feature: Support echo plugin

[agile6v]

APISIX currently provides a simple example plugin, but it does not provide useful functionality. So we can provide a useful plugin to help users understand as fully as possible how to develop an APISIX plugin.

[Akayeshmantha]

Hi @agile6v @moonming will be applying for GSoC 2020 this year. Would like to give it a try with apache APISIX. I did GSoC 2019 with openMRS. Is there a chat room which talks about the project idea.

[moonming]

@Akayeshmantha Cool, you can add your ideas to https://cwiki.apache.org/confluence/display/COMDEV/GSoC+2020+Ideas+list, and we can talk about in slack: https://the-asf.slack.com/
, and serach the apisix channel.

[agile6v]

This plugin could implement the corresponding functionality in the common phases such as init, rewrite, access, balancer, header filer, body filter and log . But the specific functionality are still being considered.

[Akayeshmantha]

Hi @membphis @moonming @agile6v I hope still this is a valid requirement.

So here we are thinking about extending the already existing example plugin if am right?.

[agile6v]

Hi @Akayeshmantha

As far as i am concerned, this plugin is still necessary to help other people understand how to implement a plugin as fully as possible.

Thanks.

[Akayeshmantha]

@agile6v so what is the path we are taking implmenting a new plugin or extending the existing plugin 🙂

[Akayeshmantha]

@membphis @moonming would like to work on this

[agile6v]

@agile6v so what is the path we are taking implmenting a new plugin or extending the existing plugin 🙂

Hi @Akayeshmantha Remember that you submitted a proposal at GSOC. How about we follow that plan?

First we implement a simple echo function and then implement a function that modify the response body. For example, adding content before or after the response body.

Thanks.

[Akayeshmantha]

@agile6v sure think that is a good way to start.

[membphis]

@agile6v

Can you provide some use cases?
For example, what configuration options are there for this plugin, and the expected execution results?

[agile6v]

Hi @Akayeshmantha This example can be used as a reference. Not sure I've made it a clear. If you have any questions, welcome to discuss here.

Thanks.

[Akayeshmantha]

Hi @agile6v
So you mean we are going to install https://github.com/openresty/echo-nginx-module#installation echo nginx module and use them for the plugin ?

Or are we going with nginx.logging()

[agile6v]

Hi @agile6v
So you mean we are going to install https://github.com/openresty/echo-nginx-module#installation echo nginx module and use them for the plugin ?

Or are we going with nginx.logging()

@Akayeshmantha We're going to implement an echo plugin, right? So we refer to its features to implement APISIX's echo plugin?

Thanks.

[moonming]

@agile6v you'd better show same specific examples in Apache APISIX

[Akayeshmantha]

Hi @agile6v so from what I get when it comes to the output_filter phase we should replicate what we have in https://github.com/openresty/echo-nginx-module/blob/master/src/ngx_http_echo_module.c#L412 ?

or simply
function _M.output_filter(conf, ctx)
ngx.var.echo_request_body hello;
end
something like this ?

[agile6v]

Hi @Akayeshmantha

We can refer to the implementation of the plugin response-rewrite. It has the ability to override the response body. In the echo plugin we implement the function like this:

function _M.body_filter(conf, ctx)
    conf.before_body + response.body + conf.after_body
end

FYI: https://github.com/openresty/lua-nginx-module#body_filter_by_lua

Hope I've described it clearly.

Thanks.

[Akayeshmantha]

@agile6v I drafted a small sample can you look in the PR ?

[Akayeshmantha]

@agile6v @membphis @moonming any idea about how it is now. Can we review it ?