MIME::Decoder::NBit(3pm) - phpMan

MIME::Decoder::NBit(3pm) User Contributed Perl Documentation MIME::Decoder::NBit(3pm)

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 "\n".
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.