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 An incremental download object attempts to fetch a file piecemeal over time
 in an effort to minimize network bandwidth usage.

 Canceling a background download does not cause the file on disk to be
 deleted.
[scriptable, uuid(6687823f-56c4-461d-93a1-7f6cb7dfbfba)]
interface nsIIncrementalDownload : nsIRequest

Attributes

 The current number of bytes downloaded so far.  This attribute is set just
 prior to calling OnStartRequest on the observer passed to the start
 method.

 This attribute has a value of -1 if the current size is unknown.
readonly attribute long long currentSize 
 The file where the download is being written.
readonly attribute nsIFile destination 
 The URI being fetched after any redirects have been followed.  This
 attribute is set just prior to calling OnStartRequest on the observer
 passed to the start method.
readonly attribute nsIURI finalURI 
 The total number of bytes for the requested file.  This attribute is set
 just prior to calling OnStartRequest on the observer passed to the start
 method.

 This attribute has a value of -1 if the total size is unknown.
readonly attribute long long totalSize 
 The URI being fetched.
readonly attribute nsIURI URI

Methods

 Initialize the incremental download object.  If the destination file
 already exists, then only the remaining portion of the file will be
 fetched.

 NOTE: The downloader will create the destination file if it does not
 already exist.  It will create the file with the permissions 0600 if
 needed.  To affect the permissions of the file, consumers of this
 interface may create an empty file at the specified destination prior to
 starting the incremental download.

 NOTE: Since this class may create a temporary file at the specified
 destination, it is advisable for the consumer of this interface to specify
 a file name for the destination that would not tempt the user into
 double-clicking it.  For example, it might be wise to append a file
 extension like ".part" to the end of the destination to protect users from
 accidentally running "blah.exe" before it is a complete file.

 @param uri
        The URI to fetch.
 @param destination
        The location where the file is to be stored.
 @param chunkSize
        The size of the chunks to fetch.  A non-positive value results in
        the default chunk size being used.
 @param intervalInSeconds
        The amount of time to wait between fetching chunks.  Pass a
        negative to use the default interval, or 0 to fetch the remaining
        part of the file in one chunk.
void init(in nsIURI uri, in nsIFile destination, in long chunkSize, in long intervalInSeconds) 
 Start the incremental download.

 @param observer
        An observer to be notified of various events.  OnStartRequest is
        called when finalURI and totalSize have been determined or when an
        error occurs.  OnStopRequest is called when the file is completely
        downloaded or when an error occurs.  If this object implements
        nsIProgressEventSink, then its OnProgress method will be called as
        data is written to the destination file.  If this object implements
        nsIInterfaceRequestor, then it will be assigned as the underlying
        channel's notification callbacks, which allows it to provide a
        nsIAuthPrompt implementation if needed by the channel, for example.
 @param ctxt
        User defined object forwarded to the observer's methods.
void start(in nsIRequestObserver observer, in nsISupports ctxt)