oracular (3) Perlbal::Manual::Hooks.3pm.gz
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.