diff --git a/src/port/snprintf.c b/src/port/snprintf.c
index a184134..851e2ae 100644
*** a/src/port/snprintf.c
--- b/src/port/snprintf.c
***************
*** 2,7 ****
--- 2,8 ----
   * Copyright (c) 1983, 1995, 1996 Eric P. Allman
   * Copyright (c) 1988, 1993
   *	The Regents of the University of California.  All rights reserved.
+  * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
***************
*** 49,56 ****
   *	SNPRINTF, VSNPRINTF and friends
   *
   * These versions have been grabbed off the net.  They have been
!  * cleaned up to compile properly and support for most of the Single Unix
!  * Specification has been added.  Remaining unimplemented features are:
   *
   * 1. No locale support: the radix character is always '.' and the '
   * (single quote) format flag is ignored.
--- 50,57 ----
   *	SNPRINTF, VSNPRINTF and friends
   *
   * These versions have been grabbed off the net.  They have been
!  * cleaned up to compile properly and support for most of the C99
!  * specification has been added.  Remaining unimplemented features are:
   *
   * 1. No locale support: the radix character is always '.' and the '
   * (single quote) format flag is ignored.
***************
*** 64,88 ****
   * 5. Space and '#' flags are not implemented.
   *
   *
!  * The result values of these functions are not the same across different
!  * platforms.  This implementation is compatible with the Single Unix Spec:
   *
!  * 1. -1 is returned only if processing is abandoned due to an invalid
!  * parameter, such as incorrect format string.  (Although not required by
!  * the spec, this happens only when no characters have yet been transmitted
!  * to the destination.)
   *
!  * 2. For snprintf and sprintf, 0 is returned if str == NULL or count == 0;
!  * no data has been stored.
   *
!  * 3. Otherwise, the number of bytes actually transmitted to the destination
!  * is returned (excluding the trailing '\0' for snprintf and sprintf).
   *
!  * For snprintf with nonzero count, the result cannot be more than count-1
!  * (a trailing '\0' is always stored); it is not possible to distinguish
!  * buffer overrun from exact fit.  This is unlike some implementations that
!  * return the number of bytes that would have been needed for the complete
!  * result string.
   */
  
  /**************************************************************
--- 65,88 ----
   * 5. Space and '#' flags are not implemented.
   *
   *
!  * Historically the result values of sprintf/snprintf varied across platforms.
!  * This implementation now follows the C99 standard:
   *
!  * 1. -1 is returned if an error is detected in the format string, or if
!  * a write to the target stream fails (as reported by fwrite).  Note that
!  * overrunning snprintf's target buffer is *not* an error.
   *
!  * 2. For successful writes to streams, the actual number of bytes written
!  * to the stream is returned.
   *
!  * 3. For successful sprintf/snprintf, the number of bytes that would have
!  * been written to an infinite-size buffer (excluding the trailing '\0')
!  * is returned.  snprintf will truncate its output to fit in the buffer
!  * (ensuring a trailing '\0' unless count == 0), but this is not reflected
!  * in the function result.
   *
!  * snprintf buffer overrun can be detected by checking for function result
!  * greater than or equal to the supplied count.
   */
  
  /**************************************************************
***************
*** 101,115 ****
  #undef	fprintf
  #undef	printf
  
! /* Info about where the formatted output is going */
  typedef struct
  {
  	char	   *bufptr;			/* next buffer output position */
  	char	   *bufstart;		/* first buffer element */
! 	char	   *bufend;			/* last buffer element, or NULL */
  	/* bufend == NULL is for sprintf, where we assume buf is big enough */
  	FILE	   *stream;			/* eventual output destination, or NULL */
! 	int			nchars;			/* # chars already sent to stream */
  	bool		failed;			/* call is a failure; errno is set */
  } PrintfTarget;
  
--- 101,127 ----
  #undef	fprintf
  #undef	printf
  
! /*
!  * Info about where the formatted output is going.
!  *
!  * dopr and subroutines will not write at/past bufend, but snprintf
!  * reserves one byte, ensuring it may place the trailing '\0' there.
!  *
!  * In snprintf, we use nchars to count the number of bytes dropped on the
!  * floor due to buffer overrun.  The correct result of snprintf is thus
!  * (bufptr - bufstart) + nchars.  (This isn't as inconsistent as it might
!  * seem: nchars is the number of emitted bytes that are not in the buffer now,
!  * either because we sent them to the stream or because we couldn't fit them
!  * into the buffer to begin with.)
!  */
  typedef struct
  {
  	char	   *bufptr;			/* next buffer output position */
  	char	   *bufstart;		/* first buffer element */
! 	char	   *bufend;			/* last+1 buffer element, or NULL */
  	/* bufend == NULL is for sprintf, where we assume buf is big enough */
  	FILE	   *stream;			/* eventual output destination, or NULL */
! 	int			nchars;			/* # chars sent to stream, or dropped */
  	bool		failed;			/* call is a failure; errno is set */
  } PrintfTarget;
  
*************** int
*** 147,163 ****
  pg_vsnprintf(char *str, size_t count, const char *fmt, va_list args)
  {
  	PrintfTarget target;
  
! 	if (str == NULL || count == 0)
! 		return 0;
  	target.bufstart = target.bufptr = str;
  	target.bufend = str + count - 1;
  	target.stream = NULL;
! 	/* target.nchars is unused in this case */
  	target.failed = false;
  	dopr(&target, fmt, args);
  	*(target.bufptr) = '\0';
! 	return target.failed ? -1 : (target.bufptr - target.bufstart);
  }
  
  int
--- 159,186 ----
  pg_vsnprintf(char *str, size_t count, const char *fmt, va_list args)
  {
  	PrintfTarget target;
+ 	char		onebyte[1];
  
! 	/*
! 	 * C99 allows the case str == NULL when count == 0.  Rather than
! 	 * special-casing this situation further down, we substitute a one-byte
! 	 * local buffer.  Callers cannot tell, since the function result doesn't
! 	 * depend on count.
! 	 */
! 	if (count == 0)
! 	{
! 		str = onebyte;
! 		count = 1;
! 	}
  	target.bufstart = target.bufptr = str;
  	target.bufend = str + count - 1;
  	target.stream = NULL;
! 	target.nchars = 0;
  	target.failed = false;
  	dopr(&target, fmt, args);
  	*(target.bufptr) = '\0';
! 	return target.failed ? -1 : (target.bufptr - target.bufstart
! 								 + target.nchars);
  }
  
  int
*************** pg_vsprintf(char *str, const char *fmt, 
*** 177,192 ****
  {
  	PrintfTarget target;
  
- 	if (str == NULL)
- 		return 0;
  	target.bufstart = target.bufptr = str;
  	target.bufend = NULL;
  	target.stream = NULL;
! 	/* target.nchars is unused in this case */
  	target.failed = false;
  	dopr(&target, fmt, args);
  	*(target.bufptr) = '\0';
! 	return target.failed ? -1 : (target.bufptr - target.bufstart);
  }
  
  int
--- 200,214 ----
  {
  	PrintfTarget target;
  
  	target.bufstart = target.bufptr = str;
  	target.bufend = NULL;
  	target.stream = NULL;
! 	target.nchars = 0;			/* not really used in this case */
  	target.failed = false;
  	dopr(&target, fmt, args);
  	*(target.bufptr) = '\0';
! 	return target.failed ? -1 : (target.bufptr - target.bufstart
! 								 + target.nchars);
  }
  
  int
*************** pg_vfprintf(FILE *stream, const char *fm
*** 213,219 ****
  		return -1;
  	}
  	target.bufstart = target.bufptr = buffer;
! 	target.bufend = buffer + sizeof(buffer) - 1;
  	target.stream = stream;
  	target.nchars = 0;
  	target.failed = false;
--- 235,241 ----
  		return -1;
  	}
  	target.bufstart = target.bufptr = buffer;
! 	target.bufend = buffer + sizeof(buffer);	/* use the whole buffer */
  	target.stream = stream;
  	target.nchars = 0;
  	target.failed = false;
*************** flushbuffer(PrintfTarget *target)
*** 256,261 ****
--- 278,287 ----
  {
  	size_t		nc = target->bufptr - target->bufstart;
  
+ 	/*
+ 	 * Don't write anything if we already failed; this is to ensure we
+ 	 * preserve the original failure's errno.
+ 	 */
  	if (!target->failed && nc > 0)
  	{
  		size_t		written;
*************** dostr(const char *str, int slen, PrintfT
*** 1035,1041 ****
  		{
  			/* buffer full, can we dump to stream? */
  			if (target->stream == NULL)
! 				return;			/* no, lose the data */
  			flushbuffer(target);
  			continue;
  		}
--- 1061,1070 ----
  		{
  			/* buffer full, can we dump to stream? */
  			if (target->stream == NULL)
! 			{
! 				target->nchars += slen; /* no, lose the data */
! 				return;
! 			}
  			flushbuffer(target);
  			continue;
  		}
*************** dopr_outch(int c, PrintfTarget *target)
*** 1054,1060 ****
  	{
  		/* buffer full, can we dump to stream? */
  		if (target->stream == NULL)
! 			return;				/* no, lose the data */
  		flushbuffer(target);
  	}
  	*(target->bufptr++) = c;
--- 1083,1092 ----
  	{
  		/* buffer full, can we dump to stream? */
  		if (target->stream == NULL)
! 		{
! 			target->nchars++;	/* no, lose the data */
! 			return;
! 		}
  		flushbuffer(target);
  	}
  	*(target->bufptr++) = c;