reftable/record: reuse message when decoding log records

Same as the preceding commit we can allocate log messages as needed when
decoding log records, thus further reducing the number of allocations.
Before:

    HEAP SUMMARY:
        in use at exit: 13,473 bytes in 122 blocks
      total heap usage: 3,068,488 allocs, 3,068,366 frees, 307,122,961 bytes allocated

After:

    HEAP SUMMARY:
        in use at exit: 13,473 bytes in 122 blocks
      total heap usage: 2,068,487 allocs, 2,068,365 frees, 305,122,946 bytes allocated

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

reftable/record.c

@@ -871,6 +871,7 @@ static int reftable_log_record_decode(void *rec, struct strbuf key,
 		switch (r->value_type) {
 		case REFTABLE_LOG_UPDATE:
 			FREE_AND_NULL(r->value.update.message);
+			r->value.update.message_cap = 0;
 			FREE_AND_NULL(r->value.update.email);
 			FREE_AND_NULL(r->value.update.name);
 			break;
@@ -943,8 +944,8 @@ static int reftable_log_record_decode(void *rec, struct strbuf key,
 		goto done;
 	string_view_consume(&in, n);
 
-	r->value.update.message =
-		reftable_realloc(r->value.update.message, dest.len + 1);
+	REFTABLE_ALLOC_GROW(r->value.update.message, dest.len + 1,
+			    r->value.update.message_cap);
 	memcpy(r->value.update.message, dest.buf, dest.len);
 	r->value.update.message[dest.len] = 0;
 

reftable/reftable-record.h

@@ -96,6 +96,7 @@ struct reftable_log_record {
 			uint64_t time;
 			int16_t tz_offset;
 			char *message;
+			size_t message_cap;
 		} update;
 	} value;
 };