chore: import upstream snapshot with attribution

server/cast/utils.go

@@ -0,0 +1,90 @@
+// Copyright 2024 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cast
+
+import (
+	"fmt"
+	"strings"
+	"unicode/utf8"
+
+	cerrors "github.com/cockroachdb/errors"
+	"gopkg.in/src-d/go-errors.v1"
+
+	pgtypes "github.com/dolthub/doltgresql/server/types"
+)
+
+// errOutOfRange is returned when a value is out of range for a given type.
+var errOutOfRange = errors.NewKind("%s out of range")
+
+// handleStringCast handles casts to the string types that may have length restrictions. Returns an error if other types
+// are passed in. Will always return the correct string, even on error, as some contexts may ignore the error.
+func handleStringCast(input string, targetType *pgtypes.DoltgresType) (string, error) {
+	tm := targetType.GetAttTypMod()
+	switch targetType.ID {
+	case pgtypes.BpChar.ID:
+		if tm == -1 {
+			return input, nil
+		}
+		maxChars, err := pgtypes.GetTypModFromCharLength("char", tm)
+		if err != nil {
+			return "", err
+		}
+		length := uint32(maxChars)
+		str, runeLength := truncateString(input, length)
+		if runeLength > length {
+			return input, cerrors.Wrap(pgtypes.ErrCastOutOfRange, fmt.Sprintf("value too long for type %s", targetType.String()))
+		} else if runeLength < length {
+			return str + strings.Repeat(" ", int(length-runeLength)), nil
+		} else {
+			return str, nil
+		}
+	case pgtypes.InternalChar.ID:
+		str, _ := truncateString(input, pgtypes.InternalCharLength)
+		return str, nil
+	case pgtypes.Name.ID:
+		// Name seems to never throw an error, regardless of the context or how long the input is
+		str, _ := truncateString(input, uint32(targetType.TypLength))
+		return str, nil
+	case pgtypes.VarChar.ID:
+		if tm == -1 {
+			return input, nil
+		}
+		length := uint32(pgtypes.GetCharLengthFromTypmod(tm))
+		str, runeLength := truncateString(input, length)
+		if runeLength > length {
+			return input, cerrors.Wrap(pgtypes.ErrCastOutOfRange, fmt.Sprintf("value too long for type %s", targetType.String()))
+		} else {
+			return str, nil
+		}
+	default:
+		return "", cerrors.Errorf("internal cast called to handle non-string type")
+	}
+}
+
+// truncateString returns a string that has been truncated to the given length. Uses the rune count rather than the
+// byte count. Returns the input string if it's smaller than the length. Also returns the rune count of the string.
+func truncateString(val string, runeLimit uint32) (string, uint32) {
+	runeLength := uint32(utf8.RuneCountInString(val))
+	if runeLength > runeLimit {
+		// TODO: figure out if there's a faster way to truncate based on rune count
+		startString := val
+		for i := uint32(0); i < runeLimit; i++ {
+			_, size := utf8.DecodeRuneInString(val)
+			val = val[size:]
+		}
+		return startString[:len(startString)-len(val)], runeLength
+	}
+	return val, runeLength
+}