Adding upstream version 0.28.1.

Signed-off-by: Daniel Baumann <daniel@debian.org>

tools/filesystem/blob/hex.go

@@ -0,0 +1,153 @@
+package blob
+
+import (
+	"fmt"
+	"strconv"
+)
+
+// Copied from gocloud.dev/blob to avoid nuances around the specific
+// HEX escaping/unescaping rules.
+//
+// -------------------------------------------------------------------
+// Copyright 2019 The Go Cloud Development Kit Authors
+//
+// 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
+//
+//     https://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.
+// -------------------------------------------------------------------
+
+// HexEscape returns s, with all runes for which shouldEscape returns true
+// escaped to "__0xXXX__", where XXX is the hex representation of the rune
+// value. For example, " " would escape to "__0x20__".
+//
+// Non-UTF-8 strings will have their non-UTF-8 characters escaped to
+// unicode.ReplacementChar; the original value is lost. Please file an
+// issue if you need non-UTF8 support.
+//
+// Note: shouldEscape takes the whole string as a slice of runes and an
+// index. Passing it a single byte or a single rune doesn't provide
+// enough context for some escape decisions; for example, the caller might
+// want to escape the second "/" in "//" but not the first one.
+// We pass a slice of runes instead of the string or a slice of bytes
+// because some decisions will be made on a rune basis (e.g., encode
+// all non-ASCII runes).
+func HexEscape(s string, shouldEscape func(s []rune, i int) bool) string {
+	// Do a first pass to see which runes (if any) need escaping.
+	runes := []rune(s)
+	var toEscape []int
+	for i := range runes {
+		if shouldEscape(runes, i) {
+			toEscape = append(toEscape, i)
+		}
+	}
+	if len(toEscape) == 0 {
+		return s
+	}
+
+	// Each escaped rune turns into at most 14 runes ("__0x7fffffff__"),
+	// so allocate an extra 13 for each. We'll reslice at the end
+	// if we didn't end up using them.
+	escaped := make([]rune, len(runes)+13*len(toEscape))
+	n := 0 // current index into toEscape
+	j := 0 // current index into escaped
+	for i, r := range runes {
+		if n < len(toEscape) && i == toEscape[n] {
+			// We were asked to escape this rune.
+			for _, x := range fmt.Sprintf("__%#x__", r) {
+				escaped[j] = x
+				j++
+			}
+			n++
+		} else {
+			escaped[j] = r
+			j++
+		}
+	}
+
+	return string(escaped[0:j])
+}
+
+// unescape tries to unescape starting at r[i].
+// It returns a boolean indicating whether the unescaping was successful,
+// and (if true) the unescaped rune and the last index of r that was used
+// during unescaping.
+func unescape(r []rune, i int) (bool, rune, int) {
+	// Look for "__0x".
+	if r[i] != '_' {
+		return false, 0, 0
+	}
+	i++
+	if i >= len(r) || r[i] != '_' {
+		return false, 0, 0
+	}
+	i++
+	if i >= len(r) || r[i] != '0' {
+		return false, 0, 0
+	}
+	i++
+	if i >= len(r) || r[i] != 'x' {
+		return false, 0, 0
+	}
+	i++
+
+	// Capture the digits until the next "_" (if any).
+	var hexdigits []rune
+	for ; i < len(r) && r[i] != '_'; i++ {
+		hexdigits = append(hexdigits, r[i])
+	}
+
+	// Look for the trailing "__".
+	if i >= len(r) || r[i] != '_' {
+		return false, 0, 0
+	}
+	i++
+	if i >= len(r) || r[i] != '_' {
+		return false, 0, 0
+	}
+
+	// Parse the hex digits into an int32.
+	retval, err := strconv.ParseInt(string(hexdigits), 16, 32)
+	if err != nil {
+		return false, 0, 0
+	}
+
+	return true, rune(retval), i
+}
+
+// HexUnescape reverses HexEscape.
+func HexUnescape(s string) string {
+	var unescaped []rune
+
+	runes := []rune(s)
+	for i := 0; i < len(runes); i++ {
+		if ok, newR, newI := unescape(runes, i); ok {
+			// We unescaped some runes starting at i, resulting in the
+			// unescaped rune newR. The last rune used was newI.
+			if unescaped == nil {
+				// This is the first rune we've encountered that
+				// needed unescaping. Allocate a buffer and copy any
+				// previous runes.
+				unescaped = make([]rune, i)
+				copy(unescaped, runes)
+			}
+			unescaped = append(unescaped, newR)
+			i = newI
+		} else if unescaped != nil {
+			unescaped = append(unescaped, runes[i])
+		}
+	}
+
+	if unescaped == nil {
+		return s
+	}
+
+	return string(unescaped)
+}