1SVK::Log::Filter(3) User Contributed Perl Documentation SVK::Log::Filter(3)
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6 SVK::Log::Filter - base class for all log filters
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9 SVK::Log::Filter is a class for displaying or otherwise processing
10 revision properties. The SVK "log" command uses filter classes to
11 handle the details of processing the revision properties. The bulk of
12 this document explains how to write those filter classes.
13 A log filter is just a Perl class with special methods. At specific
15 points while processing log information, SVK calls these methods on the
16 filter object. SVK::Log::Filter provides sensible defaults for each of
17 the methods it calls. The methods (in order of invocation) are
18 "setup", "header", "revision", "footer", "teardown". Each is fully
19 documented in the section "METHOD REFERENCE".
20
22 Although log filters which output and log filters which select are
23 exactly the same kind of objects, they are generally conceptualized
24 separately. The following tutorial provides a simple example for each
25 type of filter.
26 OUTPUT
28 For our simple output filter example, we want to display something like
29 the following
30 1. r3200 by john
32 2. r3194 by tom
33 3. r3193 by larry
34 Namely, the number the revisions we've seen, then show the actual
36 revision number from the repository and indicate the author of that
37 revision. We want this log filter to be accessible by a command like
38 "svk log --output list" The code to accomplish that is
39 1 package SVK::Log::Filter::List;
41 2 use base qw( SVK::Log::Filter );
42 3 sub setup {
44 4 my ($self) = @_;
45 5 $self->{count} = 1;
46 6 }
47 7 sub revision {
49 8 my ($self, $args) = @_;
50 9 printf "%d. r%d by %s\n",
52 10 $self->{count}++,
53 11 $args->{rev},
54 12 $args->{props}{'svn:author'}
55 13 ;
56 14 }
57 First, we must establish the name of this filter. SVK looks for
59 filters with the namespace prefix "SVK::Log::Filter". The final
60 portion of the name can either have the first letter capitalized or all
61 the letters capitalized. On line 2, we use SVK::Log::Filter as the
62 base class so that we can get the default method implementations.
63 On lines 3-6, we get to the first meat. Since we want to count the
65 revisions that we see, we have to store the information somewhere that
66 will persist between method calls. We just store it in the log filter
67 object itself. Finally, on line 6, our "setup" method is finished.
68 The return value of the method is irrelevant.
69 The "revision" method on lines 7-14 does the real work of the filter.
71 First (line 8) we extract arguments into a hashref $args. Then it
72 simply prints what we want it to display. SVK takes care of directing
73 output to the appropriate place. You'll notice that the revision
74 properties are provided as a hash. The key of the hash is the name of
75 the property and the value of the hash is the value of the property.
76 That's it. Put SVK::Log::Filter::List somewhere in @INC and SVK will
78 find it.
79 SELECTION
81 Our simple selection filter example will pass revisions based on
82 whether the revision number is even or odd. The filter accepts a
83 single argument 'odd' or 'even' indicating which revisions should be
84 passed down the pipeline. Additionally, if the filter ever encounters
85 the revision number "42" it will stop the entire pipeline and process
86 no more revisions. The invocation is something like "svk log --filter
87 'parity even'" to display all even revisions up to r42.
88 1 package SVK::Log::Filter::Parity;
90 2 use base qw( SVK::Log::Filter );
91 3 sub setup {
93 4 my ($self) = @_;
94 5 my $argument = lc $self->{argument};
96 6 $self->{bit} = $argument eq 'even' ? 0
97 7 : $argument eq 'odd' ? 1
98 8 : die "Parity argument not 'even' or 'odd'\n"
99 9 ;
100 10 }
101 11 sub revision {
103 12 my ($self, $args) = @_;
104 13 my $rev = $args->{rev};
106 14 $self->pipeline('last') if $rev == 42;
107 15 $self->pipeline('next') if $rev % 2 != $self->{bit};
108 16 }
109 There are only a few differences between this implementation and the
111 output filter implementation. The first difference is in line 5. When
112 a log filter object is created, the default "new" method creates the
113 'argument' key which contains the command-line argument provided to
114 your filter. In this case, the argument should be either 'even' or
115 'odd'. Based on the argument, we update the object to remind us what
116 parity we're looking for.
117 The unique characteristics of "revision" are the calls to the
119 "pipeline" method in lines 14 and 15. If we want to stop the pipeline
120 entirely, call "pipeline" with the argument 'last' (think "this is the
121 last revision"). The current revision and all subsequent revisions
122 will not be processed by the filter pipelin. If the argument to
123 "pipeline" is 'next' (think "go to the next revision"), the current
124 revision will not be displayed and the pipeline will proceed with the
125 next revision in sequence. If you don't call "pipeline", the current
126 revision is passed down the remainder of the pipeline so that it can be
127 processed and displayed.
128
130 This is a list of all the methods that SVK::Log::Filter implements and
131 a description of how they should be called. When defining a subclass,
132 one need only override those methods that are necessary for
133 implementing the filter. All methods have sensible defaults (namely,
134 do nothing). The methods are listed here in the order in which they
135 are called by the pipeline.
136 All methods except "new" and "pipeline" receive a single hash reference
138 as their first argument (after the invocant, of course). The
139 'Receives' section in the documentation below indicates which named
140 arguments are present in that hash.
141 new
143 Builds a new object from a hash reference. The value of any arguments
144 provided to the log filter on the command line are placed in the
145 'argument' attribute of the object. Generally, there is no need to
146 override the "new" method because the "setup" method can be overriden
147 instead.
148 setup
150 Receives: "stash"
151 This method is called once just before the filter is used for the first
153 time. It's conceptually similar to "new", but allows the filter
154 developer to ignore the creation of the filter object. This is the
155 place to do filter initialization, process command-line arguments, read
156 configuration files, connect to a database, etc.
157 header
159 Receives: "stash"
160 This method is called once just before the first revision is processed
162 but after "setup" has completed. This is an ideal place to display
163 information which should appear at the top of the log display.
164 revision
166 Receives: "paths", "rev", "props", "stash", "get_remoterev"
167 This method is called for each revision that SVK wants to process. The
169 bulk of a log filter's code implements this method. Output filters may
170 simply print the information that they want displayed. Other filters
171 should either modify the revision properties (see "props") or use
172 pipeline commands (see "pipeline") to skip irrelevant revisions.
173 footer
175 Receives: "stash"
176 This method is similar to the "header" method, but it's called once
178 after all the revisions have been displayed. This is the place to do
179 any final output.
180 teardown
182 Receives: "stash"
183 This method is called once just before the log filter is discarded.
185 This is the place to disconnect from databases, close file handles,
186 etc.
187 pipeline
189 This method is not called by the filter pipeline. Rather, it's used by
190 log filters to control the pipeline's behavior. It accepts a single
191 scalar as the argument. If the argument is 'next', the pipeline stops
192 processing the current revision (including any output filter) and
193 starts processing the next revision starting over at the beginning of
194 the pipeline. If the argument to "pipeline" is 'last', the pipeline is
195 stopped entirely (including any output filters). Once the pipeline has
196 stopped, the SVK log command finishes any final details and stops.
197
199 This section describes the possible keys and values of the hashref
200 that's provided to method calls.
201
203 If the value of this argument is true, the value is a coderef. When
204 the coderef is invoked with a single revision number as the argument,
205 it returns the number of the equivalent revision in the upstream
206 repository. The value of this key may be undefined if the logs are
207 being processed for something other than a mirror. The following code
208 may be useful when working with "get_remoterev"
209 my ( $stash, $rev, $get_remoterev)
211 = @{$args}{qw( stash rev get_remoterev )};
212 my $remote_rev = $get_remoterev ? $get_remoterev->($rev) : 'unknown';
213 print "The remote revision for r$rev is $remote_rev.\n";
214 paths
216 The value of the 'paths' argument is an SVK::Log::ChangedPaths object.
217 The object provides methods for indicating which paths were changed by
218 this revision and approximately how they were changed (modified file
219 contents, modified file properties, etc.)
220 See the documentation for SVK::Log::ChangedPaths for more details.
222 rev
224 The value of the 'rev' argument is the Subversion revision number for
225 the current revision.
226 props
228 The value of the 'props' argument is a hash reference containing all
229 the revision properties for the current revision. The keys of the hash
230 are the property names and the values of the hash are the property
231 values. For example, the author of a revision is available with
232 "$args->{'svn:author'}".
233 If you change values in the 'props' hashref, those changes are visible
235 to all subsequent filters in the pipeline. This can be useful and
236 dangerous. Dangerous if you accidentally modify a property, useful if
237 you intentionally modify a property. For instance, it's possible to
238 make a "selection" filter which uses Babelfish to translate log
239 messages from one language to another (see SVK::Log::Filter::Babelfish
240 on CPAN). By modifying the 'svn:log' property, other log filters can
241 operate on the translated log message without knowing that it's
242 translated.
243 stash
245 The value of the 'stash' argument is a reference to a hash. The stash
246 persists throughout the entire log filtering process and is provided to
247 every method that the filter pipeline calls. The stash may be used to
248 pass information from one filter to another filter in the pipeline.
249 When creating new keys in the stash, it's important to avoid
251 unintentional name collisions with other filters in the pipeline. A
252 good practice is to preface the name of each stash key with the name of
253 your filter ("myfilter_key") or to create your own hash reference
254 inside the stash ("$stash->{myfilter}{key}"). If your filter puts
255 information into the stash that other filters may want to access,
256 please document the location and format of that information for other
257 filter authors.
258
261 If the user included the "--quiet" flag when invoking "svk log" the
262 value of this key will be a true value. Otherwise, the value will be
263 false.
264
266 If the user included the "--verbose" flag when invoking "svk log" the
267 value of this key will be a true value. Otherwise, the value will be
268 false.
269perl v5.32.0 2020-07-28 SVK::Log::Filter(3)