bytelazy commented on code in PR #12391:
URL: https://github.com/apache/apisix/pull/12391#discussion_r2328757087
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apisix/plugins/grpc-transcode/response.lua:
##########
@@ -23,6 +23,48 @@ local string = string
local ngx_decode_base64 = ngx.decode_base64
local ipairs = ipairs
local pcall = pcall
+local type = type
+local pairs = pairs
+local setmetatable = setmetatable
+
+pb.option "decode_default_array"
+-- Protobuf repeated field label value
+local PROTOBUF_REPEATED_LABEL = 3
+local repeated_label = PROTOBUF_REPEATED_LABEL
+
+local function fetch_proto_array_names(proto_obj)
+ local names = {}
+ if type(proto_obj) == "table" then
+ for k,v in pairs(proto_obj) do
+ if type(v) == "table" then
+ local sub_names = fetch_proto_array_names(v)
+ for sub_name,_ in pairs(sub_names) do
+ names[sub_name] = 1
+ end
+ end
+ end
+ if proto_obj["label"] == repeated_label then
+ if proto_obj["name"] then
+ names[proto_obj["name"]] = 1
+ end
+ end
+ end
+ return names
+end
+
+local function set_default_array(tab, array_names)
+ if type(tab) ~= "table" then
+ return
+ end
+ for k, v in pairs(tab) do
+ if type(v) == "table" then
+ if array_names[k] == 1 then
+ setmetatable(v, core.json.array_mt)
+ end
+ set_default_array(v, array_names)
+ end
+ end
+end
Review Comment:
hi @nic-6443
In APISIX, empty repeated fields are decoded by lua-protobuf as plain Lua
tables ({}). By default, cjson encodes an empty table as {} rather than [].
pb.option("decode_default_array") ensures the field is always a table, but
it does not mark it as an array for JSON encoding.
Only tables with cjson.empty_array_mt (or core.json.array_mt) serialize as
[].
There’s no way to make empty repeated fields encode as [] purely via
lua-protobuf configuration. Handling this in response.lua (setting array_mt) is
the reliable solution with the current APISIX setup.
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