- ...
Sec-WebSocket-Extensions- ...
Sec-WebSocket-Accept- ...
Sec-WebSocket-Protocol- ...
Sec-WebSocket-Version- ...
Outros
Date- Contains the date and time at which the message was originated.
Link- ...
Retry-After- Indicates how long the user agent should wait before making a follow-up request.
Upgrade- This is a Proposed Internet Standard. To view a comprehensive list of all Official and Proposed Internet Standards with detailed information about each, visit this Internet Standards reference, which is updated daily. The relevant RFC document for the Upgrade header field standard is RFC 7230, section 6.7. The standard establishes rules for upgrading or changing to a different protocol on the current client, server, transport protocol connection. For example, this header standard allows a client to change from HTTP 1.1 to HTTP 2.0, assuming the server decides to acknowledge and implement the Upgrade header field. Niether party is required to accept the terms specified in the Upgrade header field. It can be used in both client and server headers. If the Upgrade header field is specified, then the sender MUST also send the Connection header field with the upgrade option specified. For details on the Connection header field please see section 6.1 of the aforementioned RFC.
Vary- Determines how to match future request headers to decide whether a cached response can be used rather than requesting a fresh one from the origin server.
X-Content-Duration- ...
X-DNS-Prefetch-Control- Controls DNS prefetching, a feature by which browsers proactively perform domain name resolution on both links that the user may choose to follow as well as URLs for items referenced by the document, including images, CSS, JavaScript, and so forth.
X-Requested-With- ...
X-UA-Compatible- ...