Merge pull request #162 from siffiejoe/exception-meta

Support table errors in LuaSockets LTN13 C implementation.

2 files changed, 41 insertions, 28 deletions

diff --git a/src/except.c b/src/except.c
index 261ac98..def35a0 100644
--- a/src/except.c
+++ b/src/except.c
@@ -12,7 +12,7 @@
 
 #if LUA_VERSION_NUM < 502
 #define lua_pcallk(L, na, nr, err, ctx, cont) \
-    ((void)ctx,(void)cont,lua_pcall(L, na, nr, err))
+    (((void)ctx),((void)cont),lua_pcall(L, na, nr, err))
 #endif
 
 #if LUA_VERSION_NUM < 503
@@ -39,12 +39,11 @@ static luaL_Reg func[] = {
 * Try factory
 \*-------------------------------------------------------------------------*/
 static void wrap(lua_State *L) {
-    lua_newtable(L);
-    lua_pushnumber(L, 1);
-    lua_pushvalue(L, -3);
-    lua_settable(L, -3);
-    lua_insert(L, -2);
-    lua_pop(L, 1);
+    lua_createtable(L, 1, 0);
+    lua_pushvalue(L, -2);
+    lua_rawseti(L, -2, 1);
+    lua_pushvalue(L, lua_upvalueindex(2));
+    lua_setmetatable(L, -2);
 }
 
 static int finalize(lua_State *L) {
@@ -58,15 +57,16 @@ static int finalize(lua_State *L) {
     } else return lua_gettop(L);
 }
 
-static int do_nothing(lua_State *L) { 
+static int do_nothing(lua_State *L) {
     (void) L;
-    return 0; 
+    return 0;
 }
 
 static int global_newtry(lua_State *L) {
     lua_settop(L, 1);
     if (lua_isnil(L, 1)) lua_pushcfunction(L, do_nothing);
-    lua_pushcclosure(L, finalize, 1);
+    lua_pushvalue(L, lua_upvalueindex(1));
+    lua_pushcclosure(L, finalize, 2);
     return 1;
 }
 
@@ -74,13 +74,16 @@ static int global_newtry(lua_State *L) {
 * Protect factory
 \*-------------------------------------------------------------------------*/
 static int unwrap(lua_State *L) {
-    if (lua_istable(L, -1)) {
-        lua_pushnumber(L, 1);
-        lua_gettable(L, -2);
-        lua_pushnil(L);
-        lua_insert(L, -2);
-        return 1;
-    } else return 0;
+    if (lua_istable(L, -1) && lua_getmetatable(L, -1)) {
+        int r = lua_rawequal(L, -1, lua_upvalueindex(2));
+        lua_pop(L, 1);
+        if (r) {
+            lua_pushnil(L);
+            lua_rawgeti(L, -2, 1);
+            return 1;
+        }
+    }
+    return 0;
 }
 
 static int protected_finish(lua_State *L, int status, lua_KContext ctx) {
@@ -110,7 +113,9 @@ static int protected_(lua_State *L) {
 }
 
 static int global_protect(lua_State *L) {
-    lua_pushcclosure(L, protected_, 1);
+    lua_settop(L, 1);
+    lua_pushvalue(L, lua_upvalueindex(1));
+    lua_pushcclosure(L, protected_, 2);
     return 1;
 }
 
@@ -118,6 +123,9 @@ static int global_protect(lua_State *L) {
 * Init module
 \*-------------------------------------------------------------------------*/
 int except_open(lua_State *L) {
-    luaL_setfuncs(L, func, 0);
+    lua_newtable(L); /* metatable for wrapped exceptions */
+    lua_pushboolean(L, 0);
+    lua_setfield(L, -2, "__metatable");
+    luaL_setfuncs(L, func, 1);
     return 0;
 }
diff --git a/src/except.h b/src/except.h
index 1e7a245..2497c05 100644
--- a/src/except.h
+++ b/src/except.h
@@ -9,21 +9,26 @@
 * error checking was taking a substantial amount of the coding. These
 * function greatly simplify the task of checking errors.
 *
-* The main idea is that functions should return nil as its first return
-* value when it finds an error, and return an error message (or value)
+* The main idea is that functions should return nil as their first return
+* values when they find an error, and return an error message (or value)
 * following nil. In case of success, as long as the first value is not nil,
 * the other values don't matter.
 *
 * The idea is to nest function calls with the "try" function. This function
-* checks the first value, and calls "error" on the second if the first is
-* nil. Otherwise, it returns all values it received. 
+* checks the first value, and, if it's falsy, wraps the second value in a
+* table with metatable and calls "error" on it. Otherwise, it returns all
+* values it received. Basically, it works like the Lua "assert" function,
+* but it creates errors targeted specifically at "protect".
 *
-* The protect function returns a new function that behaves exactly like the
-* function it receives, but the new function doesn't throw exceptions: it
-* returns nil followed by the error message instead.
+* The "newtry" function is a factory for "try" functions that call a
+* finalizer in protected mode before calling "error".
 *
-* With these two function, it's easy to write functions that throw
-* exceptions on error, but that don't interrupt the user script. 
+* The "protect" function returns a new function that behaves exactly like
+* the function it receives, but the new function catches exceptions thrown
+* by "try" functions and returns nil followed by the error message instead.
+*
+* With these three functions, it's easy to write functions that throw
+* exceptions on error, but that don't interrupt the user script.
 \*=========================================================================*/
 
 #include "lua.h"