Add. Allow set null to callbacks.

src/lcutils.c

@@ -171,8 +171,6 @@ int lcurl_set_callback(lua_State *L, lcurl_callback_t *c, int i, const char *met
   luaL_argcheck(L, !lua_isnoneornil(L, i), i, "no function present");
   luaL_argcheck(L, (top < (i + 2)), i + 2, "no arguments expected");
 
-  // if(top > (i + 1)) lua_settop(L, i + 1); // this for force ignore other arguments
-
   assert((top == i)||(top == (i + 1)));
 
   if(c->ud_ref != LUA_NOREF){
@@ -185,6 +183,19 @@ int lcurl_set_callback(lua_State *L, lcurl_callback_t *c, int i, const char *met
     c->cb_ref = LUA_NOREF;
   }
 
+  if(lutil_is_null(L, i)){
+    if(top == (i + 1)){
+      // Do we can just ignore this?
+      luaL_argcheck(L, 
+        lua_isnoneornil(L, i + 1) || lutil_is_null(L, i + 1)
+        ,i + 1, "no context allowed when set callback to null"
+      );
+    }
+    lua_pop(L, top - i + 1);
+
+    return 1;
+  }
+
   if(lua_gettop(L) == (i + 1)){// function + context
     c->ud_ref = luaL_ref(L, LCURL_LUA_REGISTRY);
     c->cb_ref = luaL_ref(L, LCURL_LUA_REGISTRY);

test/test_easy.lua

@@ -153,9 +153,16 @@ function test_reset_write_callback()
   assert_equal(c, c:setopt_writefunction(f))
   assert_equal(c, c:setopt_writefunction(f.write, f))
   assert_equal(c, c:setopt_writefunction(print))
+  assert_equal(c, c:setopt_writefunction(print, null))
+  assert_equal(c, c:setopt_writefunction(null))
+  assert_equal(c, c:setopt_writefunction(null, nil))
+  assert_equal(c, c:setopt_writefunction(null, null))
   assert_error(function()c:setopt_writefunction()end)
   assert_error(function()c:setopt_writefunction(nil)end)
   assert_error(function()c:setopt_writefunction(nil, f)end)
+  assert_error(function()c:setopt_writefunction(null, {})end)
+  assert_error(function()c:setopt_writefunction(print, {}, nil)end)
+  assert_error(function()c:setopt_writefunction(print, {}, null)end)
 end
 
 function test_write_pass_01()
@@ -210,6 +217,38 @@ function test_write_coro()
   assert_equal(co2, called)
 end
 
+function test_write_pass_null_context()
+  c = assert(curl.easy{
+    url = GET_URL;
+  })
+
+  local context
+  assert_equal(c, c:setopt_writefunction(function(ctx)
+    context = ctx
+    return true
+  end, null))
+
+  assert_equal(c, c:perform())
+  assert_equal(null, context)
+end
+
+function test_write_pass_nil_context()
+  c = assert(curl.easy{
+    url = GET_URL;
+  })
+
+  local context, called
+  assert_equal(c, c:setopt_writefunction(function(ctx)
+    context = ctx
+    called = true
+    return true
+  end, nil))
+
+  assert_equal(c, c:perform())
+  assert_true(called)
+  assert_nil(context)
+end
+
 end
 
 local _ENV = TEST_CASE'progress_callback'    if ENABLE then
@@ -381,9 +420,14 @@ function test_reset_header_callback()
   assert_equal(c, c:setopt_headerfunction(f))
   assert_equal(c, c:setopt_headerfunction(f.header, f))
   assert_equal(c, c:setopt_headerfunction(print))
+  assert_equal(c, c:setopt_headerfunction(null))
+  assert_equal(c, c:setopt_headerfunction(null, nil))
+  assert_equal(c, c:setopt_headerfunction(null, null))
   assert_error(function()c:setopt_headerfunction()end)
   assert_error(function()c:setopt_headerfunction(nil)end)
   assert_error(function()c:setopt_headerfunction(nil, f)end)
+  assert_error(function()c:setopt_headerfunction(null, {})end)
+  assert_error(function()c:setopt_headerfunction(print, {}, nil)end)
 end
 
 function test_header_pass_01()