go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/cipd/common/hash.go (about)

     1  // Copyright 2017 The LUCI Authors.
     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  
    15  package common
    16  
    17  import (
    18  	"encoding/hex"
    19  	"fmt"
    20  	"hash"
    21  	"reflect"
    22  
    23  	api "go.chromium.org/luci/cipd/api/cipd/v1"
    24  )
    25  
    26  // DefaultHashAlgo is a hash algorithm to use for deriving IDs of new package
    27  // instances. Older existing instances are allowed to use some other hash algo.
    28  const DefaultHashAlgo = api.HashAlgo_SHA256
    29  
    30  // Supported algo => its digest length (in hex encoding) + factory function.
    31  //
    32  // Actual entries are added in individual hash_*.go files, so that supported
    33  // hashes can be turned off by build flags or by omitting files when vendoring.
    34  var supportedAlgos = make([]struct {
    35  	hash         func() hash.Hash
    36  	typ          reflect.Type
    37  	hexDigestLen int
    38  }, len(api.HashAlgo_value))
    39  
    40  // registerHash is used from hash_*.go files to update supportedAlgos.
    41  func registerHashAlgo(algo api.HashAlgo, h func() hash.Hash) {
    42  	if supportedAlgos[algo].hash != nil {
    43  		panic(fmt.Sprintf("hash algo %s is already registered", algo))
    44  	}
    45  	inst := h()
    46  	supportedAlgos[algo].hash = h
    47  	supportedAlgos[algo].typ = reflect.TypeOf(inst)
    48  	supportedAlgos[algo].hexDigestLen = 2 * len(inst.Sum(nil))
    49  }
    50  
    51  // NewHash returns a hash implementation or an error if the algo is unknown.
    52  func NewHash(algo api.HashAlgo) (hash.Hash, error) {
    53  	if err := ValidateHashAlgo(algo); err != nil {
    54  		return nil, err
    55  	}
    56  	return supportedAlgos[algo].hash(), nil
    57  }
    58  
    59  // MustNewHash as like NewHash, but panics on errors.
    60  //
    61  // Appropriate for cases when the hash algo has already been validated.
    62  func MustNewHash(algo api.HashAlgo) hash.Hash {
    63  	h, err := NewHash(algo)
    64  	if err != nil {
    65  		panic(err)
    66  	}
    67  	return h
    68  }
    69  
    70  // ValidateHashAlgo returns a grpc-annotated error if the given algo is invalid,
    71  // e.g. either unspecified or not known to the current version of the code.
    72  //
    73  // Errors have InvalidArgument grpc code.
    74  func ValidateHashAlgo(h api.HashAlgo) error {
    75  	switch {
    76  	case h == api.HashAlgo_HASH_ALGO_UNSPECIFIED:
    77  		return validationErr("the hash algorithm is not specified or unrecognized")
    78  	case int(h) >= len(supportedAlgos) || supportedAlgos[h].hash == nil:
    79  		return validationErr("unsupported hash algorithm %d", h)
    80  	}
    81  	return nil
    82  }
    83  
    84  // HexDigest returns a digest string as it is used in ObjectRef.
    85  func HexDigest(h hash.Hash) string {
    86  	return hex.EncodeToString(h.Sum(nil))
    87  }
    88  
    89  // ObjectRefFromHash returns ObjectRef based on the given hash.Hash.
    90  //
    91  // `h` must be one of the supported hashes (as created by `NewHash`). Panics
    92  // otherwise.
    93  func ObjectRefFromHash(h hash.Hash) *api.ObjectRef {
    94  	typ := reflect.TypeOf(h)
    95  	for algo, props := range supportedAlgos {
    96  		if props.typ == typ {
    97  			return &api.ObjectRef{
    98  				HashAlgo:  api.HashAlgo(algo),
    99  				HexDigest: HexDigest(h),
   100  			}
   101  		}
   102  	}
   103  	panic(fmt.Sprintf("unknown hash algo %T", h))
   104  }