vpython: Add environment spec package.

vpython/spec/spec.go

Index: vpython/spec/spec.go
diff --git a/vpython/spec/spec.go b/vpython/spec/spec.go
new file mode 100644
index 0000000000000000000000000000000000000000..8fdc79e19a945fe05d67c9fe288c2a5ce7bd311e
--- /dev/null
+++ b/vpython/spec/spec.go
@@ -0,0 +1,60 @@
+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package spec
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"sort"
+
+	"github.com/luci/luci-go/vpython/api/vpython"
+
+	"github.com/luci/luci-go/common/data/sortby"
+	"github.com/luci/luci-go/common/errors"
+
+	"github.com/golang/protobuf/proto"
+)
+
+// Normalize normalizes the specification Message such that two messages
+// with identical meaning will have identical representation.
+func Normalize(spec *vpython.Spec) error {
+	sort.Sort(specPackageSlice(spec.Wheel))
+
+	// No duplicate packages. Since we're sorted, we can just check for no
+	// immediate repetitions.
+	for i, pkg := range spec.Wheel {
+		if i > 0 && pkg.Path == spec.Wheel[i-1].Path {
+			return errors.Reason("duplicate spec entries for package %(path)q").
+				D("path", pkg.Path).
+				Err()
+		}
+	}
+
+	return nil
+}
+
+// Hash hashes the contents of the supplied "spec" and returns the result as
+// a hex-encoded string.
+func Hash(spec *vpython.Spec) string {
+	data, err := proto.Marshal(spec)
+	if err != nil {
+		panic(fmt.Errorf("failed to marshal proto: %v", err))
+	}
+	hash := sha256.Sum256(data)
+	return hex.EncodeToString(hash[:])
+}
+
+type specPackageSlice []*vpython.Spec_Package
+
+func (s specPackageSlice) Len() int      { return len(s) }
+func (s specPackageSlice) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+
+func (s specPackageSlice) Less(i, j int) bool {
+	return sortby.Chain{
+		func(i, j int) bool { return s[i].Path < s[j].Path },
+		func(i, j int) bool { return s[i].Version < s[j].Version },
+	}.Use(i, j)
+}