doc/help/spec-browsing.html

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  13   CUPS Browse Protocol specification for the Common UNIX Printing System (CUPS).
  14
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  16   Copyright 1997-2005 by Easy Software Products.
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  24
  25 <H1 CLASS="title">CUPS Browse Protocol</H1>
  26
  27 <h2><a name='INTRO'>Introduction</a></h2>
  28
  29 <p>This specification describes the CUPS browsing protocol which is used for
  30 printer sharing. The protocol is a UDP/IP-based broadcast service that
  31 operates on IP service port 631 by default. Each broadcast packet describes
  32 a single printer or class being shared.</p>
  33
  34 <p>For simple networks with a single subnet, a CUPS system sharing a printer
  35 (the <em>server</em>) will periodically broadcast that printer's availability
  36 and status information to the subnet. Every other CUPS system on the subnet
  37 (the <em>clients</em>) will receive the broadcast and make that printer
  38 available to local users. If a client stops receiving broadcasts from the
  39 server, or if the server sends a special "deleted" broadcast message, the
  40 client will remove its copy of the printer.</p>
  41
  42 <p>For larger networks with multiple subnets, a relay configuration can be used
  43 where one or more client systems poll the server and then broadcast the
  44 availability and status information for the server's shared printers to the
  45 clients' local subnets.</p>
  46
  47 <p>A key feature of CUPS printer sharing is support for <em>implicit
  48 classes</em>, which are automatically-created classes for printers that are
  49 shared by multiple servers. These implicit classes provide automatic load
  50 balancing and fail-safe printing functionality transparently to the user.</p>
  51
  52
  53 <h2><a name='SECURITY'>Security Considerations</a></h2>
  54
  55 <p>Like most discovery protocols, CUPS browse packets are not encrypted or
  56 signed, so it is possible for malicious systems on a network to advertise
  57 or remove printers on that network to cause denial of service or information
  58 disclosure. In order to combat this, CUPS logs incoming browse packets and
  59 provides access controls to limit browse packet reception to known hosts.</p>
  60
  61
  62 <h2><a name='FORMAT'>Browse Packet Format</a></h2>
  63
  64 <p>Each broadcast packet is an ASCII text string of up to 1450 bytes ending
  65 with a line feed (0x0a). The general format is:</p>
  66
  67 <p class='summary'>
  68 printer-type printer-state printer-uri "printer-location" "printer-info"
  69 "printer-make-and-model" name=value name2=value2 ...
  70 </p>
  71
  72 <p>Each of the fields contains the value of the corresponding IPP attribute.
  73 The trailing "name=value" information is used to convey default job template
  74 attribute values (job-sheets-default, media-default, etc.), authentication
  75 requirements (auth-info-required), and additional IPP URI options that are
  76 requested by the server (ipp-options).</p>
  77
  78 <h3>ABNF Definition</h3>
  79
  80 <p>The following ABNF definition [RFC4234, RFC3986] defines the format of each
  81 browse packet:</p>
  82
  83 <pre class='command'>
  84 PACKET         = TYPE WSP STATE WSP URI WSP LOCATION WSP INFO WSP
  85                  MAKE-AND-MODEL WSP *[ WSP ATTR-NAME "=" ATTR-VALUE ] LF
  86
  87 TYPE           = 1*HEXDIG
  88
  89 STATE          = "3" / "4" / "5"
  90
  91 URI            = "ipp://" ( 1*NAMECHAR / IP-literal / IPv4address )
  92                  [ ":" 1*DIGIT ] ( "/printers/" / "/classes/" ) 1*NAMECHAR
  93 NAMECHAR       = %x21.22.24.26-2E.30-7E / %x25 HEXDIG HEXDIG
  94 IP-literal     = See RFC 3986
  95 IPv4address    = See RFC 3986
  96
  97 LOCATION       = QUOTED-STRING
  98 INFO           = QUOTED-STRING
  99 MAKE-AND-MODEL = QUOTED-STRING
 100
 101 ATTR-NAME      = 1*( ALPHA / DIGIT / "-" / "." )
 102 ATTR-VALUE     = QUOTED-STRING / 1*UNQUOTE-CHAR
 103
 104 QUOTED-STRING  = DQUOTE *QUOTED-CHAR DQUOTE
 105 QUOTED-CHAR    = %x20.21.23-5B.5D-7E / UTF8-CHAR / %x5C %x5C / %x5C %x22
 106 UNQUOTE-CHAR   = %x21.23-26.28-5B.5D-7E / UTF8-CHAR
 107 UTF8-CHAR      = %xC0.DF %x80.BF / %xE0.EF %x80.BF %x80.BF /
 108                  %xF0.F7 %x80.BF %x80.BF %x80.BF
 109 </pre>
 110
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