Fix. Reset options will also reset value in storage.

```Lua
-- Fixed
e:setopt_httppost(curl.form())
e:setopt_httppost(curl.form())
-- `e` store 2 form object and the will alive until `e` is alive.
```

src/lceasy.c

@@ -201,7 +201,7 @@ static int lcurl_opt_set_string_(lua_State *L, int opt, int store){
     return lcurl_fail_ex(L, p->err_mode, LCURL_ERROR_EASY, code);
   }
 
-  if(store)lcurl_storage_preserve_value(L, p->storage, 2);
+  if(store)lcurl_storage_preserve_iv(L, p->storage, opt, 2);
 
   lua_settop(L, 1);
   return 1;
@@ -264,7 +264,7 @@ static int lcurl_easy_set_POSTFIELDS(lua_State *L){
   if(code != CURLE_OK){
     return lcurl_fail_ex(L, p->err_mode, LCURL_ERROR_EASY, code);
   }
-  lcurl_storage_preserve_value(L, p->storage, 2);
+  lcurl_storage_preserve_iv(L, p->storage, CURLOPT_POSTFIELDS, 2);
   code = curl_easy_setopt(p->curl, CURLOPT_POSTFIELDSIZE, (long)len);
   if(code != CURLE_OK){
     return lcurl_fail_ex(L, p->err_mode, LCURL_ERROR_EASY, code);
@@ -285,7 +285,7 @@ static int lcurl_easy_set_HTTPPOST(lua_State *L){
     return lcurl_fail_ex(L, p->err_mode, LCURL_ERROR_EASY, code);
   }
 
-  lcurl_storage_preserve_value(L, p->storage, 2);
+  lcurl_storage_preserve_iv(L, p->storage, CURLOPT_HTTPPOST, 2);
 
   lua_settop(L, 1);
   return 1;
@@ -299,7 +299,7 @@ static int lcurl_easy_set_SHARE(lua_State *L){
     return lcurl_fail_ex(L, p->err_mode, LCURL_ERROR_EASY, code);
   }
 
-  lcurl_storage_preserve_value(L, p->storage, 2);
+  lcurl_storage_preserve_iv(L, p->storage, CURLOPT_SHARE, 2);
 
   lua_settop(L, 1);
   return 1;

src/lcutils.c

@@ -2,6 +2,9 @@
 #include "lcutils.h"
 #include "lcerror.h"
 
+#define LCURL_STORAGE_SLIST 1
+#define LCURL_STORAGE_KV    2
+
 int lcurl_storage_init(lua_State *L){
   lua_newtable(L);
   return luaL_ref(L, LCURL_LUA_REGISTRY);
@@ -15,32 +18,59 @@ void lcurl_storage_preserve_value(lua_State *L, int storage, int i){
   lua_pop(L, 1);
 }
 
-int lcurl_storage_preserve_slist(lua_State *L, int storage, struct curl_slist * list){
-  int r;
-  lua_rawgeti(L, LCURL_LUA_REGISTRY, storage);
-  lua_rawgeti(L, -1, 1); // list storage
+static void lcurl_storage_ensure_t(lua_State *L, int t){
+  lua_rawgeti(L, -1, t);
   if(!lua_istable(L, -1)){
     lua_pop(L, 1);
     lua_newtable(L);
     lua_pushvalue(L, -1);
-    lua_rawseti(L, -3, 1);
+    lua_rawseti(L, -3, LCURL_STORAGE_SLIST);
   }
+}
+
+int lcurl_storage_preserve_slist(lua_State *L, int storage, struct curl_slist * list){
+  int r;
+  lua_rawgeti(L, LCURL_LUA_REGISTRY, storage);
+  lcurl_storage_ensure_t(L, LCURL_STORAGE_SLIST);
   lua_pushlightuserdata(L, list);
   r = luaL_ref(L, -2);
   lua_pop(L, 2);
   return r;
 }
 
+void lcurl_storage_preserve_iv(lua_State *L, int storage, int i, int v){
+  v = lua_absindex(L, v);
+
+  lua_rawgeti(L, LCURL_LUA_REGISTRY, storage);
+  lcurl_storage_ensure_t(L, LCURL_STORAGE_KV);
+  lua_pushvalue(L, v);
+  lua_rawseti(L, -2, i);
+  lua_pop(L, 2);
+}
+
+void lcurl_storage_remove_i(lua_State *L, int storage, int i){
+  lua_rawgeti(L, LCURL_LUA_REGISTRY, storage);
+  lua_rawgeti(L, -1, LCURL_STORAGE_KV);
+  if(lua_istable(L, -1)){
+    lua_pushnil(L);
+    lua_rawseti(L, -3, i);
+  }
+  lua_pop(L, 2);
+}
+
 struct curl_slist* lcurl_storage_remove_slist(lua_State *L, int storage, int idx){
   struct curl_slist* list;
   assert(idx != LUA_NOREF);
   lua_rawgeti(L, LCURL_LUA_REGISTRY, storage);
-  lua_rawgeti(L, -1, 1); // list storage
+  lua_rawgeti(L, -1, LCURL_STORAGE_SLIST); // list storage
+  if(lua_istable(L, -1)){
     lua_rawgeti(L, -1, idx);
     list = lua_touserdata(L, -1);
     assert(list);
     luaL_unref(L, -2, idx);
-  lua_pop(L, 3);
+    lua_pop(L, 1);
+  }
+  lua_pop(L, 2);
   return list;
 }
 

src/lcutils.h

@@ -24,6 +24,10 @@ int lcurl_storage_preserve_slist(lua_State *L, int storage, struct curl_slist *
 
 struct curl_slist* lcurl_storage_remove_slist(lua_State *L, int storage, int idx);
 
+void lcurl_storage_preserve_iv(lua_State *L, int storage, int i, int v);
+
+void lcurl_storage_remove_i(lua_State *L, int storage, int i);
+
 int lcurl_storage_free(lua_State *L, int storage);
 
 struct curl_slist* lcurl_util_array_to_slist(lua_State *L, int t);

test/test_easy.lua

@@ -8,6 +8,15 @@ local scurl      = require "lcurl.safe"
 local url        = "http://example.com"
 local fname      = "./test.download"
 
+local function weak_ptr(val)
+  return setmetatable({value = val},{__mode = 'v'})
+end
+
+local function gc_collect()
+  collectgarbage("collect")
+  collectgarbage("collect")
+end
+
 local _ENV = TEST_CASE'write_callback' do
 
 local c, f
@@ -64,6 +73,33 @@ end
 
 end
 
+local _ENV = TEST_CASE'setopt_form' do
+
+local c
+
+function teardown()
+  if c then c:close() end
+  c = nil
+end
+
+function test()
+  local pfrom, e
+  do
+    local form = curl.form()
+    e = curl.easy{httppost = form}
+    pfrom = weak_ptr(form)
+  end
+
+  gc_collect()
+  assert(pfrom.value)
+
+  e:setopt_httppost(curl.form())
+
+  gc_collect()
+  assert(not pfrom.value)
+end
+
+end