Rlibphonenumber

A zero-allocation, high-performance Rust port of Google's libphonenumber library for parsing, formatting, and validating international phone numbers.

🌐 Live WASM Preview: Try the library directly in browser!

Used metadata version: v9.0.27
Version: 1.1.1
Base libphonenumber: 9.0.8
Min supported Rust version: 1.88.0

🛡️ Correctness

Through over 11.2 million iterations of malformed, randomized, and edge-case inputs, this library has proven zero mismatches in parsing, validation rules (is_valid, is_possible), and formatting outputs (E.164, National, International, RFC3966) compared to the upstream C++ implementation. It provides exact drop-in behavior with Rust's memory safety and high execution speed.

Performance

Performance is measured using criterion. We compare rlibphonenumber with the popular rust-phonenumber (the phonenumber crate) and phonelib crates.

All benchmarks measure the average time required to process a single phone number.

Initialization

rlibphonenumber requires initializing PhoneNumberUtil, which loads the necessary metadata. This is typically done once at application startup:

• PhoneNumberUtil::new(): ~5.33 ms

Parsing

Time required to parse a string representation into a phone number object:

Library	parse()	Notes
rlibphonenumber	~500 ns	Fastest & most reliable
rust-phonenumber	~1.66 µs	Fails on certain valid numbers.*
phonelib	Failed	Fails on certain valid numbers.

* During testing, we found that rust-phonenumber (rlp) returns an error on valid phone numbers, such as the Brazilian number "+55 11 98765-4321".

Formatting

Time required to format a parsed phone number object into various standards:

Format	rlibphonenumber	rust-phonenumber	phonelib
E164	~33 ns 🚀	~731 ns	~814 ns
International	~432 ns	~1.03 µs	~905 ns
National	~558 ns	~1.45 µs	~896 ns
RFC3966	~606 ns	~1.17 µs	~1.02 µs

Under the Hood: How is it so fast?

• Zero-Allocation Formatting: Intermediate heap allocations are eliminated. By utilizing Cow<str>, stack-allocated buffers (via a custom zero-padding itoa implementation), and a specialized Builder pattern, formatting numbers rarely touches the system allocator.
• Build-Time Anchored Regexes (RegexTriplets): Instead of allocating strings at runtime to wrap patterns in ^(?:...)$, a custom Java build script pre-compiles and wraps metadata directly into the Protobuf output. At runtime, Rust uses [..] string slicing (zero-cost) to extract exact bounds, bypassing the regex engine's O(N) linear search and forcing O(1) fast-fail anchor matching.
• Fast Hashing: Replaces the default SipHash with FxHash (rustc_hash) for ultra-low-latency metadata lookups by region code and integer keys.
• Lazy Initialization: Regular expressions are compiled lazily and cached on-demand directly inside metadata wrappers using std::sync::OnceLock, removing the locking overhead of a centralized regex cache.

Installation & Feature Flags

Add rlibphonenumber to your Cargo.toml. You can choose between the standard regex engine (fastest parsing) or the lite engine (smallest binary size).

1. Standard (Recommended for Backend/Desktop)

Uses the full regex crate. Provides maximum parsing performance.

[dependencies]
rlibphonenumber = "1.1.3"

2. Lite (Recommended for WASM/Embedded)

Uses regex-lite to significantly reduce binary size. Parsing is slower than the standard backend but still efficient enough for UI/Validation tasks. Formatting speed remains virtually identical.

(Check out our Live WASM Preview to see it in action!)

[dependencies]
rlibphonenumber = { version = "1.1.1", default-features = false, features = ["lite", "global_static"] }

Available Features

Feature	Description	Default
regex	Uses the regex crate (SIMD optimizations, large Unicode tables). Best for speed.	✅
lite	Uses regex-lite. Optimizes for binary size. Best for WASM or embedded targets.	❌
global_static	Enables the lazy-loaded global PHONE_NUMBER_UTIL instance.	✅
serde	Enables Serialize/Deserialize for PhoneNumber.	❌

Getting Started

The library exposes a global static PHONE_NUMBER_UTIL, but for most common operations, you can use methods directly on the PhoneNumber struct.

Complete Example

use rlibphonenumber::{
    PHONE_NUMBER_UTIL,
    PhoneNumber,
    PhoneNumberFormat,
    ParseError,
};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let number_string = "+1-587-530-2271";

    // 1. Parse the number
    // You can use the standard FromStr trait:
    let number: PhoneNumber = number_string.parse()?;

    println!("✅ Successfully parsed number.");
    println!("   - Country Code: {}", number.country_code());
    println!("   - National Number: {}", number.national_number());

    // 2. Validate the number
    // `is_valid()` performs a full validation (length, prefix, region rules)
    let is_valid = number.is_valid();
    println!(
        "\nIs the number valid? {}",
        if is_valid { "Yes" } else { "No" }
    );

    if !is_valid {
        return Ok(());
    }

    // 3. Format the number
    // Display trait uses E164 by default
    println!("\nDefault Display: {}", number); 

    let e164_format = number.format_as(PhoneNumberFormat::E164);
    let international_format = number.format_as(PhoneNumberFormat::International);
    let national_format = number.format_as(PhoneNumberFormat::National);
    let rfc3966_format = number.format_as(PhoneNumberFormat::RFC3966);

    println!("Formatted Outputs:");
    println!("   - E.164:         {}", e164_format);         // +15875302271
    println!("   - International: {}", international_format); // +1 587-530-2271
    println!("   - National:      {}", national_format);      // (587) 530-2271
    println!("   - RFC3966:       {}", rfc3966_format);       // tel:+1-587-530-2271

    // 4. Get additional information
    let number_type = number.get_type(); // e.g., Mobile, FixedLine
    let region_code = number.get_region_code(); // e.g., "CA"

    println!("\nInfo:");
    println!("   - Type:   {:?}", number_type);
    println!("   - Region: {:?}", region_code.unwrap_or("Unknown"));

    Ok(())
}

Serde Integration

When the serde feature is enabled, PhoneNumber serializes to a string (E.164 format) and can be deserialized from a string.

use rlibphonenumber::PhoneNumber;
use serde_json::json;

fn main() {
    let raw = "+15875302271";
    let number: PhoneNumber = raw.parse().unwrap();

    // Serializes to "+15875302271"
    let json_output = json!({ "phone": number });
    println!("{}", json_output); 
}

Differential Fuzzing

We invite anyone to verify our correctness parity. The repository includes a Dockerized environment that links Google's C++ libphonenumber side-by-side with our Rust implementation via cxx.

To run the differential fuzzer locally:

1. Clone the repository and open the provided DevContainer/Docker environment.
2. Run the full-cycle fuzz target to check fully random user inputs and ensure no panics occur:

   cargo +nightly fuzz run full-cycle

3. Run the diff-test target to compare outputs with the original library (requires the C++ library version to match the metadata version used):

   cargo +nightly fuzz run diff-test

If the fuzzer ever finds a single input where the Rust output deviates from the C++ output, it will immediately crash and save the artifact.

Manual Instantiation

By default, this crate enables the global_static feature, which initializes a thread-safe, lazy-loaded static instance PHONE_NUMBER_UTIL. This allows you to use convenience methods directly on PhoneNumber.

If you need granular control over memory usage, wish to avoid global state, or are working in a strict environment, you can disable this feature.

[dependencies]
rlibphonenumber = { version = "1.1.1", default-features = false, features = ["regex"] }

When global_static is disabled, helper methods on PhoneNumber (like .format_as(), .is_valid()) will not be available. You must instantiate the utility manually.

⚠️ Performance Note: PhoneNumberUtil::new() compiles regexes upon initialization. This is an expensive operation. Create it once and reuse it (e.g., wrap it in an Arc or pass it by reference).

use rlibphonenumber::{PhoneNumberUtil, PhoneNumber};

fn main() {
    // 1. Initialize the utility once
    let phone_util = PhoneNumberUtil::new();

    let number_str = "+15550109988";

    // 2. Parse using the instance
    if let Ok(number) = phone_util.parse(number_str, None) {
        // 3. Use the instance for validation
        let is_valid = phone_util.is_valid_number(&number).unwrap_or(false);
        println!("Valid: {}", is_valid);
    }
}

⚖️ C++ Comparison & Methodology

To ensure absolute fairness and eliminate any Foreign Function Interface (FFI) overhead, we benchmarked rlibphonenumber against Google's upstream C++ library using completely native toolchains for both languages (criterion for Rust, google/benchmark for C++).

Build Environment & Methodology

The C++ library was built from source inside a controlled Docker environment with the maximum possible performance configuration:

• Compiler: C++17 with -O3 -DNDEBUG (optimizations enabled, debug assertions disabled).
• Regex Engine: Compiled directly against Google's ultra-fast RE2 engine (-DUSE_RE2=ON, -DUSE_ICU_REGEXP=OFF), replacing the slower default ICU engine.
• Memory Allocator fairness: In the C++ formatting benchmark, the target std::string had .reserve() called before formatting to ensure the time measured represents the library's algorithm, not the underlying OS heap allocator.

Both benchmarks run over the exact same set of 12 diverse international phone numbers in a cyclic batch configuration to bypass CPU branch-predictor memorization.

Pure Native Performance Results

(Average time to process a single phone number)

Operation	C++ (libphonenumber + RE2)	Rust (rlibphonenumber)	Speedup
Parsing	~2.28 µs (2279 ns)	~0.50 µs (500 ns)	~4.5x
Format (E.164)	~63 ns	~33 ns	~1.9x
Format (International)	~2.03 µs (2028 ns)	~0.43 µs (432 ns)	~4.7x
Format (National)	~2.48 µs (2484 ns)	~0.56 µs (558 ns)	~4.4x
Format (RFC3966)	~2.42 µs (2417 ns)	~0.61 µs (606 ns)	~4.0x