util.jsonpointer: Resolve JSON Pointers per RFC 6901

teal-src/util/jsonpointer.tl

@@ -0,0 +1,46 @@
+
+local enum ptr_error
+	"invalid-table"
+	"invalid-path"
+end
+
+local function unescape_token(escaped_token : string) : string
+	local unescaped = escaped_token:gsub("~1", "/"):gsub("~0", "~")
+	return unescaped
+end
+
+local function resolve_json_pointer(ref : table, path : string) : any, ptr_error
+	local ptr_len = #path+1
+	for part, pos in path:gmatch("/([^/]*)()") do
+		local token = unescape_token(part)
+		if not ref is table then
+			return nil
+		end
+		local idx = next(ref)
+		local new_ref : any
+
+		if idx is string then
+			new_ref = ref[token]
+		elseif idx is 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 as integer == ptr_len then
+			return new_ref
+		elseif new_ref is table then
+			ref = new_ref
+		elseif not ref is table then
+			return nil, "invalid-path"
+		end
+
+	end
+	return ref
+end
+
+return {
+	resolve = resolve_json_pointer,
+}