src/mxmMidi/RawInstreamFile.py

   1 # -*- coding: ISO-8859-1 -*-
   2
   3 # standard library imports
   4 from types import StringType
   5 from struct import unpack
   6
   7 # custom import
   8 from DataTypeConverters import readBew, readVar, varLen
   9
  10
  11 class RawInstreamFile:
  12
  13     """
  14
  15     It parses and reads data from an input file. It takes care of big
  16     endianess, and keeps track of the cursor position. The midi parser
  17     only reads from this object. Never directly from the file.
  18
  19     """
  20
  21     def __init__(self, infile=''):
  22         """
  23         If 'file' is a string we assume it is a path and read from
  24         that file.
  25         If it is a file descriptor we read from the file, but we don't
  26         close it.
  27         Midi files are usually pretty small, so it should be safe to
  28         copy them into memory.
  29         """
  30         if infile:
  31             if isinstance(infile, StringType):
  32                 infile = open(infile, 'rb')
  33                 self.data = infile.read()
  34                 infile.close()
  35             else:
  36                 # don't close the f
  37                 self.data = infile.read()
  38         else:
  39             self.data = ''
  40         # start at beginning ;-)
  41         self.cursor = 0
  42
  43
  44     # setting up data manually
  45
  46     def setData(self, data=''):
  47         "Sets the data from a string."
  48         self.data = data
  49
  50     # cursor operations
  51
  52     def setCursor(self, position=0):
  53         "Sets the absolute position if the cursor"
  54         self.cursor = position
  55
  56
  57     def getCursor(self):
  58         "Returns the value of the cursor"
  59         return self.cursor
  60
  61
  62     def moveCursor(self, relative_position=0):
  63         "Moves the cursor to a new relative position"
  64         self.cursor += relative_position
  65
  66     # native data reading functions
  67
  68     def nextSlice(self, length, move_cursor=1):
  69         "Reads the next text slice from the raw data, with length"
  70         c = self.cursor
  71         slc = self.data[c:c+length]
  72         if move_cursor:
  73             self.moveCursor(length)
  74         return slc
  75
  76
  77     def readBew(self, n_bytes=1, move_cursor=1):
  78         """
  79         Reads n bytes of date from the current cursor position.
  80         Moves cursor if move_cursor is true
  81         """
  82         return readBew(self.nextSlice(n_bytes, move_cursor))
  83
  84
  85     def readVarLen(self):
  86         """
  87         Reads a variable length value from the current cursor position.
  88         Moves cursor if move_cursor is true
  89         """
  90         MAX_VARLEN = 4 # Max value varlen can be
  91         var = readVar(self.nextSlice(MAX_VARLEN, 0))
  92         # only move cursor the actual bytes in varlen
  93         self.moveCursor(varLen(var))
  94         return var
  95
  96
  97
  98 if __name__ == '__main__':
  99
 100     test_file = 'test/midifiles/minimal.mid'
 101     fis = RawInstreamFile(test_file)
 102     print fis.nextSlice(len(fis.data))
 103
 104     test_file = 'test/midifiles/cubase-minimal.mid'
 105     cubase_minimal = open(test_file, 'rb')
 106     fis2 = RawInstreamFile(cubase_minimal)
 107     print fis2.nextSlice(len(fis2.data))
 108     cubase_minimal.close()