[gpr] Replace a call to localtime with a call to absl::FormatTime.

localtime is not thread-safe, which means that client libraries can suffer from subtle data races.

PiperOrigin-RevId: 670616652

src/core/util/string.cc

@@ -29,6 +29,7 @@
 #include <time.h>
 
 #include "absl/strings/str_cat.h"
+#include "absl/time/time.h"
 
 #include <grpc/support/alloc.h>
 #include <grpc/support/string_util.h>
@@ -53,14 +54,14 @@ char* gpr_strdup(const char* src) {
 }
 
 std::string gpr_format_timespec(gpr_timespec tm) {
-  char time_buffer[35];
-  char ns_buffer[11];  // '.' + 9 digits of precision
-  struct tm* tm_info = localtime(reinterpret_cast<time_t*>(&tm.tv_sec));
-  strftime(time_buffer, sizeof(time_buffer), "%Y-%m-%dT%H:%M:%S", tm_info);
-  snprintf(ns_buffer, 11, ".%09d", tm.tv_nsec);
+  const std::string time_str =
+      absl::FormatTime("%Y-%m-%d%ET%H:%M:%S", absl::FromUnixSeconds(tm.tv_sec),
+                       absl::LocalTimeZone());
   // This loop trims off trailing zeros by inserting a null character that the
   // right point. We iterate in chunks of three because we want 0, 3, 6, or 9
   // fractional digits.
+  char ns_buffer[11];  // '.' + 9 digits of precision
+  snprintf(ns_buffer, 11, ".%09d", tm.tv_nsec);
   for (int i = 7; i >= 1; i -= 3) {
     if (ns_buffer[i] == '0' && ns_buffer[i + 1] == '0' &&
         ns_buffer[i + 2] == '0') {
@@ -73,7 +74,7 @@ std::string gpr_format_timespec(gpr_timespec tm) {
       break;
     }
   }
-  return absl::StrCat(time_buffer, ns_buffer, "Z");
+  return absl::StrCat(time_str, ns_buffer, "Z");
 }
 
 struct dump_out {