nic-6443 commented on code in PR #13904:
URL: https://github.com/apache/apisix/pull/13904#discussion_r3910430846
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apisix/core/config_yaml.lua:
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@@ -62,6 +69,37 @@ local _M = {
"cannot be restored from other workers and shared dict"
}
+-- the "config" key in the standalone-config shared dict stores
+-- "<digest length>\n<digest><json body>" instead of plain JSON, so a worker
+-- can compare digests without decoding the (potentially large) JSON on
+-- every poll
+-- the reason for combining them into a single string and writing them to
+-- only one key is to ensure concurrent safety for updates by multiple
+-- workers
+local CONFIG_DIGEST_LENGTH_SEPARATOR = "\n"
+
+function _M.encode_config(digest, raw)
+ digest = digest or ""
+ return #digest .. CONFIG_DIGEST_LENGTH_SEPARATOR .. digest .. raw
+end
+
+
+function _M.decode_config(stored)
+ local idx = find_str(stored, CONFIG_DIGEST_LENGTH_SEPARATOR, 1, true)
+ if not idx then
+ return nil, nil, "missing digest length prefix"
+ end
+
+ local digest_len = tonumber(sub_str(stored, 1, idx - 1))
+ if not digest_len then
+ return nil, nil, "invalid digest length prefix"
+ end
+
+ local digest_start = idx + 1
+ local digest_end = digest_start + digest_len - 1
+ return sub_str(stored, digest_start, digest_end), sub_str(stored,
digest_end + 1)
+end
Review Comment:
I feel it's somewhat inappropriate to put this piece of code in
`config_yaml.lua`. When I saw `config_yaml.decode_config` and
`config_yaml.encode_config` at the call site, I thought they were performing
YAML decode and encode operations, but they actually handle a custom data
structure.
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