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#! /usr/bin/env python

"""Conversions to/from quoted-printable transport encoding as per RFC-1521."""

# (Dec 1991 version).

__all__ = ["encode","decode"]

ESCAPE = '='

MAXLINESIZE = 76

HEX = '0123456789ABCDEF'

def needsquoting(c, quotetabs):

    """Decide whether a particular character needs to be quoted.

    The 'quotetabs' flag indicates whether tabs should be quoted."""

    if c == '\t':

        return not quotetabs

    return c == ESCAPE or not(' ' <= c <= '~')

def quote(c):

    """Quote a single character."""

    i = ord(c)

    return ESCAPE + HEX[i/16] + HEX[i%16]

def encode(input, output, quotetabs):

    """Read 'input', apply quoted-printable encoding, and write to 'output'.

    'input' and 'output' are files with readline() and write() methods.

    The 'quotetabs' flag indicates whether tabs should be quoted.

        """

    while 1:

        line = input.readline()

        if not line:

            break

        new = ''

        last = line[-1:]

        if last == '\n':

            line = line[:-1]

        else:

            last = ''

        prev = ''

        for c in line:

            if needsquoting(c, quotetabs):

                c = quote(c)

            if len(new) + len(c) >= MAXLINESIZE:

                output.write(new + ESCAPE + '\n')

                new = ''

            new = new + c

            prev = c

        if prev in (' ', '\t'):

            output.write(new + ESCAPE + '\n\n')

        else:

            output.write(new + '\n')

def decode(input, output):

    """Read 'input', apply quoted-printable decoding, and write to 'output'.

    'input' and 'output' are files with readline() and write() methods."""

    new = ''

    while 1:

        line = input.readline()

        if not line: break

        i, n = 0, len(line)

        if n > 0 and line[n-1] == '\n':

            partial = 0; n = n-1

            # Strip trailing whitespace

            while n > 0 and line[n-1] in " \t\r":

                n = n-1

        else:

            partial = 1

        while i < n:

            c = line[i]

            if c != ESCAPE:

                new = new + c; i = i+1

            elif i+1 == n and not partial:

                partial = 1; break

            elif i+1 < n and line[i+1] == ESCAPE:

                new = new + ESCAPE; i = i+2

            elif i+2 < n and ishex(line[i+1]) and ishex(line[i+2]):

                new = new + chr(unhex(line[i+1:i+3])); i = i+3

            else: # Bad escape sequence -- leave it in

                new = new + c; i = i+1

        if not partial:

            output.write(new + '\n')

            new = ''

    if new:

        output.write(new)

def ishex(c):

    """Return true if the character 'c' is a hexadecimal digit."""

    return '0' <= c <= '9' or 'a' <= c <= 'f' or 'A' <= c <= 'F'

def unhex(s):

    """Get the integer value of a hexadecimal number."""

    bits = 0

    for c in s:

        if '0' <= c <= '9':

            i = ord('0')

        elif 'a' <= c <= 'f':

            i = ord('a')-10

        elif 'A' <= c <= 'F':

            i = ord('A')-10

        else:

            break

        bits = bits*16 + (ord(c) - i)

    return bits

def test():

    import sys

    import getopt

    try:

        opts, args = getopt.getopt(sys.argv[1:], 'td')

    except getopt.error, msg:

        sys.stdout = sys.stderr

        print msg

        print "usage: quopri [-t | -d] [file] ..."

        print "-t: quote tabs"

        print "-d: decode; default encode"

        sys.exit(2)

    deco = 0

    tabs = 0

    for o, a in opts:

        if o == '-t': tabs = 1

        if o == '-d': deco = 1

    if tabs and deco:

        sys.stdout = sys.stderr

        print "-t and -d are mutually exclusive"

        sys.exit(2)

    if not args: args = ['-']

    sts = 0

    for file in args:

        if file == '-':

            fp = sys.stdin

        else:

            try:

                fp = open(file)

            except IOError, msg:

                sys.stderr.write("%s: can't open (%s)\n" % (file, msg))

                sts = 1

                continue

        if deco:

            decode(fp, sys.stdout)

        else:

            encode(fp, sys.stdout, tabs)

        if fp is not sys.stdin:

            fp.close()

    if sts:

        sys.exit(sts)

if __name__ == '__main__':

    test()