vpython: Add environment spec package.

vpython/spec/spec.go

+// 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/env"
+
+        "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 the same identical representation.

[iannucci, 2017/02/21 09:09:55]

"same identical"

[dnj, 2017/02/22 07:37:19]

Done.

+func Normalize(spec *env.Spec) error {
+        sort.Sort(envSpecPackageSlice(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 *env.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 envSpecPackageSlice []*env.Spec_Package
+
+func (s envSpecPackageSlice) Len() int      { return len(s) }
+func (s envSpecPackageSlice) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+func (s envSpecPackageSlice) Less(i, j int) bool {

[iannucci, 2017/02/21 09:09:55]

try sortby! https://github.com/luci/luci-go/tree/master/common/data/sortby

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)

[dnj, 2017/02/22 07:37:19]

Oh cool.

+        // Sort by Path, then Version.
+        if s[i].Path >= s[j].Path {
+                return false
+        }
+        return s[i].Version >= s[j].Version
+}