strerror_override.c

#define STRERROR_OVERRIDE_IMPL 1
#include "strerror_override.h"

/*
 * Override strerror() to get consistent output across platforms.
 */

static struct
{
	int errno_value;
	const char *errno_str;
} errno_list[] = {
/* clang-format off */
#define STRINGIFY(x) #x
#define ENTRY(x) {x, &STRINGIFY(undef_ ## x)[6]}
	ENTRY(EPERM),
	ENTRY(ENOENT),
	ENTRY(ESRCH),
	ENTRY(EINTR),
	ENTRY(EIO),
	ENTRY(ENXIO),
	ENTRY(E2BIG),
#ifdef ENOEXEC
	ENTRY(ENOEXEC),
#endif
	ENTRY(EBADF),
	ENTRY(ECHILD),
	ENTRY(EDEADLK),
	ENTRY(ENOMEM),
	ENTRY(EACCES),
	ENTRY(EFAULT),
#ifdef ENOTBLK
	ENTRY(ENOTBLK),
#endif
	ENTRY(EBUSY),
	ENTRY(EEXIST),
	ENTRY(EXDEV),
	ENTRY(ENODEV),
	ENTRY(ENOTDIR),
	ENTRY(EISDIR),
	ENTRY(EINVAL),
	ENTRY(ENFILE),
	ENTRY(EMFILE),
	ENTRY(ENOTTY),
#ifdef ETXTBSY
	ENTRY(ETXTBSY),
#endif
	ENTRY(EFBIG),
	ENTRY(ENOSPC),
	ENTRY(ESPIPE),
	ENTRY(EROFS),
	ENTRY(EMLINK),
	ENTRY(EPIPE),
	ENTRY(EDOM),
	ENTRY(ERANGE),
	ENTRY(EAGAIN),
	{ 0, (char *)0 }
};
/* clang-format on */

// Enabled during tests
static int _json_c_strerror_enable = 0;
extern char *getenv(const char *name); // Avoid including stdlib.h

#define PREFIX "ERRNO="
static char errno_buf[128] = PREFIX;
char *_json_c_strerror(int errno_in)
{
	int start_idx;
	char digbuf[20];
	int ii, jj;

	if (!_json_c_strerror_enable)
		_json_c_strerror_enable = (getenv("_JSON_C_STRERROR_ENABLE") == NULL) ? -1 : 1;
	if (_json_c_strerror_enable == -1)
		return strerror(errno_in);

	// Avoid standard functions, so we don't need to include any
	// headers, or guess at signatures.

	for (ii = 0; errno_list[ii].errno_str != (char *)0; ii++)
	{
		const char *errno_str = errno_list[ii].errno_str;
		if (errno_list[ii].errno_value != errno_in)
			continue;

		for (start_idx = sizeof(PREFIX) - 1, jj = 0; errno_str[jj] != '\0';
		     jj++, start_idx++)
		{
			errno_buf[start_idx] = errno_str[jj];
		}
		errno_buf[start_idx] = '\0';
		return errno_buf;
	}

	// It's not one of the known errno values, return the numeric value.
	for (ii = 0; errno_in >= 10; errno_in /= 10, ii++)
	{
		digbuf[ii] = "0123456789"[(errno_in % 10)];
	}
	digbuf[ii] = "0123456789"[(errno_in % 10)];

	// Reverse the digits
	for (start_idx = sizeof(PREFIX) - 1; ii >= 0; ii--, start_idx++)
	{
		errno_buf[start_idx] = digbuf[ii];
	}
	errno_buf[start_idx] = '\0';
	return errno_buf;
}