Add ESP_PLATFORM support for ISO8601 UTC datetime (RTOS targets) #37
Description
Summary
Support for ESP targets using ESP-IDF (FreeRTOS) is currently missing in the platform-specific time handling code.
ESP-IDF provides compatible time.h and sys/time.h APIs.
Problem
Code fails or is excluded when building for ESP-IDF because the platform is not detected.
Example
The following function generates an ISO-8601 UTC timestamp:
#include <sys/time.h>
#include <time.h>
int add_iso8601_utc_datetime(char *buf, size_t size)
{
time_t now;
struct tm timeinfo;
// Format: YYYY-MM-DDThh:mm:ssZ
time(&now);
gmtime_r(&now, &timeinfo);
return strftime(buf, size, "%Y-%m-%dT%H:%M:%SZ", &timeinfo);
}
This code is fully supported by ESP-IDF, which provides:
time()
gmtime_r()
strftime()
Expected behavior
ESP builds should follow the same code path as other POSIX-like systems by detecting:
#if defined(linux) || defined(APPLE) || defined(ESP_PLATFORM)
Why this matters
ESP-IDF is widely used in embedded systems and offers a POSIX-compatible time API on top of FreeRTOS.
Adding ESP_PLATFORM ensures:
consistent behavior across platforms
no need for downstream patches
improved portability for embedded targets
Proposed change
Extend the existing platform detection macros to include ESP:
#if defined(linux) || defined(APPLE) || defined(ESP_PLATFORM)
This keeps the implementation simple and avoids introducing ESP-specific code paths.
Environment
ESP-IDF: 4.x / 5.x
Target: ESP32 / ESP32-S3
RTOS: FreeRTOS (via ESP-IDF)