Slide

---

<h1>Who am I?</h1>
<div class="parent">
  <div>
    <h2>Tarik Eshaq</h2>
    <h2>Engineer at Mozilla</h2>
    <h2>Writing Rust with Kotlin for 3 years</h2>
    <h2>Work on Firefox Sync</h2>
  </div>
</div>
`tarikeshaq` on Twitter, GitHub, etc

# Overview
<ol>
  <li class="agenda-item">Why would you ever use Kotlin with Rust?</li>
</ol>

# Overview
<ol>
  <li class="agenda-item">Why would you ever use Kotlin with Rust?</li>
  <li class="agenda-item">What it means to cross the barrier between Kotlin and Rust</li>
</ol>
---

# Overview
<ol>
  <li class="agenda-item">Why would you ever use Kotlin with Rust?</li>
  <li class="agenda-item">What it means to cross the barrier between Kotlin and Rust</li>
  <li class="agenda-item">How you would cross that barrier</li>
</ol>

---
# Overview
<ol>
  <li class="agenda-item"><span><b>Why</b></span> would you ever use Kotlin with Rust?</li>
  <li class="agenda-item"><span><b>What</b></span> it means to cross the barrier between Kotlin and Rust</li>
  <li class="agenda-item"><span><b>How</b></span> you would cross that barrier</li>
</ol>
---
class: center, middle

# Why would you ever use Kotlin with Rust?

---
class: center, middle

# Why would you ever use Kotlin with Rust?
<h2>Simple Answer: <span class="red">You Probably Shouldn't</span></h2>

---
# Why

## You'd like to use an existing Rust Library
## You'd like granular memory management

---
# Why

## You'd like to use an existing Rust Library
## You'd like granular memory management
## The overhead of a runtime or GC is too expensive

---
# Why

## You'd like to use an existing Rust Library
## You'd like granular memory management
## The overhead of a runtime or GC is too expensive
## You'd like to take advantage of Rust's first class cross-platform support

---
class: center, middle
# What it means to cross the barrier between Kotlin and Rust

---
class: center, middle
# ~~What it means to cross the barrier between Kotlin and Rust~~

# What it means to cross the barrier between any langauge and another?
---
class: center, middle
# A detour: The ABI
---
class: center, middle
# A detour: The ABI

<h2>A contract that is enforced by machine code</h2>
---
class: center, middle
# A detour: The ABI

<h2>A contract that is enforced by machine code</h2>
<h3>Typically enforced by your compiler</h3>
---
class: center, middle
# A detour: The ABI

<h2>A contract that is enforced by machine code</h2>
<h3>Typically enforced by your compiler</h3>
<h3>Controls how data is layed out in memory</h3>
<h3>Controls Calling conventions</h3>

---
# ABI
.question1[
```rs
struct Question {
  content: String,
  id: u32,
  author_name: String
}
```
]

#memory .divider {
  border-bottom: 5px solid;
}

#memory p {
  margin-right: 10px;
  margin-left: 10px;
}

</style>
---
# ABI
## Calling Conventions
.parent-abi[
  <div></div>
  .slide-code1[
    ```rs
    fn add(a: i32, b: i32) -> i32 {
      a + b
    }
    ```
  ]
  <div></div>
]

---
# ABI
## Calling Conventions
.parent-abi[
  <div></div>
  .asm-code1[
  ```asm
  add:
      mov eax, edi
      add eax, esi
      ret
  ```
  ]
  <img src="../../slides/kotlinconf/cpu.drawio.png" width="300px">
]
<style>
.parent-abi {
  display: flex;
  justify-content: space-between;
}

.slide-code2 .remark-code {
  font-size: 20px
}

.remark-code {
  border-style: solid;
  border-radius: 20px;
}

.asm-code1 .remark-code {
  font-size: 30px
}
</style>
---
# ABI
## Calling Conventions
.parent-abi[
  <div></div>
  .slide-code1[
    ```rs
    add(4, 3);
    ```
  ]
  <div></div>
]

---
# ABI
## Calling Conventions
.parent-abi[
  .asm-caller[
    ```asm
      mov edi, 4
      mov esi, 3
      call add
    ```
  ]
  .asm-code2[
  ```asm
  add:
      mov eax, edi
      add eax, esi
      ret
  ```
  ]
  <div></div>
]
<style>
.slide-code2 .remark-code {
  font-size: 20px;
}
.remark-code {
  border-style: solid;
  border-radius: 20px;
}
.asm-code2 .remark-code {
  font-size: 30px;
}
.asm-caller .remark-code {
  font-size: 30px;
}
</style>
---
class: center, middle

# ~~What it means to cross the barrier between Kotlin and Rust~~

# What it means to cross the barrier between any langauge and another?

---
class: center, middle
# ~~What it means to cross the barrier between Kotlin and Rust~~

# ~~What it means to cross the barrier between any langauge and another?~~

# What it means to create a shared ABI between languages?
---
class: middle
<img src="../../slides/kotlinconf/c_meme.jpg" width="100%">
---
class: center, middle
<div class="sandwich">
  <div class="kotlin-bun">
    <h2>Kotlin</h2>
  </div>
</div>
---
class: center, middle
<div class="sandwich">
  <div class="kotlin-bun">
    <h2>Kotlin</h2>
  </div>
  <div class="down-arrow">
          &#8592;
  </div>
  <div class="kotin-c">
    <h2>C-compatable Kotlin</h2>
  </div>
</div>
---
class: center, middle
<div class="sandwich">
  <div class="kotlin-bun">
    <h2>Kotlin</h2>
  </div>
  <div class="down-arrow">
          &#8592;
  </div>
  <div class="kotin-c">
    <h2>C-compatable Kotlin</h2>
  </div>
  <div class="down-arrow">
          &#8592;
  </div>
  <div class="rust-c">
    <h2>C-compatable Rust</h2>
  </div>
</div>
---
class: center, middle
<div class="sandwich">
  <div class="kotlin-bun">
    <h2>Kotlin</h2>
  </div>
  <div class="down-arrow">
      &#8592;
  </div>
  <div class="kotin-c">
    <h2>C-compatable Kotlin</h2>
  </div>
  <div class="down-arrow">
        &#8592;
  </div>
  <div class="rust-c">
    <h2>C-compatable Rust</h2>
  </div>
  <div class="down-arrow">
        &#8592;
  </div>
  <div class="rust-bun">
    <h2>Rust</h2>
  </div>
</div>

</style>
---
class: center, middle
<div class="sandwich">
  <div class="kotlin-bun">
    <h2>Kotlin</h2>
  </div>
  <div class="arrows">
    <div class="down-arrow">
          &#8592;
    </div>
    <div class="up-arrow">
          &#8592;
    </div>
  </div>

<div class="kotin-c">
    <h2>C-compatable Kotlin</h2>
  </div>
  <div class="arrows">
    <div class="down-arrow">
          &#8592;
    </div>
    <div class="up-arrow">
          &#8592;
    </div>
  </div>
  <div class="rust-c">
    <h2>C-compatable Rust</h2>
  </div>
  <div class="arrows">
    <div class="down-arrow">
      &#8592;
    </div>
    <div class="up-arrow">
      &#8592;
    </div>
  </div>
  <div class="rust-bun">
    <h2>Rust</h2>
  </div>
</div>

.up-arrow {
  transform: rotate(90deg);
  -webkit-transform: rotate(90deg);
  font-size: 55px;
}
</style>
---
<div class="ffi-page">
  <div></div>
  <div class="sandwich">
    <div class="kotlin-bun">
      <h2>Kotlin</h2>
    </div>
    <div class="arrows">
      <div class="down-arrow">
            &#8592;
      </div>
      <div class="up-arrow">
            &#8592;
      </div>
    </div>
    <div class="ffi">
      <div class="kotin-c">
        <h2>C-compatable Kotlin</h2>
      </div>
      <div class="arrows">
        <div class="down-arrow">
              &#8592;
        </div>
        <div class="up-arrow">
              &#8592;
        </div>
      </div>
      <div class="rust-c">
        <h2>C-compatable Rust</h2>
      </div>
    </div>
    <div class="arrows">
      <div class="down-arrow">
        &#8592;
      </div>
      <div class="up-arrow">
        &#8592;
      </div>
    </div>
    <div class="rust-bun">
      <h2>Rust</h2>
    </div>
  </div>
  <div></div>
</div>

.ffi {
  border-style: solid;
  border-color: red;
  border-radius: 60%;
  padding-right: 60px;
  padding-left: 60px;
}
</style>
---
<div class="ffi-page">
  <div class="sandwich">
    <div class="kotlin-bun">
      <h2>Kotlin</h2>
    </div>
    <div class="arrows">
      <div class="down-arrow">
            &#8592;
      </div>
      <div class="up-arrow">
            &#8592;
      </div>
    </div>
    <div class="ffi">
      <div class="kotin-c">
        <h2>C-compatable Kotlin</h2>
      </div>
      <div class="arrows">
        <div class="down-arrow">
              &#8592;
        </div>
        <div class="up-arrow">
              &#8592;
        </div>
      </div>
      <div class="rust-c">
        <h2>C-compatable Rust</h2>
      </div>
    </div>
    <div class="arrows">
      <div class="down-arrow">
        &#8592;
      </div>
      <div class="up-arrow">
        &#8592;
      </div>
    </div>
    <div class="rust-bun">
      <h2>Rust</h2>
    </div>
  </div>
  <div class="right-arrow">
              &#8592;
  </div>
  <div class="ffi-name">
    <p class="ffi-name"><b>The Foreign Function Interface (FFI)</b></p>
  </div>
</div>

.sandwich {
  text-align: center;
}
</style>
---
class: center, middle

# What it means to cross the barrier between Kotlin and Rust
---
class: center, middle

# What it means to cross the barrier between Kotlin and Rust

<h2 class="it-means">It means traversing the FFI sandwich!</h2>

.sandwich-page-uniffi h3 {
  width: 40%;
  font-size: 60px;
}
</style>
---
<div class="sandwich-page-uniffi">
  <h3>UniFFI generates the inside of the FFI Sandwich, so you only worry about the buns</h3>
  <div class="sandwich">
    <div class="kotlin-bun">
      <h2>Kotlin</h2>
    </div>
    <div class="arrows">
      <div class="down-arrow">
            &#8592;
      </div>
      <div class="up-arrow">
            &#8592;
      </div>
    </div>
    <div>
    <h2>UniFFI Generated Code</h2>
    </div>
    <div class="arrows">
      <div class="down-arrow">
        &#8592;
      </div>
      <div class="up-arrow">
        &#8592;
      </div>
    </div>
    <div class="rust-bun">
      <h2>Rust</h2>
    </div>
  </div>
</div>
---
class: center, middle

# A Conference Q&A app

---
# Calling into Rust
```rs
/// The type used to add, view and
///  delete questions
pub struct QAManager {
  ...
}
/// Represents a question to be asked
pub struct Question {
  pub content: String,
  pub id: u32,
  pub author_name: String
}
```
---
.qaManager1[
```rs
impl QAManager {
  pub fn new() -> Self {
    ...
  }
  pub fn add_question(
    &self,
    question: Question
  ) {
    ...
  }
}
```
]
<style>
.qaManager1 .remark-code {
  white-space: pre-wrap;
}
</style>

---
```rs
#[derive(uniffi::Object)]
// UniFFI will make QAManager an Object
// that can be called with methods!
pub struct QAManager {
  ...
}
```
---
.qaManager1[
```rs
#[uniffi::export] // <- UniFFI will generate bindings for this block!
impl QAManager {
  #[uniffi::constructor] // <- UniFFI will make this a constructor
  pub fn new() -> Self {
    ...
  }
  pub fn add_question(
    &self,
    question: Question
  ) {
    ...
  }
}
```
]
---
.qaManager1[
```rs
#[derive(uniffi::Record)] // <- UniFFI will generate a FFI representation for this type!
pub struct Question {
  pub content: String,
  pub id: u32,
  pub author_name: String
}
```
]
---
.qaManager1[
```kotlin
// constructs a new QAManager by calling the Rust constructor
val qaManager = QAManager()

// Creates a new Question data class, does not call into Rust yet
val question = Question(
  content: "How do I use UniFFI?",
  id: 0,
  authorName: "Tarik Eshaq"
)

// Adds the question!
qaManager.addQuestion(question)
```
]
---
# Calling Back into Kotlin
.qaManager2[
  ```rs
  #[uniffi::export(with_foreign)]
  trait HttpClient {
    fn get(&self) -> Vec<Question>;
  }
  ```
]
---
# Calling Back into Kotlin
```rs
  #[uniffi::export]
  fn get_questions(
    &self,
    http_client: Arc<dyn HttpClient>
    ) -> Vec<Question> {
      let remote_questions = http_client
                              .get();
      self
        .get_local_questions()
        .append(remote_questions)
  }
```
---
# Calling Back into Kotlin
```kotlin
  class KotlinHttpClient : HttpClient {
    override function get()
        : List<Question> {
      ...
    }
  }
  ...
  val questions = qaManager
      .get_questions(KotlinHttpClient())
```
---
# Error Handling
```rs
  #[derive(uniffi::Error)]
  pub enum QAError {
    ...
  }

pub fn add_question(
    &self,
    question: Question
  ) -> Result<(), QAError> {
    ...
  }
```
---
# Calling Async Rust
```rs
#[uniffi::export]
// UniFFI also works with Async Rust!
pub async fn sync(&self) {
  ...
}
```
---
# Calling Async Rust
```kotlin
coroutineScope.launch {
  // `sync` is a suspend function!
  qaManager.sync()
}
```
---
# Calling Async Kotlin
```rs
#[uniffi::export(with_foriegn)]
pub trait HttpClient {
    async fn get(&self) -> Vec<Question>;
    async fn post(&self, Vec<Question>);
}
```
---
# Calling Async Kotlin
```kotlin
  class KotlinHttpClient : HttpClient {
    override suspend function get()
        : List<Question> {
      ...
    }
    override suspend function post(
      questions: List<question>
    ) {
      ...
    }
  }
```
---
```rs
#[uniffi::export]
async fn sync(
  &self,
  http_client: Arc<dyn HttpClient>
) {
  let remote_questions = http_client
                          .get()
                          .await;

let merged = self.merge_remote(
    &remote_questions
  );

http_client.post(merged).await;
}
```
---
class: center, middle
# Demo
<ul id="questions-list">
</ul>

<input id="question-input"/>
<button class="s-question" id="submit-question">Submit</button>
<button class="s-question" id="sync-questions">Sync</button>

.s-question {
  font-size: 20px;
  border-radius: 30px;
  padding: 20px;
  background: transparent;
}

.s-question:hover {
  background: black;
  color: white;
  cursor: pointer;
}
</style>
---
<img src="../../slides/kotlinconf/closing.png", width="800px" height="600px">
---
# You can find the slides at
## https://tarikeshaq.com/slides/kotlin-conf2024
<img src="../../slides/kotlinconf/slides-qr.png", width="300px" height="300px">

## Demo code in <https://github.com/tarikeshaq/kotlinconf2024>
---
# Links

- [UniFFI Docs](https://mozilla.github.io/uniffi-rs/)
- [UniFFI Kotlin Multiplatform Support](https://gitlab.com/trixnity/uniffi-kotlin-multiplatform-bindings)
- [Whitehouse report on securing software](https://www.whitehouse.gov/wp-content/uploads/2024/02/Final-ONCD-Technical-Report.pdf)
- [The Rust Programming Language](https://doc.rust-lang.org/book/)
- [Rust in Android](https://security.googleblog.com/2022/12/memory-safe-languages-in-android-13.html)
- [Rust is the most admiried language](https://survey.stackoverflow.co/2023/#section-admired-and-desired-programming-scripting-and-markup-languages)

---
class: center, middle

# Rust is the most admired Programming Language

\*from [stackoverflow's 2023 Developer survey](https://survey.stackoverflow.co/2023/#section-admired-and-desired-programming-scripting-and-markup-languages)

---

class: center, middle

# Why is Rust so Loved?

---

# Why is Rust so Loved?

## Memory Safety

---

# Why is Rust so Loved?

## Memory Safety

## No Garbage collection

---

# Why is Rust so Loved?

## Memory Safety

## No Garbage collection

## "Fearless concurrency"

---

# Why is Rust so Loved?

## Memory Safety

## No Garbage collection

## "Fearless concurrency"

## A built-in package manager

---

# Why is Rust so Loved?

## Memory Safety

## No Garbage collection

## "Fearless concurrency"

## A built-in package manager

## **Great inter-operability for cross-platform code**

---
class: center, middle
# Places where Rust is Used
<div class="rust-projects">
  <h2>Firefox</h2>
  <h2>Android</h2>
  <h2>AWS</h2>
  <h2>Windows</h2>
  <h2>Chrome</h2>
</div>
<h1>Your Kotlin Project? 👀</h1>
<style>
.rust-projects {
  display: flex;
  justify-content: space-between;
}
</style>
---
<div id="whitehouse">
  <img src="../../slides/kotlinconf/whitehouse.png" width="400px" height="500px">
  <blockquote id="whitehouse-quote"><q>...in most cases, using a <b>memory safe programming language</b> is the most efficient
way to substantially improve software security</q></blockquote>
</div>