| 1 | package ledger |
| 2 | |
| 3 | import ( |
| 4 | "context" |
| 5 | "encoding/json" |
| 6 | "fmt" |
| 7 | "io" |
| 8 | "net/http" |
| 9 | "strings" |
| 10 | |
| 11 | "github.com/carlosframework/platform/internal/release" |
| 12 | ) |
| 13 | |
| 14 | type Getter func(ctx context.Context, key string) ([]byte, error) |
| 15 | |
| 16 | func StoreGetter(st release.Store) Getter { |
| 17 | return func(ctx context.Context, key string) ([]byte, error) { |
| 18 | b, _, err := st.Get(ctx, key) |
| 19 | return b, err |
| 20 | } |
| 21 | } |
| 22 | |
| 23 | func HTTPGetter(client *http.Client, base string) Getter { |
| 24 | return func(ctx context.Context, key string) ([]byte, error) { |
| 25 | req, err := http.NewRequestWithContext(ctx, http.MethodGet, base+"/"+key, nil) |
| 26 | if err != nil { |
| 27 | return nil, err |
| 28 | } |
| 29 | resp, err := client.Do(req) |
| 30 | if err != nil { |
| 31 | return nil, err |
| 32 | } |
| 33 | defer resp.Body.Close() |
| 34 | if resp.StatusCode != http.StatusOK { |
| 35 | return nil, fmt.Errorf("ledger: GET %s: %s", key, resp.Status) |
| 36 | } |
| 37 | return io.ReadAll(io.LimitReader(resp.Body, MaxBlob+1)) |
| 38 | } |
| 39 | } |
| 40 | |
| 41 | type VerifyResult struct { |
| 42 | Count int |
| 43 | HeadSHA256 string |
| 44 | } |
| 45 | |
| 46 | // Verify walks HEAD back to the genesis entry, re-hashing every stored |
| 47 | // byte. It proves: HEAD's sha matches the head entry's bytes, every |
| 48 | // prev_sha256 matches the previous entry's bytes, the walk terminates at |
| 49 | // prev_key "", and the walked length equals HEAD's count. |
| 50 | func Verify(ctx context.Context, get Getter, sqid, app, name string) (VerifyResult, error) { |
| 51 | hb, err := get(ctx, HeadKey(sqid, app, name)) |
| 52 | if err != nil { |
| 53 | return VerifyResult{}, err |
| 54 | } |
| 55 | var head Head |
| 56 | if err := json.Unmarshal(hb, &head); err != nil { |
| 57 | return VerifyResult{}, fmt.Errorf("ledger: HEAD corrupt: %w", err) |
| 58 | } |
| 59 | |
| 60 | // The walk follows keys the CHAIN supplies (HEAD.json's head_key, then |
| 61 | // each entry's prev_key), so those keys are exactly as trustworthy as the |
| 62 | // bytes under verification. Pinning them to this ledger's own entries/ |
| 63 | // prefix is what stops a chain from grafting another ledger's history — |
| 64 | // or any other object in the bucket — onto its own and still verifying |
| 65 | // clean: every hash would agree, because the hashes are only ever |
| 66 | // checked against what the chain itself claims. |
| 67 | want := Prefix(sqid, app, name) + "entries/" |
| 68 | |
| 69 | key, wantSHA := head.HeadKey, head.HeadSHA256 |
| 70 | walked := 0 |
| 71 | for key != "" { |
| 72 | if walked >= head.Count { |
| 73 | return VerifyResult{}, fmt.Errorf("ledger: chain longer than HEAD count %d", head.Count) |
| 74 | } |
| 75 | if !strings.HasPrefix(key, want) { |
| 76 | return VerifyResult{}, fmt.Errorf("ledger: %s: chain leaves ledger %q — key is outside %s", key, name, want) |
| 77 | } |
| 78 | eb, err := get(ctx, key) |
| 79 | if err != nil { |
| 80 | return VerifyResult{}, fmt.Errorf("ledger: %s: %w", key, err) |
| 81 | } |
| 82 | if got := SHA256Hex(eb); got != wantSHA { |
| 83 | return VerifyResult{}, fmt.Errorf("ledger: %s: sha %s, chain says %s — bytes were altered", key, got, wantSHA) |
| 84 | } |
| 85 | var e Entry |
| 86 | if err := json.Unmarshal(eb, &e); err != nil { |
| 87 | return VerifyResult{}, fmt.Errorf("ledger: %s corrupt: %w", key, err) |
| 88 | } |
| 89 | if e.Ledger != name { |
| 90 | return VerifyResult{}, fmt.Errorf("ledger: %s: entry names ledger %q, walking %q", key, e.Ledger, name) |
| 91 | } |
| 92 | key, wantSHA = e.PrevKey, e.PrevSHA256 |
| 93 | walked++ |
| 94 | } |
| 95 | if walked != head.Count { |
| 96 | return VerifyResult{}, fmt.Errorf("ledger: walked %d entries, HEAD count %d", walked, head.Count) |
| 97 | } |
| 98 | return VerifyResult{Count: walked, HeadSHA256: head.HeadSHA256}, nil |
| 99 | } |
| 100 | |
amadan