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.

Signed-off-by: Vaidas Pilkauskas <vaidas.pilkauskas@shopify.com>

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;
@@ -1944,6 +1945,8 @@ static int handle_curl_result(struct slot_results *results)
 	} else if (results->http_code == 429) {
 		/* Store the retry_after value for use in retry logic */
 		last_retry_after = results->retry_after;
+		trace2_data_intmax("http", the_repository, "http/429-retry-after",
+				   last_retry_after);
 		return HTTP_RATE_LIMITED;
 	} else {
 		if (results->http_connectcode == 407)
@@ -2338,11 +2341,15 @@ static void sleep_for_retry(long retry_after)
 	if (retry_after > 0) {
 		unsigned int remaining;
 		warning(_("rate limited, waiting %ld seconds before retry"), retry_after);
+		trace2_region_enter("http", "retry-sleep", the_repository);
+		trace2_data_intmax("http", the_repository, "http/retry-sleep-seconds",
+				retry_after);
 		remaining = sleep(retry_after);
 		while (remaining > 0) {
 			/* Sleep was interrupted, continue sleeping */
 			remaining = sleep(remaining);
 		}
+		trace2_region_leave("http", "retry-sleep", the_repository);
 	}
 }
 
@@ -2400,10 +2407,15 @@ static int http_request_reauth(const char *url,
 			/* Handle rate limiting with retry logic */
 			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 HTTP_ERROR;
 			}
@@ -2418,6 +2430,10 @@ static int http_request_reauth(const char *url,
 					error(_("rate limited (HTTP 429) requested %ld second delay, "
 						"exceeds http.maxRetryTime of %ld seconds"),
 					      last_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", last_retry_after);
 					last_retry_after = -1; /* Reset after use */
 					return HTTP_ERROR;
 				}
@@ -2429,17 +2445,23 @@ static int http_request_reauth(const char *url,
 					/* 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 HTTP_ERROR;
 				}
-				/* 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);
-					return HTTP_ERROR;
-				}
-				/* Use configured default retry-after value */
-				sleep_for_retry(http_retry_after);
+			/* 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 HTTP_ERROR;
+			}
+			/* Use configured default retry-after value */
+			trace2_data_string("http", the_repository,
+					"http/429-retry-source", "config-default");
+			sleep_for_retry(http_retry_after);
 			}
 		} else if (ret == HTTP_REAUTH) {
 			credential_fill(the_repository, &http_auth, 1);