Add msgpack_rpc_dispatch/metadata generator

This adds a lua script which parses the contents of 'api.h'. After the api is
parsed into a metadata table. After that, it will generate:

- A msgpack blob for the metadata table. This msgpack object contains everything
  scripting engines need to generate their own wrappers for the remote API.
- The `msgpack_rpc_dispatch` function, which takes care of validating msgpack
  requests, converting arguments to C types and passing control to the
  appropriate 'api.h' function. The result is then serialized back to msgpack
  and returned to the client.

This approach was used because:

- It automatically modifies `msgpack_rpc_dispatch` to reflect API changes.
- Scripting engines that generate remote call wrappers using the msgpack
  metadata will also adapt automatically to API changes

scripts/msgpack-gen.lua

@@ -0,0 +1,135 @@
+lpeg = require('lpeg')
+msgpack = require('cmsgpack')
+
+P, R, S = lpeg.P, lpeg.R, lpeg.S
+C, Ct, Cc, Cg = lpeg.C, lpeg.Ct, lpeg.Cc, lpeg.Cg
+
+any = P(1) -- (consume one character)
+letter = R('az', 'AZ') + S('_$')
+alpha = letter + R('09')
+nl = P('\n')
+not_nl = any - nl
+ws = S(' \t') + nl
+fill = ws ^ 0
+c_comment = P('//') * (not_nl ^ 0)
+c_preproc = P('#') * (not_nl ^ 0)
+c_id = letter * (alpha ^ 0)
+c_void = P('void')
+c_raw = P('char') * fill * P('*')
+c_int = P('uint32_t')
+c_array = c_raw * fill * P('*') * Cc('array')
+c_param_type = (
+  (c_array  * Cc('array') * fill) +
+  (c_raw * Cc('raw') * fill) +
+  (c_int * Cc('integer') * (ws ^ 1))
+  )
+c_type = (c_void * Cc('none') * (ws ^ 1)) + c_param_type
+c_param = Ct(c_param_type * C(c_id))
+c_param_list = c_param * (fill * (P(',') * fill * c_param) ^ 0)
+c_params = Ct(c_void + c_param_list)
+c_proto = Ct(
+  Cg(c_type, 'rtype') * Cg(c_id, 'fname') *
+  fill * P('(') * fill * Cg(c_params, 'params') * fill * P(')') *
+  fill * P(';')
+  )
+grammar = Ct((c_proto + c_comment + c_preproc + ws) ^ 1)
+
+inputf = assert(arg[1])
+outputf = assert(arg[2])
+
+input = io.open(inputf, 'rb')
+api = grammar:match(input:read('*all'))
+input:close()
+
+-- assign a unique integer id for each api function
+for i = 1, #api do
+  api[i].id = i
+end
+
+output = io.open(outputf, 'wb')
+
+output:write([[
+#include <stdbool.h>
+#include <stdint.h>
+#include <msgpack.h>
+
+#include "api.h"
+#include "msgpack_rpc.h"
+
+static const uint8_t msgpack_metadata[] = {
+
+]])
+packed = msgpack.pack(api)
+for i = 1, #packed do
+  output:write(string.byte(packed, i)..', ')
+  if i % 10 == 0 then
+    output:write('\n  ')
+  end
+end
+output:write([[
+};
+
+bool msgpack_rpc_dispatch(msgpack_object *req, msgpack_packer *res)
+{
+  uint32_t method_id = (uint32_t)req->via.u64;
+
+  switch (method_id) {
+    case 0:
+      msgpack_rpc_response(req, res);
+      msgpack_pack_nil(res);
+      // The result is the `msgpack_metadata` byte array
+      msgpack_pack_raw(res, sizeof(msgpack_metadata));
+      msgpack_pack_raw_body(res, msgpack_metadata, sizeof(msgpack_metadata));
+      return true;
+]])
+
+for i = 1, #api do
+  local fn
+  local args = {}
+  fn = api[i]
+  output:write('\n    case '..fn.id..':')
+  for j = 1, #fn.params do
+    local expected, convert, param
+    local idx = tostring(j - 1)
+    param = fn.params[j]
+    ref = '(req->via.array.ptr[3].via.array.ptr + '..idx..')'
+    -- decide which validation/conversion to use for this argument
+    if param[1] == 'array' then
+      expected = 'MSGPACK_OBJECT_ARRAY'
+      convert = 'msgpack_rpc_array_argument'
+    elseif param[1] == 'raw' then
+      expected = 'MSGPACK_OBJECT_RAW'
+      convert = 'msgpack_rpc_raw_argument'
+    elseif param[1] == 'integer' then
+      expected = 'MSGPACK_OBJECT_POSITIVE_INTEGER'
+      convert = 'msgpack_rpc_integer_argument'
+    end
+    output:write('\n      if ('..ref..'->type != '..expected..') {')
+    output:write('\n        return msgpack_rpc_error(req, res, "Wrong argument types");')
+    output:write('\n      }')
+    table.insert(args, convert..'('..ref..')')
+  end
+  local call_args = table.concat(args, ', ')
+  -- convert the result back to msgpack
+  if fn.rtype == 'none' then
+    output:write('\n      '..fn.fname..'('..call_args..');')
+    output:write('\n      return msgpack_rpc_void_result(req, res);\n')
+  else
+    if fn.rtype == 'array' then
+      convert = 'msgpack_rpc_array_result'
+    elseif fn.rtype == 'raw' then
+      convert = 'msgpack_rpc_raw_result'
+    elseif fn.rtype == 'integer' then
+      convert = 'msgpack_rpc_integer_result'
+    end
+    output:write('\n      return '..convert..'('..fn.fname..'('..call_args..'), req, res);\n')
+  end
+end
+output:write([[
+    default:
+      abort();
+      return false;
+  }
+}
+]])
+output:close()

src/CMakeLists.txt

@@ -1,5 +1,27 @@
 include(CheckLibraryExists)
 
+if(DEFINED ENV{LUA_BINARY})
+  set(LUA_BIN $ENV{LUA_BINARY})
+else()
+  set(LUA_BIN ${DEPS_BIN_DIR}/luajit)
+endif()
+
+set(GENERATED_DIR ${PROJECT_BINARY_DIR}/src/auto)
+set(DISPATCH_GENERATOR ${PROJECT_SOURCE_DIR}/scripts/msgpack-gen.lua)
+set(API_HEADER ${PROJECT_SOURCE_DIR}/src/api.h)
+set(MSGPACK_RPC_HEADER ${PROJECT_SOURCE_DIR}/src/msgpack_rpc.h)
+set(MSGPACK_DISPATCH ${GENERATED_DIR}/msgpack_dispatch.c)
+
+file(MAKE_DIRECTORY ${GENERATED_DIR})
+
+add_custom_command(OUTPUT ${MSGPACK_DISPATCH}
+  COMMAND ${LUA_BIN} ${DISPATCH_GENERATOR} ${API_HEADER} ${MSGPACK_DISPATCH}
+  DEPENDS
+    ${API_HEADER}
+    ${MSGPACK_RPC_HEADER}
+    ${DISPATCH_GENERATOR}
+    )
+
 file( GLOB NEOVIM_SOURCES *.c )
 
 foreach(sfile ${NEOVIM_SOURCES})
@@ -11,6 +33,7 @@ endforeach()
 
 list(REMOVE_ITEM NEOVIM_SOURCES ${to_remove})
 list(APPEND NEOVIM_SOURCES "${PROJECT_BINARY_DIR}/config/auto/pathdef.c")
+list(APPEND NEOVIM_SOURCES "${MSGPACK_DISPATCH}")
 
 file( GLOB OS_SOURCES os/*.c )