I have sketched the flow of the java side of the plugin runner
[image: APISIX 运行 Java 插件.png]
And I have some questions to clarify.
1. How does the plugin runner load the client's code?
It's up to each runner to figure it out according to its own language's
ecology. Take java as an example,
the user develops with the PDK provided by us, and packages the custom
plugin code into a jar and puts it in the specified location. When the
plugin runner starts, it loads the jar package in this location by means of
a custom dynamic ClassLoader or something like that.
2. How do users develop?
Just provide the filter chain like Spring Cloud Gateway. Users can
register their own filters. And the PDK is a jar, with some defined
interfaces such as pre, post, etc., and some objects such as request,
header, etc.
3. How to debug？
Option 1: APISIX provides debugging mode for java plugins, this time
it is not APISIX to start the plugin runner, but the user himself downloads
the plugin runner code and runs the main method to start it, so as to
construct a request to access APISIX, APISIX will pass the context of the
request to the plugin runner, and then use it to debug java code.
Option 2: java remote debug.
Zexuan Luo <spacewan...@apache.org> 于2021年4月19日周一 下午6:18写道：
> Here is the new flatbuffer schema:
>
> https://github.com/spacewander/incubator-apisix/blob/step1/apisix/plugins/ext-plugin/ext-plugin.fbs
>
> Zexuan Luo <spacewan...@apache.org> 于2021年4月16日周五 下午2:52写道：
> >
> > 1. Background
> >
> > APISIX currently only supports writing plugins in Lua. If other
> > languages are supported, it will greatly broaden the APISIX ecosystem
> > and user base.
> >
> > 2. Solution
> >
> > Since WASM is not yet mature, we consider implementing it through local
> IPC.
> >
> > For the sake of discussion, the following will assume that the plugin
> > is written in Java. However, in practice, our solution can be
> > interfaced with other languages.
> >
> > 2.1 Terminology
> >
> > Several terms are defined here.
> >
> > Plugin Runner: The service that runs the plugin, written in the same
> > language as the plugin. In the first version, we assume that there
> > will be only one Plugin Runner.
> >
> > 2.2 Plugin Runner lifecycle
> >
> > To simplify user operation and reduce the difficulty of upgrading,
> > Plugin Runner is managed by APISIX.
> >
> > APISIX starts the Plugin Runner when it starts and ends it when it
> > ends. if the Plugin Runner quits in the middle, APISIX will restart it
> > automatically.
> >
> > 2.3 Timing of APISIX communication with Plugin Runner
> >
> > ```
> > Router ----> Global Plugin (written in Lua) ---> Ext Plugin
> > (ext-plugin-pre-req) ----> Lua Plugin (Router)
> > ---> Ext plugin (ext-plugin-post-req) ---> Upstream
> > ```
> >
> > Running the Ext Plugin in the Global Plugin is not supported at this
> > time, as the global logic can be executed uniformly in the Plugin
> > Runner.
> >
> > Running Ext Plugin after getting an upstream response is not supported
> > at this time. We can support it later with a buffering response.
> >
> > ext-plugin-pre runs before all non-global Lua plugins, and
> > ext-plugin-post runs after all non-global Lua plugins.
> >
> > 2.4 How APISIX communicates with Plugin Runner
> >
> > APISIX communicates with Plugin Runner through a unix socket. The
> > communication protocol is as follows.
> >
> > 2.4.1 Communication format
> >
> > ```
> > 1 byte of type + 3 bytes of length + data
> > ```
> >
> > The type can be 0 ~ 7, and the length can be [0, 8M). data length is
> > determined by length.
> > Since Ext Plugin usually does not exchange too much data, 8M should be
> > enough. The reason for taking 4 bytes is to keep the header small
> > enough to be read efficiently.
> >
> > The current type takes the following values.
> >
> > 0 means error
> > 1 means prepare_conf
> > 2 means http_req_call
> >
> > The data is serialized in capnproto, a binary serialization format.
> >
> > capnproto is supported by many programming languages:
> > https://capnproto.org/otherlang.html
> >
> > The advantages of choosing capnproto are.
> > 1. focus on serialization performance
> > 2. partial deserialization support, so that decode can be done only
> > when it is needed
> >
> > 2.4.2 Communication steps
> >
> > Each ext plugin will have the following configuration.
> >
> > ```
> > {
> > "conf": [
> > {
> > "name": "configuration name",
> > "value": "configuration value"
> > }
> > ],
> > "extra_info": [
> > ...
> > ]
> > }
> > ```
> >
> > conf can be used to set the execution configuration of the
> > plugin-related requests inside Plugin Runner.
> >
> > The default data sent to Plugin Runner is only the most common
> > information. If you want additional information, you need to declare
> > it in extra_info beforehand.
> >
> > To save communication costs, conf is sent separately.
> >
> > 1. APISIX will check if conf has a corresponding token in the local
> cache.
> > 2. If not, APISIX sends a prepare_conf request to ask Plugin Runner
> > to cache the conf and return a token.
> > (Note that Plugin Runner's cache time needs to be longer than APISIX's
> > cache time.)
> > 3. APISIX sends an http_req_call request to Plugin Runner.
> > 4. Plugin Runner executes the request and returns a response to APISIX.
> > 5. APISIX processes the request based on the response
> >
> > 2.4.3 proto
> >
> > Refer to https://capnproto.org/language.html
> >
> > The following is the proto for error
> >
> > response
> > ```
> > enum ErrorCode {
> > BAD_REQUEST @0; # Plugin Runner can't understand APISIX
> > SERVICE_UNAVAILABLE @1; # Plugin Runner can't handle the request
> > CONF_TOKEN_NOT_FOUND @2;
> > }
> > struct ErrorResp {
> > Code @0 :ErrorCode;
> > }
> > ```
> >
> > The following is the proto of prepare_conf
> >
> > request
> > ```
> > struct PrepareConfReq {
> > conf @0 :List(Pair);
> > }
> > ```
> >
> > Response
> > ```
> > struct PrepareConfResp {
> > conf_token @0 :UInt32;
> > }
> > ```
> >
> > Here is the proto for http_req_call
> >
> > request
> > ```
> > struct Pair {
> > name @0 :Text;
> > value @1 :Text;
> > }
> > struct PairData {
> > name @0 :Text;
> > value @1 :Data;
> > }
> > enum Method {
> > GET @0;
> > ...
> > }
> >
> > struct HTTPReqCallReq {
> > id @0 :UInt32;
> > src_ip @1 :Data;
> >
> > method @2 :Method;
> >
> > path @3 :Text;
> > args @4 :List(Pair);
> > headers @5 :List(Pair);
> >
> > conf_token @6 :UInt32;
> >
> > extra_info @7 :List(PairData);
> > }
> > ```
> >
> > Response
> > ```
> > struct HTTPReqCallResp {
> > id @0 :UInt32;
> >
> > struct Stop {
> > status @0 :UInt16;
> > headers @1 :List(Pair);
> > body @2 :Data;
> > }
> > struct Rewrite {
> > path @0 :Text;
> > headers @1 :List(Pair);
> > # Note that args are modified in full.
> > # Either empty, meaning no args need to be moved
> > # or the entire modified args, not the incrementally changed
> parts
> > args @2 :List(Pair);
> > }
> >
> > # What needs to be done when the response is received action
> > action :union {
> > # Do nothing
> > continue @1 :Void;
> > # Equivalent to core.response.exit(status, body), allowing
> > additional headers to be set
> > stop @2 :Stop;
> > # Rewrite the request
> > rewrite @3 :Rewrite;
> > }
> > }
> > ```
> >
> > 2.4.4 Error handling
> >
> > Logging and returning 503 error codes
> >
> > 2.4.5 Environment variables
> >
> > APISIX configures the Plugin Runner with a number of environment
> > variables when it is started.
> >
> > APISIX_LISTEN_ADDRESS: the address that the Plugin Runner needs to
> listen to
> > APISIX_CONF_EXPIRE_TIME: Plugin Runner needs to cache conf for longer
> than this
>
