[PATCH v3] fetch-pack: write effective filter to trace2

Administrators of a managed Git environment (like the one at $DAYJOB) might want to quantify the performance change of fetches with and without filters from the client's point of view, and also detect if a server does not support it. Therefore, log the filter information being sent to the server whenever a fetch (or clone) occurs. Note that this is not necessarily the same as what's specified on the CLI, because during a fetch, the configured filter is used whenever a filter is not specified on the CLI.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---
Here's v3, with an updated function name.
---
Range-diff against v2:
1:  d3ea7d3b95 ! 1:  17cef49fcc fetch-pack: write effective filter to trace2
    @@ Commit message
     
         Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
         ---
    -    Thanks everyone for your comments. I've renamed the keys and
    -    distinguished the case in which the server does not support filters
    -    following Jeff's suggestions.
    -
    -    A few small discussion points:
    -     - whether we need the print_verbose now that we have traces
    -     - should we log if no filter is specified
    -     - if yes, what key should it be logged under (I used "filter/none" for
    -       now)
    +    Here's v3, with an updated function name.
     
      ## fetch-pack.c ##
     @@ fetch-pack.c: static void mark_tips(struct fetch_negotiator *negotiator,
      	return;
      }
      
    -+static void write_and_trace_filter(struct fetch_pack_args *args,
    -+				   struct strbuf *req_buf,
    -+				   int server_supports_filter)
    ++static void send_filter(struct fetch_pack_args *args,
    ++			struct strbuf *req_buf,
    ++			int server_supports_filter)
     +{
     +	if (args->filter_options.choice) {
     +		const char *spec =
    @@ fetch-pack.c: static int find_common(struct fetch_negotiator *negotiator,
     -			expand_list_objects_filter_spec(&args->filter_options);
     -		packet_buf_write(&req_buf, "filter %s", spec);
     -	}
    -+	write_and_trace_filter(args, &req_buf, server_supports_filtering);
    ++	send_filter(args, &req_buf, server_supports_filtering);
      	packet_buf_flush(&req_buf);
      	state_len = req_buf.len;
      
    @@ fetch-pack.c: static int send_fetch_request(struct fetch_negotiator *negotiator,
     -	} else if (args->filter_options.choice) {
     -		warning("filtering not recognized by server, ignoring");
     -	}
    -+	write_and_trace_filter(args, &req_buf,
    -+			       server_supports_feature("fetch", "filter", 0));
    ++	send_filter(args, &req_buf,
    ++		    server_supports_feature("fetch", "filter", 0));
      
      	if (server_supports_feature("fetch", "packfile-uris", 0)) {
      		int i;

 fetch-pack.c | 40 ++++++++++++++++++++++++++--------------
 1 file changed, 26 insertions(+), 14 deletions(-)