digest: cleanup digester and verifier creation

Signed-off-by: Stephen J Day <stephen.day@docker.com>

algorithm.go

@@ -0,0 +1,140 @@
+package digest
+
+import (
+	"crypto"
+	"fmt"
+	"hash"
+	"io"
+)
+
+// Algorithm identifies and implementation of a digester by an identifier.
+// Note the that this defines both the hash algorithm used and the string
+// encoding.
+type Algorithm string
+
+// supported digest types
+const (
+	SHA256 Algorithm = "sha256" // sha256 with hex encoding
+	SHA384 Algorithm = "sha384" // sha384 with hex encoding
+	SHA512 Algorithm = "sha512" // sha512 with hex encoding
+
+	// Canonical is the primary digest algorithm used with the distribution
+	// project. Other digests may be used but this one is the primary storage
+	// digest.
+	Canonical = SHA256
+)
+
+var (
+	// TODO(stevvooe): Follow the pattern of the standard crypto package for
+	// registration of digests. Effectively, we are a registerable set and
+	// common symbol access.
+
+	// algorithms maps values to hash.Hash implementations. Other algorithms
+	// may be available but they cannot be calculated by the digest package.
+	algorithms = map[Algorithm]crypto.Hash{
+		SHA256: crypto.SHA256,
+		SHA384: crypto.SHA384,
+		SHA512: crypto.SHA512,
+	}
+)
+
+// Available returns true if the digest type is available for use. If this
+// returns false, New and Hash will return nil.
+func (a Algorithm) Available() bool {
+	h, ok := algorithms[a]
+	if !ok {
+		return false
+	}
+
+	// check availability of the hash, as well
+	return h.Available()
+}
+
+func (a Algorithm) String() string {
+	return string(a)
+}
+
+// Size returns number of bytes returned by the hash.
+func (a Algorithm) Size() int {
+	h, ok := algorithms[a]
+	if !ok {
+		return 0
+	}
+	return h.Size()
+}
+
+// Set implemented to allow use of Algorithm as a command line flag.
+func (a *Algorithm) Set(value string) error {
+	if value == "" {
+		*a = Canonical
+	} else {
+		// just do a type conversion, support is queried with Available.
+		*a = Algorithm(value)
+	}
+
+	return nil
+}
+
+// New returns a new digester for the specified algorithm. If the algorithm
+// does not have a digester implementation, nil will be returned. This can be
+// checked by calling Available before calling New.
+func (a Algorithm) Digester() Digester {
+	return &digester{
+		alg:  a,
+		hash: a.Hash(),
+	}
+}
+
+// New is deprecated. Use Algorithm.Digester.
+func (a Algorithm) New() Digester {
+	return a.Digester()
+}
+
+// Hash returns a new hash as used by the algorithm. If not available, the
+// method will panic. Check Algorithm.Available() before calling.
+func (a Algorithm) Hash() hash.Hash {
+	if !a.Available() {
+		// NOTE(stevvooe): A missing hash is usually a programming error that
+		// must be resolved at compile time. We don't import in the digest
+		// package to allow users to choose their hash implementation (such as
+		// when using stevvooe/resumable or a hardware accelerated package).
+		//
+		// Applications that may want to resolve the hash at runtime should
+		// call Algorithm.Available before call Algorithm.Hash().
+		panic(fmt.Sprintf("%v not available (make sure it is imported)", a))
+	}
+
+	return algorithms[a].New()
+}
+
+// FromReader returns the digest of the reader using the algorithm.
+func (a Algorithm) FromReader(rd io.Reader) (Digest, error) {
+	digester := a.New()
+
+	if _, err := io.Copy(digester.Hash(), rd); err != nil {
+		return "", err
+	}
+
+	return digester.Digest(), nil
+}
+
+// FromBytes digests the input and returns a Digest.
+func (a Algorithm) FromBytes(p []byte) Digest {
+	digester := a.New()
+
+	if _, err := digester.Hash().Write(p); err != nil {
+		// Writes to a Hash should never fail. None of the existing
+		// hash implementations in the stdlib or hashes vendored
+		// here can return errors from Write. Having a panic in this
+		// condition instead of having FromBytes return an error value
+		// avoids unnecessary error handling paths in all callers.
+		panic("write to hash function returned error: " + err.Error())
+	}
+
+	return digester.Digest()
+}
+
+// FromString digests the string input and returns a Digest.
+func (a Algorithm) FromString(s string) Digest {
+	return a.FromBytes([]byte(s))
+}

digest.go

@@ -123,6 +123,20 @@ func (d Digest) Algorithm() Algorithm {
 	return Algorithm(d[:d.sepIndex()])
 }
 
+// Verifier returns a writer object that can be used to verify a stream of
+// content against the digest. If the digest is invalid, an error will be
+// returned.
+func (d Digest) Verifier() (Verifier, error) {
+	if err := d.Validate(); err != nil {
+		return nil, err
+	}
+
+	return hashVerifier{
+		hash:   d.Algorithm().Hash(),
+		digest: d,
+	}, nil
+}
+
 // Hex returns the hex digest portion of the digest. This will panic if the
 // underlying digest is not in a valid format.
 func (d Digest) Hex() string {

digester.go

@@ -1,141 +1,6 @@
 package digest
 
-import (
-	"crypto"
-	"fmt"
-	"hash"
-	"io"
-)
-
-// Algorithm identifies and implementation of a digester by an identifier.
-// Note the that this defines both the hash algorithm used and the string
-// encoding.
-type Algorithm string
-
-// supported digest types
-const (
-	SHA256 Algorithm = "sha256" // sha256 with hex encoding
-	SHA384 Algorithm = "sha384" // sha384 with hex encoding
-	SHA512 Algorithm = "sha512" // sha512 with hex encoding
-
-	// Canonical is the primary digest algorithm used with the distribution
-	// project. Other digests may be used but this one is the primary storage
-	// digest.
-	Canonical = SHA256
-)
-
-var (
-	// TODO(stevvooe): Follow the pattern of the standard crypto package for
-	// registration of digests. Effectively, we are a registerable set and
-	// common symbol access.
-
-	// algorithms maps values to hash.Hash implementations. Other algorithms
-	// may be available but they cannot be calculated by the digest package.
-	algorithms = map[Algorithm]crypto.Hash{
-		SHA256: crypto.SHA256,
-		SHA384: crypto.SHA384,
-		SHA512: crypto.SHA512,
-	}
-)
-
-// Available returns true if the digest type is available for use. If this
-// returns false, New and Hash will return nil.
-func (a Algorithm) Available() bool {
-	h, ok := algorithms[a]
-	if !ok {
-		return false
-	}
-
-	// check availability of the hash, as well
-	return h.Available()
-}
-
-func (a Algorithm) String() string {
-	return string(a)
-}
-
-// Size returns number of bytes returned by the hash.
-func (a Algorithm) Size() int {
-	h, ok := algorithms[a]
-	if !ok {
-		return 0
-	}
-	return h.Size()
-}
-
-// Set implemented to allow use of Algorithm as a command line flag.
-func (a *Algorithm) Set(value string) error {
-	if value == "" {
-		*a = Canonical
-	} else {
-		// just do a type conversion, support is queried with Available.
-		*a = Algorithm(value)
-	}
-
-	return nil
-}
-
-// New returns a new digester for the specified algorithm. If the algorithm
-// does not have a digester implementation, nil will be returned. This can be
-// checked by calling Available before calling New.
-func (a Algorithm) New() Digester {
-	return &digester{
-		alg:  a,
-		hash: a.Hash(),
-	}
-}
-
-// Hash returns a new hash as used by the algorithm. If not available, the
-// method will panic. Check Algorithm.Available() before calling.
-func (a Algorithm) Hash() hash.Hash {
-	if !a.Available() {
-		// NOTE(stevvooe): A missing hash is usually a programming error that
-		// must be resolved at compile time. We don't import in the digest
-		// package to allow users to choose their hash implementation (such as
-		// when using stevvooe/resumable or a hardware accelerated package).
-		//
-		// Applications that may want to resolve the hash at runtime should
-		// call Algorithm.Available before call Algorithm.Hash().
-		panic(fmt.Sprintf("%v not available (make sure it is imported)", a))
-	}
-
-	return algorithms[a].New()
-}
-
-// FromReader returns the digest of the reader using the algorithm.
-func (a Algorithm) FromReader(rd io.Reader) (Digest, error) {
-	digester := a.New()
-
-	if _, err := io.Copy(digester.Hash(), rd); err != nil {
-		return "", err
-	}
-
-	return digester.Digest(), nil
-}
-
-// FromBytes digests the input and returns a Digest.
-func (a Algorithm) FromBytes(p []byte) Digest {
-	digester := a.New()
-
-	if _, err := digester.Hash().Write(p); err != nil {
-		// Writes to a Hash should never fail. None of the existing
-		// hash implementations in the stdlib or hashes vendored
-		// here can return errors from Write. Having a panic in this
-		// condition instead of having FromBytes return an error value
-		// avoids unnecessary error handling paths in all callers.
-		panic("write to hash function returned error: " + err.Error())
-	}
-
-	return digester.Digest()
-}
-
-// FromString digests the string input and returns a Digest.
-func (a Algorithm) FromString(s string) Digest {
-	return a.FromBytes([]byte(s))
-}
-
-// TODO(stevvooe): Allow resolution of verifiers using the digest type and
-// this registration system.
+import "hash"
 
 // Digester calculates the digest of written data. Writes should go directly
 // to the return value of Hash, while calling Digest will return the current

verifiers.go

@@ -17,8 +17,7 @@ type Verifier interface {
 	Verified() bool
 }
 
-// NewDigestVerifier returns a verifier that compares the written bytes
-// against a passed in digest.
+// NewDigestVerifier is deprecated. Please use Digest.Verifier.
 func NewDigestVerifier(d Digest) (Verifier, error) {
 	if err := d.Validate(); err != nil {
 		return nil, err