nsIHttpChannel

This interface allows for the modification of HTTP request parameters and the inspection of the resulting HTTP response status and headers when they become available.
Inherits from: nsIChannel Last changed in Gecko 1.3

To create an HTTP channel, use nsIIOService with a HTTP URI, for example:

var ios = Components.classes["@mozilla.org/network/io-service;1"]
                    .getService(Components.interfaces.nsIIOService);
var ch = ios.newChannel("https://www.example.com/", null, null);

Method overview

void getOriginalResponseHeader(in ACString aHeader, in nsIHttpHeaderVisitor aVisitor); Requires Gecko 49
ACString getRequestHeader(in ACString aHeader);
ACString getResponseHeader(in ACString header);
boolean isNoCacheResponse();
boolean isNoStoreResponse();
void redirectTo(in nsIURI aNewURI);
void setEmptyRequestHeader(in ACString aHeader); Requires Gecko 43
void setReferrerWithPolicy(in nsIURI referrer, in unsigned long referrerPolicy);
void setRequestHeader(in ACString aHeader, in ACString aValue, in boolean aMerge);
void setResponseHeader(in ACString header, in ACString value, in boolean merge);
void visitOriginalResponseHeaders(in nsIHttpHeaderVisitor aVisitor); Requires Gecko 49
void visitRequestHeaders(in nsIHttpHeaderVisitor aVisitor);
void visitResponseHeaders(in nsIHttpHeaderVisitor aVisitor);

Constants

Constant Description
REFERRER_POLICY_NO_REFERRER_WHEN_DOWNGRADE Default; indicates not to pass on the referrer when downgrading from https to http
REFERRER_POLICY_NO_REFERRER Indicates no referrer will be sent
REFERRER_POLICY_ORIGIN Only send the origin of the referring URI
REFERRER_POLICY_ORIGIN_WHEN_XORIGIN Same as the default; Only send the origin of the referring URI for cross-origin requests
REFERRER_POLICY_UNSAFE_URL Always send the referrer, even when downgrading from https to http

Attributes

Attribute Type Description
allowPipelining boolean

This attribute is a hint to the channel to indicate whether or not the underlying HTTP transaction should be allowed to be pipelined with other transactions. This should be set to false, for example, if the application knows that the corresponding document is likely to be very large.

This attribute is true by default, though other factors may prevent pipelining.

This attribute may only be set before the channel is opened.

Exceptions thrown

NS_ERROR_FAILURE
If set after the channel has been opened.
redirectionLimit unsigned long

This attribute specifies the number of redirects this channel is allowed to make. If zero, the channel will fail to redirect and will generate a NS_ERROR_REDIRECT_LOOP failure status.

Note: An HTTP redirect results in a new channel being created. If the new channel supports nsIHttpChannel, then it will be assigned a value to its redirectionLimit attribute one less than the value of the redirected channel's redirectionLimit attribute. The initial value for this attribute may be a configurable preference (depending on the implementation).
referrer nsIURI

Get or set the URI of the HTTP Referer: header. This is the address (URI) of the resource from which this channel's URI was obtained (see RFC2616 section 14.36).

This attribute may only be set before the channel is opened.

Note: The channel may silently refuse to set the Referer: header if the URI does not pass certain security checks (e.g., a "https://" URL will never be sent as the referrer for a plaintext HTTP request). The implementation is not required to throw an exception when the referrer URI is rejected.

Exceptions thrown

NS_ERROR_IN_PROGRESS
If set after the channel has been opened.
NS_ERROR_FAILURE Requires Gecko 48.0
If used for setting referrer during visitRequestHeaders(). Getting the value will not throw.
requestMethod ACString

Set or get the HTTP request method (default is "GET"). Setter is case insensitive; getter returns an uppercase string.

This attribute may only be set before the channel is opened.

Note: The data for a "POST" or "PUT" request can be configured via nsIUploadChannel. However, after setting the upload data, it may be necessary to set the request method explicitly. The documentation for nsIUploadChannel has further details.

Exceptions thrown

NS_ERROR_IN_PROGRESS
If set after the channel has been opened.
requestSucceeded boolean

Returns true if the HTTP response code indicates success. The value of nsIRequest.status() will be NS_OK even when processing a 404 File Not Found response because such a response may include a message body that (in some cases) should be shown to the user. Use this attribute to distinguish server error pages from normal pages, instead of comparing the response status manually against the set of valid response codes, if that is required by your application. Read only.

Exceptions thrown

NS_ERROR_NOT_AVAILABLE
If called before the response has been received (before onStartRequest()).
responseStatus unsigned long Get the HTTP response code (For example 200). Read only.

Exceptions thrown

NS_ERROR_NOT_AVAILABLE
If called before the response has been received (before onStartRequest()).
responseStatusText ACString

Get the HTTP response status text (For example "OK").

Note: This returns the raw (possibly 8-bit) text from the server. There are no assumptions made about the charset of the returned text. You have been warned!

Read only.

Exceptions thrown

NS_ERROR_NOT_AVAILABLE
If called before the response has been received (before onStartRequest()).
referrerPolicy Read only unsigned long The referrer policy in use for this channel, indicated by one of the constants listed above

Methods

getOriginalResponseHeader()

Requires Gecko 49 (Firefox 49 / Thunderbird 49 / SeaMonkey 2.46)

Get the value of a particular original response header, that is, in the same form as it came from the network. I.e. empty headers will have an empty string as value and multiple headers will not be merged as opposed to getResponseHeader().

void getOriginalResponseHeader(
  in ACString aHeader,
  in nsIHttpHeaderVisitor aVisitor
);

Parameters

aHeader
The case-insensitive name of the response header to query (For example "Set-Cookie").
aVisitor
An nsIHttpHeaderVisitor instance allowing to visit all equally named response headers.

Exceptions thrown

NS_ERROR_NOT_AVAILABLE
If called before the response has been received (before onStartRequest()) or if no header with that name is set in the response.

getRequestHeader()

Get the value of a particular request header.

ACString getRequestHeader(
  in ACString aHeader
);

Parameters

aHeader
The case-insensitive name of the request header to query (For example "Cache-Control").

Return value

The value of the request header.

Exceptions thrown

NS_ERROR_NOT_AVAILABLE
If the header is not set.

getResponseHeader()

Get the value of a particular response header.

ACString getResponseHeader(
  in ACString header
);

Parameters

header
The case-insensitive name of the response header to query (For example "Set-Cookie").

Return value

The value of the response header.

Exceptions thrown

NS_ERROR_NOT_AVAILABLE
If called before the response has been received (before onStartRequest()) or if the header is not set in the response.

isNoCacheResponse()

Returns true if the server sent the equivalent of a "Cache-control: no-cache" response header. Equivalent response headers include: "Pragma: no-cache", "Expires: 0", and "Expires" with a date value in the past relative to the value of the "Date" header.

boolean isNoCacheResponse();

Parameters

None.

Return value

Returns true if the server sent the equivalent of a "Cache-control: no-cache" response header, otherwise false.

Exceptions thrown

NS_ERROR_NOT_AVAILABLE
If called before the response has been received (before onStartRequest()).

isNoStoreResponse()

boolean isNoStoreResponse();

Parameters

None.

Return value

true if the server sent a "Cache-Control: no-store" response header.

Exceptions thrown

NS_ERROR_NOT_AVAILABLE
If called before the response has been received (before onStartRequest()).

redirectTo()

Instructs the channel to immediately redirect to a new destination. Can only be called on channels not yet opened.

This method provides no explicit conflict resolution. The last caller to call it wins.

void redirectTo(
  in nsIURI aNewURI
);

Parameters

aNewURI
The new URI to which we should redirect.

Exceptions thrown

NS_ERROR_ALREADY_OPENED
If called after the channel has been opened.

setEmptyRequestHeader()

Requires Gecko 43 (Firefox 43 / Thunderbird 43 / SeaMonkey 2.40)

This method is called to set an empty value for a particular request header. This should be used with caution in the cases where the behavior of setRequestHeader() ignoring empty header values is undesirable. This method may only be called before the channel is opened.

void setEmptyRequestHeader(
  in ACString aHeader
);

Parameters

aHeader
The case-insensitive name of the request header to set (For example "Cookie").

Exceptions thrown

NS_ERROR_IN_PROGRESS
If called after the channel has been opened.
NS_ERROR_FAILURE Requires Gecko 48.0
If called during visitRequestHeaders().

setReferrerWithPolicy()

Call this method to set the channel's referrer using the referrer policy indicated with one of the predefined constants.

void setReferrerWithPolicy(
  in nsIURI aReferrer,
  in unsigned long aReferrerPolicy
);

Parameters

aReferrer
The URI to base the referrer on.
aReferrerPolicy
The referrer policy to use when determining the referrer to use.

Exceptions thrown

NS_ERROR_FAILURE Requires Gecko 48.0
If called during visitRequestHeaders().

setRequestHeader()

This method is called to set the value of a particular request header. This method allows, for example, the cookies module to add "Cookie" headers to the outgoing HTTP request. This method may only be called before the channel is opened. If aValue is empty and aMerge is false, the header will be cleared.

void setRequestHeader(
  in ACString aHeader,
  in ACString aValue,
  in boolean aMerge
);

Parameters

aHeader
The case-insensitive name of the request header to query (For example "Cookie").
aValue
The request header value to set (For example "X=1").
aMerge
If true, the new header value will be merged with any existing values for the specified header. This flag is ignored if the specified header does not support merging (For example the "Content-Type" header can only have one value). The list of headers for which this flag is ignored is an implementation detail. If this flag is false, then the header value will be replaced with the contents of aValue.

Exceptions thrown

NS_ERROR_IN_PROGRESS
If called after the channel has been opened.
NS_ERROR_FAILURE Requires Gecko 48.0
If called during visitRequestHeaders().

setResponseHeader()

Set the value of a particular response header. This method allows, for example, the HTML content sink to inform the HTTP channel about HTTP-EQUIV headers found in HTML <META> tags. If value is empty and merge is false, the header will be cleared.

void setResponseHeader(
  in ACString header,
  in ACString value,
  in boolean merge
);

Parameters

header
The case-insensitive name of the response header to set(For example "Cache-Cookie").
value
The response header value to set (For example "no-cache").
merge
If true, the new header value will be merged with any existing values for the specified header. This flag is ignored if the specified header does not support merging (For example the "Content-Type" header can only have one value). The list of headers for which this flag is ignored is an implementation detail. If this flag is false, then the header value will be replaced with the contents of value.

Exceptions thrown

NS_ERROR_NOT_AVAILABLE
If called before the response has been received (before onStartRequest()).
NS_ERROR_ILLEGAL_VALUE
If changing the value of this response header is not allowed.
NS_ERROR_FAILURE Requires Gecko 49.0
If called during visitResponseHeaders(), visitOriginalResponseHeaders() or getOriginalResponseHeader().

visitOriginalResponseHeaders()

Requires Gecko 49 (Firefox 49 / Thunderbird 49 / SeaMonkey 2.46)

Call this method to visit all original response headers, that is, in the same form as they came from the network. I.e. empty headers will be have an empty string as value and multiple headers will not be merged as opposed to visitResponseHeaders().

Warning: Calling setResponseHeader() while visiting response headers will return a NS_ERROR_FAILURE.

void visitOriginalResponseHeaders(
  in nsIHttpHeaderVisitor aVisitor
);

Parameters

aVisitor
An nsIHttpHeaderVisitor instance allowing to visit all original response headers.

visitRequestHeaders()

Call this method to visit all request headers.

Warning: Calling setRequestHeader(), setReferrerWithPolicy() or setEmptyRequestHeader() while visiting request headers has undefined behavior until Gecko 47 (Firefox 47.0 / Thunderbird 47.0 / SeaMonkey 2.44). Starting from Gecko 48 (Firefox 48.0 / Thunderbird 48.0 / SeaMonkey 2.45) they will return a NS_ERROR_FAILURE.

void visitRequestHeaders(
  in nsIHttpHeaderVisitor aVisitor
);

Parameters

aVisitor
The header visitor instance.

visitResponseHeaders()

Call this method to visit all response headers.

Warning: Calling setResponseHeader() while visiting response headers has undefined behavior until Gecko 48 (Firefox 48.0 / Thunderbird 48.0 / SeaMonkey 2.45). Starting from Gecko 49 (Firefox 49.0 / Thunderbird 49.0 / SeaMonkey 2.46) it will return a NS_ERROR_FAILURE.

void visitResponseHeaders(
  in nsIHttpHeaderVisitor aVisitor
);

Parameters

aVisitor
The header visitor instance.

Exceptions thrown

NS_ERROR_NOT_AVAILABLE
If called before the response has been received (before onStartRequest()).

Note: Starting from Firefox 49, empty headers will be returned in case the preference network.http.keep_empty_response_headers_as_empty_string is set to true. Since Firefox 50 the preference defaults to true.

Document Tags and Contributors

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 Contributors to this page: Sebastianz, GijsKruitbosch, Sheppy, pde, kmaglione, lmorchard, teoli, trevorh, Btipling, Anant, Nickolay, Ayhfung
 Last updated by: Sebastianz,