Make the file_system_buffer filter available (#21025)

Signed-off-by: Raven Black <ravenblack@dropbox.com>

Mirrored from https://github.com/envoyproxy/envoy @ 88e3ae3cf83ef3b98e146cee739f6f1969a83ea2

envoy/extensions/filters/http/file_system_buffer/v3/file_system_buffer.proto

@@ -18,7 +18,9 @@ option go_package = "github.com/envoyproxy/go-control-plane/envoy/extensions/fil
 option (udpa.annotations.file_status).package_version_status = ACTIVE;
 option (xds.annotations.v3.file_status).work_in_progress = true;
 
-// [#not-implemented-hide:]
+// [#protodoc-title: FileSystemBufferFilterConfig]
+// [#extension: envoy.filters.http.file_system_buffer]
+
 // The behavior of the filter for a stream.
 // [#next-free-field: 6]
 message BufferBehavior {
@@ -61,7 +63,6 @@ message BufferBehavior {
   }
 }
 
-// [#not-implemented-hide:]
 // The configuration for one direction of the filter behavior.
 message StreamConfig {
   // Whether to bypass / stream / fully buffer / etc.
@@ -84,11 +85,12 @@ message StreamConfig {
   // ``memory_buffer_bytes_limit`` was 32MiB, and ``storage_buffer_queue_high_watermark_bytes``
   // was 64MiB, and the filesystem is backed up so writes are not occurring promptly,
   // then:
+  //
   // * Any request less than 32MiB will eventually pass through without ever attempting
   //   to write to disk.
   // * Any request with over 32MiB buffered will start trying to write to disk.
-  //   * If it reaches (32+64)MiB buffered and not yet written to disk, a high
-  //     watermark signal is sent to the source.
+  //   If it reaches (32+64)MiB buffered in memory (write to disk isn't keeping up), a high
+  //   watermark signal is sent to the source.
   // * Any stream whose total size exceeds
   //   ``memory_buffer_bytes_limit + storage_buffer_bytes_limit`` will provoke an error.
   //   (Note, if the recipient *is* consuming data then it is possible for such an
@@ -96,12 +98,11 @@ message StreamConfig {
   //   isn't consuming data too slowly.)
   //
   // The low watermark signal is sent when the memory buffer is at size
-  //  ``memory_buffer_bytes_limit + (storage_buffer_queue_high_watermark_bytes / 2)``.
+  // ``memory_buffer_bytes_limit + (storage_buffer_queue_high_watermark_bytes / 2)``.
   google.protobuf.UInt64Value storage_buffer_queue_high_watermark_bytes = 4;
 }
 
-// [#not-implemented-hide:]
-// Configuration for file system buffer filter.
+// A :ref:`file system buffer <config_http_filters_file_system_buffer>` filter configuration.
 //
 // Route-specific configs override only the fields they explicitly include; unset
 // fields inherit from the vhost or listener-level config, or, if never set,