apisix/doc/plugin-develop.md

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[中文](zh-cn/plugin-develop.md)

# table of contents

- [**check dependencies**](#check-dependencies)
- [**name and config**](#name-and-config)
- [**schema and check**](#schema-and-check)
- [**choose phase to run**](#choose-phase-to-run)
- [**implement the logic**](#implement-the-logic)
- [**write test case**](#write-test-case)
- [**register public API**](#register-public-api)
- [**register control API**](#register-control-api)

## check dependencies

if you have dependencies on external libraries, check the dependent items. if your plugin needs to use shared memory, it
 needs to declare in __bin/apisix__, for example :

```nginx
    lua_shared_dict plugin-limit-req     10m;
    lua_shared_dict plugin-limit-count   10m;
    lua_shared_dict prometheus-metrics   10m;
    lua_shared_dict plugin-limit-conn    10m;
    lua_shared_dict upstream-healthcheck 10m;
    lua_shared_dict worker-events        10m;

    # for openid-connect plugin
    lua_shared_dict discovery             1m; # cache for discovery metadata documents
    lua_shared_dict jwks                  1m; # cache for JWKs
    lua_shared_dict introspection        10m; # cache for JWT verification results
```

The plugin itself provides the init method. It is convenient for plugins to perform some initialization after
 the plugin is loaded.

Note : if the dependency of some plugin needs to be initialized when Nginx start, you may need to add logic to the initialization
       method "http_init" in the file __apisix.lua__, And you may need to add some processing on generated part of Nginx
       configuration file in __bin/apisix__ file. but it is easy to have an impact on the overall situation according to the
       existing plugin mechanism, we do not recommend this unless you have a complete grasp of the code.

## name and config

Determine the name and priority of the plugin, and add to conf/config-default.yaml. For example, for the example-plugin plugin,
 you need to specify the plugin name in the code (the name is the unique identifier of the plugin and cannot be
 duplicate), you can see the code in file "__apisix/plugins/example-plugin.lua__" :

```lua
local plugin_name = "example-plugin"

local _M = {
    version = 0.1,
    priority = 0,
    name = plugin_name,
    schema = schema,
    metadata_schema = metadata_schema,
}
```

Note : The priority of the new plugin cannot be the same as the priority of any existing plugin. In addition, plugins with a high priority value will be executed first in a given phase (see the definition of `phase` in [choose-phase-to-run](#choose-phase-to-run)). For example, the priority of example-plugin is 0 and the priority of ip-restriction is 3000. Therefore, the ip-restriction plugin will be executed first, then the example-plugin plugin.

in the "__conf/config-default.yaml__" configuration file, the enabled plugins (all specified by plugin name) are listed.

```yaml
plugins:                          # plugin list
  - limit-req
  - limit-count
  - limit-conn
  - key-auth
  - prometheus
  - node-status
  - jwt-auth
  - zipkin
  - ip-restriction
  - grpc-transcode
  - serverless-pre-function
  - serverless-post-function
  - openid-connect
  - proxy-rewrite
  - redirect
  ...
```

Note : the order of the plugins is not related to the order of execution.

If your plugin has a new code directory of its own, you will need to modify the `Makefile` to create directory, such as:

```
$(INSTALL) -d $(INST_LUADIR)/apisix/plugins/skywalking
$(INSTALL) apisix/plugins/skywalking/*.lua $(INST_LUADIR)/apisix/plugins/skywalking/
```

## schema and check

Write [Json Schema](https://json-schema.org) descriptions and check functions. Similarly, take the example-plugin plugin as an example to see its
 configuration data :

```json
"example-plugin" : {
    "i": 1,
    "s": "s",
    "t": [1]
}
```

Let's look at its schema description :

```lua
local schema = {
    type = "object",
    properties = {
        i = {type = "number", minimum = 0},
        s = {type = "string"},
        t = {type = "array", minItems = 1},
        ip = {type = "string"},
        port = {type = "integer"},
    },
    required = {"i"},
}
```

The schema defines a non-negative number `i`, a string `s`, a non-empty array of `t`, and `ip` / `port`. Only `i` is required.

At the same time, we need to implement the __check_schema(conf)__ method to complete the specification verification.

```lua
function _M.check_schema(conf, schema_type)
    return core.schema.check(schema, conf)
end
```

Note: the project has provided the public method "__core.schema.check__", which can be used directly to complete JSON
verification.

In addition, if the plugin needs to use some metadata, we can define the plugin `metadata_schema`, and then we can dynamically manage these metadata through the `admin api`. Example:

```lua
local metadata_schema = {
    type = "object",
    properties = {
        ikey = {type = "number", minimum = 0},
        skey = {type = "string"},
    },
    required = {"ikey", "skey"},
    additionalProperties = false,
}

local plugin_name = "example-plugin"

local _M = {
    version = 0.1,
    priority = 0,        -- TODO: add a type field, may be a good idea
    name = plugin_name,
    schema = schema,
    metadata_schema = metadata_schema,
}
```

You might have noticed the key-auth plugin has `type = 'auth'` in its definition.
When we set the type of plugin to `auth`, it means that this plugin is an authentication plugin.

An authentication plugin needs to choose a consumer after execution. For example, in key-auth plugin, it calls the `consumer.attach_consumer` to attach a consumer, which is chosen via the `apikey` header.

To interact with the `consumer` resource, this type of plugin needs to provide a `consumer_schema` to check the `plugins` configuration in the `consumer`.

Here is the consumer configuration for key-auth plugin:

```json
{
    "username": "Joe",
    "plugins": {
        "key-auth": {
            "key": "Joe's key"
        }
    }
}
```

It will be used when you try to create a [Consumer](https://github.com/apache/apisix/blob/master/doc/admin-api.md#consumer)

To validate the configuration, the plugin uses a schema like this:

```json
local consumer_schema = {
    type = "object",
    additionalProperties = false,
    properties = {
        key = {type = "string"},
    },
    required = {"key"},
}
```

Note the difference between key-auth's __check_schema(conf)__ method to example-plugin's:

```lua
-- key-auth
function _M.check_schema(conf, schema_type)
    if schema_type == core.schema.TYPE_CONSUMER then
        return core.schema.check(consumer_schema, conf)
    else
        return core.schema.check(schema, conf)
    end
end
```

```lua
-- example-plugin
function _M.check_schema(conf, schema_type)
    return core.schema.check(schema, conf)
end
```

## choose phase to run

Determine which phase to run, generally access or rewrite. If you don't know the [Openresty life cycle](https://openresty-reference.readthedocs.io/en/latest/Directives/), it's
recommended to know it in advance. For example key-auth is an authentication plugin, thus the authentication should be completed
before forwarding the request to any upstream service. Therefore, the plugin must be executed in the rewrite phases.
In APISIX, only the authentication logic can be run in the rewrite phase. Other logic needs to run before proxy should be in access phase.

The following code snippet shows how to implement any logic relevant to the plugin in the OpenResty log phase.

```lua
function _M.log(conf)
-- Implement logic here
end
```

**Note : we can't invoke `ngx.exit` or `core.respond.exit` in rewrite phase and access phase. if need to exit, just return the status and body, the plugin engine will make the exit happen with the returned status and body. [example](https://github.com/apache/apisix/blob/35269581e21473e1a27b11cceca6f773cad0192a/apisix/plugins/limit-count.lua#L177)**

## implement the logic

Write the logic of the plugin in the corresponding phase.

## write test case

For functions, write and improve the test cases of various dimensions, do a comprehensive test for your plugin! The
test cases of plugins are all in the "__t/plugin__" directory. You can go ahead to find out. APISIX uses
[****test-nginx****](https://github.com/openresty/test-nginx) as the test framework. A test case (.t file) is usually
divided into prologue and data parts by \__data\__. Here we will briefly introduce the data part, that is, the part
of the real test case. For example, the key-auth plugin:

```perl
=== TEST 1: sanity
--- config
    location /t {
        content_by_lua_block {
            local plugin = require("apisix.plugins.key-auth")
            local ok, err = plugin.check_schema({key = 'test-key'}, core.schema.TYPE_CONSUMER)
            if not ok then
                ngx.say(err)
            end

            ngx.say("done")
        }
    }
--- request
GET /t
--- response_body
done
--- no_error_log
[error]
```

A test case consists of three parts :

- __Program code__ : configuration content of Nginx location
- __Input__ : http request information
- __Output check__ : status, header, body, error log check

When we request __/t__, which config in the configuration file, the Nginx will call "__content_by_lua_block__" instruction to
 complete the Lua script, and finally return. The assertion of the use case is response_body return "done",
"__no_error_log__" means to check the "__error.log__" of Nginx. There must be no ERROR level record. The log files for the unit test
are located in the following folder: 't/servroot/logs'.

The above test case represents a simple scenario. Most scenarios will require multiple steps to validate. To do this, create multiple tests `=== TEST 1`, `=== TEST 2`, and so on. These tests will be executed sequentially, allowing you to break down scenarios into a sequence of atomic steps.

Additionally, there are some convenience testing endpoints which can be found [here](https://github.com/apache/apisix/blob/master/t/lib/server.lua#L36). For example, see [proxy-rewrite](https://github.com/apache/apisix/blob/master/t/plugin/proxy-rewrite.lua). In test 42, the upstream `uri` is made to redirect `/test?new_uri=hello` to `/hello` (which always returns `hello world`). In test 43, the response body is confirmed to equal `hello world`, meaning the proxy-rewrite configuration added with test 42 worked correctly.

Refer the following [document](how-to-build.md#test) to setup the testing framework.

### Attach the test-nginx execution process:

According to the path we configured in the makefile and some configuration items at the front of each __.t__ file, the
framework will assemble into a complete nginx.conf file. "__t/servroot__" is the working directory of Nginx and start the
Nginx instance. according to the information provided by the test case, initiate the http request and check that the
return items of HTTP include HTTP status, HTTP response header, HTTP response body and so on.

### Register public API

A plugin can register API which exposes to the public. Take jwt-auth plugin as an example, this plugin registers `GET /apisix/plugin/jwt/sign` to allow client to sign its key:

```lua
local function gen_token()
    ...
end

function _M.api()
    return {
        {
            methods = {"GET"},
            uri = "/apisix/plugin/jwt/sign",
            handler = gen_token,
        }
    }
end
```

Note that the public API is exposed to the public.
You may need to use [interceptors](plugin-interceptors.md) to protect it.

### Register control API

If you only want to expose the API to the localhost or intranet, you can expose it via [Control API](./control-api.md).

Take a look at example-plugin plugin:

```lua
local function hello()
    local args = ngx.req.get_uri_args()
    if args["json"] then
        return 200, {msg = "world"}
    else
        return 200, "world\n"
    end
end


function _M.control_api()
    return {
        {
            methods = {"GET"},
            uris = {"/v1/plugin/example-plugin/hello"},
            handler = hello,
        }
    }
end
```

If you don't change the default control API configuration, the plugin will be expose `GET /v1/plugin/example-plugin/hello` which can only be accessed via `127.0.0.1`.