7894ac5004
Several years ago we changed chr(int) so that if the database encoding is UTF8, it would interpret its argument as a Unicode code point and expand it into the appropriate multibyte sequence. However, we weren't sufficiently careful about checking validity of the input. According to RFC3629, UTF8 disallows code points above U+10FFFF (note that the predecessor standard RFC2279 was more liberal). Also, both versions of the UTF8 spec agree that Unicode surrogate-pair codes should never appear in UTF8. Because our encoding validity checks follow RFC3629, our failure to enforce these restrictions in chr() means it could be used to produce text strings that will be rejected when the database is dumped and reloaded. To ensure consistency with the input functions, let's actually apply pg_utf8_islegal() to the proposed output of chr(). Per discussion, this seems like too much of a behavioral change to back-patch, but it's not too late to squeeze it into 9.4.
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