Lib/MimeWriter.py

   1 """Generic MIME writer.
   2
   3 This module defines the class MimeWriter.  The MimeWriter class implements
   4 a basic formatter for creating MIME multi-part files.  It doesn't seek around
   5 the output file nor does it use large amounts of buffer space. You must write
   6 the parts out in the order that they should occur in the final file.
   7 MimeWriter does buffer the headers you add, allowing you to rearrange their
   8 order.
   9
  10 """
  11
  12
  13 import mimetools
  14
  15 __all__ = ["MimeWriter"]
  16
  17 class MimeWriter:
  18
  19     """Generic MIME writer.
  20
  21     Methods:
  22
  23     __init__()
  24     addheader()
  25     flushheaders()
  26     startbody()
  27     startmultipartbody()
  28     nextpart()
  29     lastpart()
  30
  31     A MIME writer is much more primitive than a MIME parser.  It
  32     doesn't seek around on the output file, and it doesn't use large
  33     amounts of buffer space, so you have to write the parts in the
  34     order they should occur on the output file.  It does buffer the
  35     headers you add, allowing you to rearrange their order.
  36
  37     General usage is:
  38
  39     f = <open the output file>
  40     w = MimeWriter(f)
  41     ...call w.addheader(key, value) 0 or more times...
  42
  43     followed by either:
  44
  45     f = w.startbody(content_type)
  46     ...call f.write(data) for body data...
  47
  48     or:
  49
  50     w.startmultipartbody(subtype)
  51     for each part:
  52         subwriter = w.nextpart()
  53         ...use the subwriter's methods to create the subpart...
  54     w.lastpart()
  55
  56     The subwriter is another MimeWriter instance, and should be
  57     treated in the same way as the toplevel MimeWriter.  This way,
  58     writing recursive body parts is easy.
  59
  60     Warning: don't forget to call lastpart()!
  61
  62     XXX There should be more state so calls made in the wrong order
  63     are detected.
  64
  65     Some special cases:
  66
  67     - startbody() just returns the file passed to the constructor;
  68       but don't use this knowledge, as it may be changed.
  69
  70     - startmultipartbody() actually returns a file as well;
  71       this can be used to write the initial 'if you can read this your
  72       mailer is not MIME-aware' message.
  73
  74     - If you call flushheaders(), the headers accumulated so far are
  75       written out (and forgotten); this is useful if you don't need a
  76       body part at all, e.g. for a subpart of type message/rfc822
  77       that's (mis)used to store some header-like information.
  78
  79     - Passing a keyword argument 'prefix=<flag>' to addheader(),
  80       start*body() affects where the header is inserted; 0 means
  81       append at the end, 1 means insert at the start; default is
  82       append for addheader(), but insert for start*body(), which use
  83       it to determine where the Content-Type header goes.
  84
  85     """
  86
  87     def __init__(self, fp):
  88         self._fp = fp
  89         self._headers = []
  90
  91     def addheader(self, key, value, prefix=0):
  92         """Add a header line to the MIME message.
  93
  94         The key is the name of the header, where the value obviously provides
  95         the value of the header. The optional argument prefix determines
  96         where the header is inserted; 0 means append at the end, 1 means
  97         insert at the start. The default is to append.
  98
  99         """
 100         lines = value.split("\n")
 101         while lines and not lines[-1]: del lines[-1]
 102         while lines and not lines[0]: del lines[0]
 103         for i in range(1, len(lines)):
 104             lines[i] = "    " + lines[i].strip()
 105         value = "\n".join(lines) + "\n"
 106         line = key + ": " + value
 107         if prefix:
 108             self._headers.insert(0, line)
 109         else:
 110             self._headers.append(line)
 111
 112     def flushheaders(self):
 113         """Writes out and forgets all headers accumulated so far.
 114
 115         This is useful if you don't need a body part at all; for example,
 116         for a subpart of type message/rfc822 that's (mis)used to store some
 117         header-like information.
 118
 119         """
 120         self._fp.writelines(self._headers)
 121         self._headers = []
 122
 123     def startbody(self, ctype, plist=[], prefix=1):
 124         """Returns a file-like object for writing the body of the message.
 125
 126         The content-type is set to the provided ctype, and the optional
 127         parameter, plist, provides additional parameters for the
 128         content-type declaration.  The optional argument prefix determines
 129         where the header is inserted; 0 means append at the end, 1 means
 130         insert at the start. The default is to insert at the start.
 131
 132         """
 133         for name, value in plist:
 134             ctype = ctype + ';\n %s=\"%s\"' % (name, value)
 135         self.addheader("Content-Type", ctype, prefix=prefix)
 136         self.flushheaders()
 137         self._fp.write("\n")
 138         return self._fp
 139
 140     def startmultipartbody(self, subtype, boundary=None, plist=[], prefix=1):
 141         """Returns a file-like object for writing the body of the message.
 142
 143         Additionally, this method initializes the multi-part code, where the
 144         subtype parameter provides the multipart subtype, the boundary
 145         parameter may provide a user-defined boundary specification, and the
 146         plist parameter provides optional parameters for the subtype.  The
 147         optional argument, prefix, determines where the header is inserted;
 148         0 means append at the end, 1 means insert at the start. The default
 149         is to insert at the start.  Subparts should be created using the
 150         nextpart() method.
 151
 152         """
 153         self._boundary = boundary or mimetools.choose_boundary()
 154         return self.startbody("multipart/" + subtype,
 155                               [("boundary", self._boundary)] + plist,
 156                               prefix=prefix)
 157
 158     def nextpart(self):
 159         """Returns a new instance of MimeWriter which represents an
 160         individual part in a multipart message.
 161
 162         This may be used to write the part as well as used for creating
 163         recursively complex multipart messages. The message must first be
 164         initialized with the startmultipartbody() method before using the
 165         nextpart() method.
 166
 167         """
 168         self._fp.write("\n--" + self._boundary + "\n")
 169         return self.__class__(self._fp)
 170
 171     def lastpart(self):
 172         """This is used to designate the last part of a multipart message.
 173
 174         It should always be used when writing multipart messages.
 175
 176         """
 177         self._fp.write("\n--" + self._boundary + "--\n")
 178
 179
 180 if __name__ == '__main__':
 181     import test.test_MimeWriter