rsproperties

A pure Rust implementation of Android's property system, providing cross-platform access to Android system properties on both Linux and Android platforms.

Supported Android Versions

This library supports Android versions from Android 9 (API level 28) to Android 16 (API level 36).

Features

• Complete Android Properties Implementation: Full Rust implementation of Android's property system - read, write, and monitor properties exactly like Android native code
• Cross-Platform Compatibility: Works seamlessly on both Android devices and Linux systems without modification
• Pure Rust Solution: No dependencies on Android's C libraries or JNI - everything implemented in safe Rust
• Real-time Property Monitoring: Watch for property changes in real-time, enabling reactive applications
• High Performance: Optimized for speed with direct memory access and zero-copy operations
• Drop-in Replacement: Compatible with Android's property naming conventions and value constraints
• Linux Emulation: Full Android property system emulation on Linux for development and testing
• Thread-Safe Design: Safe to use across multiple threads without external synchronization

Quick Start

Add rsproperties to your Cargo.toml:

[dependencies]
rsproperties = "0.4"

# Optional features
[features]
builder = ["rsproperties/builder"]  # Enable property database building

Basic Usage

use rsproperties;

// Get property with default value (no initialization needed for default configuration)
let sdk_version: String = rsproperties::get_or("ro.build.version.sdk", "0".to_string());
println!("SDK Version: {}", sdk_version);

// Get property with type parsing and default fallback
let sdk_version: i32 = rsproperties::get_or("ro.build.version.sdk", 0);
let is_debuggable: bool = rsproperties::get_or("ro.debuggable", false);

// Get property with error handling
match rsproperties::get::<String>("ro.build.version.release") {
    Ok(version) => println!("Android Version: {}", version),
    Err(e) => eprintln!("Failed to get version: {}", e),
}

// Set property (requires property service to be running)
if let Err(e) = rsproperties::set("debug.my_app.enabled", "true") {
    eprintln!("Failed to set property: {}", e);
}

Panic-free Initialization

init() and system_properties() panic when initialization fails (e.g. missing properties directory, corrupt mmap). The try_* variants surface those errors as Result instead — preferable for embedded use, tests, and any code that must not unwind through OnceLock initialization.

use rsproperties::{try_init, try_system_properties, PropertyConfig};

fn boot() -> rsproperties::Result<()> {
    try_init(PropertyConfig::with_properties_dir("/dev/__properties__"))?;
    let props = try_system_properties()?;             // &'static SystemProperties
    let sdk: i32 = rsproperties::get_or("ro.build.version.sdk", 0);
    Ok(())
}

try_init is first-write-wins: subsequent calls return Error::FileValidation without poisoning the global state. try_system_properties caches both the success and the failure in a OnceLock, so every later call observes the same outcome.

Zero-Allocation Reads (read_with)

get<T> and get_or<T> already route through a zero-allocation path, but if you want raw access to the validated value without parsing, SystemProperties::read_with hands you a &str borrowed from the seqlock-protected mmap buffer:

let props = rsproperties::system_properties();

// Compute over the value without ever allocating a String.
let prefix_len: rsproperties::Result<usize> =
    props.read_with("ro.build.version.release", |v| v.split('.').next().map(str::len).unwrap_or(0));

// Borrow into a stack buffer; the callback runs while the bytes are
// still seqlock-validated, so keep it cheap and non-blocking.
let mut buf = String::new();
props.read_with("ro.product.model", |v| buf.push_str(v))?;

This mirrors bionic's __system_property_read_callback pattern.

Property Monitoring

use rsproperties;

let system_properties = rsproperties::system_properties();

// Wait for any property change
std::thread::spawn(|| {
    if let Some(new_serial) = system_properties.wait_any() {
        println!("Properties changed, new serial: {}", new_serial);
    }
});

// Wait for specific property change
std::thread::spawn(|| {
    if let Ok(Some(prop_index)) = system_properties.find("sys.boot_completed") {
        println!("Waiting for boot completion...");
        if let Some(_) = system_properties.wait(Some(&prop_index), None) {
            println!("System boot completed!");
        }
    }
});

// Monitor multiple properties
let monitored_props = vec![
    "sys.boot_completed",
    "dev.bootcomplete",
    "service.bootanim.exit"
];

for prop_name in monitored_props {
    match system_properties.get_with_result(prop_name) {
        Ok(value) => println!("{}: {}", prop_name, value),
        Err(_) => println!("{}: <not set>", prop_name),
    }
}

Setting Properties

Setting properties requires a running property service (like rsproperties-service):

use rsproperties;

// Basic property setting
if let Err(e) = rsproperties::set("debug.my_app.enabled", "true") {
    eprintln!("Failed to set property: {}", e);
}

// Set application configuration
rsproperties::set("debug.my_app.log_level", "verbose")?;
rsproperties::set("debug.my_app.port", "8080")?;

// Set system properties (may require elevated permissions)
rsproperties::set("sys.my_service.ready", "1")?;

// Set persistent properties (survive reboots on Android)
rsproperties::set("persist.my_app.config", "production")?;

Property Setting Requirements

On Android:

• Properties are set through the property service
• Some properties require specific SELinux permissions
• ro.* properties are read-only and cannot be modified
• System properties may require root or system privileges

On Linux:

• Requires rsproperties-service to be running
• Properties are stored in memory-mapped files
• All properties are writable unless explicitly restricted

Property Setting Examples by Type

// Debug properties - usually writable by applications
rsproperties::set("debug.my_app.trace", "enabled")?;
rsproperties::set("debug.my_app.verbose", "true")?;

// Vendor properties - device-specific configuration
rsproperties::set("vendor.my_app.hw_config", "v2")?;

// Custom application properties
rsproperties::set("my.company.app.version", "1.2.3")?;
rsproperties::set("my.company.app.api_key", "abc123")?;

// System state properties
rsproperties::set("sys.my_service.status", "running")?;
rsproperties::set("sys.my_service.pid", "1234")?;

Error Handling

Error is a thiserror-derived enum with #[from] conversions for std::io::Error, rustix::io::Errno, Utf8Error, and ParseIntError. The Error::Context variant carries a panic::Location so the failing call site is preserved across error boundaries, and ContextWithLocation attaches that context to any Result whose Err implements Into<Error>.

use rsproperties::{ContextWithLocation, Error, Result};

fn read_sdk() -> Result<i32> {
    rsproperties::get::<i32>("ro.build.version.sdk")
        .context_with_location("reading ro.build.version.sdk")
}

// Batch property operations with error handling
fn set_app_config() -> Result<()> {
    for (key, value) in [
        ("debug.my_app.enabled", "true"),
        ("debug.my_app.log_level", "info"),
        ("debug.my_app.trace", "disabled"),
    ] {
        match rsproperties::set(key, value) {
            Ok(_)                            => println!("set {key}: {value}"),
            Err(Error::PermissionDenied(m))  => return Err(Error::PermissionDenied(m)),
            Err(Error::Io(e))                => return Err(Error::Io(e)),
            Err(e)                           => return Err(e),
        }
    }
    Ok(())
}

Custom Configuration

Warning: Do not use custom configuration on Android devices. Custom configuration is only intended for Linux environments or development/testing purposes.

use rsproperties::PropertyConfig;

// Configure custom directories
let config = PropertyConfig {
    properties_dir: Some("/custom/properties".into()),
    socket_dir: Some("/custom/socket".into()),
};
rsproperties::init(config);

// Using the builder pattern
let config = PropertyConfig::builder()
    .properties_dir("/my/properties")
    .socket_dir("/my/socket")
    .build();
rsproperties::init(config);

// Convenience methods
rsproperties::init(PropertyConfig::with_properties_dir("/my/props"));

Platform Support

Android

• Native Integration: Direct access to /dev/__properties__
• Property Contexts: Full SELinux property context support
• Bionic Compatibility: Compatible with Android's property implementation
• Standard Properties: Access to all standard Android properties

Linux

• Full Emulation: Complete Android property system emulation
• Socket Communication: Unix domain socket property setting
• Memory Mapping: Efficient memory-mapped property storage
• Property Service: Use with rsproperties-service for full daemon functionality

API Reference

Configuration

• PropertyConfig — public-fields struct describing the properties & socket directories
• PropertyConfig::builder() / with_properties_dir() / with_socket_dir() / with_both_dirs() — construction helpers
• init(config) — initialize globals; logs and swallows failures
• try_init(config) — initialize globals, returning Result
• properties_dir() — currently-configured properties directory
• socket_dir() — currently-configured socket directory. Priority: PropertyConfig.socket_dir (via init/try_init) > PROPERTY_SERVICE_SOCKET_DIR env var > /dev/socket

Property Operations

• get<T>(name) — parse-typed read; Err on missing / parse failure
• get_or<T>(name, default) — infallible read with fallback
• set<T>(name, value) — Display-format and send to the property service over the socket
• system_properties() — &'static SystemProperties or panic
• try_system_properties() — &'static SystemProperties or Err

SystemProperties (read side)

• read_with(name, |&str| -> R) — zero-alloc callback reader
• get_with_result(name) — String-allocating convenience wrapper
• find(name) — Result<Option<PropertyIndex>>; Ok(None) for a missing property, Err only for I/O / mmap problems
• serial(index) / context_serial() — current generation counters
• wait_any() — futex-wait for any property change
• wait(index, timeout) — futex-wait for a specific property

Wire-protocol constants & validators (rsproperties::wire)

• PROP_VALUE_MAX, PROP_NAME_MAX — AOSP wire-format size caps
• PROP_MSG_SETPROP, PROP_MSG_SETPROP2 — command IDs
• PROP_SUCCESS, PROP_ERROR — V2 response codes
• validate_property_name(name) — name charset / leading-char check
• validate_value_len(name, value) — value-length policy with the long-ro.* exception

Two socket-name constants are re-exported at the crate root for clients that want to point at a custom socket directory:

• PROPERTY_SERVICE_SOCKET_NAME — "property_service"
• PROPERTY_SERVICE_FOR_SYSTEM_SOCKET_NAME — "property_service_for_system"

Errors

• Error — non-exhaustive enum (Io, Errno, NotFound, Encoding, Parse, FileValidation, Conversion, PermissionDenied, FileSize, FileOwnership, LockError, Context)
• Result<T> = Result<T, Error>
• ContextWithLocation::context_with_location(msg) — attach panic::Location to any Result<_, impl Into<Error>>

SystemProperties write side (builder feature)

• SystemProperties::new_area(dir) — create/serialize an on-disk property area
• SystemProperties::add(name, value) — append a new entry
• SystemProperties::update(index, value) — overwrite an existing entry (seqlock-guarded)
• SystemProperties::set(name, value) — add-or-update
• load_properties_from_file(path, filter, context, &mut HashMap) — parse build.prop entries
• PropertyInfoEntry::parse_from_file(path, require_prefix_or_exact) — parse a property_contexts-format file into (Vec<PropertyInfoEntry>, Vec<Error>) (the entries that survived and the per-line errors)
• build_trie(entries, default_context, default_type) — serialize a property-info trie

Thread Safety

All operations are thread-safe and can be used concurrently:

use std::thread;

// Multiple threads can safely access properties
let handles: Vec<_> = (0..10).map(|i| {
    thread::spawn(move || {
        let prop_name = format!("debug.thread.{}", i);
        let value: String = rsproperties::get_or(&prop_name, "default".to_string());
        println!("Thread {}: {} = {}", i, prop_name, value);
    })
}).collect();

for handle in handles {
    handle.join().unwrap();
}

Building Property Databases (with builder feature)

#[cfg(feature = "builder")]
use rsproperties::{load_properties_from_file, SystemProperties};
use std::collections::HashMap;
use std::path::Path;

// Load properties from Android build.prop files
let mut properties = HashMap::new();
load_properties_from_file(
    Path::new("system_build.prop"),
    None,
    "u:r:init:s0",
    &mut properties
)?;

// Create a system properties area for testing or service
let mut system_properties = SystemProperties::new_area(Path::new("./test_props"))?;

// Add loaded properties to the area
for (key, value) in properties {
    system_properties.add(&key, &value)?;
}

// Now properties can be read normally
let sdk_version: i32 = rsproperties::get_or("ro.build.version.sdk", 0);

Constants

The library exposes Android-compatible constants. PROP_VALUE_MAX is re-exported at the crate root for source-compatibility; the canonical home (along with the wire-protocol opcodes and validators) is the wire module:

use rsproperties::{PROP_DIRNAME, PROP_VALUE_MAX};
use rsproperties::wire::{
    PROP_NAME_MAX, PROP_MSG_SETPROP2, validate_property_name, validate_value_len,
};

assert_eq!(PROP_VALUE_MAX, 92);              // buffer size including NUL; content cap = 91 bytes
assert_eq!(PROP_NAME_MAX, 32);               // V1 wire only; V2 is length-prefixed
assert_eq!(PROP_DIRNAME, "/dev/__properties__");
assert_eq!(PROP_MSG_SETPROP2, 0x00020001);

validate_property_name("ro.build.version.sdk").unwrap();
validate_value_len("ro.long.prop", &"x".repeat(200)).unwrap(); // ro.* may exceed PROP_VALUE_MAX

Performance

• Memory-mapped access: Direct memory access for optimal performance
• Zero-copy reads: Efficient property value retrieval
• Atomic operations: Thread-safe property updates
• Futex-based waiting: Efficient property change notifications

Examples

The crate includes Android-compatible command-line tools:

• getprop.rs - Android-compatible property getter with support for custom directories
• setprop.rs - Android-compatible property setter with validation and error handling

Run examples with:

# Get a property with default value
cargo run --example getprop ro.build.version.sdk 0

# Set a property
cargo run --example setprop debug.my_app.test true

Related Crates

• rsproperties-service - Full async property service daemon for Linux environments

Building

# Build the library
cargo build

# Build with all features
cargo build --all-features

# Run tests
cargo test

# Build documentation
cargo doc --open

License

Licensed under the Apache License, Version 2.0. See LICENSE for details.

Contributing

Contributions are welcome! Please ensure:

1. All tests pass: cargo test
2. Code is formatted: cargo fmt
3. No clippy warnings: cargo clippy --all-targets --all-features

This implementation is based on Android's property system and maintains compatibility with Android's property semantics and behavior.