Learning steps to develop a Droonga plugin by yourself.
This page focuses on the “adaption” by Droonga plugins.
At the last, we create a new command storeSearch based on the existing search command, with a small practical plugin.
First, let’s study basics with a simple logger plugin named sample-logger affects at the adaption phase.
We sometime need to modify incoming requests from outside to Droonga Engine. We can use a plugin for this purpose.
Let’s see how to create a plugin for the pre adaption phase, in this section.
Assume that we are going to add a new plugin to the system built in the basic tutorial.
In that tutorial, Droonga engine was placed under engine directory.
Plugins need to be placed in an appropriate directory. Let’s create the directory:
# cd engine
# mkdir -p lib/droonga/plugins
After creating the directory, the directory structure should be like this:
engine
├── catalog.json
├── fluentd.conf
└── lib
└── droonga
└── plugins
You must put codes for a plugin into a file which has the name same to the plugin itself.
Because the plugin now you creating is sample-logger, put codes into a file sample-logger.rb in the droonga/plugins directory.
lib/droonga/plugins/sample-logger.rb:
require "droonga/plugin"
module Droonga
module Plugins
module SampleLoggerPlugin
extend Plugin
register("sample-logger")
class Adapter < Droonga::Adapter
# You'll put codes to modify messages here.
end
end
end
end
This plugin does nothing except registering itself to the Droonga Engine.
sample-logger is the name of the plugin itself. You’ll use it in your catalog.json, to activate the plugin.Droonga::Adapter, under the namespace of the plugin module.catalog.jsonYou need to update catalog.json to activate your plugin.
Insert the name of the plugin "sample-logger" to the "plugins" list under the dataset, like:
catalog.json:
(snip)
"datasets": {
"Default": {
(snip)
"plugins": ["sample-logger", "groonga", "crud", "search", "dump", "status"],
(snip)
Note: you must place "sample-logger" before "search", because the sample-logger plugin depends on the search. Droonga Engine applies plugins at the pre adaption phase in the order defined in the catalog.json, so you must resolve plugin dependencies by your hand (for now).
Let’s get Droonga started.
Note that you need to specify ./lib directory in RUBYLIB environment variable in order to make ruby possible to find your plugin.
# kill $(cat fluentd.pid)
# RUBYLIB=./lib fluentd --config fluentd.conf --log fluentd.log --daemon fluentd.pid
Then, verify that the engine is correctly working. First, create a request as a JSON.
search-columbus.json:
{
"dataset" : "Default",
"type" : "search",
"body" : {
"queries" : {
"stores" : {
"source" : "Store",
"condition" : {
"query" : "Columbus",
"matchTo" : "_key"
},
"output" : {
"elements" : [
"startTime",
"elapsedTime",
"count",
"attributes",
"records"
],
"attributes" : ["_key"],
"limit" : -1
}
}
}
}
}
This is corresponding to the example to search “Columbus” in the basic tutorial.
Note that the request for the Protocol Adapter is encapsulated in "body" element.
Send the request to engine with droonga-request:
# droonga-request --tag starbucks search-columbus.json
Elapsed time: 0.021544
[
"droonga.message",
1392617533,
{
"inReplyTo": "1392617533.9644868",
"statusCode": 200,
"type": "search.result",
"body": {
"stores": {
"count": 2,
"records": [
[
"Columbus @ 67th - New York NY (W)"
],
[
"2 Columbus Ave. - New York NY (W)"
]
]
}
}
}
]
This is the search result.
The plugin we have created do nothing so far. Let’s get the plugin to do some interesting.
First of all, trap search request and log it. Update the plugin like below:
lib/droonga/plugins/sample-logger.rb:
(snip)
module SampleLoggerPlugin
extend Plugin
register("sample-logger")
class Adapter < Droonga::Adapter
input_message.pattern = ["type", :equal, "search"]
def adapt_input(input_message)
logger.info("SampleLoggerPlugin::Adapter", :message => input_message)
end
end
end
(snip)
The line beginning with input_message.pattern is a configuration.
This example defines a plugin for any incoming message with "type":"search".
See the reference manual’s configuration section
The method adapt_input is called for every incoming message matching to the pattern.
The argument input_message is a wrapped version of the incoming message.
Restart fluentd:
# kill $(cat fluentd.pid)
# RUBYLIB=./lib fluentd --config fluentd.conf --log fluentd.log --daemon fluentd.pid
Send the request same as the previous section:
# droonga-request --tag starbucks search-columbus.json
Elapsed time: 0.014714
[
"droonga.message",
1392618037,
{
"inReplyTo": "1392618037.935901",
"statusCode": 200,
"type": "search.result",
"body": {
"stores": {
"count": 2,
"records": [
[
"Columbus @ 67th - New York NY (W)"
],
[
"2 Columbus Ave. - New York NY (W)"
]
]
}
}
}
]
You will see something like below fluentd’s log in fluentd.log:
2014-02-17 15:20:37 +0900 [info]: SampleLoggerPlugin::Adapter message=#<Droonga::InputMessage:0x007f8ae3e1dd98 @raw_message={"dataset"=>"Default", "type"=>"search", "body"=>{"queries"=>{"stores"=>{"source"=>"Store", "condition"=>{"query"=>"Columbus", "matchTo"=>"_key"}, "output"=>{"elements"=>["startTime", "elapsedTime", "count", "attributes", "records"], "attributes"=>["_key"], "limit"=>-1}}}}, "replyTo"=>{"type"=>"search.result", "to"=>"127.0.0.1:64591/droonga"}, "id"=>"1392618037.935901", "date"=>"2014-02-17 15:20:37 +0900", "appliedAdapters"=>[]}>
This shows the message is received by our SampleLoggerPlugin::Adapter and then passed to Droonga. Here we can modify the message before the actual data processing.
Suppose that we want to restrict the number of records returned in the response, say 1.
What we need to do is set limit to be 1 for every request.
Update plugin like below:
lib/droonga/plugins/sample-logger.rb:
(snip)
def adapt_input(input_message)
logger.info("SampleLoggerPlugin::Adapter", :message => input_message)
input_message.body["queries"]["stores"]["output"]["limit"] = 1
end
(snip)
Like above, you can modify the incoming message via methods of the argument input_message.
See the reference manual for the message class.
Restart fluentd:
# kill $(cat fluentd.pid)
# RUBYLIB=./lib fluentd --config fluentd.conf --log fluentd.log --daemon fluentd.pid
After restart, the response always includes only one record in records section.
Send the request same as the previous:
# droonga-request --tag starbucks search-columbus.json
Elapsed time: 0.017343
[
"droonga.message",
1392618279,
{
"inReplyTo": "1392618279.0578449",
"statusCode": 200,
"type": "search.result",
"body": {
"stores": {
"count": 2,
"records": [
[
"Columbus @ 67th - New York NY (W)"
]
]
}
}
}
]
Note that count is still 2 because limit does not affect to count. See search for details of the search command.
You will see something like below fluentd’s log in fluentd.log:
2014-02-17 15:24:39 +0900 [info]: SampleLoggerPlugin::Adapter message=#<Droonga::InputMessage:0x007f956685c908 @raw_message={"dataset"=>"Default", "type"=>"search", "body"=>{"queries"=>{"stores"=>{"source"=>"Store", "condition"=>{"query"=>"Columbus", "matchTo"=>"_key"}, "output"=>{"elements"=>["startTime", "elapsedTime", "count", "attributes", "records"], "attributes"=>["_key"], "limit"=>-1}}}}, "replyTo"=>{"type"=>"search.result", "to"=>"127.0.0.1:64616/droonga"}, "id"=>"1392618279.0578449", "date"=>"2014-02-17 15:24:39 +0900", "appliedAdapters"=>[]}>
In case we need to modify outgoing messages from Droonga Engine, for example, search results, then we can do it simply by another method. In this section, we are going to define a method to adapt outgoing messages.
Let’s take logs of results of search command.
Define the adapt_output method to process outgoing messages.
Remove adapt_input at this moment for the simplicity.
lib/droonga/plugins/sample-logger.rb:
(snip)
module SampleLoggerPlugin
extend Plugin
register("sample-logger")
class Adapter < Droonga::Adapter
input_message.pattern = ["type", :equal, "search"]
def adapt_output(output_message)
logger.info("SampleLoggerPlugin::Adapter", :message => output_message)
end
end
end
(snip)
The method adapt_output is called only for outgoing messages triggered by incoming messages trapped by the plugin itself, even if there is only the matching pattern and the adapt_input method is not defined.
See the reference manual for plugin developers for more details.
Let’s restart fluentd:
# kill $(cat fluentd.pid)
# RUBYLIB=./lib fluentd --config fluentd.conf --log fluentd.log --daemon fluentd.pid
And send search request (Use the same JSON for request as in the previous section):
# droonga-request --tag starbucks search-columbus.json
Elapsed time: 0.015491
[
"droonga.message",
1392619269,
{
"inReplyTo": "1392619269.184789",
"statusCode": 200,
"type": "search.result",
"body": {
"stores": {
"count": 2,
"records": [
[
"Columbus @ 67th - New York NY (W)"
],
[
"2 Columbus Ave. - New York NY (W)"
]
]
}
}
}
]
The fluentd’s log should be like as follows:
2014-02-17 15:41:09 +0900 [info]: SampleLoggerPlugin::Adapter message=#<Droonga::OutputMessage:0x007fddcad4d5a0 @raw_message={"dataset"=>"Default", "type"=>"dispatcher", "body"=>{"stores"=>{"count"=>2, "records"=>[["Columbus @ 67th - New York NY (W)"], ["2 Columbus Ave. - New York NY (W)"]]}}, "replyTo"=>{"type"=>"search.result", "to"=>"127.0.0.1:64724/droonga"}, "id"=>"1392619269.184789", "date"=>"2014-02-17 15:41:09 +0900", "appliedAdapters"=>["Droonga::Plugins::SampleLoggerPlugin::Adapter", "Droonga::Plugins::Error::Adapter"]}>
This shows that the result of search is passed to the adapt_output method (and logged), then outputted.
Let’s modify the result at the post adaption phase.
For example, add completedAt attribute that shows the time completed the request.
Update your plugin as follows:
lib/droonga/plugins/sample-logger.rb:
(snip)
def adapt_output(output_message)
logger.info("SampleLoggerPlugin::Adapter", :message => output_message)
output_message.body["stores"]["completedAt"] = Time.now
end
(snip)
Like above, you can modify the outgoing message via methods of the argument output_message.
See the reference manual for the message class.
Restart fluentd:
# kill $(cat fluentd.pid)
# RUBYLIB=./lib fluentd --config fluentd.conf --log fluentd.log --daemon fluentd.pid
Send the same search request:
# droonga-request --tag starbucks search-columbus.json
Elapsed time: 0.013983
[
"droonga.message",
1392619528,
{
"inReplyTo": "1392619528.235121",
"statusCode": 200,
"type": "search.result",
"body": {
"stores": {
"count": 2,
"records": [
[
"Columbus @ 67th - New York NY (W)"
],
[
"2 Columbus Ave. - New York NY (W)"
]
],
"completedAt": "2014-02-17T06:45:28.247669Z"
}
}
}
]
Now you can see completedAt attribute containing the time completed the request.
The results in fluentd.log will be like this:
2014-02-17 15:45:28 +0900 [info]: SampleLoggerPlugin::Adapter message=#<Droonga::OutputMessage:0x007fd384f3ab60 @raw_message={"dataset"=>"Default", "type"=>"dispatcher", "body"=>{"stores"=>{"count"=>2, "records"=>[["Columbus @ 67th - New York NY (W)"], ["2 Columbus Ave. - New York NY (W)"]]}}, "replyTo"=>{"type"=>"search.result", "to"=>"127.0.0.1:64849/droonga"}, "id"=>"1392619528.235121", "date"=>"2014-02-17 15:45:28 +0900", "appliedAdapters"=>["Droonga::Plugins::SampleLoggerPlugin::Adapter", "Droonga::Plugins::Error::Adapter"]}>
We have learned the basics of plugins for the pre adaption phase and the post adaption phase so far. Let’s try to build more practical plugin.
You may feel the Droonga’s search command is too flexible for your purpose.
Here, we’re going to add our own storeSearch command to wrap the search command in order to provide an application-specific and simple interface, with a new plugin named store-search.
First, create the store-search plugin.
Remember, you must put codes into a file which has the name same to the plugin now you are creating.
So, the file is store-search.rb in the droonga/plugins directory. Then define your StoreSearchPlugin as follows:
lib/droonga/plugins/store-search.rb:
require "droonga/plugin"
module Droonga
module Plugins
module StoreSearchPlugin
extend Plugin
register("store-search")
class Adapter < Droonga::Adapter
input_message.pattern = ["type", :equal, "storeSearch"]
def adapt_input(input_message)
logger.info("StoreSearchPlugin::Adapter", :message => input_message)
query = input_message.body["query"]
logger.info("storeSearch", :query => query)
body = {
"queries" => {
"stores" => {
"source" => "Store",
"condition" => {
"query" => query,
"matchTo" => "_key",
},
"output" => {
"elements" => [
"startTime",
"elapsedTime",
"count",
"attributes",
"records",
],
"attributes" => [
"_key",
],
"limit" => -1,
}
}
}
}
input_message.type = "search"
input_message.body = body
end
end
end
end
end
Then update your catalog.json to activate the plugin.
Remove the sample-logger plugin previously created.
catalog.json:
(snip)
"datasets": {
"Default": {
(snip)
"plugins": ["store-search", "groonga", "crud", "search", "dump", "status"],
(snip)
Remember, you must place your plugin "store-search" before the "search" because yours depends on it.
Restart fluentd:
# kill $(cat fluentd.pid)
# RUBYLIB=./lib fluentd --config fluentd.conf --log fluentd.log --daemon fluentd.pid
Now you can use this new command by the following request:
store-search-columbus.json:
{
"dataset" : "Default",
"type" : "storeSearch",
"body" : {
"query" : "Columbus"
}
}
In order to issue this request, you need to run:
# droonga-request --tag starbucks store-search-columbus.json
Elapsed time: 0.01494
[
"droonga.message",
1392621168,
{
"inReplyTo": "1392621168.0119512",
"statusCode": 200,
"type": "storeSearch.result",
"body": {
"stores": {
"count": 2,
"records": [
[
"Columbus @ 67th - New York NY (W)"
],
[
"2 Columbus Ave. - New York NY (W)"
]
]
}
}
}
]
And you will see the result on fluentd’s log in fluentd.log:
2014-02-17 16:12:48 +0900 [info]: StoreSearchPlugin::Adapter message=#<Droonga::InputMessage:0x007fe4791d3958 @raw_message={"dataset"=>"Default", "type"=>"storeSearch", "body"=>{"query"=>"Columbus"}, "replyTo"=>{"type"=>"storeSearch.result", "to"=>"127.0.0.1:49934/droonga"}, "id"=>"1392621168.0119512", "date"=>"2014-02-17 16:12:48 +0900", "appliedAdapters"=>[]}>
2014-02-17 16:12:48 +0900 [info]: storeSearch query="Columbus"
Now we can perform store search with simple requests.
Note: look at the "type" of the response message. Now it became "storeSearch.result", from "search.result". Because it is triggered from the incoming message with the type "storeSearch", the outgoing message has the type "(incoming command).result" automatically. In other words, you don’t have to change the type of the outgoing messages, like input_message.type = "search" in the method adapt_input.
Second, let’s return results in more simple way: just an array of the names of stores.
Define the adapt_output method as follows.
lib/droonga/plugins/store-search.rb:
(snip)
module StoreSearchPlugin
extend Plugin
register("store-search")
class Adapter < Droonga::Adapter
(snip)
def adapt_output(output_message)
logger.info("StoreSearchPlugin::Adapter", :message => output_message)
records = output_message.body["stores"]["records"]
simplified_results = records.flatten
output_message.body = simplified_results
end
end
end
(snip)
The adapt_output method receives outgoing messages only corresponding to the incoming messages trapped by the plugin.
Restart fluentd:
# kill $(cat fluentd.pid)
# RUBYLIB=./lib fluentd --config fluentd.conf --log fluentd.log --daemon fluentd.pid
Send the request:
# droonga-request --tag starbucks store-search-columbus.json
Elapsed time: 0.014859
[
"droonga.message",
1392621288,
{
"inReplyTo": "1392621288.158763",
"statusCode": 200,
"type": "storeSearch.result",
"body": [
"Columbus @ 67th - New York NY (W)",
"2 Columbus Ave. - New York NY (W)"
]
}
]
The log in fluentd.log will be like this:
2014-02-17 16:14:48 +0900 [info]: StoreSearchPlugin::Adapter message=#<Droonga::InputMessage:0x007ffb8ada9d68 @raw_message={"dataset"=>"Default", "type"=>"storeSearch", "body"=>{"query"=>"Columbus"}, "replyTo"=>{"type"=>"storeSearch.result", "to"=>"127.0.0.1:49960/droonga"}, "id"=>"1392621288.158763", "date"=>"2014-02-17 16:14:48 +0900", "appliedAdapters"=>[]}>
2014-02-17 16:14:48 +0900 [info]: storeSearch query="Columbus"
2014-02-17 16:14:48 +0900 [info]: StoreSearchPlugin::Adapter message=#<Droonga::OutputMessage:0x007ffb8ad78e48 @raw_message={"dataset"=>"Default", "type"=>"dispatcher", "body"=>{"stores"=>{"count"=>2, "records"=>[["Columbus @ 67th - New York NY (W)"], ["2 Columbus Ave. - New York NY (W)"]]}}, "replyTo"=>{"type"=>"storeSearch.result", "to"=>"127.0.0.1:49960/droonga"}, "id"=>"1392621288.158763", "date"=>"2014-02-17 16:14:48 +0900", "appliedAdapters"=>["Droonga::Plugins::StoreSearchPlugin::Adapter", "Droonga::Plugins::Error::Adapter"], "originalTypes"=>["storeSearch"]}>
Now you’ve got the simplified response.
In the way just described, we can use adapter to implement the application specific search logic.
We have learned how to add a new command based only on a custom adapter and an existing command. In the process, we also have learned how to receive and modify messages, both of incoming and outgoing.
See also the reference manual for more details.