7835d261d8
Previously a useful gist, this changeset polishes the original tarsum tool into a utility that can be used to calculate content digests. Any algorithm from the digest package is supported with additional support from tarsum. This tool is very useful for quickly checking backend digests and verifying correctness. Signed-off-by: Stephen J Day <stephen.day@docker.com>
123 lines
3.2 KiB
Go
123 lines
3.2 KiB
Go
package digest
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import (
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"crypto"
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"hash"
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"io"
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)
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// Algorithm identifies and implementation of a digester by an identifier.
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// Note the that this defines both the hash algorithm used and the string
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// encoding.
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type Algorithm string
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// supported digest types
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const (
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SHA256 Algorithm = "sha256" // sha256 with hex encoding
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SHA384 Algorithm = "sha384" // sha384 with hex encoding
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SHA512 Algorithm = "sha512" // sha512 with hex encoding
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TarsumV1SHA256 Algorithm = "tarsum+v1+sha256" // supported tarsum version, verification only
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// Canonical is the primary digest algorithm used with the distribution
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// project. Other digests may be used but this one is the primary storage
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// digest.
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Canonical = SHA256
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)
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var (
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// TODO(stevvooe): Follow the pattern of the standard crypto package for
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// registration of digests. Effectively, we are a registerable set and
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// common symbol access.
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// algorithms maps values to hash.Hash implementations. Other algorithms
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// may be available but they cannot be calculated by the digest package.
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algorithms = map[Algorithm]crypto.Hash{
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SHA256: crypto.SHA256,
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SHA384: crypto.SHA384,
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SHA512: crypto.SHA512,
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}
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)
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// Available returns true if the digest type is available for use. If this
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// returns false, New and Hash will return nil.
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func (a Algorithm) Available() bool {
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h, ok := algorithms[a]
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if !ok {
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return false
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}
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// check availability of the hash, as well
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return h.Available()
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}
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func (a Algorithm) String() string {
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return string(a)
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}
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// Set implemented to allow use of Algorithm as a command line flag.
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func (a *Algorithm) Set(value string) error {
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if value == "" {
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*a = Canonical
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} else {
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// just do a type conversion, support is queried with Available.
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*a = Algorithm(value)
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}
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return nil
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}
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// New returns a new digester for the specified algorithm. If the algorithm
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// does not have a digester implementation, nil will be returned. This can be
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// checked by calling Available before calling New.
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func (a Algorithm) New() Digester {
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return &digester{
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alg: a,
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hash: a.Hash(),
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}
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}
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// Hash returns a new hash as used by the algorithm. If not available, nil is
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// returned. Make sure to check Available before calling.
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func (a Algorithm) Hash() hash.Hash {
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if !a.Available() {
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return nil
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}
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return algorithms[a].New()
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}
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// FromReader returns the digest of the reader using the algorithm.
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func (a Algorithm) FromReader(rd io.Reader) (Digest, error) {
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digester := a.New()
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if _, err := io.Copy(digester.Hash(), rd); err != nil {
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return "", err
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}
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return digester.Digest(), nil
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}
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// TODO(stevvooe): Allow resolution of verifiers using the digest type and
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// this registration system.
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// Digester calculates the digest of written data. Writes should go directly
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// to the return value of Hash, while calling Digest will return the current
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// value of the digest.
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type Digester interface {
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Hash() hash.Hash // provides direct access to underlying hash instance.
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Digest() Digest
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}
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// digester provides a simple digester definition that embeds a hasher.
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type digester struct {
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alg Algorithm
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hash hash.Hash
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}
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func (d *digester) Hash() hash.Hash {
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return d.hash
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}
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func (d *digester) Digest() Digest {
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return NewDigest(d.alg, d.hash)
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}
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