lua-resty-ffi

lua-resty-ffi provides an efficient and generic API to do hybrid programming in openresty with mainstream languages (Go, Python, Java, Rust, Node.js, etc.).

Features:

• nonblocking, in coroutine way
• simple but extensible interface, supports any C ABI compliant language
• once and for all, no need to write C/Lua codes to do coupling anymore
• high performance, faster than unix domain socket way
• generic loader library for python/java/nodejs
• any serialization message format you like

Quickstart

Take golang as an example:

cd /opt
git clone https://github.com/kingluo/lua-resty-ffi
cd lua-resty-ffi

# compile and install openresty with lua-resty-ffi
# optionally, you could specify any compile options you need, e.g.
# ./build.sh --with-pcre-jit --add-module=...
./build.sh

cd examples/go

# install golang if not yet
wget https://go.dev/dl/go1.19.3.linux-amd64.tar.gz
rm -rf /usr/local/go && tar -C /usr/local -xzf go1.19.3.linux-amd64.tar.gz
export PATH=$PATH:/usr/local/go/bin

# compile example libraries
make

# run nginx
make run

# in another terminal
curl http://localhost:20000/echo
ok

Please check the directory of each programming language for detail.

Also, check this blog post:

Implement Grpc Client in Rust for Openresty

Chinese blog

Install lua-resty-ffi via luarocks

Now it provides an optional non-intrusive way to use lua-resty-ffi.

Check this blog for detail:

http://luajit.io/posts/resolve-c-static-variables-of-main-executable-from-the-dynamic-loaded-shared-library/

• specify your openresty source path in variable $OR_SRC
• ensure openresty source are already configured and built according to your product release

luarocks config variables.OR_SRC /tmp/tmp.Z2UhJbO1Si/openresty-1.21.4.1
luarocks install lua-resty-ffi

Background

In openresty land, when you turn to implement some logic, especially to couple with third-party popular frameworks, it's likely to suck in awkward: make bricks without straw.

1. C is a low-level language, with no unified and rich libraries and ecosystems, and most modern frameworks do not support C, instead, they like Java, Python, Go. C is suitable for fundamental software.

2. Lua is an embedded and minimal programming language, which means all powers come from the host. In openresty, it means all functionalities come from lua-nginx-modules. Like C, or even worse, you have to reinvent the wheels via cosocket to do modern networking stuff. A lot of lua-resty-* was born, but they are almost semi-finished compared to native lib in other languages. For example, lua-resty-kafka doesn't support consumer groups, lua-resty-postgres doesn't support notify and prepared statements, etc. Moreover, most of those authors of lua-resty-* stop development at some stage because the lua community is so small and less attractive.

Why not WASM?

WASM has below shortages, which make it not suitable for openresty:

• no coroutine, which means you need to execute the logic from start to end and block the nginx worker process with arbitrary time
• castrated language support, e.g.
  • Go: You have to use tinygo instead, not the batteries-included official golang.
  • Rust: You have to use specialized crates to do jobs, e.g. when you need async network programming, tokio is unavailable, instead, you have to use WASI-based crates, e.g. wasmedge_wasi_socket.
  • Python: You have to use implementations that support WASM, e.g. rustpython.
• complex development, due to sandbox original intention, you have to export a lot of API from nginx

So, may I extend the openresty with modern programming languages (Go, Python, Java, Rust, etc.) and reuse their rich ecosystems directly? Yes, that's what lua-resty-ffi does.

Architecture

Concepts

Library

In Go and Rust, it means the compiled library, e.g. libffi_go_etcd.so.

In Python3, it means the loader library libffi_python3.so with native python3 modules.

In Java, it means the loader library libffi_java.so with native Java classes/jar.

In Node.js, it means the loader library libffi_nodejs.so with native nodejs modules.

Library configuration

Configuration of the library, e.g. etcd endpoints, kafka endpoints, etc.

The format could be any serialization format, e.g. json, yaml, as long as it matches the runtime

Runtime

The combination of library and configuration would init a new runtime, which represents some threads or goroutines to do jobs.

You could use the same library with different configurations, which is very common, especially for Java, Python and Node.js.

Request-Response Model

Coupling between nginx worker process and the runtime is based on message exchanges, which contain two directions:

1. Request

• the lua coroutine creates a task
• associates the task with the request message, which is C malloc() char array. Note that this char array would be freed by lua-resty-ffi, and the runtime just uses it.
• put the task into the thread-safe queue of the runtime and yield
• the runtime polls this queue

Why not call API provided by other languages?

• In Go, due to GMP model, it may block the nginx worker process
• It increases the burden for other languages to provide such API

2. Response

The runtime injects the response (also C malloc() char array) into the ngx_thread_pool_done queue directly and notify the nginx epoll loop via eventfd, the nginx would resume the lua coroutine then. Note that the response would be freed by lua-resty-ffi, so no need to care about it in your runtime.

IPC design and Benchmark

Benchmark compared to unix domain socket.

Lua API

local runtime = ngx.load_ffi(lib, cfg, opts)

Load and return the runtime

• lib shared library name. It could be an absolute file path or name only, or even a short name (e.g. for libdemo.so, the short name is demo). When the lib is name only or short name, it's searched according to LD_LIBRARY_PATH environment variable.

• cfg configuration, it could be string or nil.

• opts options table.

{
    -- the maximum queue size for pending requests to the runtime.
    -- it determines the throughput of requests if the queue is full,
    -- all following requests would fail.
    max_queue = 65536,

    -- denotes whether the symbols loaded from the library
    -- would be exported in the global namespace, which is only necessary for python3 and nodejs.
    is_global = false,

    -- by default, all libraries handles would be cached by lua-resty-ffi
    -- because currently, only python and rust could be hot-reload,
    -- and java must not be `dlclose()`
    -- unpin is used to enable hot-reload
    -- note that it's different from the unload/reload of runtime,
    -- which is application-specific behavior, but library unload/reload is
    -- done by the linker via dlopen()/dlclose().
    unpin = false,
}

This API is idempotent. The loaded runtime is cached in an internal table, where the table key is lib .. '&' .. cfg.

This function calls the libffi_init() of the library per key.

It means the same library with a different configuration would initiate a different new runtime, which is especially useful for python3, Java and Node.js.

Example:

local opts = {is_global = true}
local demo = ngx.load_ffi("ffi_python3",
    [[ffi.kafka,init,{"servers":"localhost:9092", "topic":"foobar", "group_id": "foobar"}]], opts)

local demo = ngx.load_ffi("ffi_go_etcd", "[\"localhost:2379\"]")

local ok, res_or_rc, err = runtime:call(req)

Send a request to the runtime and returns the response.

• req the request string, could be in any serialization format, e.g. json, protobuf, as long as it matches the runtime implementation.

• ok return status, true or false.

• res_or_rc response string, could be in any serialization format, e.g. json, protobuf, as long as it matches the runtime implementation. When the runtime returns non-zero rc, ok is false, and the res_or_rc is the returned value by the runtime.

• err the error string, it may exist only if ok is false. It may be nil if the runtime does not return an error.

This method is nonblocking, which means the coroutine would yield waiting for the response and resume with the return values.

Note that the method name call could be any name you like, it would be generated automatically by the __index meta function, and only used to denote the request semantics。

Example:

local ok, res
ok, res = demo:produce([[{"type":"produce", "msg":"hello"}]])
assert(ok)
ok, res = demo:produce([[{"type":"produce", "msg":"world"}]])
assert(ok)
ngx.sleep(2)
ok, res = demo:consume([[{"type":"consume"}]])
assert(ok)
ngx.say(res)

local ok, res = runtime:__unload()

Unload the runtime, after that, no request could be sent to this runtime anymore. The runtime would receive a NULL task, and it must terminate everything including the threads. Note that it's asynchronous processing, and the NULL task is appended to the queue, so all pending normal tasks would be handled first.

API provided by the runtime

int libffi_init(char* cfg, void *tq);

This API is provided by the library to initiate its logic and start the poll thread/goroutine.

cfg is a null-terminated C string, it would get freed by lua-resty-ffi after libffi_init() returns, which may be NULL.

tq is the task queue pointer, used by the below APIs.

Example:

//export libffi_init
func libffi_init(cfg *C.char, tq unsafe.Pointer) C.int {
    data := C.GoString(cfg)
    ...
    go func() {
        for {
            task := C.ngx_http_lua_ffi_task_poll(tq)
            if task == nil {
                break
            }
            var rlen C.int
            r := C.ngx_http_lua_ffi_get_req(task, &rlen)
            res := C.malloc(C.ulong(rlen))
            C.memcpy(res, unsafe.Pointer(r), C.ulong(rlen))
            C.ngx_http_lua_ffi_respond(task, 0, (*C.char)(res), rlen)
        }
    }()
    return 0
}

APIs used by the runtime

void* ngx_http_lua_ffi_task_poll(void *tq);

Poll the task from the task queue assigned to the runtime.

When it returns NULL, it denotes the runtime was unloaded, the runtime must clean up everything and not access the task queue anymore (because the task queue was deallocated)!

char* ngx_http_lua_ffi_get_req(void *tsk, int *len);

Extract the request from the task. Note that the request could be NULL, so the runtime must not use this API in this case.

void ngx_http_lua_ffi_respond(void *tsk, int rc, char* rsp, int rsp_len);

Response to the task.

All the above APIs are thread-safe. So you could use them anywhere in the thread/goroutine of your runtime.

• rc return status, 0 means successful, and other values mean failure.
• rsp response char array, may be NULL if the runtime does not need to respond to something.
• rsp_len the length of response, maybe 0 if the rsp is NULL or `\0' terminated C string.

If rc is non-zero, then the runtime may also set rsp and rsp_len if it needs to return error data.

Code hot-reload

How to do code hot-reload in lua-resty-ffi?