I wrote:
> Peter Eisentraut <peter.eisentr...@enterprisedb.com> writes:
>> I think we could consider char to be a single-byte bytea and use the
>> escape format of bytea for char. That way there is some precedent and
>> we don't add yet another encoding or escape format.
> Do you want to take that as far as changing backslash to print
> as '\\' ?
This came up again today [1], so here's a concrete proposal.
Let's use \ooo for high-bit-set chars, but keep backslash as just
backslash (so it's only semi-compatible with bytea).
regards, tom lane
[1]
https://www.postgresql.org/message-id/CAFM5RapGbBQm%2BdH%3D7K80HcvBvEWiV5Tm7N%3DNRaYURfm98YWc8A%40mail.gmail.com
diff --git a/src/backend/utils/adt/char.c b/src/backend/utils/adt/char.c
index 0df41c2253..e50293bf14 100644
--- a/src/backend/utils/adt/char.c
+++ b/src/backend/utils/adt/char.c
@@ -20,6 +20,11 @@
#include "libpq/pqformat.h"
#include "utils/builtins.h"
+#define ISOCTAL(c) (((c) >= '0') && ((c) <= '7'))
+#define TOOCTAL(c) ((c) + '0')
+#define FROMOCTAL(c) ((unsigned char) (c) - '0')
+
+
/*****************************************************************************
* USER I/O ROUTINES *
*****************************************************************************/
@@ -27,31 +32,53 @@
/*
* charin - converts "x" to 'x'
*
- * Note that an empty input string will implicitly be converted to \0.
+ * This accepts the formats charout produces. If we have multibyte input
+ * that is not in the form '\ooo', then we take its first byte as the value
+ * and silently discard the rest; this is a backwards-compatibility provision.
*/
Datum
charin(PG_FUNCTION_ARGS)
{
char *ch = PG_GETARG_CSTRING(0);
+ if (strlen(ch) == 4 && ch[0] == '\\' &&
+ ISOCTAL(ch[1]) && ISOCTAL(ch[2]) && ISOCTAL(ch[3]))
+ PG_RETURN_CHAR((FROMOCTAL(ch[1]) << 6) +
+ (FROMOCTAL(ch[2]) << 3) +
+ FROMOCTAL(ch[3]));
+ /* This will do the right thing for a zero-length input string */
PG_RETURN_CHAR(ch[0]);
}
/*
* charout - converts 'x' to "x"
*
- * Note that if the char value is \0, the resulting string will appear
- * to be empty (null-terminated after zero characters). So this is the
- * inverse of the charin() function for such data.
+ * The possible output formats are:
+ * 1. 0x00 is represented as an empty string.
+ * 2. 0x01..0x7F are represented as a single ASCII byte.
+ * 3. 0x80..0xFF are represented as \ooo (backslash and 3 octal digits).
+ * Case 3 is meant to match the traditional "escape" format of bytea.
*/
Datum
charout(PG_FUNCTION_ARGS)
{
char ch = PG_GETARG_CHAR(0);
- char *result = (char *) palloc(2);
+ char *result = (char *) palloc(5);
- result[0] = ch;
- result[1] = '\0';
+ if (IS_HIGHBIT_SET(ch))
+ {
+ result[0] = '\\';
+ result[1] = TOOCTAL(((unsigned char) ch) >> 6);
+ result[2] = TOOCTAL((((unsigned char) ch) >> 3) & 07);
+ result[3] = TOOCTAL(((unsigned char) ch) & 07);
+ result[4] = '\0';
+ }
+ else
+ {
+ /* This produces acceptable results for 0x00 as well */
+ result[0] = ch;
+ result[1] = '\0';
+ }
PG_RETURN_CSTRING(result);
}
@@ -176,15 +203,20 @@ Datum
text_char(PG_FUNCTION_ARGS)
{
text *arg1 = PG_GETARG_TEXT_PP(0);
+ char *ch = VARDATA_ANY(arg1);
char result;
/*
- * An empty input string is converted to \0 (for consistency with charin).
- * If the input is longer than one character, the excess data is silently
- * discarded.
+ * Conversion rules are the same as in charin(), but here we need to
+ * handle the empty-string case honestly.
*/
- if (VARSIZE_ANY_EXHDR(arg1) > 0)
- result = *(VARDATA_ANY(arg1));
+ if (VARSIZE_ANY_EXHDR(arg1) == 4 && ch[0] == '\\' &&
+ ISOCTAL(ch[1]) && ISOCTAL(ch[2]) && ISOCTAL(ch[3]))
+ result = (FROMOCTAL(ch[1]) << 6) +
+ (FROMOCTAL(ch[2]) << 3) +
+ FROMOCTAL(ch[3]);
+ else if (VARSIZE_ANY_EXHDR(arg1) > 0)
+ result = ch[0];
else
result = '\0';
@@ -195,13 +227,21 @@ Datum
char_text(PG_FUNCTION_ARGS)
{
char arg1 = PG_GETARG_CHAR(0);
- text *result = palloc(VARHDRSZ + 1);
+ text *result = palloc(VARHDRSZ + 4);
/*
- * Convert \0 to an empty string, for consistency with charout (and
- * because the text stuff doesn't like embedded nulls all that well).
+ * Conversion rules are the same as in charout(), but here we need to be
+ * honest about converting 0x00 to an empty string.
*/
- if (arg1 != '\0')
+ if (IS_HIGHBIT_SET(arg1))
+ {
+ SET_VARSIZE(result, VARHDRSZ + 4);
+ (VARDATA(result))[0] = '\\';
+ (VARDATA(result))[1] = TOOCTAL(((unsigned char) arg1) >> 6);
+ (VARDATA(result))[2] = TOOCTAL((((unsigned char) arg1) >> 3) & 07);
+ (VARDATA(result))[3] = TOOCTAL(((unsigned char) arg1) & 07);
+ }
+ else if (arg1 != '\0')
{
SET_VARSIZE(result, VARHDRSZ + 1);
*(VARDATA(result)) = arg1;
