  
  [1X4 [33X[0;0YHigh level functions for buffered I/O[133X[101X
  
  [33X[0;0YThe  functions in the previous sections are intended to be a possibility for
  direct  access  to  the  low level I/O functions in the C library. Thus, the
  calling conventions are strictly as in the original.[133X
  
  [33X[0;0YThe functionality described in this section is implemented completely in the
  [5XGAP[105X  language and is intended to provide a good interface for programming in
  [5XGAP[105X.  The  fundamental  object  for  I/O  on the C library level is the file
  descriptor,  which  is just a non-negative integer representing an open file
  of the process. The basic idea is to wrap up file descriptors in [5XGAP[105X objects
  that do the buffering.[133X
  
  [33X[0;0YNote  that  considerable  care  has been taken to ensure that one can do I/O
  multiplexing  with  buffered I/O. That is, one always has the possibility to
  make  sure  before  a  read  or  write  operation,  that  this read or write
  operation  will not block. This is crucial when one wants to serve more than
  one  I/O  channel  from  the same (single-threaded) [5XGAP[105X process. This design
  principle  sometimes  made it necessary to have more than one function for a
  certain  operation.  Those  functions  usually  differ  in a subtle way with
  respect to their blocking behaviour.[133X
  
  [33X[0;0YOne remark applies again to nearly all functions presented here: If an error
  is  indicated  by  the  returned value [9Xfail[109X one can use the library function
  [2XLastSystemError[102X  ([14XReference:  LastSystemError[114X)  to  find  out more about the
  cause of the error. This fact is not mentioned with every single function.[133X
  
  
  [1X4.1 [33X[0;0YTypes and the creation of [10XFile[110X[101X[1X objects[133X[101X
  
  [33X[0;0YThe wrapped file objects are in the following category:[133X
  
  [1X4.1-1 IsFile[101X
  
  [33X[1;0Y[29X[2XIsFile[102X( [3Xo[103X ) [32X Category[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfalse[109X[133X
  
  [33X[0;0YThe category of [10XFile[110X objects.[133X
  
  [33X[0;0YTo create objects in this category, one uses the following function:[133X
  
  [1X4.1-2 IO_WrapFD[101X
  
  [33X[1;0Y[29X[2XIO_WrapFD[102X( [3Xfd[103X, [3Xrbufsize[103X, [3Xwbufsize[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya [10XFile[110X object[133X
  
  [33X[0;0YThe  argument  [3Xfd[103X  must  be  a  file descriptor (i.e. an integer) or -1 (see
  below).[133X
  
  [33X[0;0Y[3Xrbufsize[103X  can  either  be  [9Xfalse[109X for unbuffered reading or an integer buffer
  size  or  a string. If it is an integer, a read buffer of that size is used.
  If it is a string, then [3Xfd[103X must be -1 and a [10XFile[110X object that reads from that
  string is created.[133X
  
  [33X[0;0Y[3Xwbufsize[103X  can  either  be  [9Xfalse[109X for unbuffered writing or an integer buffer
  size  or a string. If it is an integer, a write buffer of that size is used.
  If it is a string, then [3Xfd[103X must be -1 and a [10XFile[110X object that appends to that
  string is created.[133X
  
  [33X[0;0YThe result of this function is a new [10XFile[110X object.[133X
  
  [33X[0;0YA  convenient  way to do this for reading or writing of files on disk is the
  following function:[133X
  
  [1X4.1-3 IO_File[101X
  
  [33X[1;0Y[29X[2XIO_File[102X( [3Xfilename[103X[, [3Xmode[103X] ) [32X function[133X
  [33X[1;0Y[29X[2XIO_File[102X( [3Xfilename[103X[, [3Xbufsize[103X] ) [32X function[133X
  [33X[1;0Y[29X[2XIO_File[102X( [3Xfilename[103X, [3Xmode[103X, [3Xbufsize[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya [10XFile[110X object or [9Xfail[109X[133X
  
  [33X[0;0YThe  argument [3Xfilename[103X must be a string specifying the path name of the file
  to  work  on.  [3Xmode[103X  must  also be a string with possible values [21Xr[121X, [21Xw[121X, or [21Xa[121X,
  meaning read access, write access (with creating and truncating), and append
  access  respectively.  If  [3Xmode[103X  is  omitted,  it defaults to [21Xr[121X. [3Xbufsize[103X, if
  given,  must  be  a  positive  integer  or  [10Xfalse[110X,  otherwise it defaults to
  [10XIO.DefaultBufSize[110X. Internally, the [2XIO_open[102X ([14X3.2-43[114X) function is used and the
  result  file  descriptor  is wrapped using [2XIO_WrapFD[102X ([14X4.1-2[114X) with [3Xbufsize[103X as
  the buffer size.[133X
  
  [33X[0;0YThe  result  is  either [9Xfail[109X in case of an error or a [10XFile[110X object in case of
  success.[133X
  
  [33X[0;0YNote  that  there  is  a similar function [2XIO_FilteredFile[102X ([14X4.4-9[114X) which also
  creates  a  [10XFile[110X  object but with additional functionality with respect to a
  pipeline for filtering. It is described in its section in Section [14X4.4[114X. There
  is some more low-level functionality to acquire open file descriptors. These
  can be wrapped into [10XFile[110X objects using [2XIO_WrapFD[102X ([14X4.1-2[114X).[133X
  
  
  [1X4.2 [33X[0;0YReading and writing[133X[101X
  
  [33X[0;0YOnce a [10XFile[110X object is created, one can use the following functions on it:[133X
  
  [1X4.2-1 IO_ReadUntilEOF[101X
  
  [33X[1;0Y[29X[2XIO_ReadUntilEOF[102X( [3Xf[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya string or [9Xfail[109X[133X
  
  [33X[0;0YThis function reads all data from the file [3Xf[103X until the end of file. The data
  is returned as a [5XGAP[105X string. If the file is already at end of file, an empty
  string is returned. If an error occurs, then [9Xfail[109X is returned. Note that you
  still  have  to  call [2XIO_Close[102X ([14X4.2-16[114X) on the [10XFile[110X object to properly close
  the file later.[133X
  
  [1X4.2-2 IO_ReadBlock[101X
  
  [33X[1;0Y[29X[2XIO_ReadBlock[102X( [3Xf[103X, [3Xlen[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya string or [9Xfail[109X[133X
  
  [33X[0;0YThis function gets two arguments, the first argument [3Xf[103X must be a [10XFile[110X object
  and  the  second argument [3Xlen[103X must be a positive integer. The function tries
  to  read  [3Xlen[103X  bytes and returns a string of that length. If and only if the
  end  of  file  is  reached  earlier,  fewer  bytes are returned. If an error
  occurs,  [9Xfail[109X  is  returned. Note that this function blocks until either [3Xlen[103X
  bytes  are  read, or the end of file is reached, or an error occurs. For the
  case  of pipes or internet connections it is possible that currently no more
  data  is  available,  however, by definition the end of file is only reached
  after the connection has been closed by the other side![133X
  
  [1X4.2-3 IO_ReadLine[101X
  
  [33X[1;0Y[29X[2XIO_ReadLine[102X( [3Xf[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya string or [9Xfail[109X[133X
  
  [33X[0;0YThis  function  gets exactly one argument, which must be a [10XFile[110X object [3Xf[103X. It
  reads  one  line  of  data, where the definition of line is operating system
  dependent.  The  line  end  character(s)  are  included  in  the result. The
  function  returns a string with the line in case of success and [9Xfail[109X in case
  of   an   error.   In  the  latter  case,  one  can  query  the  error  with
  [2XLastSystemError[102X ([14XReference: LastSystemError[114X).[133X
  
  [33X[0;0YNote  that  the reading is done via the buffer of [3Xf[103X, such that this function
  will be quite fast also for large amounts of data.[133X
  
  [33X[0;0YIf  the  end  of  file  is  hit  without a line end, the rest of the file is
  returned.  If  the  file  is  already at end of file before the call, then a
  string  of  length  0  is  returned.  Note that this is not an error but the
  standard end of file convention![133X
  
  [1X4.2-4 IO_ReadLines[101X
  
  [33X[1;0Y[29X[2XIO_ReadLines[102X( [3Xf[103X[, [3Xmax[103X] ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya list of strings or [9Xfail[109X[133X
  
  [33X[0;0YThis function gets one or two arguments, the first of which must always be a
  [10XFile[110X  object  [3Xf[103X.  It  reads  lines  of data (where the definition of line is
  operating  system  dependent)  either  until  end  of file (without a second
  argument)  or up to [3Xmax[103X lines (with a second argument [3Xmax[103X. A list of strings
  with  the  result is returned, if everything went well and [9Xfail[109X oterwise. In
  the  latter  case,  one can query the error with [2XLastSystemError[102X ([14XReference:
  LastSystemError[114X).[133X
  
  [33X[0;0YNote  that  the reading is done via the buffer of [3Xf[103X, such that this function
  will be quite fast also for large amounts of data.[133X
  
  [33X[0;0YIf  the  file  is already at the end of file, the function returns a list of
  length  0.  Note  that  this  is  not  an error but the standard end of file
  convention![133X
  
  [1X4.2-5 IO_HasData[101X
  
  [33X[1;0Y[29X[2XIO_HasData[102X( [3Xf[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfalse[109X[133X
  
  [33X[0;0YThis  function  takes one argument [3Xf[103X which must be a [10XFile[110X object. It returns
  [9Xtrue[109X  or  [9Xfalse[109X  according to whether there is data to read available in the
  file  [3Xf[103X.  A  return  value  of [9Xtrue[109X guarantees that the next call to [2XIO_Read[102X
  ([14X4.2-6[114X)  on  that file will succeed without blocking and return at least one
  byte or an empty string to indicate the end of file.[133X
  
  [1X4.2-6 IO_Read[101X
  
  [33X[1;0Y[29X[2XIO_Read[102X( [3Xf[103X, [3Xlen[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya string or [9Xfail[109X[133X
  
  [33X[0;0YThe function gets two arguments, the first of which must be a [10XFile[110X object [3Xf[103X.
  The  second  argument must be a positive integer. The function reads data up
  to  [3Xlen[103X bytes. A string with the result is returned, if everything went well
  and  [9Xfail[109X  otherwise.  In  the  latter  case,  one  can query the error with
  [2XLastSystemError[102X ([14XReference: LastSystemError[114X).[133X
  
  [33X[0;0YNote  that  the reading is done via the buffer of [3Xf[103X, such that this function
  will be quite fast also for large amounts of data.[133X
  
  [33X[0;0YIf the file is already at the end of the file, the function returns a string
  of length 0. Note that this is not an error![133X
  
  [33X[0;0YIf  a  previous call to [2XIO_HasData[102X ([14X4.2-5[114X) or to [2XIO_Select[102X ([14X4.3-3[114X) indicated
  that  there  is  data  available  to  read,  then  it is guaranteed that the
  function [2XIO_Read[102X does not block and returns at least one byte if the file is
  not yet at end of file and an empty string otherwise.[133X
  
  [1X4.2-7 IO_Write[101X
  
  [33X[1;0Y[29X[2XIO_Write[102X( [3Xf[103X[, [3Xthings[103X, [3X...[103X] ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Yan integer or [9Xfail[109X[133X
  
  [33X[0;0YThis  function  can get an arbitrary number of arguments, the first of which
  must  be  a  [10XFile[110X object [3Xf[103X. All the other arguments are just written to [3Xf[103X if
  they  are  strings. Otherwise, the [9XString[109X function is called on them and the
  result is written out to [3Xf[103X.[133X
  
  [33X[0;0YNote  that  the writing is done buffered. That is, the data is first written
  to  the buffer and only really written out after the buffer is full or after
  the user explicitly calls [2XIO_Flush[102X ([14X4.2-10[114X) on [3Xf[103X.[133X
  
  [33X[0;0YThe  result is either the number of bytes written in case of success or [9Xfail[109X
  in  case  of  an  error.  In  the  latter case the error can be queried with
  [2XLastSystemError[102X ([14XReference: LastSystemError[114X).[133X
  
  [33X[0;0YNote  that  this function blocks until all data is at least written into the
  buffer and might block until data can be sent again if the buffer is full.[133X
  
  [1X4.2-8 IO_WriteLine[101X
  
  [33X[1;0Y[29X[2XIO_WriteLine[102X( [3Xf[103X, [3Xline[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Yan integer or [9Xfail[109X[133X
  
  [33X[0;0YBehaves like [2XIO_Write[102X ([14X4.2-7[114X) but works on a single string [3Xline[103X and sends an
  (operating  system  dependent)  end of line string afterwards. Also [2XIO_Flush[102X
  ([14X4.2-10[114X)  is  called automatically after the operation, such that one can be
  sure,  that  the  data  is  actually  written  out  after  the  function has
  completed.[133X
  
  [1X4.2-9 IO_WriteLines[101X
  
  [33X[1;0Y[29X[2XIO_WriteLines[102X( [3Xf[103X, [3Xlist[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Yan integer or [9Xfail[109X[133X
  
  [33X[0;0YBehaves  like [2XIO_Write[102X ([14X4.2-7[114X) but works on a list of strings [3Xlist[103X and sends
  an  (operating system dependent) end of line string after each string in the
  list.  Also  [2XIO_Flush[102X  ([14X4.2-10[114X) is called automatically after the operation,
  such  that  one can be sure, that the data is actually written out after the
  function has completed.[133X
  
  [1X4.2-10 IO_Flush[101X
  
  [33X[1;0Y[29X[2XIO_Flush[102X( [3Xf[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfail[109X[133X
  
  [33X[0;0YThis  function  gets  one argument [3Xf[103X, which must be a [10XFile[110X object. It writes
  out  all  the data that is in the write buffer. This is not necessary before
  the  call  to  the  function  [2XIO_Close[102X  ([14X4.2-16[114X),  since that function calls
  [2XIO_Flush[102X  automatically.  However,  it  is  necessary to call [2XIO_Flush[102X after
  calls  to  [2XIO_Write[102X ([14X4.2-7[114X) to be sure that the data is really sent out. The
  function returns [9Xtrue[109X if everything goes well and [9Xfail[109X if an error occurs.[133X
  
  [33X[0;0YRemember  that  the functions [2XIO_WriteLine[102X ([14X4.2-8[114X) and [2XIO_WriteLines[102X ([14X4.2-9[114X)
  implicitly call [2XIO_Flush[102X after they are done.[133X
  
  [33X[0;0YNote  that  this  function might block until all data is actually written to
  the file descriptor.[133X
  
  [1X4.2-11 IO_WriteFlush[101X
  
  [33X[1;0Y[29X[2XIO_WriteFlush[102X( [3Xf[103X[, [3Xthings[103X] ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Yan integer or [9Xfail[109X[133X
  
  [33X[0;0YThis  function  behaves like [2XIO_Write[102X ([14X4.2-7[114X) followed by a call to [2XIO_Flush[102X
  ([14X4.2-10[114X).  It returns either the number of bytes written or [9Xfail[109X if an error
  occurs.[133X
  
  [1X4.2-12 IO_ReadyForWrite[101X
  
  [33X[1;0Y[29X[2XIO_ReadyForWrite[102X( [3Xf[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfalse[109X[133X
  
  [33X[0;0YThis  function  takes one argument [3Xf[103X which must be a [10XFile[110X object. It returns
  [9Xtrue[109X  or  [9Xfalse[109X  according to whether the file [3Xf[103X is ready to write. A return
  value  of [9Xtrue[109X guarantees that the next call to [2XIO_WriteNonBlocking[102X ([14X4.2-13[114X)
  on that file will succeed without blocking and accept at least one byte.[133X
  
  [1X4.2-13 IO_WriteNonBlocking[101X
  
  [33X[1;0Y[29X[2XIO_WriteNonBlocking[102X( [3Xf[103X, [3Xst[103X, [3Xpos[103X, [3Xlen[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Yan integer or [9Xfail[109X[133X
  
  [33X[0;0YThis  function  takes four arguments. The first one [3Xf[103X must be a [10XFile[110X object,
  the second [3Xst[103X a string, and the arguments [3Xpos[103X and [3Xlen[103X must be integers, such
  that  positions  [22X[3Xpos[103X+1[122X  until [22X[3Xpos[103X+[3Xlen[103X[122X are bound in [3Xst[103X. The function tries to
  write  up  to  [3Xlen[103X  bytes  from  [3Xst[103X  from position [22X[3Xpos[103X+1[122X to the file [3Xf[103X. If a
  previous call to [2XIO_ReadyForWrite[102X ([14X4.2-12[114X) or to [2XIO_Select[102X ([14X4.3-3[114X) indicates
  that  [3Xf[103X  is  writable,  then  it  is  guaranteed  that the following call to
  [2XIO_WriteNonBlocking[102X  will  not  block  and accept at least one byte of data.
  Note  that it is not guaranteed that all [3Xlen[103X bytes are written. The function
  returns the number of bytes written or [9Xfail[109X if an error occurs.[133X
  
  [1X4.2-14 IO_ReadyForFlush[101X
  
  [33X[1;0Y[29X[2XIO_ReadyForFlush[102X( [3Xf[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfalse[109X[133X
  
  [33X[0;0YThis  function  takes one argument [3Xf[103X which must be a [10XFile[110X object. It returns
  [9Xtrue[109X  or  [9Xfalse[109X  according to whether the file [3Xf[103X is ready to flush. A return
  value  of [9Xtrue[109X guarantees that the next call to [2XIO_FlushNonBlocking[102X ([14X4.2-15[114X)
  on  that file will succeed without blocking and flush out at least one byte.
  Note  that this does not guarantee, that this call succeeds to flush out the
  whole content of the buffer![133X
  
  [1X4.2-15 IO_FlushNonBlocking[101X
  
  [33X[1;0Y[29X[2XIO_FlushNonBlocking[102X( [3Xf[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X, [9Xfalse[109X, or [9Xfail[109X[133X
  
  [33X[0;0YThis  function takes one argument [3Xf[103X which must be a [10XFile[110X object. It tries to
  write  all  data  in  the  writing  buffer  to  the file descriptor. If this
  succeeds, the function returns [9Xtrue[109X and [9Xfalse[109X otherwise. If an error occurs,
  [9Xfail[109X  is  returned.  If  a  previous  call  to  [2XIO_ReadyForFlush[102X ([14X4.2-14[114X) or
  [2XIO_Select[102X  ([14X4.3-3[114X) indicated that [3Xf[103X is flushable, then it is guaranteed that
  the following call to [2XIO_FlushNonBlocking[102X does not block. However, it is not
  guaranteed that [9Xtrue[109X is returned from that call.[133X
  
  [1X4.2-16 IO_Close[101X
  
  [33X[1;0Y[29X[2XIO_Close[102X( [3Xf[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfail[109X[133X
  
  [33X[0;0YThis  function  closes the [10XFile[110X object [3Xf[103X after writing all data in the write
  buffer  out  and closing the file descriptor. All buffers are freed. In case
  of  an  error,  the  function returns [9Xfail[109X and otherwise [9Xtrue[109X. Note that for
  pipes  to  other  processes this function collects data about the terminated
  processes using [2XIO_WaitPid[102X ([14X3.2-66[114X).[133X
  
  
  [1X4.3 [33X[0;0YOther functions[133X[101X
  
  [1X4.3-1 IO_GetFD[101X
  
  [33X[1;0Y[29X[2XIO_GetFD[102X( [3Xf[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Yan integer[133X
  
  [33X[0;0YThis  function  returns  the  real  file  descriptor that is behind the [10XFile[110X
  object [3Xf[103X.[133X
  
  [1X4.3-2 IO_GetWBuf[101X
  
  [33X[1;0Y[29X[2XIO_GetWBuf[102X( [3Xf[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya string or [9Xfalse[109X[133X
  
  [33X[0;0YThis  function  gets  one argument [3Xf[103X which must be a [10XFile[110X object and returns
  the  writing buffer of that [10XFile[110X object. This is necessary for [10XFile[110X objects,
  that  are  not  associated  to  a  real  file  descriptor  but  just collect
  everything  that  was  written in their writing buffer. Remember to use this
  function before closing the [10XFile[110X object.[133X
  
  [1X4.3-3 IO_Select[101X
  
  [33X[1;0Y[29X[2XIO_Select[102X( [3Xr[103X, [3Xw[103X, [3Xf[103X, [3Xe[103X, [3Xt1[103X, [3Xt2[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Yan integer or [9Xfail[109X[133X
  
  [33X[0;0YThis  function  is  the  corresponding  function  to  [2XIO_select[102X ([14X3.2-55[114X) for
  buffered file access. It behaves similarly to that function. The differences
  are  the  following:  There are four lists of files [3Xr[103X, [3Xw[103X, [3Xf[103X, and [3Xe[103X. They all
  can contain either integers (standing for file descriptors) or [10XFile[110X objects.
  The  list  [3Xr[103X is for checking, whether files or file descriptors are ready to
  read, the list [3Xw[103X is for checking whether they are ready to write, the list [3Xf[103X
  is  for  checking  whether  they  are  ready to flush, and the list [3Xe[103X is for
  checking whether they have exceptions.[133X
  
  [33X[0;0YFor  [10XFile[110X  objects  it is always first checked, whether there is either data
  available  in a reading buffer or space in a writing buffer. If so, they are
  immediately  reported  to  be  ready  (this  feature  makes the list of [10XFile[110X
  objects to test for flushability necessary). For the remaining files and for
  all specified file descriptors, the function [2XIO_select[102X ([14X3.2-55[114X) is called to
  get  an  overview  about  readiness. The timeout values [3Xt1[103X and [3Xt2[103X are set to
  zero for immediate returning if one of the requested buffers were ready.[133X
  
  [33X[0;0Y[2XIO_Select[102X  returns the number of files or file descriptors that are ready to
  serve or [9Xfail[109X if an error occurs.[133X
  
  [33X[0;0YThe following function is a convenience function for directory access:[133X
  
  [1X4.3-4 IO_ListDir[101X
  
  [33X[1;0Y[29X[2XIO_ListDir[102X( [3Xpathname[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya list of strings or [9Xfail[109X[133X
  
  [33X[0;0YThis  function  gets  a string containing a path name as single argument and
  returns a list of strings that are the names of the files in that directory,
  or [9Xfail[109X, if an error occurred.[133X
  
  [1X4.3-5 ChangeDirectoryCurrent[101X
  
  [33X[1;0Y[29X[2XChangeDirectoryCurrent[102X( [3Xpathname[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X on success and [9Xfail[109X on failure[133X
  
  [33X[0;0YChanges the current directory. Returns [9Xtrue[109X on success and [9Xfail[109X on failure.[133X
  
  [33X[0;0YThe  following function is used to create strings describing a pair of an IP
  address  and  a  port  number  in a binary way. These strings can be used in
  connection  with the C library functions [10Xconnect[110X, [10Xbind[110X, [10Xrecvfrom[110X, and [10Xsendto[110X
  for the arguments needing such address pairs.[133X
  
  [1X4.3-6 IO_MakeIPAddressPort[101X
  
  [33X[1;0Y[29X[2XIO_MakeIPAddressPort[102X( [3Xipstring[103X, [3Xportnr[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya string[133X
  
  [33X[0;0YThis  function  gets  a  string  [3Xipstring[103X  containing  an  IP address in dot
  notation,  i.e. four numbers in the range from 0 to 255 separated by dots [21X.[121X,
  and an integer [3Xportnr[103X, which is a port number. The result is a string of the
  correct length to be used for the low level C library functions, wherever IP
  address port number pairs are needed. The string [3Xipstring[103X can also be a host
  name, which is then looked up using [2XIO_gethostbyname[102X ([14X3.2-23[114X) to find the IP
  address.[133X
  
  [1X4.3-7 IO_Environment[101X
  
  [33X[1;0Y[29X[2XIO_Environment[102X(  ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya record or [9Xfail[109X[133X
  
  [33X[0;0YTakes  no  arguments,  uses  [2XIO_environ[102X  ([14X3.3-2[114X)  to get the environment and
  returns  a  record  in  which  the  component  names  are  the  names of the
  environment  variables  and  the  values  are  the  values. This can then be
  changed  and  the  changed  record can be given to [2XIO_MakeEnvList[102X ([14X4.3-8[114X) to
  produce  again  a  list  which  can  be used for [2XIO_execve[102X ([14X3.2-13[114X) as third
  argument.[133X
  
  [1X4.3-8 IO_MakeEnvList[101X
  
  [33X[1;0Y[29X[2XIO_MakeEnvList[102X( [3Xr[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya list of strings[133X
  
  [33X[0;0YTakes  a  record  as  returned by [2XIO_Environment[102X ([14X4.3-7[114X) and turns it into a
  list of strings as needed by [2XIO_execve[102X ([14X3.2-13[114X) as third argument.[133X
  
  
  [1X4.4 [33X[0;0YInter process communication[133X[101X
  
  [1X4.4-1 IO_FindExecutable[101X
  
  [33X[1;0Y[29X[2XIO_FindExecutable[102X( [3Xpath[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Y[9Xfail[109X or the path to an executable[133X
  
  [33X[0;0YIf  the path name [3Xpath[103X contains a slash, this function simply checks whether
  the string [3Xpath[103X refers to an executable file. If so, [3Xpath[103X is returned as is.
  Otherwise, [9Xfail[109X is returned. If the path name [3Xpath[103X does not contain a slash,
  all  directories  in  the  environment  variable  [11XPATH[111X  are  searched for an
  executable  with  name  [3Xpath[103X.  If  so,  the  full path to that executable is
  returned, otherwise [9Xfail[109X.[133X
  
  [33X[0;0YThis  function  is  used  whenever  one  of  the following functions gets an
  argument that should refer to an executable.[133X
  
  [1X4.4-2 IO_CloseAllFDs[101X
  
  [33X[1;0Y[29X[2XIO_CloseAllFDs[102X( [3Xexceptions[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ynothing[133X
  
  [33X[0;0YCloses all file descriptors except those listed in [3Xexceptions[103X, which must be
  a list of integers.[133X
  
  [1X4.4-3 IO_Popen[101X
  
  [33X[1;0Y[29X[2XIO_Popen[102X( [3Xpath[103X, [3Xargv[103X, [3Xmode[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya [10XFile[110X object or [9Xfail[109X[133X
  
  [33X[0;0YThe  argument  [3Xpath[103X  must  refer  to  an  executable  file  in  the sense of
  [2XIO_FindExecutable[102X ([14X4.4-1[114X).[133X
  
  [33X[0;0YStarts  a  child  process using the executable in [3Xpath[103X with either stdout or
  stdin  being  a  pipe.  The argument [3Xmode[103X must be either the string [21X[10Xr[110X[121X or the
  string [21X[10Xw[110X[121X.[133X
  
  [33X[0;0YIn  the  first  case,  the  standard output of the child process will be the
  writing  end  of  a pipe. A [10XFile[110X object for reading connected to the reading
  end  of  the  pipe is returned. The standard input and standard error of the
  child process will be the same as in the calling [5XGAP[105X process.[133X
  
  [33X[0;0YIn  the  second  case,  the  standard input of the child process will be the
  reading  end  of  a pipe. A [10XFile[110X object for writing connected to the writing
  end  of  the pipe is returned. The standard output and standard error of the
  child process will be the same as in the calling [5XGAP[105X process.[133X
  
  [33X[0;0YIn case of an error, [9Xfail[109X is returned.[133X
  
  [33X[0;0YThe  process  will  usually die, when the pipe is closed, but can also do so
  without  that.  The  [10XFile[110X  object  remembers  the  process ID of the started
  process  and  the  [2XIO_Close[102X ([14X4.2-16[114X) function then calls [2XIO_WaitPid[102X ([14X3.2-66[114X)
  for it to acquire information about the terminated process.[133X
  
  [33X[0;0YNote     that     [2XIO_Popen[102X    activates    our    SIGCHLD    handler    (see
  [2XIO_InstallSIGCHLDHandler[102X ([14X3.3-3[114X)).[133X
  
  [33X[0;0YIn  either case the [10XFile[110X object will have the attribute [21X[9XProcessID[109X[121X set to the
  process ID of the child process.[133X
  
  [1X4.4-4 IO_Popen2[101X
  
  [33X[1;0Y[29X[2XIO_Popen2[102X( [3Xpath[103X, [3Xargv[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya record or [9Xfail[109X[133X
  
  [33X[0;0YThe  argument  [3Xpath[103X  must  refer  to  an  executable  file  in  the sense of
  [2XIO_FindExecutable[102X ([14X4.4-1[114X).[133X
  
  [33X[0;0YA  new  child  process is started using the executable in [3Xpath[103X. The standard
  input and standard output of it are pipes. The writing end of the input pipe
  and the reading end of the output pipe are returned as [10XFile[110X objects bound to
  two  components [21X[10Xstdin[110X[121X and [21X[10Xstdout[110X[121X (resp.) of the returned record. This means,
  you  have to [13Xwrite[113X to [21X[10Xstdin[110X[121X and [13Xread[113X from [21X[10Xstdout[110X[121X in the calling [5XGAP[105X process.
  The  standard  error of the child process will be the same as the one of the
  calling [5XGAP[105X process.[133X
  
  [33X[0;0YReturns [9Xfail[109X if an error occurred.[133X
  
  [33X[0;0YThe  process  will  usually  die,  when one of the pipes is closed. The [10XFile[110X
  objects  remember the process ID of the called process and the function call
  to [2XIO_Close[102X ([14X4.2-16[114X) for the [10Xstdout[110X object will call [2XIO_WaitPid[102X ([14X3.2-66[114X) for
  it to acquire information about the terminated process.[133X
  
  [33X[0;0YNote     that    [2XIO_Popen2[102X    activates    our    SIGCHLD    handler    (see
  [2XIO_InstallSIGCHLDHandler[102X ([14X3.3-3[114X)).[133X
  
  [33X[0;0YBoth [10XFile[110X objects will have the attribute [21X[9XProcessID[109X[121X set to the process ID of
  the  child  process,  which  will  also be bound to the [21X[9Xpid[109X[121X component of the
  returned record.[133X
  
  [1X4.4-5 IO_Popen3[101X
  
  [33X[1;0Y[29X[2XIO_Popen3[102X( [3Xpath[103X, [3Xargv[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya record or [9Xfail[109X[133X
  
  [33X[0;0YThe  argument  [3Xpath[103X  must  refer  to  an  executable  file  in  the sense of
  [2XIO_FindExecutable[102X ([14X4.4-1[114X).[133X
  
  [33X[0;0YA  new  child  process  is started using the executable in [3Xpath[103X The standard
  input,  standard output, and standard error of it are pipes. The writing end
  of the input pipe, the reading end of the output pipe and the reading end of
  the  error  pipe are returned as [10XFile[110X objects bound to two components [21X[10Xstdin[110X[121X,
  [21X[10Xstdout[110X[121X,  and  [21X[10Xstderr[110X[121X (resp.) of the returned record. This means, you have to
  [13Xwrite[113X to [21X[10Xstdin[110X[121X and [13Xread[113X from [21X[10Xstdout[110X[121X and [21X[10Xstderr[110X[121X in the calling [5XGAP[105X process.[133X
  
  [33X[0;0YReturns [9Xfail[109X if an error occurred.[133X
  
  [33X[0;0YThe  process  will  usually  die, when one of the pipes is closed. All three
  [10XFile[110X  objects  will remember the process ID of the newly created process and
  the  call  to the [2XIO_Close[102X ([14X4.2-16[114X) function for the [10Xstdout[110X object will call
  [2XIO_WaitPid[102X ([14X3.2-66[114X) for it to acquire information about the terminated child
  process.[133X
  
  [33X[0;0YNote     that    [2XIO_Popen3[102X    activates    our    SIGCHLD    handler    (see
  [2XIO_InstallSIGCHLDHandler[102X ([14X3.3-3[114X)).[133X
  
  [33X[0;0YAll  three [10XFile[110X objects will have the attribute [21X[9XProcessID[109X[121X set to the process
  ID  of  the  child process, which will also be bound to the [21X[9Xpid[109X[121X component of
  the returned record.[133X
  
  [1X4.4-6 IO_StartPipeline[101X
  
  [33X[1;0Y[29X[2XIO_StartPipeline[102X( [3Xprogs[103X, [3Xinfd[103X, [3Xoutfd[103X, [3Xswitcherror[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya record or [9Xfail[109X[133X
  
  [33X[0;0YThe  argument  [3Xprogs[103X  is a list of pairs, the first entry being a path to an
  executable  (in  the  sense  of  [2XIO_FindExecutable[102X  ([14X4.4-1[114X)),  the second an
  argument  list,  the  argument  [3Xinfd[103X is an open file descriptor for reading,
  [3Xoutfd[103X  is  an  open file descriptor for writing, both can be replaced by the
  string  [21X[9Xopen[109X[121X  in  which  case  a  new  pipe  will  be  opened.  The argument
  [3Xswitcherror[103X is a boolean indicating whether standard error channels are also
  switched to the corresponding output channels.[133X
  
  [33X[0;0YThis  function  starts  up  all  processes and connects them with pipes. The
  input of the first is switched to [3Xinfd[103X and the output of the last to [3Xoutfd[103X.[133X
  
  [33X[0;0YReturns  a  record  with the following components: [9Xpids[109X is a list of process
  ids if everything worked. For each process for which some error occurred the
  corresponding  pid  is  replaced  by  [9Xfail[109X.  The [9Xstdin[109X component is equal to
  [9Xfalse[109X,  or  to  the  file descriptor of the writing end of the newly created
  pipe  which  is  connected  to  the  standard  input of the first of the new
  processes if [3Xinfd[103X was [21X[9Xopen[109X[121X. The [9Xstdout[109X component is equal to [9Xfalse[109X or to the
  file  descriptor  of  the  reading  end  of  the newly created pipe which is
  connected  to  the standard output of the last of the new processes if [3Xoutfd[103X
  was [21X[9Xopen[109X[121X.[133X
  
  [33X[0;0YNote  that  the  SIGCHLD  handler  of  the  [5XIO[105X  package is installed by this
  function  (see  [2XIO_InstallSIGCHLDHandler[102X  ([14X3.3-3[114X))  and  that it lies in the
  responsibility  of  the  caller  to  use  [2XIO_WaitPid[102X ([14X3.2-66[114X) to ask for the
  status  information  of all child processes after their termination, or call
  [2XIO_IgnorePid[102X ([14X3.2-67[114X) to ignore the return value of a process.[133X
  
  [1X4.4-7 IO_StringFilterFile[101X
  
  [33X[1;0Y[29X[2XIO_StringFilterFile[102X( [3Xprogs[103X, [3Xfilename[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya string or [9Xfail[109X[133X
  
  [33X[0;0YReads the file with the name [3Xfilename[103X, however, a pipeline is created by the
  processes  described  by  [3Xprogs[103X (see [2XIO_StartPipeline[102X ([14X4.4-6[114X)) to filter the
  content  of  the  file  through  the  pipeline. The result is put into a [5XGAP[105X
  string and returned. If something goes wrong, [9Xfail[109X is returned.[133X
  
  [1X4.4-8 IO_FileFilterString[101X
  
  [33X[1;0Y[29X[2XIO_FileFilterString[102X( [3Xfilename[103X, [3Xprogs[103X, [3Xst[103X[, [3Xappend[103X] ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya string or [9Xfail[109X[133X
  
  [33X[0;0YWrites  the  content  of  the  string [3Xst[103X to the file with the name [3Xfilename[103X,
  however,  a  pipeline  is  created  by the processes described by [3Xprogs[103X (see
  [2XIO_StartPipeline[102X  ([14X4.4-6[114X))  to  filter the content of the string through the
  pipeline.  The  result  is put into the file. If the boolean value [3Xappend[103X is
  given  and  equal  to  [9Xtrue[109X,  then  the data will be appended to the already
  existing file. If something goes wrong, [9Xfail[109X is returned.[133X
  
  [1X4.4-9 IO_FilteredFile[101X
  
  [33X[1;0Y[29X[2XIO_FilteredFile[102X( [3Xprogs[103X, [3Xfilename[103X[, [3Xmode[103X][, [3Xbufsize[103X] ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya [10XFile[110X object or [9Xfail[109X[133X
  
  [33X[0;0YThis  function is similar to [2XIO_File[102X ([14X4.1-3[114X) and behaves nearly identically.
  The  only  difference  is  that a filtering pipeline is switched between the
  file  and  the [10XFile[110X object such that all things read or written respectively
  are filtered through this pipeline of processes.[133X
  
  [33X[0;0YThe  [10XFile[110X  object remembers the started processes and upon the final call to
  [2XIO_Close[102X  ([14X4.2-16[114X)  automatically  uses  the [2XIO_WaitPid[102X ([14X3.2-66[114X) function to
  acquire  information  from  the  terminated  processes in the pipeline after
  their  termination.  This  means  that  you  do  not have to call [2XIO_WaitPid[102X
  ([14X3.2-66[114X) any more after the call to [2XIO_Close[102X ([14X4.2-16[114X).[133X
  
  [33X[0;0YNote    that    [2XIO_FilteredFile[102X   activates   our   SIGCHLD   handler   (see
  [2XIO_InstallSIGCHLDHandler[102X ([14X3.3-3[114X)).[133X
  
  [33X[0;0YThe [10XFile[110X object will have the attribute [21X[9XProcessID[109X[121X set to the list of process
  IDs of the child processes.[133X
  
  [1X4.4-10 IO_CompressedFile[101X
  
  [33X[1;0Y[29X[2XIO_CompressedFile[102X( [3Xfilename[103X[, [3Xmode[103X][, [3Xbufsize[103X] ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya [10XFile[110X object or [9Xfail[109X[133X
  
  [33X[0;0YThis  function is a convenience wrapper around [2XIO_FilteredFile[102X ([14X4.4-9[114X) which
  handles a number of common compressed file formats transparently, by calling
  an external program. The arguments to this function are identical to [2XIO_File[102X
  ([14X4.1-3[114X). If the extension to [3Xfilename[103X is one of gz, bz2 or xz, then the file
  is   transparently   compressed/uncompressed   using   gzip,   bzip2  or  xz
  respectively.  If  the  extension is none of these, then the command behaves
  identically to [2XIO_File[102X ([14X4.1-3[114X).[133X
  
  [33X[0;0YNote  that  as this function calls [2XIO_FilteredFile[102X ([14X4.4-9[114X), it will activate
  our SIGCHLD handler (see [2XIO_InstallSIGCHLDHandler[102X ([14X3.3-3[114X)).[133X
  
  [33X[0;0YWhen  compression  /  decompression is active, the [10XFile[110X object will have the
  attribute [21X[9XProcessID[109X[121X set to the list of process IDs of the child processes.[133X
  
  [1X4.4-11 IO_SendStringBackground[101X
  
  [33X[1;0Y[29X[2XIO_SendStringBackground[102X( [3Xf[103X, [3Xst[103X ) [32X function[133X
  
  [33X[0;0YThis  functions  uses  [2XIO_Write[102X  ([14X4.2-7[114X) to write the whole string [3Xst[103X to the
  [10XFile[110X  object  [3Xf[103X.  However,  this  is  done  by  forking  off a child process
  identical  to the calling [5XGAP[105X process that does the sending. The calling [5XGAP[105X
  process  returns  immediately,  even before anything has been sent away with
  the result [9Xtrue[109X. The forked off sender process terminates itself immediately
  after it has sent all data away.[133X
  
  [33X[0;0YThe  reason for having this function available is the following: If one uses
  [2XIO_Popen2[102X  ([14X4.4-4[114X)  or  [2XIO_Popen3[102X  ([14X4.4-5[114X)  to start up a child process with
  standard  input  and  standard output being a pipe, then one usually has the
  problem,  that the child process starts reading some data, but then wants to
  write  data,  before it received all data coming. If the calling [5XGAP[105X process
  would  first  try to write all data and only start to read the output of the
  child process after sending away all data, a deadlock situation would occur.
  This is avoided with the forking and backgrounding approach.[133X
  
  [33X[0;0YRemember  to close the writing end of the standard input pipe in the calling
  [5XGAP[105X  process  directly  after  [2XIO_SendStringBackground[102X has returned, because
  otherwise  the  child  process  might  not notice that all data has arrived,
  because  the  pipe  persists! See the file [11Xpopen2.g[111X in the [11Xexample[111X directory
  for an example.[133X
  
  [33X[0;0YNote that with most modern operating systems the forking off of an identical
  child  process  does in fact [13Xnot[113X mean a duplication of the total main memory
  used by both processes, because the operating system kernel will use [21Xcopy on
  write[121X.  However,  if a garbage collection happens to become necessary during
  the  sending  of  the  data  in  the  forked off sending process, this might
  trigger doubled memory usage.[133X
  
  [1X4.4-12 IO_PipeThrough[101X
  
  [33X[1;0Y[29X[2XIO_PipeThrough[102X( [3Xcmd[103X, [3Xargs[103X, [3Xinput[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya string or [9Xfail[109X[133X
  
  [33X[0;0YStarts  the  process  with the executable given by the file name [3Xcmd[103X (in the
  sense of [2XIO_FindExecutable[102X ([14X4.4-1[114X)) with arguments in the argument list [3Xargs[103X
  (a  list  of  strings). The standard input and output of the started process
  are  connected  via  pipes to the calling process. The content of the string
  [3Xinput[103X  is  written  to  the  standard  input  of  the called process and its
  standard output is read and returned as a string.[133X
  
  [33X[0;0YAll  the  necessary I/O multiplexing and non-blocking I/O to avoid deadlocks
  is done in this function.[133X
  
  [33X[0;0YThis  function properly does [2XIO_WaitPid[102X ([14X3.2-66[114X) to wait for the termination
  of  the  child  process but does not restore the original [5XGAP[105X SIGCHLD signal
  handler (see [2XIO_InstallSIGCHLDHandler[102X ([14X3.3-3[114X)).[133X
  
  [1X4.4-13 IO_PipeThroughWithError[101X
  
  [33X[1;0Y[29X[2XIO_PipeThroughWithError[102X( [3Xcmd[103X, [3Xargs[103X, [3Xinput[103X ) [32X function[133X
  [6XReturns:[106X  [33X[0;10Ya record or [9Xfail[109X[133X
  
  [33X[0;0YStarts  the  process  with the executable given by the file name [3Xcmd[103X (in the
  sense of [2XIO_FindExecutable[102X ([14X4.4-1[114X)) with arguments in the argument list [3Xargs[103X
  (a  list  of  strings).  The standard input, output and error of the started
  process  are  connected via pipes to the calling process. The content of the
  string  [3Xinput[103X is written to the standard input of the called process and its
  standard  output and error are read and returned as a record with components
  [9Xout[109X and [9Xerr[109X, which are strings.[133X
  
  [33X[0;0YAll  the  necessary I/O multiplexing and non-blocking I/O to avoid deadlocks
  is done in this function.[133X
  
  [33X[0;0YThis  function properly does [2XIO_WaitPid[102X ([14X3.2-66[114X) to wait for the termination
  of  the  child  process but does not restore the original [5XGAP[105X SIGCHLD signal
  handler (see [2XIO_InstallSIGCHLDHandler[102X ([14X3.3-3[114X)).[133X
  
  [33X[0;0YThe  functions  returns  either  [9Xfail[109X  if  an error occurred, or otherwise a
  record with components [9Xout[109X and [9Xerr[109X which are bound to strings containing the
  full  standard  output  and standard error of the called process, and [9Xstatus[109X
  which is the status returned from the exiting process.[133X
  
