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segment.go
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segment.go
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// Copyright 2017-2018 Stratumn SAS. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package chainscript
import (
"bytes"
"context"
"github.com/pkg/errors"
)
// Segment errors.
var (
ErrLinkHashMismatch = errors.New("link hash from meta doesn't equal hashed link")
ErrMissingBackend = errors.New("evidence backend is missing")
ErrMissingProvider = errors.New("evidence provider is missing")
ErrMissingProof = errors.New("evidence proof is missing")
ErrDuplicateEvidence = errors.New("evidence already exists for the given backend and provider")
)
// LinkHash returns the link hash.
func (s *Segment) LinkHash() LinkHash {
return s.Meta.LinkHash
}
// SetLinkHash computes and sets the link hash.
func (s *Segment) SetLinkHash() error {
linkHash, err := s.Link.Hash()
if err != nil {
return err
}
if s.Meta == nil {
s.Meta = &SegmentMeta{}
}
s.Meta.LinkHash = linkHash
return nil
}
// Validate checks for errors in a segment
func (s *Segment) Validate(ctx context.Context) error {
if s.Link == nil {
return ErrMissingLink
}
if s.Meta == nil || len(s.Meta.LinkHash) == 0 {
return ErrMissingLinkHash
}
linkHash, err := s.Link.Hash()
if err != nil {
return err
}
if !bytes.Equal(linkHash, s.Meta.LinkHash) {
return ErrLinkHashMismatch
}
return s.Link.Validate(ctx)
}
// AddEvidence adds an evidence to the segment.
func (s *Segment) AddEvidence(evidence *Evidence) error {
err := evidence.Validate()
if err != nil {
return err
}
if e := s.GetEvidence(evidence.Backend, evidence.Provider); e != nil {
return ErrDuplicateEvidence
}
if s.Meta == nil {
s.Meta = &SegmentMeta{}
}
s.Meta.Evidences = append(s.Meta.Evidences, evidence)
return nil
}
// GetEvidence gets an evidence from a provider in a given backend.
func (s *Segment) GetEvidence(backend, provider string) *Evidence {
if s.Meta == nil {
return nil
}
for _, e := range s.Meta.Evidences {
if e.Backend == backend && e.Provider == provider {
return e
}
}
return nil
}
// FindEvidences finds all evidences from a specific backend.
func (s *Segment) FindEvidences(backend string) []*Evidence {
if s.Meta == nil {
return nil
}
var results []*Evidence
for _, e := range s.Meta.Evidences {
if e.Backend == backend {
results = append(results, e)
}
}
return results
}