nsIContentSniffer

netwerk/base/public/nsIContentSniffer.idlScriptable

Content sniffer interface. Components implementing this interface can determine a MIME type from a chunk of bytes.

Inherits from: nsISupports Last changed in Gecko 1.9 (Firefox 3)

To implement this interface use net-content-sniffers category. See netwerk/build/nsNetCID.h about NS_CONTENT_SNIFFER_CATEGORY.

Method overview

ACString getMIMETypeFromContent(in nsIRequest aRequest, [const,array,size_is(aLength)] in octet aData, in unsigned long aLength);

Methods

getMIMETypeFromContent()

Given a chunk of data, determines a MIME type. Information from the given request may be used in order to make a better decision.

Note: Implementations should consider the request read-only. Especially, they should not attempt to set the content type property that subclasses of nsIRequest might offer.

ACString getMIMETypeFromContent(
  in nsIRequest aRequest,
  [const,array,size_is(aLength)] in octet aData,
  in unsigned long aLength
);

Parameters

aRequest: The request where this data came from. May be null.
aData: Data to check.
aLength: Length of the data.

Return value

The content type.

Example

How to read content from aData.

    let charset = "ISO-8859-1";
    try {
      // this pref has been removed, see Bug 910192
      charset = Services.prefs.getComplexValue("intl.charset.default",
                                                Ci.nsIPrefLocalizedString).data;
    } catch (e) {
    }
                                                  
    let conv = Cc["@mozilla.org/intl/scriptableunicodeconverter"]
               .createInstance(Ci.nsIScriptableUnicodeConverter);
    conv.charset = charset;
    try {
      let str = conv.convertFromByteArray(aData, aLength);
      if (str.substring(0, 5) == "%PDF-") 
        return "application/pdf"; // we detected a pdf file
    } catch (e) {
      // try to get information from aRequest
    }