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| 1 | +// Sequential GVAS property stream walker. |
| 2 | +// Walks top-level properties by reading their headers. |
| 3 | +// Skips struct values by scanning forward for the next valid property name. |
| 4 | + |
| 5 | +using System.Collections.Generic; |
| 6 | +using System.Text; |
| 7 | + |
| 8 | +namespace NotAlterra.Gvas; |
| 9 | + |
| 10 | +public record GvasProperty(string Name, string Type, uint Size, uint ArrayIndex, object? Value); |
| 11 | + |
| 12 | +public static class PropertyWalker |
| 13 | +{ |
| 14 | + public static List<GvasProperty> WalkAll(byte[] data) |
| 15 | + { |
| 16 | + var props = new List<GvasProperty>(); |
| 17 | + |
| 18 | + int gvasStart = IndexOfMagic(data, "GVAS"); |
| 19 | + if (gvasStart < 0) return props; |
| 20 | + |
| 21 | + int offset = gvasStart + 12; // past "GVAS" + FileVersion + PackageVersion |
| 22 | + int headerEnd = FindSaveGameClassName(data, gvasStart); |
| 23 | + if (headerEnd <= offset) return props; |
| 24 | + offset = headerEnd; |
| 25 | + |
| 26 | + while (offset < data.Length) |
| 27 | + { |
| 28 | + var (propName, nameEnd) = BinaryReader.ReadFName(data, offset); |
| 29 | + if (propName == null || nameEnd <= offset) break; |
| 30 | + |
| 31 | + if (propName == "None") |
| 32 | + { offset = nameEnd; break; } |
| 33 | + |
| 34 | + offset = nameEnd; |
| 35 | + var (typeName, typeEnd) = BinaryReader.ReadFName(data, offset); |
| 36 | + if (typeName == null || typeEnd <= offset) break; |
| 37 | + offset = typeEnd; |
| 38 | + |
| 39 | + uint propSize = BinaryReader.ReadU32(data, offset) ?? 0; |
| 40 | + offset += 4; |
| 41 | + uint arrayIndex = BinaryReader.ReadU32(data, offset) ?? 0; |
| 42 | + offset += 4; |
| 43 | + |
| 44 | + object? value = null; |
| 45 | + int consumed = (int)propSize; |
| 46 | + |
| 47 | + switch (typeName) |
| 48 | + { |
| 49 | + case "IntProperty": |
| 50 | + if (propSize >= 4) value = BinaryReader.ReadU32(data, offset); |
| 51 | + break; |
| 52 | + case "FloatProperty": |
| 53 | + if (propSize >= 4) |
| 54 | + { |
| 55 | + var bits = BinaryReader.ReadU32(data, offset); |
| 56 | + if (bits.HasValue) value = BitConverter.ToSingle(BitConverter.GetBytes(bits.Value), 0); |
| 57 | + } |
| 58 | + break; |
| 59 | + case "DoubleProperty": |
| 60 | + value = BinaryReader.ReadF64(data, offset); |
| 61 | + break; |
| 62 | + case "BoolProperty": |
| 63 | + if (propSize >= 1) value = data[offset] != 0; |
| 64 | + break; |
| 65 | + case "StrProperty": |
| 66 | + case "TextProperty": |
| 67 | + { var (s, _) = BinaryReader.ReadFString(data, offset); value = s; } |
| 68 | + break; |
| 69 | + case "NameProperty": |
| 70 | + { var (s, _) = BinaryReader.ReadFName(data, offset); value = s; } |
| 71 | + break; |
| 72 | + case "StructProperty": |
| 73 | + // Skip struct value by name + data; find end by scanning for next property |
| 74 | + consumed = SkipStruct(data, offset, propSize); |
| 75 | + value = consumed >= 0 ? "(struct)" : null; |
| 76 | + if (consumed < 0) consumed = (int)propSize; |
| 77 | + break; |
| 78 | + case "ByteProperty": |
| 79 | + { |
| 80 | + var (enumType, enumEnd) = BinaryReader.ReadFName(data, offset); |
| 81 | + if (enumType != null && enumEnd > offset && enumEnd < offset + propSize) |
| 82 | + value = data[enumEnd]; |
| 83 | + else if (propSize >= 1) value = data[offset]; |
| 84 | + } |
| 85 | + break; |
| 86 | + case "EnumProperty": |
| 87 | + { |
| 88 | + var (innerType, innerEnd) = BinaryReader.ReadFName(data, offset); |
| 89 | + if (innerType != null) |
| 90 | + { |
| 91 | + var (enumValue, valEnd) = BinaryReader.ReadFName(data, innerEnd); |
| 92 | + if (enumValue != null) value = $"{innerType}.{enumValue}"; |
| 93 | + } |
| 94 | + } |
| 95 | + break; |
| 96 | + default: |
| 97 | + value = $"({typeName}:{propSize}b)"; |
| 98 | + break; |
| 99 | + } |
| 100 | + |
| 101 | + if (consumed < 0) consumed = 0; |
| 102 | + if (offset + consumed > data.Length) consumed = data.Length - offset; |
| 103 | + |
| 104 | + props.Add(new GvasProperty(propName, typeName, propSize, arrayIndex, value)); |
| 105 | + offset += consumed; |
| 106 | + } |
| 107 | + |
| 108 | + return props; |
| 109 | + } |
| 110 | + |
| 111 | + // Skip a struct value: read struct_type_name FName + its data. |
| 112 | + // Returns the number of bytes consumed from 'offset'. |
| 113 | + private static int SkipStruct(byte[] data, int offset, uint propSize) |
| 114 | + { |
| 115 | + int start = offset; |
| 116 | + var (sname, snameEnd) = BinaryReader.ReadFName(data, offset); |
| 117 | + if (sname == null || snameEnd <= offset) return (int)propSize; |
| 118 | + |
| 119 | + // After struct name, scan for the end of struct data. |
| 120 | + // The struct value is not a GVAS property stream — it's binary C++ data. |
| 121 | + // We need to find where it ends by looking for the next top-level property. |
| 122 | + // Strategy: scan forward for a valid FName that looks like a property name. |
| 123 | + int end = FindNextProperty(data, snameEnd, start + 100000); |
| 124 | + if (end > snameEnd) |
| 125 | + return end - start; |
| 126 | + |
| 127 | + // Fallback: use propSize (might be wrong but better than infinite loop) |
| 128 | + return (int)propSize; |
| 129 | + } |
| 130 | + |
| 131 | + // Scan forward for the start of the next top-level property. |
| 132 | + // Looks for known property names with valid FName length prefixes. |
| 133 | + private static int FindNextProperty(byte[] data, int searchStart, int searchEnd) |
| 134 | + { |
| 135 | + searchEnd = Math.Min(searchEnd, data.Length); |
| 136 | + string[] knownProps = { |
| 137 | + "SlotName", "DisplayName", "GameMode", "LevelName", "bIsMultiplayerSave", |
| 138 | + "bWasMultiplayerSave", "BuildNumber", "BuildBranch", "SavesCount", |
| 139 | + "LatestVersion", "DataVersion", "EngineVersion", "MTime", |
| 140 | + "CreatedAt", "LastModified", "None" |
| 141 | + }; |
| 142 | + |
| 143 | + for (int i = searchStart; i <= searchEnd - 10; i++) |
| 144 | + { |
| 145 | + foreach (var name in knownProps) |
| 146 | + { |
| 147 | + if (i + name.Length > data.Length) continue; |
| 148 | + bool match = true; |
| 149 | + for (int j = 0; j < name.Length; j++) |
| 150 | + if (data[i + j] != name[j]) { match = false; break; } |
| 151 | + if (!match) continue; |
| 152 | + |
| 153 | + // Verify FName length prefix |
| 154 | + int prefixLen = BitConverter.ToInt32(data, i - 4); |
| 155 | + if (prefixLen != name.Length + 1) continue; |
| 156 | + if (data[i + name.Length] != 0) continue; |
| 157 | + |
| 158 | + return i - 4; // Return start of this property |
| 159 | + } |
| 160 | + } |
| 161 | + return -1; |
| 162 | + } |
| 163 | + |
| 164 | + private static int FindSaveGameClassName(byte[] data, int gvasStart) |
| 165 | + { |
| 166 | + int searchEnd = Math.Min(data.Length, gvasStart + 4096); |
| 167 | + for (int i = gvasStart + 12; i <= searchEnd - 10; i++) |
| 168 | + { |
| 169 | + if (data[i] != '/' || data[i + 1] != 'S' || data[i + 2] != 'c') continue; |
| 170 | + int rawLen = BitConverter.ToInt32(data, i - 4); |
| 171 | + if (rawLen <= 0 || rawLen > 500) continue; |
| 172 | + if (i - 4 + rawLen > data.Length) continue; |
| 173 | + if (data[i + rawLen - 1] != 0) continue; |
| 174 | + |
| 175 | + int propStart = i + rawLen; |
| 176 | + while (propStart < data.Length && data[propStart] == 0) propStart++; |
| 177 | + return propStart; |
| 178 | + } |
| 179 | + return -1; |
| 180 | + } |
| 181 | + |
| 182 | + private static int IndexOfMagic(byte[] data, string magic) |
| 183 | + { |
| 184 | + var m = Encoding.UTF8.GetBytes(magic); |
| 185 | + int max = Math.Min(data.Length, 512); |
| 186 | + for (int i = 0; i <= max - 4; i++) |
| 187 | + if (data[i] == m[0] && data[i + 1] == m[1] && data[i + 2] == m[2] && data[i + 3] == m[3]) |
| 188 | + return i; |
| 189 | + return -1; |
| 190 | + } |
| 191 | + |
| 192 | + public static Dictionary<string, object?> WalkToDict(byte[] data) |
| 193 | + { |
| 194 | + var dict = new Dictionary<string, object?>(); |
| 195 | + foreach (var prop in WalkAll(data)) |
| 196 | + dict[prop.Name] = prop.Value; |
| 197 | + return dict; |
| 198 | + } |
| 199 | +} |
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