1 | package HTTP::Negotiate;
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2 |
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3 | $VERSION = "5.835";
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4 | sub Version { $VERSION; }
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5 |
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6 | require 5.002;
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7 | require Exporter;
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8 | @ISA = qw(Exporter);
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9 | @EXPORT = qw(choose);
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10 |
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11 | require HTTP::Headers;
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12 |
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13 | $DEBUG = 0;
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14 |
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15 | sub choose ($;$)
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16 | {
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17 | my($variants, $request) = @_;
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18 | my(%accept);
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19 |
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20 | unless (defined $request) {
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21 | # Create a request object from the CGI environment variables
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22 | $request = HTTP::Headers->new;
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23 | $request->header('Accept', $ENV{HTTP_ACCEPT})
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24 | if $ENV{HTTP_ACCEPT};
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25 | $request->header('Accept-Charset', $ENV{HTTP_ACCEPT_CHARSET})
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26 | if $ENV{HTTP_ACCEPT_CHARSET};
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27 | $request->header('Accept-Encoding', $ENV{HTTP_ACCEPT_ENCODING})
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28 | if $ENV{HTTP_ACCEPT_ENCODING};
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29 | $request->header('Accept-Language', $ENV{HTTP_ACCEPT_LANGUAGE})
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30 | if $ENV{HTTP_ACCEPT_LANGUAGE};
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31 | }
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32 |
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33 | # Get all Accept values from the request. Build a hash initialized
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34 | # like this:
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35 | #
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36 | # %accept = ( type => { 'audio/*' => { q => 0.2, mbx => 20000 },
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37 | # 'audio/basic' => { q => 1 },
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38 | # },
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39 | # language => { 'no' => { q => 1 },
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40 | # }
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41 | # );
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42 |
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43 | $request->scan(sub {
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44 | my($key, $val) = @_;
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45 |
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46 | my $type;
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47 | if ($key =~ s/^Accept-//) {
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48 | $type = lc($key);
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49 | }
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50 | elsif ($key eq "Accept") {
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51 | $type = "type";
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52 | }
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53 | else {
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54 | return;
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55 | }
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56 |
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57 | $val =~ s/\s+//g;
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58 | my $default_q = 1;
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59 | for my $name (split(/,/, $val)) {
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60 | my(%param, $param);
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61 | if ($name =~ s/;(.*)//) {
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62 | for $param (split(/;/, $1)) {
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63 | my ($pk, $pv) = split(/=/, $param, 2);
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64 | $param{lc $pk} = $pv;
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65 | }
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66 | }
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67 | $name = lc $name;
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68 | if (defined $param{'q'}) {
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69 | $param{'q'} = 1 if $param{'q'} > 1;
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70 | $param{'q'} = 0 if $param{'q'} < 0;
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71 | }
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72 | else {
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73 | $param{'q'} = $default_q;
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74 |
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75 | # This makes sure that the first ones are slightly better off
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76 | # and therefore more likely to be chosen.
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77 | $default_q -= 0.0001;
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78 | }
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79 | $accept{$type}{$name} = \%param;
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80 | }
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81 | });
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82 |
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83 | # Check if any of the variants specify a language. We do this
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84 | # because it influences how we treat those without (they default to
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85 | # 0.5 instead of 1).
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86 | my $any_lang = 0;
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87 | for $var (@$variants) {
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88 | if ($var->[5]) {
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89 | $any_lang = 1;
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90 | last;
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91 | }
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92 | }
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93 |
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94 | if ($DEBUG) {
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95 | print "Negotiation parameters in the request\n";
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96 | for $type (keys %accept) {
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97 | print " $type:\n";
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98 | for $name (keys %{$accept{$type}}) {
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99 | print " $name\n";
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100 | for $pv (keys %{$accept{$type}{$name}}) {
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101 | print " $pv = $accept{$type}{$name}{$pv}\n";
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102 | }
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103 | }
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104 | }
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105 | }
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106 |
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107 | my @Q = (); # This is where we collect the results of the
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108 | # quality calculations
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109 |
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110 | # Calculate quality for all the variants that are available.
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111 | for (@$variants) {
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112 | my($id, $qs, $ct, $enc, $cs, $lang, $bs) = @$_;
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113 | $qs = 1 unless defined $qs;
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114 | $ct = '' unless defined $ct;
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115 | $bs = 0 unless defined $bs;
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116 | $lang = lc($lang) if $lang; # lg tags are always case-insensitive
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117 | if ($DEBUG) {
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118 | print "\nEvaluating $id (ct='$ct')\n";
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119 | printf " qs = %.3f\n", $qs;
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120 | print " enc = $enc\n" if $enc && !ref($enc);
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121 | print " enc = @$enc\n" if $enc && ref($enc);
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122 | print " cs = $cs\n" if $cs;
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123 | print " lang = $lang\n" if $lang;
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124 | print " bs = $bs\n" if $bs;
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125 | }
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126 |
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127 | # Calculate encoding quality
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128 | my $qe = 1;
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129 | # If the variant has no assigned Content-Encoding, or if no
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130 | # Accept-Encoding field is present, then the value assigned
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131 | # is "qe=1". If *all* of the variant's content encodings
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132 | # are listed in the Accept-Encoding field, then the value
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133 | # assigned is "qw=1". If *any* of the variant's content
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134 | # encodings are not listed in the provided Accept-Encoding
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135 | # field, then the value assigned is "qe=0"
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136 | if (exists $accept{'encoding'} && $enc) {
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137 | my @enc = ref($enc) ? @$enc : ($enc);
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138 | for (@enc) {
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139 | print "Is encoding $_ accepted? " if $DEBUG;
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140 | unless(exists $accept{'encoding'}{$_}) {
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141 | print "no\n" if $DEBUG;
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142 | $qe = 0;
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143 | last;
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144 | }
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145 | else {
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146 | print "yes\n" if $DEBUG;
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147 | }
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148 | }
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149 | }
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150 |
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151 | # Calculate charset quality
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152 | my $qc = 1;
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153 | # If the variant's media-type has no charset parameter,
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154 | # or the variant's charset is US-ASCII, or if no Accept-Charset
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155 | # field is present, then the value assigned is "qc=1". If the
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156 | # variant's charset is listed in the Accept-Charset field,
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157 | # then the value assigned is "qc=1. Otherwise, if the variant's
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158 | # charset is not listed in the provided Accept-Encoding field,
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159 | # then the value assigned is "qc=0".
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160 | if (exists $accept{'charset'} && $cs && $cs ne 'us-ascii' ) {
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161 | $qc = 0 unless $accept{'charset'}{$cs};
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162 | }
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163 |
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164 | # Calculate language quality
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165 | my $ql = 1;
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166 | if ($lang && exists $accept{'language'}) {
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167 | my @lang = ref($lang) ? @$lang : ($lang);
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168 | # If any of the variant's content languages are listed
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169 | # in the Accept-Language field, the the value assigned is
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170 | # the largest of the "q" parameter values for those language
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171 | # tags.
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172 | my $q = undef;
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173 | for (@lang) {
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174 | next unless exists $accept{'language'}{$_};
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175 | my $this_q = $accept{'language'}{$_}{'q'};
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176 | $q = $this_q unless defined $q;
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177 | $q = $this_q if $this_q > $q;
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178 | }
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179 | if(defined $q) {
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180 | $DEBUG and print " -- Exact language match at q=$q\n";
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181 | }
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182 | else {
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183 | # If there was no exact match and at least one of
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184 | # the Accept-Language field values is a complete
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185 | # subtag prefix of the content language tag(s), then
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186 | # the "q" parameter value of the largest matching
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187 | # prefix is used.
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188 | $DEBUG and print " -- No exact language match\n";
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189 | my $selected = undef;
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190 | for $al (keys %{ $accept{'language'} }) {
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191 | if (index($al, "$lang-") == 0) {
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192 | # $lang starting with $al isn't enough, or else
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193 | # Accept-Language: hu (Hungarian) would seem
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194 | # to accept a document in hup (Hupa)
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195 | $DEBUG and print " -- $al ISA $lang\n";
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196 | $selected = $al unless defined $selected;
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197 | $selected = $al if length($al) > length($selected);
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198 | }
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199 | else {
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200 | $DEBUG and print " -- $lang isn't a $al\n";
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201 | }
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202 | }
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203 | $q = $accept{'language'}{$selected}{'q'} if $selected;
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204 |
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205 | # If none of the variant's content language tags or
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206 | # tag prefixes are listed in the provided
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207 | # Accept-Language field, then the value assigned
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208 | # is "ql=0.001"
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209 | $q = 0.001 unless defined $q;
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210 | }
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211 | $ql = $q;
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212 | }
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213 | else {
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214 | $ql = 0.5 if $any_lang && exists $accept{'language'};
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215 | }
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216 |
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217 | my $q = 1;
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218 | my $mbx = undef;
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219 | # If no Accept field is given, then the value assigned is "q=1".
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220 | # If at least one listed media range matches the variant's media
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221 | # type, then the "q" parameter value assigned to the most specific
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222 | # of those matched is used (e.g. "text/html;version=3.0" is more
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223 | # specific than "text/html", which is more specific than "text/*",
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224 | # which in turn is more specific than "*/*"). If not media range
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225 | # in the provided Accept field matches the variant's media type,
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226 | # then the value assigned is "q=0".
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227 | if (exists $accept{'type'} && $ct) {
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228 | # First we clean up our content-type
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229 | $ct =~ s/\s+//g;
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230 | my $params = "";
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231 | $params = $1 if $ct =~ s/;(.*)//;
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232 | my($type, $subtype) = split("/", $ct, 2);
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233 | my %param = ();
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234 | for $param (split(/;/, $params)) {
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235 | my($pk,$pv) = split(/=/, $param, 2);
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236 | $param{$pk} = $pv;
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237 | }
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238 |
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239 | my $sel_q = undef;
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240 | my $sel_mbx = undef;
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241 | my $sel_specificness = 0;
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242 |
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243 | ACCEPT_TYPE:
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244 | for $at (keys %{ $accept{'type'} }) {
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245 | print "Consider $at...\n" if $DEBUG;
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246 | my($at_type, $at_subtype) = split("/", $at, 2);
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247 | # Is it a match on the type
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248 | next if $at_type ne '*' && $at_type ne $type;
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249 | next if $at_subtype ne '*' && $at_subtype ne $subtype;
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250 | my $specificness = 0;
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251 | $specificness++ if $at_type ne '*';
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252 | $specificness++ if $at_subtype ne '*';
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253 | # Let's see if content-type parameters also match
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254 | while (($pk, $pv) = each %param) {
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255 | print "Check if $pk = $pv is true\n" if $DEBUG;
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256 | next unless exists $accept{'type'}{$at}{$pk};
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257 | next ACCEPT_TYPE
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258 | unless $accept{'type'}{$at}{$pk} eq $pv;
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259 | print "yes it is!!\n" if $DEBUG;
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260 | $specificness++;
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261 | }
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262 | print "Hurray, type match with specificness = $specificness\n"
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263 | if $DEBUG;
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264 |
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265 | if (!defined($sel_q) || $sel_specificness < $specificness) {
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266 | $sel_q = $accept{'type'}{$at}{'q'};
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267 | $sel_mbx = $accept{'type'}{$at}{'mbx'};
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268 | $sel_specificness = $specificness;
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269 | }
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270 | }
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271 | $q = $sel_q || 0;
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272 | $mbx = $sel_mbx;
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273 | }
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274 |
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275 | my $Q;
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276 | if (!defined($mbx) || $mbx >= $bs) {
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277 | $Q = $qs * $qe * $qc * $ql * $q;
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278 | }
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279 | else {
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280 | $Q = 0;
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281 | print "Variant's size is too large ==> Q=0\n" if $DEBUG;
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282 | }
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283 |
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284 | if ($DEBUG) {
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285 | $mbx = "undef" unless defined $mbx;
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286 | printf "Q=%.4f", $Q;
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287 | print " (q=$q, mbx=$mbx, qe=$qe, qc=$qc, ql=$ql, qs=$qs)\n";
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288 | }
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289 |
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290 | push(@Q, [$id, $Q, $bs]);
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291 | }
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292 |
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293 |
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294 | @Q = sort { $b->[1] <=> $a->[1] || $a->[2] <=> $b->[2] } @Q;
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295 |
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296 | return @Q if wantarray;
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297 | return undef unless @Q;
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298 | return undef if $Q[0][1] == 0;
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299 | $Q[0][0];
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300 | }
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301 |
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302 | 1;
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303 |
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304 | __END__
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305 |
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306 |
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307 | =head1 NAME
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308 |
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309 | HTTP::Negotiate - choose a variant to serve
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310 |
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311 | =head1 SYNOPSIS
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312 |
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313 | use HTTP::Negotiate qw(choose);
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314 |
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315 | # ID QS Content-Type Encoding Char-Set Lang Size
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316 | $variants =
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317 | [['var1', 1.000, 'text/html', undef, 'iso-8859-1', 'en', 3000],
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318 | ['var2', 0.950, 'text/plain', 'gzip', 'us-ascii', 'no', 400],
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319 | ['var3', 0.3, 'image/gif', undef, undef, undef, 43555],
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320 | ];
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321 |
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322 | @preferred = choose($variants, $request_headers);
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323 | $the_one = choose($variants);
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324 |
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325 | =head1 DESCRIPTION
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326 |
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327 | This module provides a complete implementation of the HTTP content
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328 | negotiation algorithm specified in F<draft-ietf-http-v11-spec-00.ps>
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329 | chapter 12. Content negotiation allows for the selection of a
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330 | preferred content representation based upon attributes of the
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331 | negotiable variants and the value of the various Accept* header fields
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332 | in the request.
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333 |
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334 | The variants are ordered by preference by calling the function
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335 | choose().
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336 |
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337 | The first parameter is reference to an array of the variants to
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338 | choose among.
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339 | Each element in this array is an array with the values [$id, $qs,
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340 | $content_type, $content_encoding, $charset, $content_language,
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341 | $content_length] whose meanings are described
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342 | below. The $content_encoding and $content_language can be either a
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343 | single scalar value or an array reference if there are several values.
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344 |
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345 | The second optional parameter is either a HTTP::Headers or a HTTP::Request
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346 | object which is searched for "Accept*" headers. If this
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347 | parameter is missing, then the accept specification is initialized
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348 | from the CGI environment variables HTTP_ACCEPT, HTTP_ACCEPT_CHARSET,
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349 | HTTP_ACCEPT_ENCODING and HTTP_ACCEPT_LANGUAGE.
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350 |
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351 | In an array context, choose() returns a list of [variant
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352 | identifier, calculated quality, size] tuples. The values are sorted by
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353 | quality, highest quality first. If the calculated quality is the same
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354 | for two variants, then they are sorted by size (smallest first). I<E.g.>:
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355 |
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356 | (['var1', 1, 2000], ['var2', 0.3, 512], ['var3', 0.3, 1024]);
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357 |
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358 | Note that also zero quality variants are included in the return list
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359 | even if these should never be served to the client.
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360 |
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361 | In a scalar context, it returns the identifier of the variant with the
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362 | highest score or C<undef> if none have non-zero quality.
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363 |
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364 | If the $HTTP::Negotiate::DEBUG variable is set to TRUE, then a lot of
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365 | noise is generated on STDOUT during evaluation of choose().
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366 |
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367 | =head1 VARIANTS
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368 |
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369 | A variant is described by a list of the following values. If the
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370 | attribute does not make sense or is unknown for a variant, then use
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371 | C<undef> instead.
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372 |
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373 | =over 3
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374 |
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375 | =item identifier
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376 |
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377 | This is a string that you use as the name for the variant. This
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378 | identifier for the preferred variants returned by choose().
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379 |
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380 | =item qs
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381 |
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382 | This is a number between 0.000 and 1.000 that describes the "source
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383 | quality". This is what F<draft-ietf-http-v11-spec-00.ps> says about this
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384 | value:
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385 |
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386 | Source quality is measured by the content provider as representing the
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387 | amount of degradation from the original source. For example, a
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388 | picture in JPEG form would have a lower qs when translated to the XBM
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389 | format, and much lower qs when translated to an ASCII-art
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390 | representation. Note, however, that this is a function of the source
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391 | - an original piece of ASCII-art may degrade in quality if it is
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392 | captured in JPEG form. The qs values should be assigned to each
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393 | variant by the content provider; if no qs value has been assigned, the
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394 | default is generally "qs=1".
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395 |
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396 | =item content-type
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397 |
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398 | This is the media type of the variant. The media type does not
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399 | include a charset attribute, but might contain other parameters.
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400 | Examples are:
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401 |
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402 | text/html
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403 | text/html;version=2.0
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404 | text/plain
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405 | image/gif
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406 | image/jpg
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407 |
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408 | =item content-encoding
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409 |
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410 | This is one or more content encodings that has been applied to the
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411 | variant. The content encoding is generally used as a modifier to the
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412 | content media type. The most common content encodings are:
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413 |
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414 | gzip
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415 | compress
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416 |
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417 | =item content-charset
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418 |
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419 | This is the character set used when the variant contains text.
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420 | The charset value should generally be C<undef> or one of these:
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421 |
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422 | us-ascii
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423 | iso-8859-1 ... iso-8859-9
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424 | iso-2022-jp
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425 | iso-2022-jp-2
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426 | iso-2022-kr
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427 | unicode-1-1
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428 | unicode-1-1-utf-7
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429 | unicode-1-1-utf-8
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430 |
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431 | =item content-language
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432 |
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433 | This describes one or more languages that are used in the variant.
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434 | Language is described like this in F<draft-ietf-http-v11-spec-00.ps>: A
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435 | language is in this context a natural language spoken, written, or
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436 | otherwise conveyed by human beings for communication of information to
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437 | other human beings. Computer languages are explicitly excluded.
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438 |
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439 | The language tags are defined by RFC 3066. Examples
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440 | are:
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441 |
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442 | no Norwegian
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443 | en International English
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444 | en-US US English
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445 | en-cockney
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446 |
|
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447 | =item content-length
|
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448 |
|
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449 | This is the number of bytes used to represent the content.
|
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450 |
|
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451 | =back
|
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452 |
|
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453 | =head1 ACCEPT HEADERS
|
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454 |
|
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455 | The following Accept* headers can be used for describing content
|
---|
456 | preferences in a request (This description is an edited extract from
|
---|
457 | F<draft-ietf-http-v11-spec-00.ps>):
|
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458 |
|
---|
459 | =over 3
|
---|
460 |
|
---|
461 | =item Accept
|
---|
462 |
|
---|
463 | This header can be used to indicate a list of media ranges which are
|
---|
464 | acceptable as a response to the request. The "*" character is used to
|
---|
465 | group media types into ranges, with "*/*" indicating all media types
|
---|
466 | and "type/*" indicating all subtypes of that type.
|
---|
467 |
|
---|
468 | The parameter q is used to indicate the quality factor, which
|
---|
469 | represents the user's preference for that range of media types. The
|
---|
470 | parameter mbx gives the maximum acceptable size of the response
|
---|
471 | content. The default values are: q=1 and mbx=infinity. If no Accept
|
---|
472 | header is present, then the client accepts all media types with q=1.
|
---|
473 |
|
---|
474 | For example:
|
---|
475 |
|
---|
476 | Accept: audio/*;q=0.2;mbx=200000, audio/basic
|
---|
477 |
|
---|
478 | would mean: "I prefer audio/basic (of any size), but send me any audio
|
---|
479 | type if it is the best available after an 80% mark-down in quality and
|
---|
480 | its size is less than 200000 bytes"
|
---|
481 |
|
---|
482 |
|
---|
483 | =item Accept-Charset
|
---|
484 |
|
---|
485 | Used to indicate what character sets are acceptable for the response.
|
---|
486 | The "us-ascii" character set is assumed to be acceptable for all user
|
---|
487 | agents. If no Accept-Charset field is given, the default is that any
|
---|
488 | charset is acceptable. Example:
|
---|
489 |
|
---|
490 | Accept-Charset: iso-8859-1, unicode-1-1
|
---|
491 |
|
---|
492 |
|
---|
493 | =item Accept-Encoding
|
---|
494 |
|
---|
495 | Restricts the Content-Encoding values which are acceptable in the
|
---|
496 | response. If no Accept-Encoding field is present, the server may
|
---|
497 | assume that the client will accept any content encoding. An empty
|
---|
498 | Accept-Encoding means that no content encoding is acceptable. Example:
|
---|
499 |
|
---|
500 | Accept-Encoding: compress, gzip
|
---|
501 |
|
---|
502 |
|
---|
503 | =item Accept-Language
|
---|
504 |
|
---|
505 | This field is similar to Accept, but restricts the set of natural
|
---|
506 | languages that are preferred in a response. Each language may be
|
---|
507 | given an associated quality value which represents an estimate of the
|
---|
508 | user's comprehension of that language. For example:
|
---|
509 |
|
---|
510 | Accept-Language: no, en-gb;q=0.8, de;q=0.55
|
---|
511 |
|
---|
512 | would mean: "I prefer Norwegian, but will accept British English (with
|
---|
513 | 80% comprehension) or German (with 55% comprehension).
|
---|
514 |
|
---|
515 | =back
|
---|
516 |
|
---|
517 |
|
---|
518 | =head1 COPYRIGHT
|
---|
519 |
|
---|
520 | Copyright 1996,2001 Gisle Aas.
|
---|
521 |
|
---|
522 | This library is free software; you can redistribute it and/or
|
---|
523 | modify it under the same terms as Perl itself.
|
---|
524 |
|
---|
525 | =head1 AUTHOR
|
---|
526 |
|
---|
527 | Gisle Aas <[email protected]>
|
---|
528 |
|
---|
529 | =cut
|
---|