sfdisc.3

Introduction to Library Functions                       SFDISC(3)

NAME
     sfdisc - sfio disciplines

SYNOPSIS
     #include  <sfdisc.h>

     extern Sfdisc_t*    dcnewskable(Sfio_t* f);
     extern int                    dcdelskable(Sfdisc_t* disc);

     extern Sfdisc_t*    dcnewtee(Sfio_t* tee);
     extern int                    dcdeltee(Sfdisc_t* disc);

     extern Sfdisc_t*    dcnewfilter(char* cmd);
     extern int                    dcdelfilter(Sfdisc_t* disc);

     extern Sfdisc_t*    dcnewsubstream(Sfio_t* f, long offset, long extent);
     extern int                    dcdelsubstream(Sfdisc_t* disc);

     extern Sfdisc_t*    dcnewlzw(void);
     extern int                    dcdellzw(Sfdisc_t* disc);

     extern Sfdisc_t*    dcnewunion(Sfio_t** flist, int n);
     extern int                    dcdelunion(Sfdisc_t* disc);

DESCRIPTION
     I/O disciplines are used to extend the data processing power
     of sfio streams. The convention for using the disciplines in
     this package is to use the call dcnewXXX() to create a  dis-
     cipline of the type XXX and to use dcdelXXX() to destroy it.
     A discipline is enable by  inserting  it  into  the  desired
     stream  using the sfdisc() call. A discipline can be used on
     only one stream. It is unsafe to share a discipline  on  two
     or  more  streams  since  the discipline may maintain states
     between successive IO calls.  For multiple uses,  dcnewXXX()
     should  be  used  to  create  a distinct discipline for each
     stream.  Each  discipline  structure  is  equipped  with  an
     exception  handler  that  causes  self-destruction  when the
     associated stream is closed.

    Sfdisc_t* dcnewskable(Sfio_t* f);
    int dcdelskable(Sfdisc_t* disc);
     dcnewskable() creates a discipline that when inserted on the
     stream f will ensure that f is seekable.  If f is originally
     unseekable, data will be shadowed in a temporary file stream
     to  allow seekability.  dcnewskable() returns the discipline
     on success and NULL on failure.

    Sfdisc_t* dcnewtee(Sfio_t* tee);
    int dcdeltee(Sfdisc_t* disc);
     dcnewtee() creates a discipline that when  inserted  into  a
     stream  f  will duplicate to the stream tee any data written

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Introduction to Library Functions                       SFDISC(3)

     to f.  dcnewtee() returns the discipline on success and NULL
     on failure.

    Sfdisc_t* dcnewfilter(char* cmd);
    int dcdelfilter(Sfdisc_t* disc);
     dcnewfilter() creates a discipline that when inserted into a
     stream  f will run the command cmd to process any input data
     before making it available to the application.  For example,
     dcnewfilter("uncompress") is an equivalent but slower alter-
     native to the lzw discipline below.   dcnewfilter()  returns
     the discipline on success and NULL on failure.

    Sfdisc_t*  dcnewsubstream(Sfio_t*  base,  long  offset,  long
     extent);
    int dcdelsubstream(Sfdisc_t* disc);
     dcnewsubstream() creates a discipline that reserves  a  por-
     tion  of  the  stream  base  starting  at offset with length
     extent and makes this portion appear as if it is  a  stream.
     When this discipline is inserted into a stream, it will make
     cause all IO operations on this stream to take place in  the
     reserved  portion  of  the  base  stream.   dcnewsubstream()
     returns the discipline on success and NULL on failure.

    Sfdisc_t* dcnewlzw(void);
    int dcdellzw(Sfdisc_t* disc);
     dcnewlzw() creates a discipline that when  inserted  into  a
     stream  f  will  run  the uncompress algorithm on input data
     from f before making it available to the  application.  This
     is  useful to allow applications to process data from a file
     packed with the UNIX compress utility as if the data  is  in
     plain  text.   dcnewlzw()  returns the discipline on success
     and NULL on failure.

    Sfdisc_t* dcnewunion(Sfio_t** list, int n);
    int dcdelunion(Sfdisc_t* disc);
     dcnewunion() creates a discipline  that  concatenates  input
     data  from  all  n  streams  in  list.  When inserted into a
     stream f, this discipline will cause all input operations on
     f to come from the merged data stream.  dcnewunion() returns
     the discipline on success and NULL on failure.

ACKNOWLEDGEMENTS
     Dave Korn contributed the substream discipline.  Jim  Arnold
     contributed the lzw discipline.

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Introduction to Library Functions                       SFDISC(3)

NOTES
     Since we are not sure of the legal responsibilities concern-
     ing the lzw patent, the lzw discipline is not currently dis-
     tributed with any release of sfio outside of AT&T.

AUTHOR
     Kiem-Phong Vo, kpv@research.att.com.

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