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package amp
import (
"crypto/rand"
"encoding/base64"
"fmt"
"strings"
)
// EncodePath encodes data in a way that is suitable for the suffix of an AMP
// cache URL.
func EncodePath(data []byte) string {
var cacheBreaker [9]byte
_, err := rand.Read(cacheBreaker[:])
if err != nil {
panic(err)
}
b64 := base64.RawURLEncoding.EncodeToString
return "0" + b64(cacheBreaker[:]) + "/" + b64(data)
}
// DecodePath decodes data from a path suffix as encoded by EncodePath. The path
// must have already been trimmed of any directory prefix (as might be present
// in, e.g., an HTTP request). That is, the first character of path should be
// the "0" message format indicator.
func DecodePath(path string) ([]byte, error) {
if len(path) < 1 {
return nil, fmt.Errorf("missing format indicator")
}
version := path[0]
rest := path[1:]
switch version {
case '0':
// Ignore everything else up to and including the final slash
// (there must be at least one slash).
i := strings.LastIndexByte(rest, '/')
if i == -1 {
return nil, fmt.Errorf("missing data")
}
return base64.RawURLEncoding.DecodeString(rest[i+1:])
default:
return nil, fmt.Errorf("unknown format indicator %q", version)
}
}
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