fix(brotli-plugin): Skip brotli compression for upstream compressed response

apisix/plugins/brotli.lua

@@ -163,6 +163,11 @@ function _M.header_filter(conf, ctx)
         return
     end
 
+    local content_encoded = ngx_header["Content-Encoding"]
+    if content_encoded then
+        -- Don't compress if Content-Encoding is present in upstream data
+        return
+    end
     local types = conf.types
     local content_type = ngx_header["Content-Type"]
     if not content_type then

docs/en/latest/plugins/brotli.md

@@ -47,6 +47,12 @@ sudo sh -c "echo /usr/local/brotli/lib >> /etc/ld.so.conf.d/brotli.conf"
 sudo ldconfig
 ```
 
+:::caution
+
+If the upstream is returning compressed response, than brotli plugin won't be able to compress. 
+
+:::
+
 ## Attributes
 
 | Name           | Type                 | Required | Default       | Valid values | Description                                                                             |