Change strutil.StringFromBytes to depend on Go 1.3.

Change-Id: I83fd1369a199dba7ef41227df4d0b95d9a16aabb

pkg/schema/schema.go

@@ -41,12 +41,28 @@ import (
 	"unicode/utf8"
 
 	"camlistore.org/pkg/blob"
+	"camlistore.org/pkg/strutil"
 	"camlistore.org/pkg/types"
 	"camlistore.org/third_party/github.com/bradfitz/latlong"
 	"camlistore.org/third_party/github.com/camlistore/goexif/exif"
 	"camlistore.org/third_party/github.com/camlistore/goexif/tiff"
 )
 
+func init() {
+	// Intern common strings as used by schema blobs (camliType values), to reduce
+	// index memory usage, which uses strutil.StringFromBytes.
+	strutil.RegisterCommonString(
+		"bytes",
+		"claim",
+		"directory",
+		"file",
+		"permanode",
+		"share",
+		"static-set",
+		"symlink",
+	)
+}
+
 // MaxSchemaBlobSize represents the upper bound for how large
 // a schema blob may be.
 const MaxSchemaBlobSize = 1 << 20

pkg/strutil/intern.go

@@ -16,39 +16,24 @@ limitations under the License.
 
 package strutil
 
-// StringFromBytes returns string(v), minimizing copies for common values of v.
+var internStr = map[string]string{}
+
+// RegisterCommonString adds common strings to the interned string
+// table.  This should be called during init from the main
+// goroutine, not later at runtime.
+func RegisterCommonString(s ...string) {
+	for _, v := range s {
+		internStr[v] = v
+	}
+}
+
+// StringFromBytes returns string(v), minimizing copies for common values of v
+// as previously registered with RegisterCommonString.
 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]
+	// In Go 1.3, this string conversion in the map lookup does not allocate
+	// to make a new string. We depend on Go 1.3, so this is always free:
+	if s, ok := internStr[string(v)]; ok {
+		return s
 	}
 	return string(v)
 }
-
-// NOTE: must be sorted
-var commonStrings = []string{
-	"bytes",
-	"claim",
-	"directory",
-	"file",
-	"permanode",
-	"share",
-	"static-set",
-	"symlink",
-}