http: add trace2 logging for retry operations

Add trace2 instrumentation to HTTP 429 retry operations to enable
monitoring and debugging of rate limit scenarios in production
environments.

The trace2 logging captures:

  * Retry attempt numbers (http/429-retry-attempt) to track retry
    progression and identify how many attempts were needed

  * Retry-After header values (http/429-retry-after) from server
    responses to understand server-requested delays

  * Actual sleep durations (http/retry-sleep-seconds) within trace2
    regions (http/retry-sleep) to measure time spent waiting

  * Error conditions (http/429-error) such as "retries-exhausted",
    "exceeds-max-retry-time", "no-retry-after-config", and
    "config-exceeds-max-retry-time" for diagnosing failures

  * Retry source (http/429-retry-source) indicating whether delay
    came from server header or config default

This instrumentation provides complete visibility into retry behavior,
enabling operators to monitor rate limiting patterns, diagnose retry
failures, and optimize retry configuration based on real-world data.

Author: vaidas-shopify

http.c

@@ -23,6 +23,7 @@
 #include "odb.h"
 #include "tempfile.h"
 #include "date.h"
+#include "trace2.h"
 
 static struct trace_key trace_curl = TRACE_KEY_INIT(CURL);
 static int trace_curl_data = 1;
@@ -1738,6 +1739,8 @@ void run_active_slot(struct active_request_slot *slot)
 
 	if (waiting_for_delay) {
 		warning(_("rate limited, waiting %ld seconds before retry"), slot->retry_delay_seconds);
+	trace2_data_intmax("http", the_repository, "http/retry-sleep-seconds",
+		slot->retry_delay_seconds);
 		start_time = slot->retry_delay_start;
 	}
 
@@ -1753,6 +1756,7 @@ void run_active_slot(struct active_request_slot *slot)
 			}
 
 			if (elapsed_time.tv_sec >= slot->retry_delay_seconds) {
+				trace2_region_leave("http", "retry-sleep", the_repository);
 				slot->retry_delay_seconds = -1;
 				waiting_for_delay = 0;
 
@@ -1995,6 +1999,8 @@ static int handle_curl_result(struct slot_results *results)
 			return HTTP_REAUTH;
 		}
 	} else if (results->http_code == 429) {
+		trace2_data_intmax("http", the_repository, "http/429-retry-after",
+			results->retry_after);
 		return HTTP_RATE_LIMITED;
 	} else {
 		if (results->http_connectcode == 407)
@@ -2421,10 +2427,16 @@ static void sleep_for_retry(struct active_request_slot *slot, long retry_after)
 static long handle_rate_limit_retry(int *rate_limit_retries, long slot_retry_after)
 {
 	int retry_attempt = http_max_retries - *rate_limit_retries + 1;
+
+	trace2_data_intmax("http", the_repository, "http/429-retry-attempt",
+		retry_attempt);
+
 	if (*rate_limit_retries <= 0) {
 		/* Retries are disabled or exhausted */
 		if (http_max_retries > 0) {
 			error(_("too many rate limit retries, giving up"));
+			trace2_data_string("http", the_repository,
+				"http/429-error", "retries-exhausted");
 		}
 		return -1;
 	}
@@ -2439,6 +2451,10 @@ static long handle_rate_limit_retry(int *rate_limit_retries, long slot_retry_aft
 			error(_("rate limited (HTTP 429) requested %ld second delay, "
 				"exceeds http.maxRetryTime of %ld seconds"),
 			      slot_retry_after, http_max_retry_time);
+			trace2_data_string("http", the_repository,
+				  "http/429-error", "exceeds-max-retry-time");
+			trace2_data_intmax("http", the_repository,
+				  "http/429-requested-delay", slot_retry_after);
 			return -1;
 		}
 		return slot_retry_after;
@@ -2448,16 +2464,21 @@ static long handle_rate_limit_retry(int *rate_limit_retries, long slot_retry_aft
 			/* Not configured - exit with error */
 			error(_("rate limited (HTTP 429) and no Retry-After header provided. "
 				"Configure http.retryAfter or set GIT_HTTP_RETRY_AFTER."));
+			trace2_data_string("http", the_repository,
+				"http/429-error", "no-retry-after-config");
 			return -1;
 		}
 		/* Check if configured default exceeds maximum allowed */
 		if (http_retry_after > http_max_retry_time) {
 			error(_("configured http.retryAfter (%ld seconds) exceeds "
 				"http.maxRetryTime (%ld seconds)"),
 			      http_retry_after, http_max_retry_time);
+			trace2_data_string("http", the_repository,
+					"http/429-error", "config-exceeds-max-retry-time");
 			return -1;
 		}
-
+		trace2_data_string("http", the_repository,
+			"http/429-retry-source", "config-default");
 		return http_retry_after;
 	}
 }