Simple memory testing for gae/wrapper

go/src/infra/gae/libs/wrapper/memory/binutils.go

Index: go/src/infra/gae/libs/wrapper/memory/binutils.go
diff --git a/go/src/infra/gae/libs/wrapper/memory/binutils.go b/go/src/infra/gae/libs/wrapper/memory/binutils.go
new file mode 100644
index 0000000000000000000000000000000000000000..b66a22e85e3048c70e35e977303f18c1a10c5738
--- /dev/null
+++ b/go/src/infra/gae/libs/wrapper/memory/binutils.go
@@ -0,0 +1,79 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package memory
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"math"
+
+	"github.com/luci/luci-go/common/funnybase"
+)
+
+func writeString(buf *bytes.Buffer, s string) {
+	funnybase.WriteUint(buf, uint64(len(s)))
+	buf.WriteString(s)

[Vadim Sh., 2015/05/24 19:43:26]

writeBytes(buf, []byte(s))

to be symmetric with readString that uses readBytes.

[iannucci, 2015/05/24 20:33:54]

I did this to avoid a copy (which I think is what []byte(string) does, right?)

+}
+
+func readString(buf *bytes.Buffer) (string, error) {
+	b, err := readBytes(buf)
+	if err != nil {
+		return "", err
+	}
+	return string(b), nil
+}
+
+func writeBytes(buf *bytes.Buffer, b []byte) {
+	funnybase.WriteUint(buf, uint64(len(b)))
+	buf.Write(b)
+}
+
+func readBytes(buf *bytes.Buffer) ([]byte, error) {
+	val, err := funnybase.ReadUint(buf)

[Vadim Sh., 2015/05/24 19:43:26]

I don't fully understand yet where this function is used, but if it is used to
decode something coming from a wire, some simple size check wouldn't hurt, e.g

if val > 64 MB {
  return nil, "Are you mad?"
}

[iannucci, 2015/05/24 20:33:54]

Good idea. It can actually be 2MB I think (since it's mostly for encoding []byte
in entities, which are limited to 1MB anyway)

+	if err != nil {
+		return nil, err
+	}
+	retBuf := make([]byte, val)
+	n, _ := buf.Read(retBuf) // err is either io.EOF or nil for bytes.Buffer
+	if uint64(n) != val {
+		return nil, fmt.Errorf("readBytes: expected %d bytes but read %d", val, n)
+	}
+	return retBuf, err
+}
+
+func writeFloat64(buf *bytes.Buffer, v float64) {
+	// byte-ordered floats http://stereopsis.com/radix.html
+	bits := math.Float64bits(v)
+	bits = bits ^ (-(bits >> 63) | (1 << 63))
+	data := make([]byte, 8)
+	binary.BigEndian.PutUint64(data, bits)
+	buf.Write(data)
+}
+
+func readFloat64(buf *bytes.Buffer) (float64, error) {
+	// byte-ordered floats http://stereopsis.com/radix.html
+	data := make([]byte, 8)
+	_, err := buf.Read(data)
+	if err != nil {
+		return 0, err
+	}
+	bits := binary.BigEndian.Uint64(data)
+	return math.Float64frombits(bits ^ (((bits >> 63) - 1) | (1 << 63))), nil
+}
+
+func btoi(b bool) byte {
+	if b {
+		return 1
+	}
+	return 0
+}
+
+func itob(v byte) bool {
+	if v != 0 {
+		return true
+	}
+	return false
+}