Advertise trace2 SID in protocol capabilities

In order to more easily debug remote operations, it is useful to be able to inspect both client-side and server-side traces. This series allows clients to record the server's trace2 session ID, and vice versa, by advertising the SID in a new "trace2-sid" protocol capability.

Changes since V1:
* Added a public trace2_session_id() function to trace2.{h,c}. Used this in place of tr2_sid_get().
* Fixed a style issue regarding using NULL rather than 0.

Josh Steadmon (11):
docs: new capability to advertise trace2 SIDs
docs: new trace2.advertiseSID option
trace2: add a public function for getting the SID
upload-pack: advertise trace2 SID in v0 capabilities
receive-pack: advertise trace2 SID in v0 capabilities
serve: advertise trace2 SID in v2 capabilities
transport: log received server trace2 SID
fetch-pack: advertise trace2 SID in capabilities upload-pack, serve: log received client trace2 SID
send-pack: advertise trace2 SID in capabilities
receive-pack: log received client trace2 SID

 Documentation/config/trace2.txt               |  4 +
 .../technical/protocol-capabilities.txt       | 13 ++-
 Documentation/technical/protocol-v2.txt       |  9 +++
 builtin/receive-pack.c                        | 15 ++++
 fetch-pack.c                                  | 10 +++
 send-pack.c                                   |  8 ++
 serve.c                                       | 18 +++++
 t/t5705-trace2-sid-in-capabilities.sh         | 79 +++++++++++++++++++
 trace2.c                                      |  5 ++
 trace2.h                                      |  2 +
 transport.c                                   | 10 +++
 upload-pack.c                                 | 22 +++++-
 12 files changed, 192 insertions(+), 3 deletions(-)
 create mode 100755 t/t5705-trace2-sid-in-capabilities.sh

Range-diff against v1:

 -:  ---------- >  1:  d04028c3c7 docs: new capability to advertise trace2 SIDs
 -:  ---------- >  2:  5d5097b671 docs: new trace2.advertiseSID option
 -:  ---------- >  3:  7f42aacd2b trace2: add a public function for getting the SID
 1:  c07bf8aede !  4:  4912af5f2b upload-pack: advertise trace2 SID in v0 capabilities
    @@ Commit message
     
      ## upload-pack.c ##
    -@@
    - #include "commit-graph.h"
    - #include "commit-reach.h"
    - #include "shallow.h"
    -+#include "trace2/tr2_sid.h"
    - 
    - /* Remember to update object flag allocation in object.h */
    - #define THEY_HAVE	(1u << 11)
     @@ upload-pack.c: struct upload_pack_data {
      	unsigned done : 1;					/* v2 only */
      	unsigned allow_ref_in_want : 1;				/* v2 only */
    @@ upload-pack.c: static void format_symref_info(struct strbuf *buf, struct string_
      
     +static void format_trace2_info(struct strbuf *buf, struct upload_pack_data *d) {
     +	if (d->advertise_trace2_sid && trace2_is_enabled())
    -+		strbuf_addf(buf, " trace2-sid=%s", tr2_sid_get());
    ++		strbuf_addf(buf, " trace2-sid=%s", trace2_session_id());
     +}
     +
      static int send_ref(const char *refname, const struct object_id *oid,
 2:  d42118ac41 !  5:  7003189c81 receive-pack: advertise trace2 SID in v0 capabilities
    @@ Commit message
     
      ## builtin/receive-pack.c ##
    -@@
    - #include "commit-reach.h"
    - #include "worktree.h"
    - #include "shallow.h"
    -+#include "trace2/tr2_sid.h"
    - 
    - static const char * const receive_pack_usage[] = {
    - 	N_("git receive-pack <git-dir>"),
     @@ builtin/receive-pack.c: static int receive_unpack_limit = -1;
      static int transfer_unpack_limit = -1;
      static int advertise_atomic_push = 1;
    @@ builtin/receive-pack.c: static void show_ref(const char *path, const struct obje
      		if (advertise_push_options)
      			strbuf_addstr(&cap, " push-options");
     +		if (advertise_trace2_sid && trace2_is_enabled())
    -+			strbuf_addf(&cap, " trace2-sid=%s", tr2_sid_get());
    ++			strbuf_addf(&cap, " trace2-sid=%s", trace2_session_id());
      		strbuf_addf(&cap, " object-format=%s", the_hash_algo->name);
      		strbuf_addf(&cap, " agent=%s", git_user_agent_sanitized());
      		packet_write_fmt(1, "%s %s%c%s\n",
 3:  ff80f70d33 !  6:  9573428cc0 serve: advertise trace2 SID in v2 capabilities
    @@ Commit message
     
      ## serve.c ##
     @@
    - #include "ls-refs.h"
      #include "serve.h"
      #include "upload-pack.h"
    -+#include "trace2/tr2_sid.h"
    -+
    -+static int advertise_trace2_sid;
      
    ++static int advertise_trace2_sid;
    ++
      static int always_advertise(struct repository *r,
      			    struct strbuf *value)
    + {
     @@ serve.c: static int object_format_advertise(struct repository *r,
      	return 1;
      }
    @@ serve.c: static int object_format_advertise(struct repository *r,
     +	if (!advertise_trace2_sid || !trace2_is_enabled())
     +		return 0;
     +	if (value)
    -+		strbuf_addstr(value, tr2_sid_get());
    ++		strbuf_addstr(value, trace2_session_id());
     +	return 1;
     +}
     +
 4:  1519767ead =  7:  21bdbf23f3 transport: log received server trace2 SID
 5:  ee4b3a7a55 !  8:  11b5b1b54f fetch-pack: advertise trace2 SID in capabilities
    @@ Commit message
     
      ## fetch-pack.c ##
    -@@
    - #include "fetch-negotiator.h"
    - #include "fsck.h"
    - #include "shallow.h"
    -+#include "trace2/tr2_sid.h"
    - 
    - static int transfer_unpack_limit = -1;
    - static int fetch_unpack_limit = -1;
     @@ fetch-pack.c: static int fetch_fsck_objects = -1;
      static int transfer_fsck_objects = -1;
      static int agent_supported;
    @@ fetch-pack.c: static int find_common(struct fetch_negotiator *negotiator,
      			if (agent_supported)    strbuf_addf(&c, " agent=%s",
      							    git_user_agent_sanitized());
     +			if (advertise_trace2_sid && server_sent_trace2_sid && trace2_is_enabled())
    -+				strbuf_addf(&c, " trace2-sid=%s", tr2_sid_get());
    ++				strbuf_addf(&c, " trace2-sid=%s", trace2_session_id());
      			if (args->filter_options.choice)
      				strbuf_addstr(&c, " filter");
      			packet_buf_write(&req_buf, "want %s%s\n", remote_hex, c.buf);
    @@ fetch-pack.c: static int send_fetch_request(struct fetch_negotiator *negotiator,
      	if (server_supports_v2("agent", 0))
      		packet_buf_write(&req_buf, "agent=%s", git_user_agent_sanitized());
     +	if (advertise_trace2_sid && server_supports_v2("trace2-sid", 0) && trace2_is_enabled())
    -+		packet_buf_write(&req_buf, "trace2-sid=%s", tr2_sid_get());
    ++		packet_buf_write(&req_buf, "trace2-sid=%s", trace2_session_id());
      	if (args->server_options && args->server_options->nr &&
      	    server_supports_v2("server-option", 1)) {
      		int i;
 6:  b160941c65 !  9:  23f44bc904 upload-pack, serve: log received client trace2 SID
    @@ upload-pack.c: static void receive_needs(struct upload_pack_data *data,
      		if (data->allow_filter &&
      		    parse_feature_request(features, "filter"))
      			data->filter_capability_requested = 1;
    -+		if ((arg = parse_feature_value(features, "trace2-sid", &feature_len, 0)))
    ++		if ((arg = parse_feature_value(features, "trace2-sid", &feature_len, NULL)))
     +		{
     +			char *client_sid = xstrndup(arg, feature_len);
     +			trace2_data_string("trace2", NULL, "client-sid", client_sid);
 7:  609958bd1a ! 10:  c0b1ffc6d8 send-pack: advertise trace2 SID in capabilities
    @@ Commit message
     
      ## send-pack.c ##
    -@@
    - #include "gpg-interface.h"
    - #include "cache.h"
    - #include "shallow.h"
    -+#include "trace2/tr2_sid.h"
    - 
    - int option_parse_push_signed(const struct option *opt,
    - 			     const char *arg, int unset)
     @@ send-pack.c: int send_pack(struct send_pack_args *args,
      	int use_sideband = 0;
      	int quiet_supported = 0;
    @@ send-pack.c: int send_pack(struct send_pack_args *args,
      	if (agent_supported)
      		strbuf_addf(&cap_buf, " agent=%s", git_user_agent_sanitized());
     +	if (advertise_trace2_sid && server_sent_trace2_sid && trace2_is_enabled())
    -+		strbuf_addf(&cap_buf, " trace2-sid=%s", tr2_sid_get());
    ++		strbuf_addf(&cap_buf, " trace2-sid=%s", trace2_session_id());
      
      	/*
      	 * NEEDSWORK: why does delete-refs have to be so specific to

8: 3bc412fc39 = 11: c47eddd9df receive-pack: log received client trace2 SID

2.29.1.341.ge80a0c044ae-goog