# Reference

## Termination

It is questionable whether a library should be able to terminate an application. Any API function can signal an error (ex.: cannot allocate memory), so the engine use the termination approach with this port function.

```c
/**
 * Signal the port that jerry experienced a fatal failure from which it cannot
 * recover.
 *
 * @param code gives the cause of the error.
 *
 * Note: jerry expects the function not to return.
 *
 * Example: a libc-based port may implement this with exit() or abort(), or both.
 */
void jerry_port_fatal (jerry_fatal_code_t code);
```

Error codes

```c
typedef enum
{
  ERR_OUT_OF_MEMORY = 10,
  ERR_SYSCALL = 11,
  ERR_REF_COUNT_LIMIT = 12,
  ERR_FAILED_INTERNAL_ASSERTION = 120
} jerry_fatal_code_t;
```

## I/O

These are the only I/O functions jerry calls.

```c
/**
 * Print a string to the console. The function should implement a printf-like
 * interface, where the first argument specifies a format string on how to
 * stringify the rest of the parameter list.
 *
 * This function is only called with strings coming from the executed ECMAScript
 * wanting to print something as the result of its normal operation.
 *
 * It should be the port that decides what a "console" is.
 *
 * Example: a libc-based port may implement this with vprintf().
 */
void jerry_port_console (const char *fmt, ...);

/**
 * Jerry log levels. The levels are in severity order
 * where the most serious levels come first.
 */
typedef enum
{
  JERRY_LOG_LEVEL_ERROR,    /**< the engine will terminate after the message is printed */
  JERRY_LOG_LEVEL_WARNING,  /**< a request is aborted, but the engine continues its operation */
  JERRY_LOG_LEVEL_DEBUG,    /**< debug messages from the engine, low volume */
  JERRY_LOG_LEVEL_TRACE     /**< detailed info about engine internals, potentially high volume */
} jerry_log_level_t;

/**
 * Display or log a debug/error message. The function should implement a printf-like
 * interface, where the first argument specifies the log level
 * and the second argument specifies a format string on how to stringify the rest
 * of the parameter list.
 *
 * This function is only called with messages coming from the jerry engine as
 * the result of some abnormal operation or describing its internal operations 
 * (e.g., data structure dumps or tracing info).
 *
 * It should be the port that decides whether error and debug messages are logged to
 * the console, or saved to a database or to a file.
 * 
 * Example: a libc-based port may implement this with vfprintf(stderr) or 
 * vfprintf(logfile), or both, depending on log level.
 */
void jerry_port_log (jerry_log_level_t level, const char *fmt, ...);
```

## Date

```c
/**
 * Jerry time zone structure
 */
typedef struct
{
  int offset;                /**< minutes from west */
  int daylight_saving_time;  /**< daylight saving time (1 - DST applies, 0 - not on DST) */
} jerry_time_zone_t;

/**
 * Get timezone and daylight saving data
 *
 * @return true  - if success
 *         false - otherwise
 */
bool jerry_port_get_time_zone (jerry_time_zone_t *);

/**
 * Get system time
 *
 * @return milliseconds since Unix epoch
 */
double jerry_port_get_current_time (void);
```

# How to port JerryScript

This section describes a basic port implementation which was created for Unix based systems.

## Termination

```c
#include <stdlib.h>
#include "jerry-port.h"

/**
 * Default implementation of jerry_port_fatal.
 */
void jerry_port_fatal (jerry_fatal_code_t code)
{
  exit (code);
} /* jerry_port_fatal */
```

## I/O

```c
#include <stdarg.h>
#include "jerry-port.h"

/**
 * Provide console message implementation for the engine.
 */
void
jerry_port_console (const char *format, /**< format string */
                    ...) /**< parameters */
{
  va_list args;
  va_start (args, format);
  vfprintf (stdout, format, args);
  va_end (args);
} /* jerry_port_console */

/**
 * Provide log message implementation for the engine.
 *
 * Note:
 *      This example ignores the log level.
 */
void
jerry_port_log (jerry_log_level_t level, /**< log level */
                const char *format, /**< format string */
                ...)  /**< parameters */
{
  va_list args;
  va_start (args, format);
  vfprintf (stderr, format, args);
  va_end (args);
} /* jerry_port_log */
```

## Date

```c
#include <sys/time.h>
#include "jerry-port.h"

/**
 * Default implementation of jerry_port_get_time_zone.
 */
bool jerry_port_get_time_zone (jerry_time_zone_t *tz_p)
{
  struct timeval tv;
  struct timezone tz;

  /* gettimeofday may not fill tz, so zero-initializing */
  tz.tz_minuteswest = 0;
  tz.tz_dsttime = 0;

  if (gettimeofday (&tv, &tz) != 0)
  {
    return false;
  }

  tz_p->offset = tz.tz_minuteswest;
  tz_p->daylight_saving_time = tz.tz_dsttime > 0 ? 1 : 0;

  return true;
} /* jerry_port_get_time_zone */

/**
 * Default implementation of jerry_port_get_current_time.
 */
double jerry_port_get_current_time ()
{
  struct timeval tv;

  if (gettimeofday (&tv, NULL) != 0)
  {
    return 0;
  }

  return ((double) tv.tv_sec) * 1000.0 + ((double) tv.tv_usec) / 1000.0;
} /* jerry_port_get_current_time */
```