util.jsonpointer: Resolve JSON Pointers per RFC 6901

1 files changed, 40 insertions, 0 deletions

diff --git a/util/jsonpointer.lua b/util/jsonpointer.lua
new file mode 100644
index 00000000..7c657266
--- /dev/null
+++ b/util/jsonpointer.lua
@@ -0,0 +1,40 @@
+local function unescape_token(escaped_token)
+	local unescaped = escaped_token:gsub("~1", "/"):gsub("~0", "~")
+	return unescaped
+end
+
+local function resolve_json_pointer(ref, path)
+	local ptr_len = #path + 1
+	for part, pos in path:gmatch("/([^/]*)()") do
+		local token = unescape_token(part)
+		if not (type(ref) == "table") then
+			return nil
+		end
+		local idx = next(ref)
+		local new_ref
+
+		if type(idx) == "string" then
+			new_ref = ref[token]
+		elseif math.type(idx) == "integer" then
+			local i = tonumber(token)
+			if token == "-" then
+				i = #ref + 1
+			end
+			new_ref = ref[i]
+		else
+			return nil, "invalid-table"
+		end
+
+		if pos == ptr_len then
+			return new_ref
+		elseif type(new_ref) == "table" then
+			ref = new_ref
+		elseif not (type(ref) == "table") then
+			return nil, "invalid-path"
+		end
+
+	end
+	return ref
+end
+
+return { resolve = resolve_json_pointer }