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Manual Reference Pages  -  MAIL::SPF::SERVER (3)

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NAME

Mail::SPF::Server - Server class for processing SPF requests

CONTENTS

SYNOPSIS



    use Mail::SPF;

    my $spf_server  = Mail::SPF::Server->new(
        # Optional custom default for authority explanation:
        default_authority_explanation =>
            See http://www.%{d}/why/id=%{S};ip=%{I};r=%{R}
    );

    my $result      = $spf_server->process($request);



DESCRIPTION

<B>Mail::SPF::ServerB> is a server class for processing SPF requests. Each server instance can be configured with specific processing parameters. Also, the default Net::DNS::Resolver DNS resolver used for making DNS look-ups can be overridden with a custom resolver object.

    Constructor

The following constructor is provided:
<B>new(%options)B>: returns Mail::SPF::Server Creates a new server object for processing SPF requests.

%options is a list of key/value pairs representing any of the following options:
<B>default_authority_explanationB> A string denoting the default (not macro-expanded) authority explanation string to use if the authority domain does not specify an explanation string of its own. Defaults to:



    Please see http://www.openspf.org/Why?s=%{_scope};id=%{S};ip=%{C};r=%{R}



As can be seen from the default, a non-standard _scope pseudo macro is supported that expands to the name of the identity’s scope. (Note: Do not use any non-standard macros in explanation strings published in DNS.)

<B>hostnameB> A string denoting the local system’s fully qualified host name that should be used for expanding the r macro in explanation strings. Defaults to the system’s configured host name.
<B>dns_resolverB> An optional DNS resolver object. If none is specified, a new Net::DNS::Resolver object is used. The resolver object may be of a different class, but it must provide an interface similar to Net::DNS::Resolver — at least the send and errorstring methods must be supported, and the send method must return either an object of class Net::DNS::Packet, or, in the case of an error, <B>undefB>.
<B>query_rr_typesB> For which RR types to query when looking up and selecting SPF records. The following values are supported:
<B>Mail::SPF::Server->query_rr_type_allB> Both TXT and SPF type RRs.
<B>Mail::SPF::Server->query_rr_type_txtB> (default) TXT type RRs only.
<B>Mail::SPF::Server->query_rr_type_spfB> SPF type RRs only.

For years <B>Mail::SPFB> has defaulted to looking up both SPF and TXT type RRs as recommended by RFC 4408. Experience has shown, however, that a significant portion of name servers suffer from serious brain damage with regard to the handling of queries for RR types that are unknown to them, such as the SPF RR type. Consequently <B>Mail::SPFB> now defaults to looking up only TXT type RRs. This may be overridden by setting the <B>query_rr_typesB> option.

See RFC 4408, 3.1.1, for a discussion of the topic, as well as the description of the select_record method.

<B>max_dns_interactive_termsB> An integer denoting the maximum number of terms (mechanisms and modifiers) per SPF check that perform DNS look-ups, as defined in RFC 4408, 10.1, paragraph 6. If <B>undefB> is specified, there is no limit on the number of such terms. Defaults to <B>10B>, which is the value defined in RFC 4408.

A value above the default is strongly discouraged for security reasons. A value below the default has implications with regard to the predictability of SPF results. Only deviate from the default if you know what you are doing!

<B>max_name_lookups_per_termB> An integer denoting the maximum number of DNS name look-ups per term (mechanism or modifier), as defined in RFC 4408, 10.1, paragraph 7. If <B>undefB> is specified, there is no limit on the number of look-ups performed. Defaults to <B>10B>, which is the value defined in RFC 4408.

A value above the default is strongly discouraged for security reasons. A value below the default has implications with regard to the predictability of SPF results. Only deviate from the default if you know what you are doing!

<B>max_name_lookups_per_mx_mechB>
<B>max_name_lookups_per_ptr_mechB> An integer denoting the maximum number of DNS name look-ups per <B>mxB> or <B>ptrB> mechanism, respectively. Defaults to the value of the max_name_lookups_per_term option. See there for additional information and security notes.
<B>max_void_dns_lookupsB> An integer denoting the maximum number of void DNS look-ups per SPF check, i.e. the number of DNS look-ups that were caused by DNS-interactive terms and macros (as defined in RFC 4408, 10.1, paragraphs 6 and 7) and that are allowed to return an empty answer with RCODE 0 or RCODE 3 (NXDOMAIN) before processing is aborted with a permerror result. If <B>undefB> is specified, there is no stricter limit on the number of void DNS look-ups beyond the usual processing limits. Defaults to <B>2B>.

Specifically, the DNS look-ups that are subject to this limit are those caused by the a, mx, ptr, and exists mechanisms and the p macro.

A value of <B>2B> is likely to prevent effective DoS attacks against third-party victim domains. However, a definite limit may cause permerror results even with certain (overly complex) innocent sender policies where useful results would normally be returned.

    Class methods

The following class methods are provided:
<B>result_classB>: returns class
<B>result_class($name)B>: returns class Returns a Mail::SPF::Result descendent class determined from the given result name via the server’s inherent result base class, or returns the server’s inherent result base class if no result name is given. This method may also be used as an instance method.

Note: Do not write code invoking class methods on literal result class names as this would ignore any derivative result classes provided by <B>Mail::SPFB> extension modules.

<B>throw_result($name, B>$request<B>)B>: throws Mail::SPF::Result
<B>throw_result($name, B>$request<B>, B>$text<B>)B>: throws Mail::SPF::Result Throws a Mail::SPF::Result descendant determined from the given result name via the server’s inherent result base class, passing an optional result text and associating the given Mail::SPF::Request object with the result object. This method may also be used as an instance method.

Note: Do not write code invoking throw on literal result class names as this would ignore any derivative result classes provided by <B>Mail::SPFB> extension modules.

    Instance methods

The following instance methods are provided:
<B>process($request)B>: returns Mail::SPF::Result Processes the given Mail::SPF::Request object, queries the authoritative domain for an SPF sender policy (see the description of the select_record method), evaluates the policy with regard to the given identity and other request parameters, and returns a Mail::SPF::Result object denoting the result of the policy evaluation. See RFC 4408, 4, and RFC 4406, 4, for details.
<B>select_record($request)B>: returns Mail::SPF::Record; throws Mail::SPF::EDNSError, Mail::SPF::ENoAcceptableRecord, Mail::SPF::ERedundantAcceptableRecords, Mail::SPF::ESyntaxError Queries the authority domain of the given Mail::SPF::Request object for SPF sender policy records and, if multiple records are available, selects the record of the highest acceptable record version that covers the requested scope.

More precisely, the following algorithm is performed (assuming that both TXT and SPF RR types are being queried):
1. Determine the authority domain, the set of acceptable SPF record versions, and the identity scope from the given request object.
2. Query the authority domain for SPF records of the SPF DNS RR type, discarding any records that are of an inacceptable version or do not cover the desired scope.

If this yields no SPF records, query the authority domain for SPF records of the TXT DNS RR type, discarding any records that are of an inacceptable version or do not cover the desired scope.

If still no acceptable SPF records could be found, throw a Mail::SPF::ENoAcceptableRecord exception.

3. Discard all records but those of the highest acceptable version found.

If exactly one record remains, return it. Otherwise, throw a Mail::SPF::ERedundantAcceptableRecords exception.

If the querying of either RR type has been disabled via the new constructor’s query_rr_types option, the respective part in step 2 will be skipped.

Mail::SPF::EDNSError exceptions due to DNS look-ups and Mail::SPF::ESyntaxError exceptions due to invalid acceptable records may also be thrown.

<B>get_acceptable_records_from_packet($packet, B>$rr_type<B>, \@versions, B>$scope<B>, B>$domain<B>)B>: returns list of Mail::SPF::Record Filters from the given Net::DNS::Packet object all resource records of the given RR type and for the given domain name, discarding any records that are not SPF records at all, that are of an inacceptable SPF record version, or that do not cover the given scope. Returns a list of acceptable records.
<B>dns_lookup($domain, B>$rr_type<B>)B>: returns Net::DNS::Packet; throws Mail::SPF::EDNSTimeout, Mail::SPF::EDNSError Queries the DNS using the configured resolver for resource records of the desired type at the specified domain and returns a Net::DNS::Packet object if an answer packet was received. Throws a Mail::SPF::EDNSTimeout exception if a DNS time-out occurred. Throws a Mail::SPF::EDNSError exception if an error (other than RCODE 3 AKA NXDOMAIN) occurred.
<B>count_dns_interactive_term($request)B>: throws Mail::SPF::EProcessingLimitExceeded Increments by one the count of DNS-interactive mechanisms and modifiers that have been processed so far during the evaluation of the given Mail::SPF::Request object. If this exceeds the configured limit (see the new constructor’s max_dns_interactive_terms option), throws a Mail::SPF::EProcessingLimitExceeded exception.

This method is supposed to be called by the match and process methods of Mail::SPF::Mech and Mail::SPF::Mod sub-classes before (and only if) they do any DNS look-ups.

<B>count_void_dns_lookup($request)B>: throws Mail::SPF::EProcessingLimitExceeded Increments by one the count of void DNS look-ups that have occurred so far during the evaluation of the given Mail::SPF::Request object. If this exceeds the configured limit (see the new constructor’s max_void_dns_lookups option), throws a Mail::SPF::EProcessingLimitExceeded exception.

This method is supposed to be called by any code after any calls to the dns_lookup method whenever (i) no answer records were returned, and (ii) this fact is a possible indication of a DoS attack against a third-party victim domain, and (iii) the number of void look-ups is not already constrained otherwise (as for example is the case with the include mechanism and the redirect modifier). Specifically, this applies to look-ups performed by the a, mx, ptr, and exists mechanisms and the p macro.

<B>default_authority_explanationB>: returns Mail::SPF::MacroString Returns the default authority explanation as a MacroString object. See the description of the new constructor’s default_authority_explanation option.
<B>hostnameB>: returns string Returns the local system’s host name. See the description of the new constructor’s hostname option.
<B>dns_resolverB>: returns Net::DNS::Resolver or compatible object Returns the DNS resolver object of the server object. See the description of the new constructor’s dns_resolver option.
<B>query_rr_typesB>: returns integer Returns a value denoting the RR types for which to query when looking up and selecting SPF records. See the description of the new constructor’s query_rr_types option.
<B>max_dns_interactive_termsB>: returns integer
<B>max_name_lookups_per_termB>: returns integer
<B>max_name_lookups_per_mx_mechB>: returns integer
<B>max_name_lookups_per_ptr_mechB>: returns integer
<B>max_void_dns_lookupsB>: returns integer Return the limit values of the server object. See the description of the new constructor’s corresponding options.

SEE ALSO

Mail::SPF, Mail::SPF::Request, Mail::SPF::Result

<http://tools.ietf.org/html/rfc4408>

For availability, support, and license information, see the README file included with Mail::SPF.

AUTHORS

Julian Mehnle <julian@mehnle.net>, Shevek <cpan@anarres.org>
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