# HttpHeaders class

Headers for HTTP requests and responses.

In some situations, headers are immutable:

- HttpRequest and HttpClientResponse always have immutable headers.

- HttpResponse and HttpClientRequest have immutable headers from the moment the body is written to.

In these situations, the mutating methods throw exceptions.

For all operations on HTTP headers the header name is case-insensitive.

To set the value of a header use the `set()` method:

    request.headers.set(HttpHeaders.cacheControlHeader,
                        'max-age=3600, must-revalidate');

To retrieve the value of a header use the `value()` method:

    print(request.headers.value(HttpHeaders.userAgentHeader));

An HttpHeaders object holds a list of values for each name as the standard allows. In most cases a name holds only a single value, The most common mode of operation is to use `set()` for setting a value, and `value()` for retrieving a value.

## Constructors

HttpHeaders()

## Properties

chunkedTransferEncoding ↔ bool
  Gets and sets the chunked transfer encoding header value.
  read / write
contentLength ↔ int
  Gets and sets the content length header value.
  read / write
contentType ↔ ContentType
  Gets and sets the content type. Note that the content type in the header will only be updated if this field is set directly. Mutating the returned current value will have no effect.
  read / write
date ↔ DateTime
  Gets and sets the date. The value of this property will reflect the 'date' header.
  read / write
expires ↔ DateTime
  Gets and sets the expiry date. The value of this property will reflect the 'expires' header.
  read / write
host ↔ String
  Gets and sets the host part of the 'host' header for the connection.
  read / write
ifModifiedSince ↔ DateTime
  Gets and sets the "if-modified-since" date. The value of this property will reflect the "if-modified-since" header.
  read / write
persistentConnection ↔ bool
  Gets and sets the persistent connection header value.
  read / write
port ↔ int
  Gets and sets the port part of the 'host' header for the connection.
  read / write
hashCode → int
  The hash code for this object. [...]
  read-only, inherited
runtimeType → Type
  A representation of the runtime type of the object.
  read-only, inherited

## Methods

add(String name, Object value) → void
  Adds a header value. The header named `name` will have the value `value` added to its list of values. Some headers are single valued, and for these adding a value will replace the previous value. If the value is of type DateTime a HTTP date format will be applied. If the value is a `List` each element of the list will be added separately. For all other types the default `toString` method will be used.
clear() → void
  Remove all headers. Some headers have system supplied values and for these the system supplied values will still be added to the collection of values for the header.
forEach(void f(String name, List<String> values)) → void
  Enumerates the headers, applying the function `f` to each header. The header name passed in `name` will be all lower case.
noFolding(String name) → void
  Disables folding for the header named `name` when sending the HTTP header. By default, multiple header values are folded into a single header line by separating the values with commas. The 'set-cookie' header has folding disabled by default.
remove(String name, Object value) → void
  Removes a specific value for a header name. Some headers have system supplied values and for these the system supplied values will still be added to the collection of values for the header.
removeAll(String name) → void
  Removes all values for the specified header name. Some headers have system supplied values and for these the system supplied values will still be added to the collection of values for the header.
set(String name, Object value) → void
  Sets a header. The header named `name` will have all its values cleared before the value `value` is added as its value.
value(String name) → String
  Convenience method for the value for a single valued header. If there is no header with the provided name, `null` will be returned. If the header has more than one value an exception is thrown.
noSuchMethod(Invocation invocation) → dynamic
  Invoked when a non-existent method or property is accessed. [...]
  inherited
toString() → String
  Returns a string representation of this object.
  inherited

## Operators

operator [](String name) → List<String>
  Returns the list of values for the header named `name`. If there is no header with the provided name, `null` will be returned.
operator ==(dynamic other) → bool
  The equality operator. [...]
  inherited

## Constants

ACCEPT → const String
  @Deprecated("Use acceptHeader instead")
  `acceptHeader`
ACCEPT_CHARSET → const String
  @Deprecated("Use acceptCharsetHeader instead")
  `acceptCharsetHeader`
ACCEPT_ENCODING → const String
  @Deprecated("Use acceptEncodingHeader instead")
  `acceptEncodingHeader`
ACCEPT_LANGUAGE → const String
  @Deprecated("Use acceptLanguageHeader instead")
  `acceptLanguageHeader`
ACCEPT_RANGES → const String
  @Deprecated("Use acceptRangesHeader instead")
  `acceptRangesHeader`
acceptCharsetHeader → const String
  `"accept-charset"`
acceptEncodingHeader → const String
  `"accept-encoding"`
acceptHeader → const String
  `"accept"`
acceptLanguageHeader → const String
  `"accept-language"`
acceptRangesHeader → const String
  `"accept-ranges"`
AGE → const String
  @Deprecated("Use ageHeader instead")
  `ageHeader`
ageHeader → const String
  `"age"`
ALLOW → const String
  @Deprecated("Use allowHeader instead")
  `allowHeader`
allowHeader → const String
  `"allow"`
AUTHORIZATION → const String
  @Deprecated("Use authorizationHeader instead")
  `authorizationHeader`
authorizationHeader → const String
  `"authorization"`
CACHE_CONTROL → const String
  @Deprecated("Use cacheControlHeader instead")
  `cacheControlHeader`
cacheControlHeader → const String
  `"cache-control"`
CONNECTION → const String
  @Deprecated("Use connectionHeader instead")
  `connectionHeader`
connectionHeader → const String
  `"connection"`
CONTENT_ENCODING → const String
  @Deprecated("Use contentEncodingHeader instead")
  `contentEncodingHeader`
CONTENT_LANGUAGE → const String
  @Deprecated("Use contentLanguageHeader instead")
  `contentLanguageHeader`
CONTENT_LENGTH → const String
  @Deprecated("Use contentLengthHeader instead")
  `contentLengthHeader`
CONTENT_LOCATION → const String
  @Deprecated("Use contentLocationHeader instead")
  `contentLocationHeader`
CONTENT_MD5 → const String
  @Deprecated("Use contentMD5Header instead")
  `contentMD5Header`
CONTENT_RANGE → const String
  @Deprecated("Use contentRangeHeader instead")
  `contentRangeHeader`
CONTENT_TYPE → const String
  @Deprecated("Use contentTypeHeader instead")
  `contentTypeHeader`
contentEncodingHeader → const String
  `"content-encoding"`
contentLanguageHeader → const String
  `"content-language"`
contentLengthHeader → const String
  `"content-length"`
contentLocationHeader → const String
  `"content-location"`
contentMD5Header → const String
  `"content-md5"`
contentRangeHeader → const String
  `"content-range"`
contentTypeHeader → const String
  `"content-type"`
COOKIE → const String
  @Deprecated("Use cookieHeader instead")
  `cookieHeader`
cookieHeader → const String
  `"cookie"`
DATE → const String
  @Deprecated("Use dateHeader instead")
  `dateHeader`
dateHeader → const String
  `"date"`
ENTITY_HEADERS → const List<String>
  @Deprecated("Use entityHeaders instead")
  `entityHeaders`
entityHeaders → const List<String>
  `const [allowHeader, contentEncodingHeader, contentLanguageHeader, contentLengthHeader, contentLocationHeader, contentMD5Header, contentRangeHeader, contentTypeHeader, expiresHeader, lastModifiedHeader…`
ETAG → const String
  @Deprecated("Use etagHeader instead")
  `etagHeader`
etagHeader → const String
  `"etag"`
EXPECT → const String
  @Deprecated("Use expectHeader instead")
  `expectHeader`
expectHeader → const String
  `"expect"`
EXPIRES → const String
  @Deprecated("Use expiresHeader instead")
  `expiresHeader`
expiresHeader → const String
  `"expires"`
FROM → const String
  @Deprecated("Use fromHeader instead")
  `fromHeader`
fromHeader → const String
  `"from"`
GENERAL_HEADERS → const List<String>
  @Deprecated("Use generalHeaders instead")
  `generalHeaders`
generalHeaders → const List<String>
  `const [cacheControlHeader, connectionHeader, dateHeader, pragmaHeader, trailerHeader, transferEncodingHeader, upgradeHeader, viaHeader, warningHeader]`
HOST → const String
  @Deprecated("Use hostHeader instead")
  `hostHeader`
hostHeader → const String
  `"host"`
IF_MATCH → const String
  @Deprecated("Use ifMatchHeader instead")
  `ifMatchHeader`
IF_MODIFIED_SINCE → const String
  @Deprecated("Use ifModifiedSinceHeader instead")
  `ifModifiedSinceHeader`
IF_NONE_MATCH → const String
  @Deprecated("Use ifNoneMatchHeader instead")
  `ifNoneMatchHeader`
IF_RANGE → const String
  @Deprecated("Use ifRangeHeader instead")
  `ifRangeHeader`
IF_UNMODIFIED_SINCE → const String
  @Deprecated("Use ifUnmodifiedSinceHeader instead")
  `ifUnmodifiedSinceHeader`
ifMatchHeader → const String
  `"if-match"`
ifModifiedSinceHeader → const String
  `"if-modified-since"`
ifNoneMatchHeader → const String
  `"if-none-match"`
ifRangeHeader → const String
  `"if-range"`
ifUnmodifiedSinceHeader → const String
  `"if-unmodified-since"`
LAST_MODIFIED → const String
  @Deprecated("Use lastModifiedHeader instead")
  `lastModifiedHeader`
lastModifiedHeader → const String
  `"last-modified"`
LOCATION → const String
  @Deprecated("Use locationHeader instead")
  `locationHeader`
locationHeader → const String
  `"location"`
MAX_FORWARDS → const String
  @Deprecated("Use maxForwardsHeader instead")
  `maxForwardsHeader`
maxForwardsHeader → const String
  `"max-forwards"`
PRAGMA → const String
  @Deprecated("Use pragmaHeader instead")
  `pragmaHeader`
pragmaHeader → const String
  `"pragma"`
PROXY_AUTHENTICATE → const String
  @Deprecated("Use proxyAuthenticateHeader instead")
  `proxyAuthenticateHeader`
PROXY_AUTHORIZATION → const String
  @Deprecated("Use proxyAuthorizationHeader instead")
  `proxyAuthorizationHeader`
proxyAuthenticateHeader → const String
  `"proxy-authenticate"`
proxyAuthorizationHeader → const String
  `"proxy-authorization"`
RANGE → const String
  @Deprecated("Use rangeHeader instead")
  `rangeHeader`
rangeHeader → const String
  `"range"`
REFERER → const String
  @Deprecated("Use refererHeader instead")
  `refererHeader`
refererHeader → const String
  `"referer"`
REQUEST_HEADERS → const List<String>
  @Deprecated("Use requestHeaders instead")
  `requestHeaders`
requestHeaders → const List<String>
  `const [acceptHeader, acceptCharsetHeader, acceptEncodingHeader, acceptLanguageHeader, authorizationHeader, expectHeader, fromHeader, hostHeader, ifMatchHeader, ifModifiedSinceHeader, ifNoneMatchHeader…`
RESPONSE_HEADERS → const List<String>
  @Deprecated("Use responseHeaders instead")
  `responseHeaders`
responseHeaders → const List<String>
  `const [acceptRangesHeader, ageHeader, etagHeader, locationHeader, proxyAuthenticateHeader, retryAfterHeader, serverHeader, varyHeader, wwwAuthenticateHeader]`
RETRY_AFTER → const String
  @Deprecated("Use retryAfterHeader instead")
  `retryAfterHeader`
retryAfterHeader → const String
  `"retry-after"`
SERVER → const String
  @Deprecated("Use serverHeader instead")
  `serverHeader`
serverHeader → const String
  `"server"`
SET_COOKIE → const String
  @Deprecated("Use setCookieHeader instead")
  `setCookieHeader`
setCookieHeader → const String
  `"set-cookie"`
TE → const String
  @Deprecated("Use teHeader instead")
  `teHeader`
teHeader → const String
  `"te"`
TRAILER → const String
  @Deprecated("Use trailerHeader instead")
  `trailerHeader`
trailerHeader → const String
  `"trailer"`
TRANSFER_ENCODING → const String
  @Deprecated("Use transferEncodingHeader instead")
  `transferEncodingHeader`
transferEncodingHeader → const String
  `"transfer-encoding"`
UPGRADE → const String
  @Deprecated("Use upgradeHeader instead")
  `upgradeHeader`
upgradeHeader → const String
  `"upgrade"`
USER_AGENT → const String
  @Deprecated("Use userAgentHeader instead")
  `userAgentHeader`
userAgentHeader → const String
  `"user-agent"`
VARY → const String
  @Deprecated("Use varyHeader instead")
  `varyHeader`
varyHeader → const String
  `"vary"`
VIA → const String
  @Deprecated("Use viaHeader instead")
  `viaHeader`
viaHeader → const String
  `"via"`
WARNING → const String
  @Deprecated("Use warningHeader instead")
  `warningHeader`
warningHeader → const String
  `"warning"`
WWW_AUTHENTICATE → const String
  @Deprecated("Use wwwAuthenticateHeader instead")
  `wwwAuthenticateHeader`
wwwAuthenticateHeader → const String
  `"www-authenticate"`