util.stanza: Add method for extracting a single attribute value

Sometimes you only care about a single attribute, but the child tag
itself may be optional, leading to needing `tag and tag.attr.foo` or
`stanza:find("tag@foo")`.

The `:find()` method is fairly complex, so avoiding it for this kind of
simpler use case is a win.

1 files changed, 8 insertions, 0 deletions

diff --git a/util/stanza.lua b/util/stanza.lua
index a14be5f0..b75a1f32 100644
--- a/util/stanza.lua
+++ b/util/stanza.lua
@@ -176,6 +176,14 @@ function stanza_mt:get_child_text(name, xmlns)
 	return nil;
 end
 
+function stanza_mt:get_child_attr(name, xmlns, attr)
+	local tag = self:get_child(name, xmlns);
+	if tag then
+		return tag.attr[attr];
+	end
+	return nil;
+end
+
 function stanza_mt:child_with_name(name)
 	for _, child in ipairs(self.tags) do
 		if child.name == name then return child; end