94 lines
2.1 KiB
Go
94 lines
2.1 KiB
Go
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package attest
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import (
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"bytes"
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"crypto/sha256"
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"encoding/hex"
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"encoding/json"
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"fmt"
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"sort"
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)
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// sha256hex returns the hex-encoded SHA-256 of b.
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func sha256hex(b []byte) string {
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sum := sha256.Sum256(b)
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return hex.EncodeToString(sum[:])
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}
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// jsonMarshalSortedKeys produces a stable JSON encoding with keys sorted
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// recursively in every object. This is the stability we need for hashing;
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// it is NOT a full RFC 8785 implementation (no number-canonicalisation,
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// no string-escape canonicalisation), but all values we hash are strings,
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// nulls, maps, or arrays of those, which stay stable under encoding/json.
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func jsonMarshalSortedKeys(v any) ([]byte, error) {
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// Round-trip through generic unmarshal to get the canonical shape, then
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// emit sorted. For our (small, well-shaped) inputs this is cheap.
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first, err := json.Marshal(v)
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if err != nil {
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return nil, err
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}
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var any_ any
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if err := json.Unmarshal(first, &any_); err != nil {
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return nil, err
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}
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var buf bytes.Buffer
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if err := writeSorted(&buf, any_); err != nil {
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return nil, err
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}
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return buf.Bytes(), nil
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}
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func writeSorted(buf *bytes.Buffer, v any) error {
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switch x := v.(type) {
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case nil:
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buf.WriteString("null")
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case bool:
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if x {
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buf.WriteString("true")
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} else {
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buf.WriteString("false")
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}
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case float64:
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// json.Unmarshal gives floats for all numbers. In our payloads we
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// never emit raw numbers; everything is a string.
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b, _ := json.Marshal(x)
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buf.Write(b)
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case string:
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b, _ := json.Marshal(x)
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buf.Write(b)
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case []any:
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buf.WriteByte('[')
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for i, el := range x {
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if i > 0 {
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buf.WriteByte(',')
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}
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if err := writeSorted(buf, el); err != nil {
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return err
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}
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}
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buf.WriteByte(']')
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case map[string]any:
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keys := make([]string, 0, len(x))
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for k := range x {
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keys = append(keys, k)
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}
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sort.Strings(keys)
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buf.WriteByte('{')
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for i, k := range keys {
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if i > 0 {
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buf.WriteByte(',')
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}
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kb, _ := json.Marshal(k)
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buf.Write(kb)
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buf.WriteByte(':')
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if err := writeSorted(buf, x[k]); err != nil {
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return err
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}
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}
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buf.WriteByte('}')
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default:
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return fmt.Errorf("writeSorted: unsupported type %T", v)
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}
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return nil
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}
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