cmd/go/internal/cache: add support definitions

There is no cache here yet. This CL defines ActionID, Hash, and HashFile,
which the new content-based staleness code can use. Eventually we'll
put a real cache implementation here, but it's not necessary yet.

Change-Id: Ide433cb449f4dbe658694453f348c947642df79b
Reviewed-on: https://go-review.googlesource.com/67311
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

diff --git a/src/cmd/go/internal/cache/cache.go b/src/cmd/go/internal/cache/cache.go
new file mode 100644 (file)
index 0000000..97afe95
--- /dev/null
+++ b/src/cmd/go/internal/cache/cache.go
@@ -0,0 +1,13 @@
+// Copyright 2017 The Go 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 cache implements a package cache,
+// or more properly a build artifact cache,
+// but our only cached build artifacts are packages.
+package cache
+
+// An ActionID is a cache action key, the hash of a complete description of a
+// repeatable computation (command line, environment variables,
+// input file contents, executable contents).
+type ActionID [HashSize]byte

diff --git a/src/cmd/go/internal/cache/hash.go b/src/cmd/go/internal/cache/hash.go
new file mode 100644 (file)
index 0000000..edb2d31
--- /dev/null
+++ b/src/cmd/go/internal/cache/hash.go
@@ -0,0 +1,73 @@
+// Copyright 2017 The Go 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 cache
+
+import (
+       "crypto/sha256"
+       "fmt"
+       "hash"
+       "io"
+       "os"
+)
+
+const debugHash = false
+
+// HashSize is the number of bytes in a hash.
+const HashSize = 32
+
+// A Hash provides access to the canonical hash function used to index the cache.
+// The current implementation uses SHA256, but clients must not assume this.
+type Hash struct {
+       h    hash.Hash
+       name string // for debugging
+}
+
+// NewHash returns a new Hash.
+// The caller is expected to Write data to it and then call Sum.
+func NewHash(name string) *Hash {
+       h := &Hash{h: sha256.New(), name: name}
+       if debugHash {
+               fmt.Fprintf(os.Stderr, "HASH[%s]\n", h.name)
+       }
+       return h
+}
+
+// Write writes data to the running hash.
+func (h *Hash) Write(b []byte) (int, error) {
+       if debugHash {
+               fmt.Fprintf(os.Stderr, "HASH[%s]: %q\n", h.name, b)
+       }
+       return h.h.Write(b)
+}
+
+// Sum returns the hash of the data written previously.
+func (h *Hash) Sum() [HashSize]byte {
+       var out [HashSize]byte
+       h.h.Sum(out[:0])
+       if debugHash {
+               fmt.Fprintf(os.Stderr, "HASH[%s]: %x\n", h.name, out)
+       }
+       return out
+}
+
+// HashFile returns the hash of the named file.
+func HashFile(file string) ([HashSize]byte, error) {
+       h := sha256.New()
+       f, err := os.Open(file)
+       if err != nil {
+               if debugHash {
+                       fmt.Fprintf(os.Stderr, "HASH %s: %v\n", file, err)
+               }
+               return [HashSize]byte{}, err
+       }
+       io.Copy(h, f)
+       f.Close()
+       var out [HashSize]byte
+       h.Sum(out[:0])
+       if debugHash {
+               fmt.Fprintf(os.Stderr, "HASH %s: %x\n", file, out)
+       }
+       return out, nil
+}

diff --git a/src/cmd/go/internal/cache/hash_test.go b/src/cmd/go/internal/cache/hash_test.go
new file mode 100644 (file)
index 0000000..493d393
--- /dev/null
+++ b/src/cmd/go/internal/cache/hash_test.go
@@ -0,0 +1,46 @@
+// Copyright 2017 The Go 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 cache
+
+import (
+       "fmt"
+       "io/ioutil"
+       "os"
+       "testing"
+)
+
+func TestHash(t *testing.T) {
+       h := NewHash("alice")
+       h.Write([]byte("hello world"))
+       sum := fmt.Sprintf("%x", h.Sum())
+       want := "b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9"
+       if sum != want {
+               t.Errorf("hash(hello world) = %v, want %v", sum, want)
+       }
+}
+
+func TestHashFile(t *testing.T) {
+       f, err := ioutil.TempFile("", "cmd-go-test-")
+       if err != nil {
+               t.Fatal(err)
+       }
+       name := f.Name()
+       fmt.Fprintf(f, "hello world")
+       defer os.Remove(name)
+       if err := f.Close(); err != nil {
+               t.Fatal(err)
+       }
+
+       var h ActionID // make sure hash result is assignable to ActionID
+       h, err = HashFile(name)
+       if err != nil {
+               t.Fatal(err)
+       }
+       sum := fmt.Sprintf("%x", h)
+       want := "b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9"
+       if sum != want {
+               t.Errorf("hash(hello world) = %v, want %v", sum, want)
+       }
+}