NAME¶
Perlbal::Manual::Hooks - How Perlbal's hooks work
VERSION¶
Perlbal 1.78.
DESCRIPTION¶
Basically, a hook is a bit of code that is run at certain stages in the requests
that Perlbal handles.There are all kinds of hooks available and they all do
different things. Some are only applicable to some of the roles and others are
applicable only to certain classes. Each hook is described in detail below,
but first a description of the basics of a hook.
In general, you define a hook by calling the "register_hook" method on
a Perlbal::Service object. You specify what hook you are interested in and
provide a reference to a subroutine that will be called with the parameters
particular to that hook.
There are three types of hooks:
Global hooks¶
These are hooks that are defined on a global scale. They are set like so:
Perlbal::register_global_hook('foo', sub { return 0; });
That would define a global hook named foo that would return 0 when it's called.
(Return codes from hooks will be explained below)
Global hooks are useful to define management commands. See
"manage_command" under Perlbal::Manual::Plugins for more
information.
Service handler hooks¶
A handler hook is attached to a particular service. These hooks are called one
at a time until one hook returns 1. At that point, no further hooks are
called. For example:
$service->register_hook('bar', sub {
# do something
return 1;
});
When this hook runs, it would return 1, signalling to Perlbal that it had done
what it needed to do and that Perlbal shouldn't call any further hooks. You
can use this type of hook to create sets of plugins that all handle different
types of requests, and when one hook had handled a request it wouldn't
continue telling other hooks about the request.
backend_client_assigned
Happens right after a backend is assigned to a client, but before we've talked
to the backend and asked it to do something. If you return a true value, the
process is stopped and you will manually have to send the client's request to
the backend, etc.
Called in Perlbal::BackendHTTP.
Available in role "reverse_proxy".
backend_readable_verify
When the backend is about to start sending the response.
Called in Perlbal::BackendHTTP.
Available in all roles.
backend_response_received
Called as soon as response headers are read from the backend. If you return a
true value, will stop all handling at that point.
Called in Perlbal::BackendHTTP.
Available in all roles.
backend_write_verify
When the backend is ready to receive the request.
Called in Perlbal::BackendHTTP.
Available in all roles.
concat_get_poststat_file_missing
Called when a missing file was requested in a request for multiple files
concatenated, right before sending the 404 response. Return a true value to
overtake the connection.
Called in Perlbal::ClientHTTPBase.
Available in role "web_server".
See also "concat_get_poststat_pre_send",
"static_get_poststat_file_missing" and
"static_get_poststat_pre_send".
concat_get_poststat_pre_send
Called when the resulting file of a request for multiple files concatenated is
about to be sent, right before the 200 response code is added as a header.
Return a true value to overtake the connection.
Called in Perlbal::ClientHTTPBase.
Available in role "web_server".
See also "concat_get_poststat_file_missing",
"static_get_poststat_file_missing" and
"static_get_poststat_pre_send".
handle_put
Called when handling a PUT request.
Called in Perlbal::ClientHTTP.
Available in role "web_server".
make_high_priority
Called when a request is received and right before we're about to determine if
this request is high priority or not. Return a true value to make the request
high priority; false to leave it alone. Note that this is only called when the
request isn't already high priority due to cookie priority scheduling, which
is done inside Perlbal::Service.
Called in Perlbal::ClientProxy.
Available in all roles.
make_low_priority
Called when a request is received and right before we're about to determine if
this request is high priority or not. Return a true value to make the request
low priority; false to leave it alone.
Called in Perlbal::ClientProxy.
Available in all roles.
modify_response_headers
Called when we've set all the headers, and are about to serve a file. You can
change or add response headers at this point, or cancel the process by
returning a true value. You will have to send the response to the client
yourself if you do this.
Called in Perlbal::ClientHTTPBase.
Available in role "web_server".
proxy_read_request
Called on the request before we send the request to a backend.
Called in Perlbal::ClientProxy.
Available in all roles.
put_writeout
Called when there is some put data to write out.
Called in Perlbal::ClientHTTP.
Available in role "web_server".
reproxy_fh_finished
Called when a reproxy file has completed and is about to close the file handle.
You can cancel the process by returning a true value (in which case you will
have to close the reproxy_fh yourself).
Called in Perlbal::ClientHTTPBase.
Available in role "web_server".
reproxy_response_received
Called as soon as response headers are read from a reproxied backend. If you
return a true value, will stop all handling at that point.
Called in Perlbal::ClientProxy.
Available in role "reverse_proxy".
return_to_base
Called when a request has been finished, and control of the Client* object is
about to be transferred back to ownership by a service selector. Return a true
value if the perlbal core action in this situation should be bypassed.
Called in Perlbal::ClientHTTPBase.
Available in all roles.
start_file_reproxy
Called when we've been told to reproxy a file. If you return a true value,
Perlbal will not perform any operations on the file and will simply return.
You can also change the file in the scalar ref passed as the second parameter.
Called in Perlbal::ClientProxy; receives $filename_ref, a reference to the
filename.
Available in role "reverse_proxy".
start_http_request
A generic hook that works for both webserver and proxy modes, run after either
the specific "start_proxy_request" or "start_web_request"
hooks below. Like those, you return true from this hook to takeover the
connection.
Called in Perlbal::ClientProxy and Perlbal::ClientHTTP.
Available in roles "reverse_proxy" and "web_server".
start_proxy_request
Called as soon as we've read in headers from a user but right before we've
requested a backend connection. If a true value is returned, Perlbal will not
request a backend.
Called in Perlbal::ClientProxy.
Available in role "reverse_proxy".
start_send_file
Called when we've opened a file and are about to start sending it to the user
using sendfile. Return a true value to cancel the default sending.
Called in Perlbal::ClientHTTPBase.
Available in role "web_server".
start_serve_request
Called when we're about to serve a local file, before we've done any work. You
can change the file served by modifying $uri_ref, or cancel the process by
returning a true value.
Called in Perlbal::ClientHTTPBase; receives $uri_ref, a reference to the URI.
Available in role "web_server".
start_web_request
When a service has gotten headers and is about to serve it. Return a true value
to cancel the default handling of web requests.
Called in Perlbal::ClientHTTP.
Available in role "web_server".
static_get_poststat_file_missing
Called when a missing static single file was requested, right before sending the
404 response. Return a true value to overtake the connection.
Called in Perlbal::ClientHTTPBase.
Available in role "web_server".
See also "concat_get_poststat_file_missing",
"concat_get_poststat_pre_send" and
"static_get_poststat_pre_send".
static_get_poststat_pre_send
Called when a static single file is about to be sent, right before the 200
response code is added as a header. Return a true value to overtake the
connection.
Called in Perlbal::ClientHTTPBase.
Available in role "web_server".
See also "concat_get_poststat_file_missing",
"concat_get_poststat_pre_send" and
"static_get_poststat_file_missing".
Service general hooks¶
These hooks are defined the same way as above, but general hooks are all run.
The return code is ignored. This can be useful for putting in code that
records statistics about an action or something to that effect.
end_proxy_request
This hook is called when the Perlbal::ClientProxy object is being closed.
Available in role "reverse_proxy".
SEE ALSO¶
Perlbal::Manual::Internals, Perlbal::Manual::Plugins.