Zero-Copy in Rust: Challenges and Solutions

TL;DR

• Zero-copy reduces memory allocations, CPU cycles, and improves CPU cache utilization, leading to better performance, especially with large data sets.
• Managing reference lifetimes to ensure they remain valid without copying data.
• Use references or pointers to access data directly, avoiding unnecessary copies. Utilize Rust's references and types like Cow (Copy-On-Write) for efficient data handling.

Introduction

The concept of zero-copy in Rust refers to a technique of working with data in memory without making unnecessary copies, which significantly improves performance, particularly in high-throughput and low-latency environments.

Since no data is copied, zero-copy, facilitated by references, leads to significant performance gains:

• Reduced Memory Allocations: No need to allocate new structures just to copy data.
• Reduced CPU Cycles: The CPU doesn't spend time copying memory blocks. This is especially important for large amounts of data (network packets, large files).
• Better CPU Cache Utilization: Data remains in its original memory location, increasing the chances it's already in the CPU cache, which reduces latency for accessing main memory.

It represents one of the most interesting challenges in the ecosystem: how to deserialize data without copying its content, while respecting the strict rules of the borrow checker ?

This synthesis explores the different approaches developed by the Rust community.

The Fundamental Problem

In Rust, zero-copy consists of creating data structures that directly reference bytes from an input buffer, without copying this data. The main challenge lies in lifetime management: how to ensure that references remain valid ?

Basic Principles

1. Avoiding Unnecessary Copies: Rather than copying data from one location to another, references or pointers are used to directly access the original data. This reduces memory overhead and improves performance.
2. Using References: In Rust, this can be achieved using references (&) or types like Cow (Copy-On-Write), which allow working with borrowed or owned data transparently.

Zero-Copy Examples in Rust

Using "reference" In Rust, a "reference" (e.g., &T or &mut T) is a safe pointer that borrows access to data owned by someone else, without taking ownership of that data. When you obtain a reference, Rust doesn't copy the underlying data. It simply gives you a way to access it right where it already exists in memory.

Instead of copying bytes from a buffer (like a Vec<u8> or a [u8] array) into a new data structure, you get a reference (&MyStruct) that "views" those bytes as the structure directly.

fn main() {
    // 1. Defining a variable that owns its data
    let mut greeting = String::from("Hello, Rustacean!");
    println!("Original string (owned): {}", greeting);

    // 2. Passing a reference to a function (immutable reference)
    print_message(&greeting);
    println!("After print_message (original still owned): {}", greeting);

    // 3. Passing a mutable reference to a function
    change_message(&mut greeting);
    println!("After change_message (original modified): {}", greeting);

    // 4. Multiple immutable references are allowed
    let r1 = &greeting;
    let r2 = &greeting;
    println!("Multiple immutable references: {} and {}", r1, r2);

    // 5. Demonstrating borrowing scope
    {
        let r3 = &greeting; // r3 is created here
        println!("Inside block, using r3: {}", r3);
    } // r3 goes out of scope here, meaning the borrow ends

    change_message(&mut greeting);
    println!("After block and another change: {}", greeting);
}

fn print_message(message: &String) {
    println!("Printing message: {}", message);
    // message.push_str(" (modified)"); // This would cause a compile-time error!
}

fn change_message(message: &mut String) {
    message.push_str(" How are you?");
    println!("Message modified inside function: {}", message);
}

Full code with comments, here !

Rust references are inextricably linked to lifetimes. Lifetimes are a key feature of Rust's borrowing system that ensures memory safety. When you have a reference &'a T, Rust guarantees that the data pointed to by this reference (T) will live at least as long as the reference itself.

fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
    if x.len() > y.len() {
        x
    } else {
        y
    }
}

fn main() {
    let string1 = String::from("abcd");
    let string2 = "xyz";

    let result = longest(string1.as_str(), string2);
    println!("The longest string is '{}'", result);

    println!("\n--- Illustrating lifetime constraints ---");

    let string3 = String::from("long string is long");

    { // inner scope starts
        let string4 = String::from("xyz"); // string4 is created here
        let result2 = longest(string3.as_str(), string4.as_str());
        println!("The longest string between '{}' and '{}' is '{}'", string3, string4, result2);
    } // string4 goes out of scope here. Its data is dropped.
    // println!("result2 outside scope: {}", result2); // This would not compile!

    println!("\n--- Another example with different lifetimes ---");

    let string5 = String::from("qu");
    let result3;
    {
        let string6 = String::from("abcdefg");
        result3 = longest(string5.as_str(), string6.as_str());
        println!("Inside scope: The longest is '{}'", result3);
    } // string6 goes out of scope here.

    // println!("Outside scope: The longest is '{}'", result3); // This would not compile!

    let string7 = String::from("short");
    let result4;
    let string8 = String::from("very long string here");
    {
        result4 = longest(string7.as_str(), string8.as_str());
        println!("Inside scope (result4): The longest is '{}'", result4);
    } // Only string7 goes out of scope here.

    println!("Outside scope (result4): The longest is '{}'", result4);
}

Full code with comments, here !

Using Cow The Cow type (Copy-On-Write) is a classic example of zero-copy in Rust. It lets you work with data either by borrowing or owning it, without the need to copy it unnecessarily.

use std::borrow::Cow;

fn process_data<'a>(data: Cow<'a, str>) {
    match data {
        Cow::Borrowed(b) => println!("Data borrowed: {}", b),
        Cow::Owned(o)    => println!("Data owned: {}", o),
    }
}

fn main() {
    let borrowed: &str   = "Hello, world!";
    let owned:    String = "Hello, world!".to_string();

    process_data(Cow::Borrowed(borrowed));
    process_data(Cow::Owned(owned));
}

Full code with comments, here !

The type Cow is a smart pointer providing clone-on-write functionality: it can enclose and provide immutable access to borrowed data, and clone the data lazily when mutation or ownership is required. The type is designed to work with general borrowed data via the Borrow trait.

In our example, pass borrowed data wrapped in Cow::Borrowed, no copying occurs heren, we're just wrapping the existing &str. This is the most efficient case zero-copy operation.

Pass owned data wrapped in Cow::Owned, the String moves into the Cow, transferring ownership. No additional copying occurs since the data was already owned.

Zero-Copy Deserialization

Zero-copy deserialization is a technique where data is read directly from a buffer without being copied into a new data structure. This is particularly useful for binary data formats.

use zerocopy::{FromBytes, IntoBytes};

#[derive(Debug, PartialEq, FromBytes)]
#[repr(C)] // Important: Ensures a C-compatible field layout
struct MyData {
    id       : u32,
    value    : u16,
    is_active: u8,
    _padding : [u8; 1],   // Explicit padding to align is_active
}

fn main() {
    let raw_bytes: [u8; 8] = [
        0x01, 0x00, 0x00, 0x00, // id:        1    (u32 little-endian)
        0x02, 0x00,             // value:     2    (u16 little-endian)
        0x01,                   // is_active: true (bool)
        0x00,                   // _padding
    ];

    println!("Raw bytes: {:?}", raw_bytes);

    let binding: Option<MyData>  = MyData::read_from(&raw_bytes);
    let my_data: Option<&MyData> = binding.as_ref();

    match my_data {
        Some(data) => {
            println!("\nInterpreted data (zero-copy): {:?}", data);
            println!("ID: {}", data.id);
            println!("Value: {}", data.value);
            println!("Is Active: {}", data.is_active);
        } None => {
            println!("\nError: Could not read MyData from raw bytes. Size mismatch.");
        }
    }

    let original_data: MyData = MyData {
        id       : 42,
        value    : 123,
        is_active: 1,
        _padding : [0],
    };

    println!("\nOriginal structure: {:?}", original_data);
    let bytes_from_struct_id: &[u8]        = original_data.id.as_bytes();
    let bytes_from_struct_value: &[u8]     = original_data.value.as_bytes();
    let bytes_from_struct_is_active: &[u8] = original_data.is_active.as_bytes();
    let bytes_from_struct_padding: &[u8]   = original_data._padding.as_bytes();

    println!("Bytes generated from structure (zero-copy)");
    println!("  Field `id`       : {:?}", bytes_from_struct_id);
    println!("  Field `value`    : {:?}", bytes_from_struct_value);
    println!("  Field `is_active`: {:?}", bytes_from_struct_is_active);
    println!("  Field `_padding` : {:?}", bytes_from_struct_padding);
}

Full code with comments, here !

So many tools

While Cow and zerocopy are commonly used tools for zero-copy data access in Rust, they are by no means the only options available. The Rust ecosystem provides several other powerful crates tailored to different zero-copy scenarios.

The yoke crate is particularly useful when you need to tie borrowed data to an owned container, ensuring safe lifetimes without manual lifetime gymnastics.

For more advanced cases like "self-referential-structs" where part of a structure borrows from another part ouroboros provides safe abstractions that would otherwise be impossible in safe Rust.

Additionally, the bytemuck crate enables zero-cost casting between raw bytes and plain data structures, assuming alignment and layout guarantees are met.

Together, these tools as many others, offer a rich toolbox for building fast and memory-efficient applications while preserving Rust’s safety guarantees.

Application to the Pinocchio Framework for Solana

The Pinocchio framework for Solana represents an excellent example of practical application of zero-copy techniques in a high-performance blockchain context. Since Solana is designed to process thousands of transactions per second, every performance optimization matters.

Comparison with Anchor

Unlike Anchor, another popular framework for developing Solana programs, Pinocchio is designed to be minimalist and dependency-free.

Anchor provides advanced features automatic IDL (Interface Description Language) generation and macros to simplify development. But this comes with increased complexity and larger binary sizes.

Conclusion

Zero-copy in Rust is not just a low-level optimization, it’s a mindset that influences how data is accessed, moved, and processed. By avoiding unnecessary memory allocations and leveraging Rust’s powerful type system, developers can achieve significant performance gains, especially in systems where latency, memory footprint, and CPU cycles matter deeply.

Throughout this article, we’ve explored how Rust enables zero-copy patterns through lifetimes, references, smart pointers like Cow, and libraries such as zerocopy.

In the context of Solana and the Pinocchio framework, these techniques become essential for creating performant blockchain applications.

The application of these concepts to Solana shows how Rust optimizations can have a direct impact on user experience and transaction costs. Pinocchio demonstrates that it is possible to achieve significant performance gains while maintaining the security and reliability required for decentralized financial applications.

The continued evolution of these techniques suggests a future where blockchain applications can compete in performance with traditional systems, paving the way for new use cases requiring ultra-low latency and high throughput.

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Credits : Franck Maussand

Feel free to check out my previous articles on Medium (🇫🇷 / 🇬🇧) !

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Additionals Resources

Explications:

• Zero-copy - Wikipedia
• Not a Yoking Matter (Zero-Copy #1) - In Pursuit of Laziness
• Zero-Copy designs in Rust
• The Magic of zerocopy

Lifetime:

• Lifetimes in Rust aren't that hard
• Validating References with Lifetimes - The Rust Programming Language
• Lifetimes - Rust By Example

Cow:

• Cow in std::borrow - Rust

Zerocopy:

• crates.io: zerocopy
• zerocopy - Rust

Yoke:

• crates.io: yoke
• Yoke in yoke - Rust

Bytemuck

• crates.io: bytemuck
• bytemuck - Rust

Solana Frameworks:

• Anchor: Zero Copy
• GitHub - solana-developers/anchor-zero-copy-example: Explaining on some examples heap, stack and account size limits and zero copy.
• GitHub - anza-xyz/pinocchio: Create Solana programs with no dependencies attached
• crates.io: Light Zero Copy
• light_zero_copy - Rust

Misc:

• Rust: Efficient Zero-Copy Parsing with nom and bytes | by Byte Blog - Freedium
• Zero-copy deserialization - rkyv
• Rust: The joy of safe zero-copy parsers