Inherits From:nsIRequest

The nsIChannel interface allows clients to construct "GET" requests for specific protocols, and manage them in a uniform way. Once a channel is created (via nsIIOService::newChannel), parameters for that request may be set by using the channel attributes, or by QI'ing to a subclass of nsIChannel for protocol-specific parameters. Then, the URI can be fetched by calling nsIChannel::open or nsIChannel::asyncOpen.

After a request has been completed, the channel is still valid for accessing protocol-specific results. For example, QI'ing to nsIHttpChannel allows response headers to be retrieved for the corresponding http transaction.

An object of this interface should be created in the following way:

ioService.newChannel(uri, charset, baseuri);

This interface is implemented by the following components:


Set (e.g., by the docshell) to indicate whether or not the channel corresponds to a document URI.
If the end consumer for this load has been retargeted after discovering it's content, this flag will be set:
This flag is set to indicate that onStopRequest may be followed by another onStartRequest/onStopRequest pair. This flag is, for example, used by the multipart/replace stream converter.
PRUint32 LOAD_REPLACE = 262144
Set (e.g., by the docshell) to indicate whether or not the channel corresponds to an initial document URI load (e.g., link click).
Set (e.g., by the URILoader) to indicate whether or not the end consumer for this load has been determined.
PRUint32 LOAD_TARGETED = 1048576


ACString contentCharset

The character set of the channel's content if available and if applicable. This attribute only applies to textual data.

The value of the contentCharset attribute is a mixedcase string.

PRInt32 contentLength

The length of the data associated with the channel if available. A value of -1 indicates that the content length is unknown.

Callers should prefer getting the "content-length" property as 64-bit value by QIing the channel to nsIPropertyBag2, if that interface is exposed by the channel.

ACString contentType

The MIME type of the channel's content if available.

NOTE: the content type can often be wrongly specified (e.g., wrong file extension, wrong MIME type, wrong document type stored on a server, etc.), and the caller most likely wants to verify with the actual data.

Setting contentType before the channel has been opened provides a hint to the channel as to what the MIME type is. The channel may ignore this hint in deciding on the actual MIME type that it will report.

Setting contentType after onStartRequest has been fired or after open() is called will override the type determined by the channel.

Setting contentType between the time that asyncOpen() is called and the time when onStartRequest is fired has undefined behavior at this time.

The value of the contentType attribute is a lowercase string. A value assigned to this attribute will be parsed and normalized as follows: 1- any parameters (delimited with a ';') will be stripped. 2- if a charset parameter is given, then its value will replace the the contentCharset attribute of the channel. 3- the stripped contentType will be lowercased. Any implementation of nsIChannel must follow these rules.

nsIInterfaceRequestor notificationCallbacks

The notification callbacks for the channel. This is set by clients, who wish to provide a means to receive progress, status and protocol-specific notifications. If this value is NULL, the channel implementation may use the notification callbacks from its load group. The channel may also query the notification callbacks from its load group if its notification callbacks do not supply the requested interface.

Interfaces commonly requested include: nsIProgressEventSink, nsIPrompt, and nsIAuthPrompt.

When the channel is done, it must not continue holding references to this object.

NOTE: A channel implementation should take care when "caching" an interface pointer queried from its notification callbacks. If the notification callbacks are changed, then a cached interface pointer may become invalid and may therefore need to be re-queried.

nsIURI originalURI

The original URI used to construct the channel. This is used in the case of a redirect or URI "resolution" (e.g. resolving a resource: URI to a file: URI) so that the original pre-redirect URI can still be obtained.

NOTE: this is distinctly different from the http Referer (referring URI), which is typically the page that contained the original URI (accessible from nsIHttpChannel).

nsISupports owner

The owner, corresponding to the entity that is responsible for this channel. Used by the security manager to grant or deny privileges to mobile code loaded from this channel.

NOTE: this is a strong reference to the owner, so if the owner is also holding a strong reference to the channel, care must be taken to explicitly drop its reference to the channel.

readonly nsISupports securityInfo

Transport-level security information (if any) corresponding to the channel.

readonly nsIURI URI

The URI corresponding to the channel. Its value is immutable.


void asyncOpen ( nsIStreamListener listener , nsISupports context ) nsIInputStream open ( )

void asyncOpen ( nsIStreamListener listener , nsISupports context )

Asynchronously open this channel. Data is fed to the specified stream listener as it becomes available. The stream listener's methods are called on the thread that calls asyncOpen and are not called until after asyncOpen returns.

listener: the nsIStreamListener implementation
context: an opaque parameter forwarded to listener's methods

nsIInputStream open ( )

Synchronously open the channel.

NOTE: nsIChannel implementations are not required to implement this method. Moreover, since this method may block the calling thread, it should not be called on a thread that processes UI events.

blocking input stream to the channel's data.


This interface is the type of the following properties:

nsIDocumentLoader.documentChannel, nsIMsgQuote.quoteChannel, nsIMultiPartChannel.baseChannel, nsIURIChecker.baseChannel, nsIUnicharStreamLoader.channel, nsIXMLHttpRequest.channel

This interface is passed as an argument to the following methods:

imgILoader.loadImageWithChannel, nsIChannelEventSink.onChannelRedirect, nsICharsetResolver.requestCharset, nsICookiePermission.canAccess, nsICookiePermission.canSetCookie, nsICookieService.getCookieString, nsICookieService.getCookieStringFromHttp, nsICookieService.setCookieString, nsICookieService.setCookieStringFromHttp, nsIDocumentLoaderFactory.createInstance, nsIHttpEventSink.onRedirect, nsIImageLoadingContent.loadImageWithChannel, nsIMimeEmitter.Initialize, nsIRefreshURI.setupRefreshURI, nsIStreamLoader.init, nsISyncLoadDOMService.loadDocument, nsISyncLoadDOMService.loadDocumentAsXML, nsISyncLoadDOMService.loadLocalDocument, nsISyncLoadDOMService.loadLocalXBLDocument, nsIURILoader.openURI, nsIUnicharStreamLoader.init, nsIWebBrowserPersist.saveChannel

This interface is returned from the following methods:

nsIAboutModule.newChannel, nsIIOService.newChannel, nsIIOService.newChannelFromURI, nsIProtocolHandler.newChannel, nsIProxiedProtocolHandler.newProxiedChannel

Reference documentation is generated from Mozilla's source.

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