MIME::Head(3pm) User Contributed Perl Documentation MIME::Head(3pm)
NAME
MIME::Head - MIME message header (a subclass of Mail::Header)
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...
Construction
### Create a new, empty header, and populate it manually:
$head = MIME::Head->new;
$head->replace('content-type', 'text/plain; charset=US-ASCII');
$head->replace('content-length', $len);
### Parse a new header from a filehandle:
$head = MIME::Head->read(\*STDIN);
### Parse a new header from a file, or a readable pipe:
$testhead = MIME::Head->from_file("/tmp/test.hdr");
$a_b_head = MIME::Head->from_file("cat a.hdr b.hdr |");
Output
### Output to filehandle:
$head->print(\*STDOUT);
### Output as string:
print STDOUT $head->as_string;
print STDOUT $head->stringify;
Getting field contents
### Is this a reply?
$is_reply = 1 if ($head->get('Subject') =~ /^Re: /);
### Get receipt information:
print "Last received from: ", $head->get('Received', 0);
@all_received = $head->get('Received');
### Print the subject, or the empty string if none:
print "Subject: ", $head->get('Subject',0);
### Too many hops? Count 'em and see!
if ($head->count('Received') > 5) { ...
### Test whether a given field exists
warn "missing subject!" if (! $head->count('subject'));
Setting field contents
### Declare this to be an HTML header:
$head->replace('Content-type', 'text/html');
Manipulating field contents
### Get rid of internal newlines in fields:
$head->unfold;
### Decode any Q- or B-encoded-text in fields (DEPRECATED):
$head->decode;
Getting high-level MIME information
### Get/set a given MIME attribute:
unless ($charset = $head->mime_attr('content-type.charset')) {
$head->mime_attr("content-type.charset" => "US-ASCII");
}
### The content type (e.g., "text/html"):
$mime_type = $head->mime_type;
### The content transfer encoding (e.g., "quoted-printable"):
$mime_encoding = $head->mime_encoding;
### The recommended name when extracted:
$file_name = $head->recommended_filename;
### The boundary text, for multipart messages:
$boundary = $head->multipart_boundary;
DESCRIPTION
A class for parsing in and manipulating RFC-822 message headers, with
some methods geared towards standard (and not so standard) MIME fields
as specified in the various Multipurpose Internet Mail Extensions RFCs
(starting with RFC 2045)
PUBLIC INTERFACE
Creation, input, and output
new [ARG],[OPTIONS]
Class method, inherited. Creates a new header object. Arguments
are the same as those in the superclass.
from_file EXPR,OPTIONS
Class or instance method. For convenience, you can use this to
parse a header object in from EXPR, which may actually be any
expression that can be sent to open() so as to return a readable
filehandle. The "file" will be opened, read, and then closed:
### Create a new header by parsing in a file:
my $head = MIME::Head->from_file("/tmp/test.hdr");
Since this method can function as either a class constructor or an
instance initializer, the above is exactly equivalent to:
### Create a new header by parsing in a file:
my $head = MIME::Head->new->from_file("/tmp/test.hdr");
On success, the object will be returned; on failure, the undefined
value.
The OPTIONS are the same as in new(), and are passed into new() if
this is invoked as a class method.
Note: This is really just a convenience front-end onto "read()",
provided mostly for backwards-compatibility with MIME-parser 1.0.
read FILEHANDLE
Instance (or class) method. This initializes a header object by
reading it in from a FILEHANDLE, until the terminating blank line
is encountered. A syntax error or end-of-stream will also halt
processing.
Supply this routine with a reference to a filehandle glob; e.g.,
"\*STDIN":
### Create a new header by parsing in STDIN:
$head->read(\*STDIN);
On success, the self object will be returned; on failure, a false
value.
Note: in the MIME world, it is perfectly legal for a header to be
empty, consisting of nothing but the terminating blank line. Thus,
we can't just use the formula that "no tags equals error".
Warning: as of the time of this writing, Mail::Header::read did not
flag either syntax errors or unexpected end-of-file conditions (an
EOF before the terminating blank line). MIME::ParserBase takes
this into account.
Getting/setting fields
The following are methods related to retrieving and modifying the
header fields. Some are inherited from Mail::Header, but I've kept the
documentation around for convenience.
add TAG,TEXT,[INDEX]
Instance method, inherited. Add a new occurrence of the field
named TAG, given by TEXT:
### Add the trace information:
$head->add('Received',
'from eryq.pr.mcs.net by gonzo.net with smtp');
Normally, the new occurrence will be appended to the existing
occurrences. However, if the optional INDEX argument is 0, then
the new occurrence will be prepended. If you want to be explicit
about appending, specify an INDEX of -1.
Warning: this method always adds new occurrences; it doesn't
overwrite any existing occurrences... so if you just want to change
the value of a field (creating it if necessary), then you probably
don't want to use this method: consider using "replace()" instead.
count TAG
Instance method, inherited. Returns the number of occurrences of a
field; in a boolean context, this tells you whether a given field
exists:
### Was a "Subject:" field given?
$subject_was_given = $head->count('subject');
The TAG is treated in a case-insensitive manner. This method
returns some false value if the field doesn't exist, and some true
value if it does.
decode [FORCE]
Instance method, DEPRECATED. Go through all the header fields,
looking for RFC 1522 / RFC 2047 style "Q" (quoted-printable, sort
of) or "B" (base64) encoding, and decode them in-place. Fellow
Americans, you probably don't know what the hell I'm talking about.
Europeans, Russians, et al, you probably do. ":-)".
This method has been deprecated. See "decode_headers" in
MIME::Parser for the full reasons. If you absolutely must use it
and don't like the warning, then provide a FORCE:
"I_NEED_TO_FIX_THIS"
Just shut up and do it. Not recommended.
Provided only for those who need to keep old scripts functioning.
"I_KNOW_WHAT_I_AM_DOING"
Just shut up and do it. Not recommended.
Provided for those who REALLY know what they are doing.
What this method does. For an example, let's consider a valid
email header you might get:
From: =?US-ASCII?Q?Keith_Moore?= <moore@cs.utk.edu>
To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= <keld@dkuug.dk>
CC: =?ISO-8859-1?Q?Andr=E9_?= Pirard <PIRARD@vm1.ulg.ac.be>
Subject: =?ISO-8859-1?B?SWYgeW91IGNhbiByZWFkIHRoaXMgeW8=?=
=?ISO-8859-2?B?dSB1bmRlcnN0YW5kIHRoZSBleGFtcGxlLg==?=
=?US-ASCII?Q?.._cool!?=
That basically decodes to (sorry, I can only approximate the Latin
characters with 7 bit sequences /o and 'e):
From: Keith Moore <moore@cs.utk.edu>
To: Keld J/orn Simonsen <keld@dkuug.dk>
CC: Andr'e Pirard <PIRARD@vm1.ulg.ac.be>
Subject: If you can read this you understand the example... cool!
Note: currently, the decodings are done without regard to the
character set: thus, the Q-encoding "=F8" is simply translated to
the octet (hexadecimal "F8"), period. For piece-by-piece decoding
of a given field, you want the array context of
"MIME::Words::decode_mimewords()".
Warning: the CRLF+SPACE separator that splits up long encoded words
into shorter sequences (see the Subject: example above) gets lost
when the field is unfolded, and so decoding after unfolding causes
a spurious space to be left in the field. THEREFORE: if you're
going to decode, do so BEFORE unfolding!
This method returns the self object.
Thanks to Kent Boortz for providing the idea, and the baseline
RFC-1522-decoding code.
delete TAG,[INDEX]
Instance method, inherited. Delete all occurrences of the field
named TAG.
### Remove some MIME information:
$head->delete('MIME-Version');
$head->delete('Content-type');
get TAG,[INDEX]
Instance method, inherited. Get the contents of field TAG.
If a numeric INDEX is given, returns the occurrence at that index,
or undef if not present:
### Print the first and last 'Received:' entries (explicitly):
print "First, or most recent: ", $head->get('received', 0);
print "Last, or least recent: ", $head->get('received',-1);
If no INDEX is given, but invoked in a scalar context, then INDEX
simply defaults to 0:
### Get the first 'Received:' entry (implicitly):
my $most_recent = $head->get('received');
If no INDEX is given, and invoked in an array context, then all
occurrences of the field are returned:
### Get all 'Received:' entries:
my @all_received = $head->get('received');
NOTE: The header(s) returned may end with a newline. If you don't
want this, then chomp the return value.
get_all FIELD
Instance method. Returns the list of all occurrences of the field,
or the empty list if the field is not present:
### How did it get here?
@history = $head->get_all('Received');
Note: I had originally experimented with having "get()" return all
occurrences when invoked in an array context... but that causes a
lot of accidents when you get careless and do stuff like this:
print "\u$field: ", $head->get($field);
It also made the intuitive behaviour unclear if the INDEX argument
was given in an array context. So I opted for an explicit approach
to asking for all occurrences.
print [OUTSTREAM]
Instance method, override. Print the header out to the given
OUTSTREAM, or the currently-selected filehandle if none. The
OUTSTREAM may be a filehandle, or any object that responds to a
print() message.
The override actually lets you print to any object that responds to
a print() method. This is vital for outputting MIME entities to
scalars.
Also, it defaults to the currently-selected filehandle if none is
given (not STDOUT!), so please supply a filehandle to prevent
confusion.
stringify
Instance method. Return the header as a string. You can also
invoke it as "as_string".
If you set the variable $MIME::Entity::BOUNDARY_DELIMITER to a
string, that string will be used as line-end delimiter. If it is
not set, the line ending will be a newline character (\n)
unfold [FIELD]
Instance method, inherited. Unfold (remove newlines in) the text
of all occurrences of the given FIELD. If the FIELD is omitted,
all fields are unfolded. Returns the "self" object.
MIME-specific methods
All of the following methods extract information from the following
fields:
Content-type
Content-transfer-encoding
Content-disposition
Be aware that they do not just return the raw contents of those fields,
and in some cases they will fill in sensible (I hope) default values.
Use "get()" or "mime_attr()" if you need to grab and process the raw
field text.
Note: some of these methods are provided both as a convenience and for
backwards-compatibility only, while others (like
recommended_filename()) really do have to be in MIME::Head to work
properly, since they look for their value in more than one field.
However, if you know that a value is restricted to a single field, you
should really use the Mail::Field interface to get it.
mime_attr ATTR,[VALUE]
A quick-and-easy interface to set/get the attributes in structured
MIME fields:
$head->mime_attr("content-type" => "text/html");
$head->mime_attr("content-type.charset" => "US-ASCII");
$head->mime_attr("content-type.name" => "homepage.html");
This would cause the final output to look something like this:
Content-type: text/html; charset=US-ASCII; name="homepage.html"
Note that the special empty sub-field tag indicates the anonymous
first sub-field.
Giving VALUE as undefined will cause the contents of the named
subfield to be deleted:
$head->mime_attr("content-type.charset" => undef);
Supplying no VALUE argument just returns the attribute's value, or
undefined if it isn't there:
$type = $head->mime_attr("content-type"); ### text/html
$name = $head->mime_attr("content-type.name"); ### homepage.html
In all cases, the new/current value is returned.
mime_encoding
Instance method. Try real hard to determine the content transfer
encoding (e.g., "base64", "binary"), which is returned in all-
lowercase.
If no encoding could be found, the default of "7bit" is returned I
quote from RFC 2045 section 6.1:
This is the default value -- that is, "Content-Transfer-Encoding: 7BIT"
is assumed if the Content-Transfer-Encoding header field is not present.
I do one other form of fixup: "7_bit", "7-bit", and "7 bit" are
corrected to "7bit"; likewise for "8bit".
mime_type [DEFAULT]
Instance method. Try "real hard" to determine the content type
(e.g., "text/plain", "image/gif", "x-weird-type", which is returned
in all-lowercase. "Real hard" means that if no content type could
be found, the default (usually "text/plain") is returned. From RFC
2045 section 5.2:
Default RFC 822 messages without a MIME Content-Type header are
taken by this protocol to be plain text in the US-ASCII character
set, which can be explicitly specified as:
Content-type: text/plain; charset=us-ascii
This default is assumed if no Content-Type header field is specified.
Unless this is a part of a "multipart/digest", in which case
"message/rfc822" is the default. Note that you can also set the
default, but you shouldn't: normally only the MIME parser uses this
feature.
multipart_boundary
Instance method. If this is a header for a multipart message,
return the "encapsulation boundary" used to separate the parts.
The boundary is returned exactly as given in the "Content-type:"
field; that is, the leading double-hyphen ("--") is not prepended.
Well, almost exactly... this passage from RFC 2046 dictates that we
remove any trailing spaces:
If a boundary appears to end with white space, the white space
must be presumed to have been added by a gateway, and must be deleted.
Returns undef (not the empty string) if either the message is not
multipart or if there is no specified boundary.
recommended_filename
Instance method. Return the recommended external filename. This
is used when extracting the data from the MIME stream. The
filename is always returned as a string in Perl's internal format
(the UTF8 flag may be on!)
Returns undef if no filename could be suggested.
NOTES
Why have separate objects for the entity, head, and body?
See the documentation for the MIME-tools distribution for the
rationale behind this decision.
Why assume that MIME headers are email headers?
I quote from Achim Bohnet, who gave feedback on v.1.9 (I think he's
using the word "header" where I would use "field"; e.g., to refer
to "Subject:", "Content-type:", etc.):
There is also IMHO no requirement [for] MIME::Heads to look
like [email] headers; so to speak, the MIME::Head [simply stores]
the attributes of a complex object, e.g.:
new MIME::Head type => "text/plain",
charset => ...,
disposition => ..., ... ;
I agree in principle, but (alas and dammit) RFC 2045 says
otherwise. RFC 2045 [MIME] headers are a syntactic subset of
RFC-822 [email] headers.
In my mind's eye, I see an abstract class, call it MIME::Attrs,
which does what Achim suggests... so you could say:
my $attrs = new MIME::Attrs type => "text/plain",
charset => ...,
disposition => ..., ... ;
We could even make it a superclass of MIME::Head: that way,
MIME::Head would have to implement its interface, and allow itself
to be initialized from a MIME::Attrs object.
However, when you read RFC 2045, you begin to see how much MIME
information is organized by its presence in particular fields. I
imagine that we'd begin to mirror the structure of RFC 2045 fields
and subfields to such a degree that this might not give us a
tremendous gain over just having MIME::Head.
Why all this "occurrence" and "index" jazz? Isn't every field unique?
Aaaaaaaaaahh....no.
Looking at a typical mail message header, it is sooooooo tempting
to just store the fields as a hash of strings, one string per hash
entry. Unfortunately, there's the little matter of the "Received:"
field, which (unlike "From:", "To:", etc.) will often have multiple
occurrences; e.g.:
Received: from gsfc.nasa.gov by eryq.pr.mcs.net with smtp
(Linux Smail3.1.28.1 #5) id m0tStZ7-0007X4C;
Thu, 21 Dec 95 16:34 CST
Received: from rhine.gsfc.nasa.gov by gsfc.nasa.gov
(5.65/Ultrix3.0-C) id AA13596;
Thu, 21 Dec 95 17:20:38 -0500
Received: (from eryq@localhost) by rhine.gsfc.nasa.gov
(8.6.12/8.6.12) id RAA28069;
Thu, 21 Dec 1995 17:27:54 -0500
Date: Thu, 21 Dec 1995 17:27:54 -0500
From: Eryq <eryq@rhine.gsfc.nasa.gov>
Message-Id: <199512212227.RAA28069@rhine.gsfc.nasa.gov>
To: eryq@eryq.pr.mcs.net
Subject: Stuff and things
The "Received:" field is used for tracing message routes, and
although it's not generally used for anything other than human
debugging, I didn't want to inconvenience anyone who actually
wanted to get at that information.
I also didn't want to make this a special case; after all, who
knows what other fields could have multiple occurrences in the
future? So, clearly, multiple entries had to somehow be stored
multiple times... and the different occurrences had to be
retrievable.
SEE ALSO
Mail::Header, Mail::Field, MIME::Words, MIME::Tools
AUTHOR
Eryq (eryq@zeegee.com), ZeeGee Software Inc (http://www.zeegee.com).
Dianne Skoll (dianne@skoll.ca)
All rights reserved. This program is free software; you can
redistribute it and/or modify it under the same terms as Perl itself.
The more-comprehensive filename extraction is courtesy of Lee E.
Brotzman, Advanced Data Solutions.
perl v5.34.0 2022-07-10 MIME::Head(3pm)
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