fdiary opened a new issue #8539:
URL: https://github.com/apache/trafficserver/issues/8539
Hi !
If ATS receives a POST request to 'fresh cache existing' URL, we have
CACHE_LOOKUP_HIT_FRESH status. But such ATS will never return such fresh cache
regardless if POST request (that should be always sent to the backend) succeeds
or not. I believe the status should be something else (maybe CACHE_LOOKUP_SKIP
?), by the following reason.
[background]
I am writing a Lua plugin script, that modifies response body. To do that, I
want uncompressed response from the backend, thus I use compress plugin, later
than lua plugin in plugin.config, to 'remove Accept-Encoding sent to the
backend' and 'compress response from ATS'.
* plugin.config
```
tslua.so modify_body.lua
compress.so compress.config
```
* modify.lua
```lua
function do_global_read_response()
ts.hook(TS_LUA_HOOK_SEND_RESPONSE_HDR, modify_body)
end
function do_global_cache_lookup_complete()
if ts.http.get_cache_lookup_status() == TS_LUA_CACHE_LOOKUP_HIT_FRESH
then
ts.hook(TS_LUA_HOOK_SEND_RESPONSE_HDR, modify_body)
end
end
function modify_body(data, end_of_stream)
...
end
```
* compress.config
```
cache false
remove-accept-encoding true
compressible-content-type text/*
```
In case of GET request having fresh cache,
1. (lua) cache_lookup_complete; register transform hook to modify body,
because of CACHE_LOOKUP_HIT_FRESH status
2. (compress) cache_lookup_complete: register transform hook to compress
response, because of CACHE_LOOKUP_HIT_FRESH status
https://github.com/apache/trafficserver/blob/d0a44f86345c9125946978efbbf837a720fc9537/plugins/compress/compress.cc#L884-L891
So transform is invoked 1. -> 2. order, that is good.
In case of GET/POST request withoug fresh cache, the following will happen,
that is good.
1. (lua) cache_lookup_complete; do nothing, because of
non-CACHE_LOOKUP_HIT_FRESH status
2. (compress) cache_lookup_complete: do nothing, because of
non-CACHE_LOOKUP_HIT_FRESH status
3. (lua) read_response; register transform hook to modify body
4. (compress) read_response: register transform hook to compress response
So transform is invoked 3. -> 4. order, that is good.
in case of POST request having fresh cache, the following will happen, that
is NOT good.
1. (lua) cache_lookup_complete; register transform hook to modify body,
because of CACHE_LOOKUP_HIT_FRESH status, but it is not used as we will anyway
have another response from the backend
2. (compress) cache_lookup_complete: register transform hook to compress
response, because of CACHE_LOOKUP_HIT_FRESH status
3. (lua) read_response; register transform hook to modify body
4. (compress) read_response: compress plugin does NOT register transform
hook, if it is done in cache_lookup_complete stage.
So transform is invoked 2. -> 3. order for the final response, that is NOT
good, i.e. for the 'response from the backend to this POST request', compress
plugin's compress transform is invoked first, thus Lua script's modify_body
function gets compressed result.
(also compress plugin does nothing in send_request timing if transform is
registered in cache_lookup_complete timing, `remove-access-encoding true` is
not effective for this case)
To avoid this issue, I patched compress plugin so that it does NOT register
transform hook in cache_lookup_complete timing, in case of POST request. But
similar issue can happen for any plugin and it breaks expected hook timing
order by plugin order in plugin.config.
This is why I would like to propose another status than
CACHE_LOOKUP_HIT_FRESH for POST request.
Thanks in advance !
Kazuhiko
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