Apple Binary Property List Format

Overview

Apple Binary Property List (applebplist) is a binary-encoded variant of Apple's Property List format. These files store serialized objects and configuration data in a compact binary format used extensively throughout macOS, iOS, and other Apple operating systems for storing application preferences, system configuration, and structured data.

Technical Details

File Extension: .plist
MIME Type: application/x-plist
Format Type: Binary serialization
Byte Order: Big-endian
Magic Number: bplist00 (8 bytes)
Platform: Apple ecosystems

Binary plist files contain:

• Serialized Foundation objects (NSString, NSNumber, NSArray, NSDictionary)
• Efficient binary encoding
• Object reference system
• Offset tables for random access

Key Features

• Compact Storage: Smaller file sizes compared to XML plists
• Fast Parsing: Optimized for quick loading
• Type Preservation: Maintains original object types
• Random Access: Direct object access without full parsing
• Cross-Platform: Supported across Apple platforms
• Backwards Compatible: Can be converted to/from XML format

Binary Structure

Binary Plist Structure:
├── Header (8 bytes)
│   └── "bplist00"
├── Objects Table
│   ├── Object 0 (root)
│   ├── Object 1
│   └── Object n
├── Offset Table
│   ├── Offset to Object 0
│   ├── Offset to Object 1
│   └── Offset to Object n
└── Trailer (32 bytes)
    ├── Offset table info
    ├── Number of objects
    └── Root object index

Object Types

Primitive Types

0x00: null
0x08: false
0x09: true
0x0F: fill byte

0x1n: integer (n = byte length - 1)
0x2n: real (n = byte length - 1)
0x3n: date (n = byte length - 1)

0x4n: data (n = byte length)
0x5n: ASCII string (n = byte length)
0x6n: Unicode string (n = byte length)

0xAn: array (n = element count)
0xDn: dictionary (n = key-value pairs)

Common Use Cases

1. System Preferences: Application and system settings
2. Configuration Files: Application configuration data
3. Cache Files: Temporary data storage
4. Metadata Storage: File and application metadata
5. IPC Communication: Inter-process data exchange
6. Bundle Information: App bundle metadata

Working with Binary Plists

Command Line Tools

# Convert binary to XML
plutil -convert xml1 file.plist

# Convert XML to binary
plutil -convert binary1 file.plist

# Check plist syntax
plutil -lint file.plist

# Display plist contents
defaults read file.plist

macOS Utilities

# Read plist values
defaults read com.apple.dock persistent-apps

# Write plist values
defaults write com.example.app PreferenceName -string "value"

# Delete plist keys
defaults delete com.example.app PreferenceName

Programming APIs

Objective-C/Swift

// Reading binary plist
NSData *data = [NSData dataWithContentsOfFile:@"config.plist"];
NSPropertyListFormat format;
NSError *error;
id plist = [NSPropertyListSerialization 
    propertyListWithData:data
    options:NSPropertyListImmutable
    format:&format
    error:&error];

// Writing binary plist
NSData *binaryData = [NSPropertyListSerialization 
    dataWithPropertyList:plist
    format:NSPropertyListBinaryFormat_v1_0
    options:0
    error:&error];
[binaryData writeToFile:@"output.plist" atomically:YES];

Swift

// Reading binary plist
if let data = NSData(contentsOfFile: "config.plist") {
    do {
        let plist = try PropertyListSerialization.propertyList(
            from: data as Data,
            options: [],
            format: nil
        )
        print(plist)
    } catch {
        print("Error reading plist: \(error)")
    }
}

// Writing binary plist
let dictionary = ["key": "value", "number": 42]
do {
    let data = try PropertyListSerialization.data(
        fromPropertyList: dictionary,
        format: .binary,
        options: 0
    )
    try data.write(to: URL(fileURLWithPath: "output.plist"))
} catch {
    print("Error writing plist: \(error)")
}

Python

import plistlib

# Reading binary plist
with open('config.plist', 'rb') as f:
    plist_data = plistlib.load(f)
    print(plist_data)

# Writing binary plist
data = {
    'StringValue': 'Hello World',
    'NumberValue': 42,
    'BooleanValue': True,
    'ArrayValue': [1, 2, 3],
    'DictValue': {'nested': 'value'}
}

with open('output.plist', 'wb') as f:
    plistlib.dump(data, f, fmt=plistlib.FMT_BINARY)

File Locations

System Preferences

# User preferences
~/Library/Preferences/com.apple.dock.plist
~/Library/Preferences/com.apple.finder.plist

# System preferences
/Library/Preferences/SystemConfiguration/preferences.plist

# Application preferences
~/Library/Preferences/com.company.app.plist

Application Bundles

# App bundle info
MyApp.app/Contents/Info.plist

# Framework info
Framework.framework/Versions/A/Resources/Info.plist

# Plugin bundle info
Plugin.bundle/Contents/Info.plist

Advanced Features

Keyed Archiving

// NSKeyedArchiver with plist format
NSData *archivedData = [NSKeyedArchiver archivedDataWithRootObject:object
    requiringSecureCoding:YES
    error:&error];

// Custom archiving
NSMutableData *data = [NSMutableData data];
NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] 
    initForWritingWithMutableData:data];
[archiver setOutputFormat:NSPropertyListBinaryFormat_v1_0];
[archiver encodeObject:object forKey:@"root"];
[archiver finishEncoding];

Performance Optimization

// Lazy loading for large plists
NSPropertyListReadOptions options = NSPropertyListMutableContainersAndLeaves;
NSInputStream *stream = [NSInputStream inputStreamWithFileAtPath:path];
[stream open];
id plist = [NSPropertyListSerialization 
    propertyListWithStream:stream
    options:options
    format:NULL
    error:&error];
[stream close];

Security Considerations

Data Validation

// Validate plist structure
if ([plist isKindOfClass:[NSDictionary class]]) {
    NSDictionary *dict = (NSDictionary *)plist;
    NSString *version = dict[@"version"];
    if ([version isKindOfClass:[NSString class]]) {
        // Safe to use
    }
}

Secure Coding

// Use secure coding for sensitive data
NSError *error;
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:sensitiveData
    requiringSecureCoding:YES
    error:&error];

Troubleshooting

Common Issues

# Corrupted plist
plutil -lint broken.plist
# Error: Invalid plist

# Fix corrupted plist
cp broken.plist backup.plist
plutil -convert xml1 backup.plist
# Edit XML manually, then convert back
plutil -convert binary1 backup.plist

Debugging Tools

# Hex dump binary plist
hexdump -C file.plist | head -20

# Check plist format
file file.plist
# file.plist: Apple binary property list

# Convert and compare
plutil -convert xml1 -o temp.xml file.plist
diff original.xml temp.xml

Best Practices

Performance

• Use binary format for frequently accessed files
• Consider lazy loading for large datasets
• Cache parsed data when appropriate
• Use streaming for very large plists

Compatibility

• Test with different macOS/iOS versions
• Validate data types after loading
• Handle missing keys gracefully
• Provide fallback defaults

Security

• Validate all loaded data
• Use secure coding for sensitive information
• Limit plist file permissions appropriately
• Monitor for unauthorized modifications

Binary property lists remain a cornerstone of Apple's data storage architecture, providing efficient serialization while maintaining the flexibility and type safety that makes them ideal for system and application configuration management.