How to work today

Work in pairs (coding + reflections).

Keep 3 tabs open:

• this recitation instruction
• your code editor + terminal
• a Google Doc for reflections. Create a new tab for your pair in the Reflection Doc

Learning goals (today)

By the end you should be able to:

• read Axum route + handler signatures
• extend serde structs with optional JSON fields
• convert HashMap data into an ordered JSON response
• test local API behavior with curlie and tester.sh

Connection to last week

Last week:

• you used iterators and closures to transform collections
• you practiced filter, map, collect, and consumers like sum

This week:

• those same iterator ideas help build API responses
• you will turn HashMap entries into a Vec
• then sort the results by nearest due date

Starter project

• week14-rust-api
• work mainly in src/main.rs, src/util.rs, and src/todos.rs

Run:

cd recitations/week14-rust-api
cargo run

In another terminal:

bash tester.sh http://localhost:5000

Current API

Task 1: Add due-date support

#[derive(Serialize, Deserialize, Clone)]
pub struct NewTodo {
    task: String,
    // add: due_date: Option<String>
}

#[derive(Serialize, Deserialize, Clone)]
pub struct Todo {
    task: String,
    pub done: bool,
    // add the same optional field here too
}

Task 2: Add the sorted endpoint

Work in src/todos.rs and src/main.rs.

pub async fn get_sorted_by_due_date(
    State(_todo_list): State<SharedTodoList>,
) -> (StatusCode, Json<Vec<TodoWithId>>) {
    todo!("implement GET /todos/by_due_date")
}

Also connect the route in main.rs:

.route("/todos/by_due_date", get(todos::get_sorted_by_due_date))

Part 2: Reflection + Submit

No grammar check. Don't overcorrect. Answer these:

• Where did week13 iterator methods show up in today's API work?
• What was the trickiest Axum or serde detail?
• How did you decide to handle todos with no due date?

Submit your attendance in the google form: https://forms.gle/tYEtKjJunM1wb2we6

Hint

If you are stuck, come here later.

Why not return a HashMap?

• HashMap does not preserve any meaningful order
• a sorted response should be a JSON array
• TodoWithId keeps the todo id after leaving the map

Example response:

[
  { "id": "todo2", "task": "finish slides", "done": false, "due_date": "2026-04-17" },
  { "id": "todo4", "task": "submit lab", "done": false, "due_date": "2026-04-18" }
]

Suggested order

1. Add due_date to NewTodo and Todo.
2. Update Todo::new and From<NewTodo> for Todo.
3. Test POST and PUT with a due_date.
4. Add the new route in main.rs.
5. Implement get_sorted_by_due_date().
6. Re-run tester.sh.

Useful iterator pattern

let mut items: Vec<TodoWithId> = todo_list
    .iter()
    .map(|(id, todo)| TodoWithId {
        id: id.clone(),
        todo: todo.clone(),
    })
    .collect();

Then sort the vector before returning it:

items.sort_by_key(|item| {
    // choose a key that puts earlier due dates first
});

JSON examples

Create with a due date:

{ "task": "submit lab", "due_date": "2026-04-18" }

Update with a due date:

{ "task": "finish slides", "done": false, "due_date": "2026-04-17" }

If you use ISO strings like YYYY-MM-DD, simple string ordering matches date ordering.

Testing workflow tester.sh

• POST /todos with a due_date
• PUT /todos/{todo} with earlier and later dates
• POST /todos without a due date
• GET /todos/by_due_date

Use it to verify:

• old requests still work
• due dates appear in JSON responses
• todos are ordered the way you intended

Common gotchas

• forgetting to update both NewTodo and Todo
• forgetting to copy due_date in From<NewTodo>
• adding the handler but not wiring the route in main.rs
• trying to return a sorted HashMap
• not deciding what to do with None due dates

Q/A

• Option<String> is enough for this recitation. You do not need a date crate.
• ISO date strings such as 2026-04-17 sort correctly as plain strings.
• One reasonable approach is to sort by a tuple that puts None last.
• Read the compiler error literally. In Rust it usually tells you the exact type mismatch.