pgtype.Hstore: Fix quoting of whitespace; Add test

Before this change, the Hstore text protocol did not quote keys or
values containing non-space whitespace ("\r\n\v\t"). This causes
inserts with these values to fail with errors like:

    ERROR: Syntax error near "r" at position 17 (SQLSTATE XX000)

The previous version also quoted curly braces ("{}"), but they don't
seem to require quoting.

It is possible that it would be easier to just always quote the
values, which is what Postgres does when encoding its text protocol,
but this is a smaller change.

pgtype/hstore.go

@@ -272,9 +272,15 @@ func (c HstoreCodec) DecodeValue(m *Map, oid uint32, format int16, src []byte) (
 }
 
 func quoteHstoreElementIfNeeded(src string) string {
-	if src == "" || (len(src) == 4 && strings.ToLower(src) == "null") || strings.ContainsAny(src, ` {},"\=>`) {
+	// Double-quote keys and values that include whitespace, commas, =s or >s. To include a double
+	// quote or a backslash in a key or value, escape it with a backslash.
+	// From: https://www.postgresql.org/docs/current/hstore.html
+	// whitespace appears to be defined as the isspace() C function: \t\n\v\f\r\n and space
+	const quoteRequiredChars = `,"\=> ` + "\t\n\v\f\r"
+	if src == "" || (len(src) == 4 && strings.ToLower(src) == "null") || strings.ContainsAny(src, quoteRequiredChars) {
 		return quoteArrayElement(src)
 	}
+
 	return src
 }
 

pgtype/hstore_test.go

@@ -122,6 +122,12 @@ func TestHstoreCodec(t *testing.T) {
 		`=>`,
 		` `,
 		`\ / / \\ => " ' " '`,
+		"line1\nline2",
+		"tab\tafter",
+		"vtab\vafter",
+		"form\\ffeed",
+		"carriage\rreturn",
+		"curly{}braces",
 	}
 	for _, s := range specialStrings {
 		// Special key values