rate-limiting

name	rate-limiting
description	Use when working with per-model daily request counters, rate limit errors, the America/Los_Angeles reset logic, or RPD quota enforcement.

Rate Limiting Design

Overview

rs-summarizer implements per-model daily request counters to prevent exceeding Gemini API quotas. Counters reset at the start of each calendar day in America/Los_Angeles timezone.

Architecture

Rate limiting state lives in AppState (shared across all requests):

pub struct AppState {
    pub model_counts: Arc<RwLock<HashMap<String, u32>>>,
    pub last_reset_day: Arc<RwLock<Option<NaiveDate>>>,
    // ...
}

RateLimiter API

File: src/services/rate_limiter.rs

pub struct RateLimiter;

impl RateLimiter {
    /// Returns true if request is allowed, false if rate limited.
    pub async fn check_rate_limit(
        model: &ModelOption,
        model_counts: &Arc<RwLock<HashMap<String, u32>>>,
        last_reset_day: &Arc<RwLock<Option<NaiveDate>>>,
    ) -> bool;

    /// Increment counter after spawning a task.
    pub async fn increment_counter(
        model_name: &str,
        model_counts: &Arc<RwLock<HashMap<String, u32>>>,
    );
}

Daily Reset Logic

maybe_reset_counters() is called on every check_rate_limit():

1. Compute today's date in America/Los_Angeles (approximated as UTC-8)
2. Compare with last_reset_day
3. If different day (or first run): clear all counters, update last_reset_day
4. If same day: no-op

fn today_la() -> NaiveDate {
    let utc_now = chrono::Utc::now();
    let la_time = utc_now - chrono::Duration::hours(8);
    la_time.date_naive()
}

Note: Uses fixed UTC-8 offset (PST approximation). For DST-aware handling, chrono-tz could be added.

Usage in Route Handler

// In process_transcript():
let allowed = RateLimiter::check_rate_limit(&model, &app.model_counts, &app.last_reset_day).await;
if !allowed {
    return Html("<p>Rate limit exceeded...</p>".to_string());
}

// After spawning task:
RateLimiter::increment_counter(&input.model, &app.model_counts).await;

Model Limits

Each ModelOption has rpd_limit (requests per day). The counter is compared against this:

let current_count = counts.get(&model.name).copied().unwrap_or(0);
current_count < model.rpd_limit  // true = allowed

Relevant Files

• src/services/rate_limiter.rs — Rate limiter implementation
• src/state.rs — ModelOption.rpd_limit field
• src/routes/mod.rs — Check + increment in process_transcript()

Browser Test

test_rate_limit_error_display (port 4453) verifies the rate limit UI end-to-end: creates a model with rpd_limit=1, submits once (exhausts limit), submits again, and asserts "Rate limit exceeded" is shown with no polling partial. Run with: cargo test --test integration_browser test_rate_limit_error_display -- --ignored