strutil: add StringFromBytes

Change-Id: Ie396dd58c48a724e044ecd4f8dc28712e7091f9f

pkg/strutil/intern.go

@@ -0,0 +1,51 @@
+/*
+Copyright 2013 The Camlistore 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
+
+     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 strutil
+
+// StringFromBytes returns string(v), minimizing copies for common values of v.
+func StringFromBytes(v []byte) string {
+	// From net/textproto's reader.go...
+	if len(v) == 0 {
+		return ""
+	}
+	lo, hi := 0, len(commonStrings)
+	for i, c := range v {
+		if lo < hi {
+			for lo < hi && (len(commonStrings[lo]) <= i || commonStrings[lo][i] < c) {
+				lo++
+			}
+			for hi > lo && commonStrings[hi-1][i] > c {
+				hi--
+			}
+		} else {
+			break
+		}
+	}
+	if lo < hi && len(commonStrings[lo]) == len(v) {
+		return commonStrings[lo]
+	}
+	return string(v)
+}
+
+// NOTE: must be sorted
+var commonStrings = []string{
+	"claim",
+	"directory",
+	"file",
+	"permanode",
+	"static-set",
+}

pkg/strutil/strconv.go

@@ -0,0 +1,117 @@
+/*
+Copyright 2013 The Camlistore 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
+
+     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 strutil
+
+import (
+	"errors"
+	"strconv"
+)
+
+// ParseUintBytes is like strconv.ParseUint, but using a []byte.
+func ParseUintBytes(s []byte, base int, bitSize int) (n uint64, err error) {
+	var cutoff, maxVal uint64
+
+	if bitSize == 0 {
+		bitSize = int(strconv.IntSize)
+	}
+
+	s0 := s
+	switch {
+	case len(s) < 1:
+		err = strconv.ErrSyntax
+		goto Error
+
+	case 2 <= base && base <= 36:
+		// valid base; nothing to do
+
+	case base == 0:
+		// Look for octal, hex prefix.
+		switch {
+		case s[0] == '0' && len(s) > 1 && (s[1] == 'x' || s[1] == 'X'):
+			base = 16
+			s = s[2:]
+			if len(s) < 1 {
+				err = strconv.ErrSyntax
+				goto Error
+			}
+		case s[0] == '0':
+			base = 8
+		default:
+			base = 10
+		}
+
+	default:
+		err = errors.New("invalid base " + strconv.Itoa(base))
+		goto Error
+	}
+
+	n = 0
+	cutoff = cutoff64(base)
+	maxVal = 1<<uint(bitSize) - 1
+
+	for i := 0; i < len(s); i++ {
+		var v byte
+		d := s[i]
+		switch {
+		case '0' <= d && d <= '9':
+			v = d - '0'
+		case 'a' <= d && d <= 'z':
+			v = d - 'a' + 10
+		case 'A' <= d && d <= 'Z':
+			v = d - 'A' + 10
+		default:
+			n = 0
+			err = strconv.ErrSyntax
+			goto Error
+		}
+		if int(v) >= base {
+			n = 0
+			err = strconv.ErrSyntax
+			goto Error
+		}
+
+		if n >= cutoff {
+			// n*base overflows
+			n = 1<<64 - 1
+			err = strconv.ErrRange
+			goto Error
+		}
+		n *= uint64(base)
+
+		n1 := n + uint64(v)
+		if n1 < n || n1 > maxVal {
+			// n+v overflows
+			n = 1<<64 - 1
+			err = strconv.ErrRange
+			goto Error
+		}
+		n = n1
+	}
+
+	return n, nil
+
+Error:
+	return n, &strconv.NumError{Func: "ParseUint", Num: string(s0), Err: err}
+}
+
+// Return the first number n such that n*base >= 1<<64.
+func cutoff64(base int) uint64 {
+	if base < 2 {
+		return 0
+	}
+	return (1<<64-1)/uint64(base) + 1
+}

pkg/strutil/strutil_test.go

@@ -48,3 +48,12 @@ func TestAppendSplitN(t *testing.T) {
 		}
 	}
 }
+
+func TestStringFromBytes(t *testing.T) {
+	for _, s := range []string{"foo", "permanode", "file", "zzzz"} {
+		got := StringFromBytes([]byte(s))
+		if got != s {
+			t.Errorf("StringFromBytes(%q) didn't round-trip; got %q instead", s, got)
+		}
+	}
+}