2 files changed, 30 insertions, 5 deletions
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 24ea0487e7f..63dda75ae52 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -135,16 +135,23 @@ static void outChar(StringInfo str, char c);
  *	  Convert an ordinary string (eg, an identifier) into a form that
  *	  will be decoded back to a plain token by read.c's functions.
  *
- *	  If a null or empty string is given, it is encoded as "<>".
+ *	  If a null string pointer is given, it is encoded as '<>'.
+ *	  An empty string is encoded as '""'.  To avoid ambiguity, input
+ *	  strings beginning with '<' or '"' receive a leading backslash.
  */
 void
 outToken(StringInfo str, const char *s)
 {
-	if (s == NULL || *s == '\0')
+	if (s == NULL)
 	{
 		appendStringInfoString(str, "<>");
 		return;
 	}
+	if (*s == '\0')
+	{
+		appendStringInfoString(str, "\"\"");
+		return;
+	}
 
 	/*
 	 * Look for characters or patterns that are treated specially by read.c
@@ -178,6 +185,13 @@ outChar(StringInfo str, char c)
 {
 	char		in[2];
 
+	/* Traditionally, we've represented \0 as <>, so keep doing that */
+	if (c == '\0')
+	{
+		appendStringInfoString(str, "<>");
+		return;
+	}
+
 	in[0] = c;
 	in[1] = '\0';
 
@@ -636,7 +650,8 @@ _outString(StringInfo str, const String *node)
 {
 	/*
 	 * We use outToken to provide escaping of the string's content, but we
-	 * don't want it to do anything with an empty string.
+	 * don't want it to convert an empty string to '""', because we're putting
+	 * double quotes around the string already.
 	 */
 	appendStringInfoChar(str, '"');
 	if (node->sval[0] != '\0')
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 89a9a50f7cb..b4ff855f7c6 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -178,8 +178,18 @@
 
 #define strtobool(x)  ((*(x) == 't') ? true : false)
 
-#define nullable_string(token,length)  \
-	((length) == 0 ? NULL : debackslash(token, length))
+static char *
+nullable_string(const char *token, int length)
+{
+	/* outToken emits <> for NULL, and pg_strtok makes that an empty string */
+	if (length == 0)
+		return NULL;
+	/* outToken emits "" for empty string */
+	if (length == 2 && token[0] == '"' && token[1] == '"')
+		return pstrdup("");
+	/* otherwise, we must remove protective backslashes added by outToken */
+	return debackslash(token, length);
+}
 
 
 /*