github.com/uber/kraken@v0.1.4/core/digester.go (about)

     1  // Copyright (c) 2016-2019 Uber Technologies, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  package core
    15  
    16  import (
    17  	"crypto"
    18  	"encoding/hex"
    19  	"hash"
    20  	"io"
    21  )
    22  
    23  const (
    24  	// SHA256 is the only algorithm supported.
    25  	SHA256 = "sha256"
    26  )
    27  
    28  // Digester calculates the digest of data stream.
    29  type Digester struct {
    30  	hash hash.Hash
    31  }
    32  
    33  // NewDigester instantiates and returns a new Digester object.
    34  func NewDigester() *Digester {
    35  	return &Digester{
    36  		hash: crypto.SHA256.New(),
    37  	}
    38  }
    39  
    40  // Digest returns the digest of existing data.
    41  func (d *Digester) Digest() Digest {
    42  	digest, err := NewSHA256DigestFromHex(hex.EncodeToString(d.hash.Sum(nil)))
    43  	if err != nil {
    44  		// This should never fail.
    45  		panic(err)
    46  	}
    47  	return digest
    48  }
    49  
    50  // FromReader returns the digest of data from reader.
    51  func (d Digester) FromReader(rd io.Reader) (Digest, error) {
    52  	if _, err := io.Copy(d.hash, rd); err != nil {
    53  		return Digest{}, err
    54  	}
    55  
    56  	return d.Digest(), nil
    57  }
    58  
    59  // FromBytes digests the input and returns a Digest.
    60  func (d Digester) FromBytes(p []byte) (Digest, error) {
    61  	if _, err := d.hash.Write(p); err != nil {
    62  		return Digest{}, err
    63  	}
    64  
    65  	return d.Digest(), nil
    66  }
    67  
    68  // Tee allows d to calculate a digest of r while the caller reads from the
    69  // returned reader.
    70  func (d Digester) Tee(r io.Reader) io.Reader {
    71  	return io.TeeReader(r, d.hash)
    72  }