1# class MkMemoIO implements  file-like objects that read/write a
2# memo field in a Metakit database (either on file, or in memory).
3#
4# A simple adaptation of the StringIO.py module, by Jean-Claude Wippler.
5#
6# This implements (nearly) all stdio methods.
7#
8# f = MkMemoIO(view, memoprop, rownum) # setup for view[rownum].memoprop
9# f.close()       # explicitly release resources held
10# flag = f.isatty()   # always false
11# pos = f.tell()    # get current position
12# f.seek(pos)     # set current position
13# f.seek(pos, mode)   # mode 0: absolute; 1: relative; 2: relative to EOF
14# buf = f.read()    # read until EOF
15# buf = f.read(n)   # read up to n bytes
16# buf = f.readline()  # read until end of line ('\n') or EOF
17# list = f.readlines()# list of f.readline() results until EOF
18# f.write(buf)      # write at current position
19# f.writelines(list)  # for line in list: f.write(line)
20# f.getvalue()      # return whole file's contents as a string
21#
22# Notes:
23# - fileno() is left unimplemented so that code which uses it triggers
24# an exception early.
25# - Seeking beyond EOF and then writing will insert garbage, unlike the
26# StringIO class which clears, and from which this code was adapted.
27# - There's a simple test set (see end of this file).
28# - write() has an optional "resize" to insert (>0) or delete (<0) bytes.
29# To merely insert/delete, write an empty string.  The resize value is
30# adjusted to a "reasonable" range.  Inserted bytes are *not* cleared.
31
32import string, sys
33
34class MkMemoIO:
35  def __init__(self, view, memo, row):
36    self.view = view
37    self.memo = memo
38    self.row = row
39    self.pos = 0
40    self.closed = 0
41    self.softspace = 0
42  def close(self):
43    if not self.closed:
44      self.closed = 1
45      del self.view, self.memo, self.row, self.pos
46  def isatty(self):
47    if self.closed:
48      raise ValueError, "I/O operation on closed file"
49    return 0
50  def seek(self, pos, mode = 0):
51    if self.closed:
52      raise ValueError, "I/O operation on closed file"
53    if mode == 1:
54      pos = pos + self.pos
55    elif mode == 2:
56      pos = pos + self.view.itemsize(self.memo, self.row)
57    self.pos = max(0, pos)
58  def tell(self):
59    if self.closed:
60      raise ValueError, "I/O operation on closed file"
61    return self.pos
62  def read(self, n = -1):
63    if self.closed:
64      raise ValueError, "I/O operation on closed file"
65    if n == 0:
66      return ""
67    r = self.view.access(self.memo, self.row, self.pos, n)
68    self.pos = self.pos + len(r)
69    return r
70  def readline(self, length=None):
71    if self.closed:
72      raise ValueError, "I/O operation on closed file"
73    remain = self.view.itemsize(self.memo, self.row) - self.pos
74    if length is None:
75      length = remain
76    length = min(length, remain)
77    i = -1
78    oldpos = self.pos
79    for o in xrange(0, length, 100):
80      i = string.find(self.read(100), '\n')
81      if i >= 0:
82        break
83    self.pos = oldpos
84    if i >= 0:
85      length = o+i+1
86    return self.read(length)
87  def readlines(self):
88    lines = []
89    line = self.readline()
90    while line:
91      lines.append(line)
92      line = self.readline()
93    return lines
94  def write(self, s, resize=0):
95    if self.closed:
96      raise ValueError, "I/O operation on closed file"
97    self.view.modify(self.memo, self.row, s, self.pos, resize)
98    self.pos = self.pos + len(s)
99  def writelines(self, list):
100    for line in list: self.write(line)
101  def flush(self):
102    if self.closed:
103      raise ValueError, "I/O operation on closed file"
104  def getvalue(self):
105    return self.view.access(self.memo, self.row, 0)
106
107
108# A little test suite
109
110def test():
111  import Mk4py
112  mk=Mk4py
113  db=mk.storage()
114  vw=db.getas('v[m:M]')
115  vw.append()
116  if sys.argv[1:]:
117     file = sys.argv[1]
118  else:
119     file = '/etc/passwd'
120  lines = open(file, 'r').readlines()
121  text = open(file, 'r').read()
122  f = MkMemoIO(vw,vw.m,0)
123  for line in lines[:-2]:
124    f.write(line)
125  f.writelines(lines[-2:])
126  if f.getvalue() != text:
127    raise RuntimeError, 'write failed'
128  length = f.tell()
129  print 'File length =', length
130  f.seek(len(lines[0]))
131  f.write(lines[1])
132  f.seek(0)
133  print 'First line =', `f.readline()`
134  here = f.tell()
135  line = f.readline()
136  print 'Second line =', `line`
137  f.seek(-len(line), 1)
138  line2 = f.read(len(line))
139  if line != line2:
140    raise RuntimeError, 'bad result after seek back'
141  f.seek(len(line2), 1)
142  list = f.readlines()
143  line = list[-1]
144  f.seek(f.tell() - len(line))
145  line2 = f.read()
146  if line != line2:
147    raise RuntimeError, 'bad result after seek back from EOF'
148  print 'Read', len(list), 'more lines'
149  print 'File length =', f.tell()
150  if f.tell() != length:
151    raise RuntimeError, 'bad length'
152  f.close()
153
154if __name__ == '__main__':
155  test()
156