First go at Lua bindings.

1 files changed, 254 insertions, 0 deletions

diff --git a/lang_ext/lua/upb.c b/lang_ext/lua/upb.c
new file mode 100644
index 0000000..ac7f188
--- /dev/null
+++ b/lang_ext/lua/upb.c
@@ -0,0 +1,254 @@
+/*
+ * upb - a minimalist implementation of protocol buffers.
+ *
+ * Copyright (c) 2009 Joshua Haberman.  See LICENSE for details.
+ *
+ * A Lua extension for upb.
+ */
+
+#include "lauxlib.h"
+#include "upb_def.h"
+
+/* lupb_def *******************************************************************/
+
+// All the def types share the same C layout, even though they are differen Lua
+// types with different metatables.
+typedef struct {
+  upb_def *def;
+} lupb_def;
+
+static void lupb_pushnewdef(lua_State *L, upb_def *def) {
+  lupb_def *ldef = lua_newuserdata(L, sizeof(lupb_def));
+  ldef->def = def;
+  const char *type_name;
+  switch(def->type) {
+    case UPB_DEF_MSG:
+      type_name = "upb.msgdef";
+      break;
+    case UPB_DEF_ENUM:
+      type_name = "upb.enumdef";
+      break;
+    default:
+      luaL_error(L, "unknown deftype %d", def->type);
+  }
+  luaL_getmetatable(L, type_name);
+  lua_setmetatable(L, -2);
+}
+
+static lupb_def *lupb_msgdef_check(lua_State *L, int narg) {
+  return luaL_checkudata(L, narg, "upb.msgdef");
+}
+
+static lupb_def *lupb_enumdef_check(lua_State *L, int narg) {
+  return luaL_checkudata(L, narg, "upb.enumdef");
+}
+
+static int lupb_msgdef_gc(lua_State *L) {
+  lupb_def *ldef = lupb_msgdef_check(L, 1);
+  upb_def_unref(ldef->def);
+  return 0;
+}
+
+static int lupb_enumdef_gc(lua_State *L) {
+  lupb_def *ldef = lupb_enumdef_check(L, 1);
+  upb_def_unref(ldef->def);
+  return 0;
+}
+
+static const struct luaL_Reg lupb_msgdef_methods[] = {
+  {"__gc", lupb_msgdef_gc},
+  {NULL, NULL}
+};
+
+static const struct luaL_Reg lupb_enumdef_methods[] = {
+  {"__gc", lupb_enumdef_gc},
+  {NULL, NULL}
+};
+
+
+/* lupb_symtab ****************************************************************/
+
+// lupb_symtab caches the Lua objects it vends (defs) via lookup or resolve.
+// It does this (instead of creating a new Lua object every time) for two
+// reasons:
+// * it uses less memory, because we can reuse existing objects.
+// * it gives the expected equality semantics, eg. symtab[sym] == symtab[sym].
+//
+// The downside is a bit of complexity.  We need a place to store these
+// cached defs; the only good answer is in the metatable.  This means we need
+// a new metatable for every symtab instance (instead of one shared by all
+// instances).  Since this is different than the regular pattern, we can't
+// use luaL_checkudata(), we have to implement it ourselves.
+typedef struct {
+  upb_symtab *symtab;
+} lupb_symtab;
+
+static int lupb_symtab_gc(lua_State *L);
+
+// Inherits a ref on the symtab.
+static void lupb_pushnewsymtab(lua_State *L, upb_symtab *symtab) {
+  lupb_symtab *lsymtab = lua_newuserdata(L, sizeof(lupb_symtab));
+  lsymtab->symtab = symtab;
+  // Create its metatable (see note above about mt-per-object).
+  lua_createtable(L, 0, 1);
+  luaL_getmetatable(L, "upb.symtab");
+  lua_setfield(L, -2, "__index");  // Uses the type metatable to find methods.
+  lua_pushcfunction(L, lupb_symtab_gc);
+  lua_setfield(L, -2, "__gc");
+
+  // Put this metatable in the registry so we can find it for type validation.
+  lua_pushlightuserdata(L, lsymtab);
+  lua_pushvalue(L, -2);
+  lua_rawset(L, LUA_REGISTRYINDEX);
+
+  // Set the symtab's metatable.
+  lua_setmetatable(L, -2);
+}
+
+// Checks that narg is a proper lupb_symtab object.  If it is, leaves its
+// metatable on the stack for cache lookups/updates.
+lupb_symtab *lupb_symtab_check(lua_State *L, int narg) {
+  lupb_symtab *symtab = lua_touserdata(L, narg);
+  if (symtab != NULL) {
+    if (lua_getmetatable(L, narg)) {
+      // We use a metatable-per-object to support memoization of defs.
+      lua_pushlightuserdata(L, symtab);
+      lua_rawget(L, LUA_REGISTRYINDEX);
+      if (lua_rawequal(L, -1, -2)) {  // Does it have the correct mt?
+        lua_pop(L, 1);  // Remove one copy of the mt, keep the other.
+        return symtab;
+      }
+    }
+  }
+  luaL_typerror(L, narg, "upb.symtab");
+  return NULL;  // Placate the compiler; luaL_typerror will longjmp out of here.
+}
+
+static int lupb_symtab_gc(lua_State *L) {
+  lupb_symtab *s = lupb_symtab_check(L, 1);
+  upb_symtab_unref(s->symtab);
+
+  // Remove its metatable from the registry.
+  lua_pushlightuserdata(L, s);
+  lua_pushnil(L);
+  lua_rawset(L, LUA_REGISTRYINDEX);
+  return 0;
+}
+
+// "mt" is the index of the metatable, -1 is the fqname of this def.
+// Leaves the Lua object for the def at the top of the stack.
+// Inherits a ref on "def".
+static void lupb_symtab_getorcreate(lua_State *L, upb_def *def, int mt) {
+  // We may have this def cached, in which case we should return the same Lua
+  // object (as long as the value in the underlying symtab has not changed.
+  lua_rawget(L, mt);
+  if (!lua_isnil(L, -1)) {
+    // Def is cached, make sure it hasn't changed.
+    lupb_def *ldef = lua_touserdata(L, -1);
+    if (!ldef) luaL_error(L, "upb's internal cache is corrupt.");
+    if (ldef->def == def) {
+      // Cache is good, we can just return the cached value.
+      upb_def_unref(def);
+      return;
+    }
+  }
+  // Cached entry didn't exist or wasn't good.
+  lua_pop(L, 1);  // Remove bad cached value.
+  lupb_pushnewdef(L, def);
+
+  // Set it in the cache.
+  lua_pushvalue(L, 2);  // push name (arg to this function).
+  lua_pushvalue(L, -2); // push the new def.
+  lua_rawset(L, mt);    // set in the cache (the mt).
+}
+
+static int lupb_symtab_lookup(lua_State *L) {
+  lupb_symtab *s = lupb_symtab_check(L, 1);
+  size_t len;
+  const char *name = luaL_checklstring(L, 2, &len);
+  upb_string namestr = UPB_STACK_STRING_LEN(name, len);
+  upb_def *def = upb_symtab_lookup(s->symtab, &namestr);
+  if (!def) {
+    // There shouldn't be a value in our cache either because the symtab
+    // currently provides no API for deleting syms from a table.  In case
+    // this changes in the future, we explicitly delete from the cache here.
+    lua_pushvalue(L, 2);  // push name (arg to this function).
+    lua_pushnil(L);
+    lua_rawset(L, -3);  // lupb_symtab_check() left our mt on the stack.
+
+    // Return nil because the symbol was not found.
+    lua_pushnil(L);
+    return 1;
+  } else {
+    lua_pushvalue(L, 2);
+    lupb_symtab_getorcreate(L, def, 3);
+    return 1;
+  }
+}
+
+static int lupb_symtab_getdefs(lua_State *L) {
+  lupb_symtab *s = lupb_symtab_check(L, 1);
+  upb_deftype_t type = luaL_checkint(L, 2);
+  int count;
+  upb_def **defs = upb_symtab_getdefs(s->symtab, &count, type);
+
+  // Create the table in which we will return the defs.
+  lua_createtable(L, 0, count);
+  int ret = lua_gettop(L);
+
+  for (int i = 0; i < count; i++) {
+    upb_def *def = defs[i];
+    // Look it up in the cache by name.
+    upb_string *name = def->fqname;
+    lua_pushlstring(L, upb_string_getrobuf(name), upb_string_len(name));
+    lua_pushvalue(L, -1);  // Push it again since the getorcreate consumes one.
+    lupb_symtab_getorcreate(L, def, 3);
+
+    // Add it to our return table.
+    lua_settable(L, ret);
+  }
+  return 1;
+}
+
+static int lupb_symtab_add_descriptorproto(lua_State *L) {
+  lupb_symtab *s = lupb_symtab_check(L, 1);
+  upb_symtab_add_descriptorproto(s->symtab);
+  return 0;  // No args to return.
+}
+
+static const struct luaL_Reg lupb_symtab_methods[] = {
+  {"add_descriptorproto", lupb_symtab_add_descriptorproto},
+  //{"addfds", lupb_symtab_addfds},
+  {"getdefs", lupb_symtab_getdefs},
+  {"lookup", lupb_symtab_lookup},
+  //{"resolve", lupb_symtab_resolve},
+  {NULL, NULL}
+};
+
+
+/* lupb toplevel **************************************************************/
+
+static int lupb_symtab_new(lua_State *L) {
+  upb_symtab *s = upb_symtab_new();
+  lupb_pushnewsymtab(L, s);
+  return 1;
+}
+
+static const struct luaL_Reg lupb_toplevel_methods[] = {
+  {"symtab", lupb_symtab_new},
+  {NULL, NULL}
+};
+
+int luaopen_upb(lua_State *L) {
+  luaL_newmetatable(L, "upb.msgdef");
+  luaL_register(L, NULL, lupb_msgdef_methods);
+
+  luaL_newmetatable(L, "upb.enumdef");
+  luaL_register(L, NULL, lupb_enumdef_methods);
+
+  luaL_newmetatable(L, "upb.symtab");
+  luaL_register(L, NULL, lupb_symtab_methods);
+
+  luaL_register(L, "upb", lupb_toplevel_methods);
+  return 1;  // Return package table.
+}