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package v4
import (
"encoding/hex"
"strings"
"time"
"github.com/aws/aws-sdk-go/aws/credentials"
)
type credentialValueProvider interface {
Get() (credentials.Value, error)
}
// StreamSigner implements signing of event stream encoded payloads
type StreamSigner struct {
region string
service string
credentials credentialValueProvider
prevSig []byte
}
// NewStreamSigner creates a SigV4 signer used to sign Event Stream encoded messages
func NewStreamSigner(region, service string, seedSignature []byte, credentials *credentials.Credentials) *StreamSigner {
return &StreamSigner{
region: region,
service: service,
credentials: credentials,
prevSig: seedSignature,
}
}
// GetSignature takes an event stream encoded headers and payload and returns a signature
func (s *StreamSigner) GetSignature(headers, payload []byte, date time.Time) ([]byte, error) {
credValue, err := s.credentials.Get()
if err != nil {
return nil, err
}
sigKey := deriveSigningKey(s.region, s.service, credValue.SecretAccessKey, date)
keyPath := buildSigningScope(s.region, s.service, date)
stringToSign := buildEventStreamStringToSign(headers, payload, s.prevSig, keyPath, date)
signature := hmacSHA256(sigKey, []byte(stringToSign))
s.prevSig = signature
return signature, nil
}
func buildEventStreamStringToSign(headers, payload, prevSig []byte, scope string, date time.Time) string {
return strings.Join([]string{
"AWS4-HMAC-SHA256-PAYLOAD",
formatTime(date),
scope,
hex.EncodeToString(prevSig),
hex.EncodeToString(hashSHA256(headers)),
hex.EncodeToString(hashSHA256(payload)),
}, "\n")
}
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