1docs::api::APR::Error(3U)ser Contributed Perl Documentatidooncs::api::APR::Error(3)
2
6 APR::Error - Perl API for APR/Apache/mod_perl exceptions
7
9 eval { $obj->mp_method() };
10 if ($@ && $ref $@ eq 'APR::Error' && $@ == $some_code) {
11 # handle the exception
12 }
13 else {
14 die $@; # rethrow it
15 }
16
18 "APR::Error" handles APR/Apache/mod_perl exceptions for you, while
19 leaving you in control.
20 Apache and APR API return a status code for almost all methods, so if
22 you didn't check the return code and handled any possible problems, you
23 may have silent failures which may cause all kind of obscure problems.
24 On the other hand checking the status code after each call is just too
25 much of a kludge and makes quick prototyping/development almost
26 impossible, not talking about the code readability. Having methods
27 return status codes, also complicates the API if you need to return
28 other values.
29 Therefore to keep things nice and make the API readable we decided to
31 not return status codes, but instead throw exceptions with "APR::Error"
32 objects for each method that fails. If you don't catch those
33 exceptions, everything works transparently - perl will intercept the
34 exception object and "die()" with a proper error message. So you get
35 all the errors logged without doing any work.
36 Now, in certain cases you don't want to just die, but instead the error
38 needs to be trapped and handled. For example if some IO operation times
39 out, may be it is OK to trap that and try again. If we were to die with
40 an error message, you would have had to match the error message, which
41 is ugly, inefficient and may not work at all if locale error strings
42 are involved. Therefore you need to be able to get the original status
43 code that Apache or APR has generated. And the exception objects give
44 you that if you want to. Moreover the objects contain additional
45 information, such as the function name (in case you were eval'ing
46 several commands in one block), file and line number where that
47 function was invoked from. More attributes could be added in the
48 future.
49 "APR::Error" uses Perl operator overloading, such that in boolean and
51 numerical contexts, the object returns the status code; in the string
52 context the full error message is returned.
53 When intercepting exceptions you need to check whether $@ is an object
55 (reference). If your application uses other exception objects you
56 additionally need to check whether this is a an "APR::Error" object.
57 Therefore most of the time this is enough:
58 eval { $obj->mp_method() };
60 if ($@ && $ref $@ && $@ == $some_code)
61 warn "handled exception: $@";
62 }
63 But with other, non-mod_perl, exception objects you need to do:
65 eval { $obj->mp_method() };
67 if ($@ && $ref $@ eq 'APR::Error' && $@ == $some_code)
68 warn "handled exception: $@";
69 }
70 In theory you could even do:
72 eval { $obj->mp_method() };
74 if ($@ && $@ == $some_code)
75 warn "handled exception: $@";
76 }
77 but it's possible that the method will die with a plain string and not
79 an object, in which case "$@ == $some_code" won't quite work. Remember
80 that mod_perl throws exception objects only when Apache and APR fail,
81 and in a few other special cases of its own (like "exit").
82 warn "handled exception: $@" if $@ && $ref $@;
84 There are two ways to figure out whether an error fits your case. In
86 most cases you just compare $@ with an the error constant. For example
87 if a socket has a timeout set and the data wasn't read within the
88 timeout limit a "APR::Const::TIMEUP")
89 use APR::Const -compile => qw(TIMEUP);
91 $sock->timeout_set(1_000_000); # 1 sec
92 my $buff;
93 eval { $sock->recv($buff, BUFF_LEN) };
94 if ($@ && ref $@ && $@ == APR::Const::TIMEUP) {
95 }
97 However there are situations, where on different Operating Systems a
99 different error code will be returned. In which case to simplify the
100 code you should use the special subroutines provided by the
101 "APR::Status" class. One such condition is socket "recv()" timeout,
102 which on Unix throws the "EAGAIN" error, but on other system it throws
103 a different error. In this case "APR::Status::is_EAGAIN" should be
104 used.
105 Let's look at a complete example. Here is a code that performs a socket
107 read:
108 my $rlen = $sock->recv(my $buff, 1024);
110 warn "read $rlen bytes\n";
111 and in certain cases it times out. The code will die and log the reason
113 for the failure, which is fine, but later on you may decide that you
114 want to have another attempt to read before dying and add some fine
115 grained sleep time between attempts, which can be achieved with
116 "select". Which gives us:
117 use APR::Status ();
119 # ....
120 my $tries = 0;
121 my $buffer;
122 RETRY: my $rlen = eval { $sock->recv($buffer, SIZE) };
123 if ($@)
124 die $@ unless ref $@ && APR::Status::is_EAGAIN($@);
125 if ($tries++ < 3) {
126 # sleep 250msec
127 select undef, undef, undef, 0.25;
128 goto RETRY;
129 }
130 else {
131 # do something else
132 }
133 }
134 warn "read $rlen bytes\n"
135 Notice that we handle non-object and non-"APR::Error" exceptions as
137 well, by simply re-throwing them.
138 Finally, the class is called "APR::Error" because it needs to be used
140 outside mod_perl as well, when called from "APR" applications written
141 in Perl.
142
144 "cluck"
145 "cluck" is an equivalent of "Carp::cluck" that works with "APR::Error"
146 exception objects.
147 "confess"
149 "confess" is an equivalent of "Carp::confess" that works with
150 "APR::Error" exception objects.
151 "strerror"
153 Convert APR error code to its string representation.
154 $error_str = APR::Error::strerror($rc);
156 ret: $rc ( "APR::Const status constant" )
158 The numerical value for the return (error) code
159 ret: $error_str ( string )
161 The string error message corresponding to the numerical value
162 inside $rc. (Similar to the C function strerror(3))
163 since: 2.0.00
165 Example:
167 Try to retrieve the bucket brigade, and if the return value doesn't
169 indicate success or end of file (usually in protocol handlers) die, but
170 give the user the human-readable version of the error and not just the
171 code.
172 my $rc = $c->input_filters->get_brigade($bb_in,
174 Apache2::Const::MODE_GETLINE);
175 if ($rc != APR::Const::SUCCESS && $rc != APR::Const::EOF) {
176 my $error = APR::Error::strerror($rc);
177 die "get_brigade error: $rc: $error\n";
178 }
179 It's probably a good idea not to omit the numerical value in the error
181 message, in case the error string is generated with non-English locale.
182
184 mod_perl 2.0 documentation.
185
187 mod_perl 2.0 and its core modules are copyrighted under The Apache
188 Software License, Version 2.0.
189
191 The mod_perl development team and numerous contributors.
192perl v5.28.0 2016-10-27 docs::api::APR::Error(3)