mime::decoder::nbit(3) [suse man page]
MIME::Decoder::NBit(3) User Contributed Perl Documentation MIME::Decoder::NBit(3) NAME
MIME::Decoder::NBit - encode/decode a "7bit" or "8bit" stream SYNOPSIS
A generic decoder object; see MIME::Decoder for usage. DESCRIPTION
This is a MIME::Decoder subclass for the "7bit" and "8bit" content transfer encodings. These are not "encodings" per se: rather, they are simply assertions of the content of the message. From RFC-2045 Section 6.2.: Three transformations are currently defined: identity, the "quoted- printable" encoding, and the "base64" encoding. The domains are "binary", "8bit" and "7bit". The Content-Transfer-Encoding values "7bit", "8bit", and "binary" all mean that the identity (i.e. NO) encoding transformation has been performed. As such, they serve simply as indicators of the domain of the body data, and provide useful information about the sort of encoding that might be needed for transmission in a given transport system. In keeping with this: as of MIME-tools 4.x, this class does no modification of its input when encoding; all it does is attempt to detect violations of the 7bit/8bit assertion, and issue a warning (one per message) if any are found. Legal 7bit data RFC-2045 Section 2.7 defines legal "7bit" data: "7bit data" refers to data that is all represented as relatively short lines with 998 octets or less between CRLF line separation sequences [RFC-821]. No octets with decimal values greater than 127 are allowed and neither are NULs (octets with decimal value 0). CR (decimal value 13) and LF (decimal value 10) octets only occur as part of CRLF line separation sequences. Legal 8bit data RFC-2045 Section 2.8 defines legal "8bit" data: "8bit data" refers to data that is all represented as relatively short lines with 998 octets or less between CRLF line separation sequences [RFC-821]), but octets with decimal values greater than 127 may be used. As with "7bit data" CR and LF octets only occur as part of CRLF line separation sequences and no NULs are allowed. How decoding is done The decoder does a line-by-line pass-through from input to output, leaving the data unchanged except that an end-of-line sequence of CRLF is converted to a newline " ". Given the line-oriented nature of 7bit and 8bit, this seems relatively sensible. How encoding is done The encoder does a line-by-line pass-through from input to output, and simply attempts to detect violations of the "7bit"/"8bit" domain. The default action is to warn once per encoding if violations are detected; the warnings may be silenced with the QUIET configuration of MIME::Tools. SEE ALSO
MIME::Decoder AUTHOR
Eryq (eryq@zeegee.com), ZeeGee Software Inc (http://www.zeegee.com). All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.12.1 2008-06-30 MIME::Decoder::NBit(3)
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MIME::Decoder(3) User Contributed Perl Documentation MIME::Decoder(3) NAME
MIME::Decoder - an object for decoding the body part of a MIME stream SYNOPSIS
Before reading further, you should see MIME::Tools to make sure that you understand where this module fits into the grand scheme of things. Go on, do it now. I'll wait. Ready? Ok... Decoding a data stream Here's a simple filter program to read quoted-printable data from STDIN (until EOF) and write the decoded data to STDOUT: use MIME::Decoder; $decoder = new MIME::Decoder 'quoted-printable' or die "unsupported"; $decoder->decode(*STDIN, *STDOUT); Encoding a data stream Here's a simple filter program to read binary data from STDIN (until EOF) and write base64-encoded data to STDOUT: use MIME::Decoder; $decoder = new MIME::Decoder 'base64' or die "unsupported"; $decoder->encode(*STDIN, *STDOUT); Non-standard encodings You can write and install your own decoders so that MIME::Decoder will know about them: use MyBase64Decoder; install MyBase64Decoder 'base64'; You can also test if a given encoding is supported: if (supported MIME::Decoder 'x-uuencode') { ### we can uuencode! } DESCRIPTION
This abstract class, and its private concrete subclasses (see below) provide an OO front end to the actions of... o Decoding a MIME-encoded stream o Encoding a raw data stream into a MIME-encoded stream. The constructor for MIME::Decoder takes the name of an encoding ("base64", "7bit", etc.), and returns an instance of a subclass of MIME::Decoder whose "decode()" method will perform the appropriate decoding action, and whose "encode()" method will perform the appropriate encoding action. PUBLIC INTERFACE
Standard interface If all you are doing is using this class, here's all you'll need... new ENCODING Class method, constructor. Create and return a new decoder object which can handle the given ENCODING. my $decoder = new MIME::Decoder "7bit"; Returns the undefined value if no known decoders are appropriate. best ENCODING Class method, constructor. Exactly like new(), except that this defaults any unsupported encoding to "binary", after raising a suitable warning (it's a fatal error if there's no binary decoder). my $decoder = best MIME::Decoder "x-gzip64"; Will either return a decoder, or a raise a fatal exception. decode INSTREAM,OUTSTREAM Instance method. Decode the document waiting in the input handle INSTREAM, writing the decoded information to the output handle OUTSTREAM. Read the section in this document on I/O handles for more information about the arguments. Note that you can still supply old-style unblessed filehandles for INSTREAM and OUTSTREAM. Returns true on success, throws exception on failure. encode INSTREAM,OUTSTREAM Instance method. Encode the document waiting in the input filehandle INSTREAM, writing the encoded information to the output stream OUTSTREAM. Read the section in this document on I/O handles for more information about the arguments. Note that you can still supply old-style unblessed filehandles for INSTREAM and OUTSTREAM. Returns true on success, throws exception on failure. encoding Instance method. Return the encoding that this object was created to handle, coerced to all lowercase (e.g., "base64"). head [HEAD] Instance method. Completely optional: some decoders need to know a little about the file they are encoding/decoding; e.g., x-uu likes to have the filename. The HEAD is any object which responds to messages like: $head->mime_attr('content-disposition.filename'); supported [ENCODING] Class method. With one arg (an ENCODING name), returns truth if that encoding is currently handled, and falsity otherwise. The ENCODING will be automatically coerced to lowercase: if (supported MIME::Decoder '7BIT') { ### yes, we can handle it... } else { ### drop back six and punt... } With no args, returns a reference to a hash of all available decoders, where the key is the encoding name (all lowercase, like '7bit'), and the value is true (it happens to be the name of the class that handles the decoding, but you probably shouldn't rely on that). You may safely modify this hash; it will not change the way the module performs its lookups. Only "install" can do that. Thanks to Achim Bohnet for suggesting this method. Subclass interface If you are writing (or installing) a new decoder subclass, there are some other methods you'll need to know about: decode_it INSTREAM,OUTSTREAM Abstract instance method. The back-end of the decode method. It takes an input handle opened for reading (INSTREAM), and an output handle opened for writing (OUTSTREAM). If you are writing your own decoder subclass, you must override this method in your class. Your method should read from the input handle via "getline()" or "read()", decode this input, and print the decoded data to the output handle via "print()". You may do this however you see fit, so long as the end result is the same. Note that unblessed references and globrefs are automatically turned into I/O handles for you by "decode()", so you don't need to worry about it. Your method must return either "undef" (to indicate failure), or 1 (to indicate success). It may also throw an exception to indicate failure. encode_it INSTREAM,OUTSTREAM Abstract instance method. The back-end of the encode method. It takes an input handle opened for reading (INSTREAM), and an output handle opened for writing (OUTSTREAM). If you are writing your own decoder subclass, you must override this method in your class. Your method should read from the input handle via "getline()" or "read()", encode this input, and print the encoded data to the output handle via "print()". You may do this however you see fit, so long as the end result is the same. Note that unblessed references and globrefs are automatically turned into I/O handles for you by "encode()", so you don't need to worry about it. Your method must return either "undef" (to indicate failure), or 1 (to indicate success). It may also throw an exception to indicate failure. filter IN, OUT, COMMAND... Class method, utility. If your decoder involves an external program, you can invoke them easily through this method. The command must be a "filter": a command that reads input from its STDIN (which will come from the IN argument) and writes output to its STDOUT (which will go to the OUT argument). For example, here's a decoder that un-gzips its data: sub decode_it { my ($self, $in, $out) = @_; $self->filter($in, $out, "gzip -d -"); } The usage is similar to IPC::Open2::open2 (which it uses internally), so you can specify COMMAND as a single argument or as an array. init ARGS... Instance method. Do any necessary initialization of the new instance, taking whatever arguments were given to "new()". Should return the self object on success, undef on failure. install ENCODINGS... Class method. Install this class so that each encoding in ENCODINGS is handled by it: install MyBase64Decoder 'base64', 'x-base64super'; You should not override this method. uninstall ENCODINGS... Class method. Uninstall support for encodings. This is a way to turn off the decoding of "experimental" encodings. For safety, always use MIME::Decoder directly: uninstall MIME::Decoder 'x-uu', 'x-uuencode'; You should not override this method. DECODER SUBCLASSES
You don't need to "use" any other Perl modules; the following "standard" subclasses are included as part of MIME::Decoder: Class: Handles encodings: ------------------------------------------------------------ MIME::Decoder::Binary binary MIME::Decoder::NBit 7bit, 8bit MIME::Decoder::Base64 base64 MIME::Decoder::QuotedPrint quoted-printable The following "non-standard" subclasses are also included: Class: Handles encodings: ------------------------------------------------------------ MIME::Decoder::UU x-uu, x-uuencode MIME::Decoder::Gzip64 x-gzip64 ** requires gzip! NOTES
Input/Output handles As of MIME-tools 2.0, this class has to play nice with the new MIME::Body class... which means that input and output routines cannot just assume that they are dealing with filehandles. Therefore, all that MIME::Decoder and its subclasses require (and, thus, all that they can assume) is that INSTREAMs and OUTSTREAMs are objects which respond to a subset of the messages defined in the IO::Handle interface; minimally: print getline read(BUF,NBYTES) Thanks to Achim Bohnet for suggesting this more-generic I/O model. Writing a decoder If you're experimenting with your own encodings, you'll probably want to write a decoder. Here are the basics: 1. Create a module, like "MyDecoder::", for your decoder. Declare it to be a subclass of MIME::Decoder. 2. Create the following instance methods in your class, as described above: decode_it encode_it init 3. In your application program, activate your decoder for one or more encodings like this: require MyDecoder; install MyDecoder "7bit"; ### use MyDecoder to decode "7bit" install MyDecoder "x-foo"; ### also use MyDecoder to decode "x-foo" To illustrate, here's a custom decoder class for the "quoted-printable" encoding: package MyQPDecoder; @ISA = qw(MIME::Decoder); use MIME::Decoder; use MIME::QuotedPrint; ### decode_it - the private decoding method sub decode_it { my ($self, $in, $out) = @_; local $_; while (defined($_ = $in->getline)) { my $decoded = decode_qp($_); $out->print($decoded); } 1; } ### encode_it - the private encoding method sub encode_it { my ($self, $in, $out) = @_; my ($buf, $nread) = ('', 0); while ($in->read($buf, 60)) { my $encoded = encode_qp($buf); $out->print($encoded); } 1; } That's it. The task was pretty simple because the "quoted-printable" encoding can easily be converted line-by-line... as can even "7bit" and "8bit" (since all these encodings guarantee short lines, with a max of 1000 characters). The good news is: it is very likely that it will be similarly-easy to write a MIME::Decoder for any future standard encodings. The "binary" decoder, however, really required block reads and writes: see "MIME::Decoder::Binary" for details. SEE ALSO
MIME::Tools, other MIME::Decoder subclasses. AUTHOR
Eryq (eryq@zeegee.com), ZeeGee Software Inc (http://www.zeegee.com). All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. 1; perl v5.18.2 2013-11-14 MIME::Decoder(3)