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| 1 | +import 'dart:convert' show base64, utf8; |
| 2 | + |
| 3 | +import 'package:convert/convert.dart'; |
| 4 | +import 'package:crypto/crypto.dart'; |
| 5 | +import 'package:ndef/ndef.dart' as ndef; |
| 6 | + |
| 7 | +const _bitcoinNfcTypePrefix = 'urn:nfc:ext:'; |
| 8 | +const _bitcoinPsbtType = 'bitcoin.org:psbt'; |
| 9 | +const _bitcoinTxnType = 'bitcoin.org:txn'; |
| 10 | +const _bitcoinSha256Type = 'bitcoin.org:sha256'; |
| 11 | +const _jsonMimeType = 'application/json'; |
| 12 | + |
| 13 | +String? payloadFromNdefRecords(List<ndef.NDEFRecord> records) { |
| 14 | + if (records.isEmpty) return null; |
| 15 | + |
| 16 | + final bitcoinPayload = _payloadFromBitcoinExternalRecords(records); |
| 17 | + if (bitcoinPayload != null || _hasBitcoinPayloadRecord(records)) { |
| 18 | + return bitcoinPayload; |
| 19 | + } |
| 20 | + |
| 21 | + return _payloadFromRecord(records.last); |
| 22 | +} |
| 23 | + |
| 24 | +String? _payloadFromBitcoinExternalRecords(List<ndef.NDEFRecord> records) { |
| 25 | + final txnPayload = _externalPayloadForType(records, _bitcoinTxnType); |
| 26 | + if (txnPayload != null) { |
| 27 | + if (!_matchesSha256Checksum(records, txnPayload)) return null; |
| 28 | + return hex.encode(txnPayload); |
| 29 | + } |
| 30 | + |
| 31 | + final psbtPayload = _externalPayloadForType(records, _bitcoinPsbtType); |
| 32 | + if (psbtPayload != null) { |
| 33 | + if (!_matchesSha256Checksum(records, psbtPayload)) return null; |
| 34 | + return base64.encode(psbtPayload); |
| 35 | + } |
| 36 | + |
| 37 | + return null; |
| 38 | +} |
| 39 | + |
| 40 | +bool _hasBitcoinPayloadRecord(List<ndef.NDEFRecord> records) { |
| 41 | + return _hasExternalRecordForType(records, _bitcoinTxnType) || |
| 42 | + _hasExternalRecordForType(records, _bitcoinPsbtType); |
| 43 | +} |
| 44 | + |
| 45 | +String? _payloadFromRecord(ndef.NDEFRecord record) { |
| 46 | + if (record is ndef.TextRecord) { |
| 47 | + final text = record.text; |
| 48 | + return text == null || text.isEmpty ? null : text; |
| 49 | + } |
| 50 | + |
| 51 | + if (record is ndef.ExternalRecord) { |
| 52 | + final payload = record.payload; |
| 53 | + if (payload == null || payload.isEmpty) return null; |
| 54 | + return hex.encode(payload); |
| 55 | + } |
| 56 | + |
| 57 | + if (record is ndef.MimeRecord && record.decodedType == _jsonMimeType) { |
| 58 | + final payload = record.payload; |
| 59 | + if (payload == null || payload.isEmpty) return null; |
| 60 | + |
| 61 | + try { |
| 62 | + return utf8.decode(payload); |
| 63 | + } on FormatException { |
| 64 | + return null; |
| 65 | + } |
| 66 | + } |
| 67 | + |
| 68 | + return null; |
| 69 | +} |
| 70 | + |
| 71 | +List<int>? _externalPayloadForType(List<ndef.NDEFRecord> records, String type) { |
| 72 | + for (final record in records.whereType<ndef.ExternalRecord>()) { |
| 73 | + if (_normalizedExternalType(record) != type) continue; |
| 74 | + |
| 75 | + final payload = record.payload; |
| 76 | + if (payload == null || payload.isEmpty) return null; |
| 77 | + return payload; |
| 78 | + } |
| 79 | + |
| 80 | + return null; |
| 81 | +} |
| 82 | + |
| 83 | +bool _hasExternalRecordForType(List<ndef.NDEFRecord> records, String type) { |
| 84 | + return records.whereType<ndef.ExternalRecord>().any( |
| 85 | + (record) => _normalizedExternalType(record) == type, |
| 86 | + ); |
| 87 | +} |
| 88 | + |
| 89 | +String? _normalizedExternalType(ndef.ExternalRecord record) { |
| 90 | + final decodedType = record.decodedType; |
| 91 | + if (decodedType == null || decodedType.isEmpty) return null; |
| 92 | + |
| 93 | + if (decodedType.startsWith(_bitcoinNfcTypePrefix)) { |
| 94 | + return decodedType.substring(_bitcoinNfcTypePrefix.length); |
| 95 | + } |
| 96 | + |
| 97 | + return decodedType; |
| 98 | +} |
| 99 | + |
| 100 | +bool _matchesSha256Checksum(List<ndef.NDEFRecord> records, List<int> payload) { |
| 101 | + final expectedHash = _externalPayloadForType(records, _bitcoinSha256Type); |
| 102 | + if (expectedHash == null) return true; |
| 103 | + |
| 104 | + return _bytesEqual(expectedHash, sha256.convert(payload).bytes); |
| 105 | +} |
| 106 | + |
| 107 | +bool _bytesEqual(List<int> left, List<int> right) { |
| 108 | + if (left.length != right.length) return false; |
| 109 | + |
| 110 | + for (var i = 0; i < left.length; i++) { |
| 111 | + if (left[i] != right[i]) return false; |
| 112 | + } |
| 113 | + |
| 114 | + return true; |
| 115 | +} |
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