Simplify and standardize conversions between TEXT datums and ordinary C

strings.  This patch introduces four support functions cstring_to_text,
cstring_to_text_with_len, text_to_cstring, and text_to_cstring_buffer, and
two macros CStringGetTextDatum and TextDatumGetCString.  A number of
existing macros that provided variants on these themes were removed.

Most of the places that need to make such conversions now require just one
function or macro call, in place of the multiple notational layers that used
to be needed.  There are no longer any direct calls of textout or textin,
and we got most of the places that were using handmade conversions via
memcpy (there may be a few still lurking, though).

This commit doesn't make any serious effort to eliminate transient memory
leaks caused by detoasting toasted text objects before they reach
text_to_cstring.  We changed PG_GETARG_TEXT_P to PG_GETARG_TEXT_PP in a few
places where it was easy, but much more could be done.

Brendan Jurd and Tom Lane

src/backend/utils/adt/varchar.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/varchar.c,v 1.126 2008/01/01 19:45:53 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/varchar.c,v 1.127 2008/03/25 22:42:44 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -203,21 +203,16 @@ bpcharin(PG_FUNCTION_ARGS)
 
 /*
  * Convert a CHARACTER value to a C string.
+ *
+ * Uses the text conversion functions, which is only appropriate if BpChar
+ * and text are equivalent types.
  */
 Datum
 bpcharout(PG_FUNCTION_ARGS)
 {
-	BpChar	   *s = PG_GETARG_BPCHAR_PP(0);
-	char	   *result;
-	int			len;
+	Datum		txt = PG_GETARG_DATUM(0);
 
-	/* copy and add null term */
-	len = VARSIZE_ANY_EXHDR(s);
-	result = (char *) palloc(len + 1);
-	memcpy(result, VARDATA_ANY(s), len);
-	result[len] = '\0';
-
-	PG_RETURN_CSTRING(result);
+	PG_RETURN_CSTRING(TextDatumGetCString(txt));
 }
 
 /*
@@ -403,19 +398,17 @@ bpchar_name(PG_FUNCTION_ARGS)
 
 /* name_bpchar()
  * Converts a NameData type to a bpchar type.
+ *
+ * Uses the text conversion functions, which is only appropriate if BpChar
+ * and text are equivalent types.
  */
 Datum
 name_bpchar(PG_FUNCTION_ARGS)
 {
 	Name		s = PG_GETARG_NAME(0);
 	BpChar	   *result;
-	int			len;
-
-	len = strlen(NameStr(*s));
-	result = (BpChar *) palloc(VARHDRSZ + len);
-	memcpy(VARDATA(result), NameStr(*s), len);
-	SET_VARSIZE(result, VARHDRSZ + len);
 
+	result = (BpChar *) cstring_to_text(NameStr(*s));
 	PG_RETURN_BPCHAR_P(result);
 }
 
@@ -454,6 +447,9 @@ bpchartypmodout(PG_FUNCTION_ARGS)
  *
  * If the input string is too long, raise an error, unless the extra
  * characters are spaces, in which case they're truncated.  (per SQL)
+ *
+ * Uses the C string to text conversion function, which is only appropriate
+ * if VarChar and text are equivalent types.
  */
 static VarChar *
 varchar_input(const char *s, size_t len, int32 atttypmod)
@@ -481,10 +477,7 @@ varchar_input(const char *s, size_t len, int32 atttypmod)
 		len = mbmaxlen;
 	}
 
-	result = (VarChar *) palloc(len + VARHDRSZ);
-	SET_VARSIZE(result, len + VARHDRSZ);
-	memcpy(VARDATA(result), s, len);
-
+	result = (VarChar *) cstring_to_text_with_len(s, len);
 	return result;
 }
 
@@ -510,21 +503,16 @@ varcharin(PG_FUNCTION_ARGS)
 
 /*
  * Convert a VARCHAR value to a C string.
+ *
+ * Uses the text to C string conversion function, which is only appropriate
+ * if VarChar and text are equivalent types.
  */
 Datum
 varcharout(PG_FUNCTION_ARGS)
 {
-	VarChar    *s = PG_GETARG_VARCHAR_PP(0);
-	char	   *result;
-	int32		len;
+	Datum		txt = PG_GETARG_DATUM(0);
 
-	/* copy and add null term */
-	len = VARSIZE_ANY_EXHDR(s);
-	result = palloc(len + 1);
-	memcpy(result, VARDATA_ANY(s), len);
-	result[len] = '\0';
-
-	PG_RETURN_CSTRING(result);
+	PG_RETURN_CSTRING(TextDatumGetCString(txt));
 }
 
 /*