nsIChannel
From MDC
The nsIChannel interface allows clients to construct "GET" requests for specific protocols, and manage them in a uniform way.
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nsIChannel is defined in http://mxr.mozilla.org/mozilla/source/netwerk/base/public/nsIChannel.idl .
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.
[edit] Methods
[edit] open()
nsIInputStream open();
Synchronously open the channel.
@return blocking input stream to the channel's data.
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.
NOTE: Implementations should throw NS_ERROR_IN_PROGRESS if the channel is reopened.
[edit] asyncOpen()
void asyncOpen(in nsIStreamListener aListener, in nsISupports aContext);
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. If asyncOpen returns successfully, the channel promises to call at least onStartRequest and onStopRequest.
If the nsIRequest object passed to the stream listener's methods is not this channel, an appropriate onChannelRedirect notification needs to be sent to the notification callbacks before onStartRequest is called. Once onStartRequest is called, all following method calls on aListener will get the request that was passed to onStartRequest.
If the channel's and loadgroup's notification callbacks do not provide an nsIChannelEventSink when onChannelRedirect would be called, that's equivalent to having called onChannelRedirect.
If asyncOpen returns successfully, the channel is responsible for keeping itself alive until it has called onStopRequest on aListener or called onChannelRedirect.
Implementations are allowed to synchronously add themselves to the associated load group (if any).
NOTE: Implementations should throw NS_ERROR_ALREADY_OPENED if the channel is reopened.
@param aListener the nsIStreamListener implementation @param aContext an opaque parameter forwarded to aListener's methods @see nsIChannelEventSink for onChannelRedirect
[edit] Attributes
| Attribute | Type | Description |
originalURI
| nsIURI
| 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) |
URI
| readonly nsIURI
| The URI corresponding to the channel. Its value is immutable. |
owner
| nsISupports
| 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. |
notificationCallbacks
| nsIInterfaceRequestor
| 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/nsIAuthPrompt2. 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. |
securityInfo
| readonly nsISupports
| Transport-level security information (if any) corresponding to the channel. |
contentType
| readonly ACString
| 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. |
contentCharset
| readonly ACString
| 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. |
contentLength
| readonly long
| 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. |
[edit] Constants
Channel specific load flags:
Bits 22-31 are reserved for future use by this interface or one of its derivatives (e.g., see nsICachingChannel).
| Constant | Value | Description |
LOAD_DOCUMENT_URI
| 16
| Set (e.g., by the docshell) to indicate whether or not the channel corresponds to a document URI. |
LOAD_RETARGETED_DOCUMENT_URI
| 17
| If the end consumer for this load has been retargeted after discovering its content, this flag will be set: |
LOAD_REPLACE
| 18
| This flag is set to indicate that this channel is replacing another channel. This means that:
1) the stream listener this channel will be notifying was initially passed to the asyncOpen method of some other channel and 2) this channel's URI is a better identifier of the resource being accessed than this channel's originalURI. This flag can be set, for example, for redirects or for cases when a single channel has multiple parts to it (and thus can follow onStopRequest with another onStartRequest/onStopRequest pair, each pair for a different request). |
LOAD_INITIAL_DOCUMENT_URI
| 19
| Set (e.g., by the docshell) to indicate whether or not the channel corresponds to an initial document URI load (e.g., link click). |
LOAD_TARGETED
| 20
| Set (e.g., by the URILoader) to indicate whether or not the end consumer for this load has been determined. |
LOAD_CALL_CONTENT_SNIFFERS
| 21
| If this flag is set, the channel should call the content sniffers as described in nsNetCID.h about NS_CONTENT_SNIFFER_CATEGORY.
Note: Channels may ignore this flag; however, new channel implementations should only do so with good reason. |