The Annoyance Filter.pdf - Fourmilab

82 FLASH STREAM DECODER ANNOYANCE-FILTER §100
100. Flash stream decoder.
The flashStream is a specialisation of applicationStringParser which contains all of the logic needed
to parse a Macromedia Flash script (.swf) file. This class remains abstract in that it does not implement
the nextString method; that is left for the flashTextExtractor class, of which this class is the parent.
This decoder is based on the swfparse.cpp program written by David Michie, which is available on
the OpenSWF.org site.
〈 Class definitions 10 〉 +≡
class flashStream : public applicationStringParser {
protected:
〈 Flash file tag values 110 〉;
〈 Flash file action codes 111 〉;
〈 Flash text field mode definitions 112 〉;
〈 Flash file data structures 113 〉; /∗ Header fields ∗/
unsigned char sig [3]; /∗ Signature: “FWS” in ASCII ∗/
unsigned char version ; /∗ Version number ∗/
unsigned int fileLength ; /∗ Length of entire file in bytes ∗/
rect frameSize ; /∗ Frame size in TWIPS ∗/
unsigned short frameRate ; /∗ Frames per second (8.8 bit fixed) ∗/
unsigned short frameCount ; /∗ Total frames in animation ∗/
/∗ Current tag information ∗/
tagType tType ; /∗ Tag type ∗/
unsigned int tDataLen ; /∗ Length of data chunk ∗/ /∗ Bit stream decoder storage ∗/
unsigned int bitBuf , bitPos ;
public:
flashStream(mailFolder ∗f = Λ)
: applicationStringParser(f) { }
void readHeader (void); /∗ Read header into memory ∗/
void describe (ostream &os = cout ); /∗ Describe stream ∗/
bool nextTag (void); /∗ Read next tag identifier and length of tag data ∗/
/∗ Retrieve properties of current tag ∗/
tagType getTagType (void) const
{
return tType ;
}
unsigned int getTagDataLength (void) const
{
return tDataLen ;
}
void ignoreTag (unsigned int lookedAhead = 0);
/∗ Ignore data for tag we aren’t interested in ∗/
virtual void close (void)
{
applicationStringParser ::close ( );
}
protected:
〈 Read 16 and 32 bit quantities from Flash file 108 〉; /∗ Skip n bytes of the input stream ∗/
void skip8n (const int n)
{
for (int i = 0; (¬eof ) ∧ (i < n); i++) {