Updating the rate-limiter documentation with a simpler example

3 files changed, 168 insertions, 117 deletions

diff --git a/docs/user_guide/index.md b/docs/user_guide/index.md
index d3f8309..cb57eb6 100644
--- a/docs/user_guide/index.md
+++ b/docs/user_guide/index.md
@@ -20,7 +20,7 @@ In this guide, we will cover the most used features, operations and settings of
 * [Examples: take control of the request](modify_filter.md)
 * [Connection pooling and reuse](pooling.md)
 * [Handling failures and failover](failover.md)
-* [RateLimiter quickstart](ratelimiter.md)
+* [RateLimiter quickstart](rate_limiter.md)
 
 ## Advanced topics (WIP)
 * [Pingora internals](internals.md)
diff --git a/docs/user_guide/rate_limiter.md b/docs/user_guide/rate_limiter.md
new file mode 100644
index 0000000..fe337a1
--- /dev/null
+++ b/docs/user_guide/rate_limiter.md
@@ -0,0 +1,167 @@
+# **RateLimiter quickstart**
+Pingora provides a crate `pingora-limits` which provides a simple and easy to use rate limiter for your application. Below is an example of how you can use [`Rate`](https://docs.rs/pingora-limits/latest/pingora_limits/rate/struct.Rate.html) to create an application that uses multiple limiters to restrict the rate at which requests can be made on a per-app basis (determined by a request header).
+
+## Steps
+1. Add the following dependencies to your `Cargo.toml`:
+   ```toml
+   async-trait="0.1"
+   pingora = { version = "0.3", features = [ "lb" ] }
+   pingora-limits = "0.3.0"
+   once_cell = "1.19.0"
+   ```
+2. Declare a global rate limiter map to store the rate limiter for each client. In this example, we use `appid`.
+3. Override the `request_filter` method in the `ProxyHttp` trait to implement rate limiting.
+   1. Retrieve the client appid from header.
+   2. Retrieve the current window requests from the rate limiter map. If there is no rate limiter for the client, create a new one and insert it into the map.
+   3. If the current window requests exceed the limit, return 429 and set RateLimiter associated headers.
+   4. If the request is not rate limited, return `Ok(false)` to continue the request.
+
+## Example
+```rust
+use async_trait::async_trait;
+use once_cell::sync::Lazy;
+use pingora::http::ResponseHeader;
+use pingora::prelude::*;
+use pingora_limits::rate::Rate;
+use std::sync::Arc;
+use std::time::Duration;
+
+fn main() {
+    let mut server = Server::new(Some(Opt::default())).unwrap();
+    server.bootstrap();
+    let mut upstreams = LoadBalancer::try_from_iter(["1.1.1.1:443", "1.0.0.1:443"]).unwrap();
+    // Set health check
+    let hc = TcpHealthCheck::new();
+    upstreams.set_health_check(hc);
+    upstreams.health_check_frequency = Some(Duration::from_secs(1));
+    // Set background service
+    let background = background_service("health check", upstreams);
+    let upstreams = background.task();
+    // Set load balancer
+    let mut lb = http_proxy_service(&server.configuration, LB(upstreams));
+    lb.add_tcp("0.0.0.0:6188");
+
+    // let rate = Rate
+    server.add_service(background);
+    server.add_service(lb);
+    server.run_forever();
+}
+
+pub struct LB(Arc<LoadBalancer<RoundRobin>>);
+
+impl LB {
+    pub fn get_request_appid(&self, session: &mut Session) -> Option<String> {
+        match session
+            .req_header()
+            .headers
+            .get("appid")
+            .map(|v| v.to_str())
+        {
+            None => None,
+            Some(v) => match v {
+                Ok(v) => Some(v.to_string()),
+                Err(_) => None,
+            },
+        }
+    }
+}
+
+// Rate limiter
+static RATE_LIMITER: Lazy<Rate> = Lazy::new(|| Rate::new(Duration::from_secs(1)));
+
+// max request per second per client
+static MAX_REQ_PER_SEC: isize = 1;
+
+#[async_trait]
+impl ProxyHttp for LB {
+    type CTX = ();
+
+    fn new_ctx(&self) {}
+
+    async fn upstream_peer(
+        &self,
+        _session: &mut Session,
+        _ctx: &mut Self::CTX,
+    ) -> Result<Box<HttpPeer>> {
+        let upstream = self.0.select(b"", 256).unwrap();
+        // Set SNI
+        let peer = Box::new(HttpPeer::new(upstream, true, "one.one.one.one".to_string()));
+        Ok(peer)
+    }
+
+    async fn upstream_request_filter(
+        &self,
+        _session: &mut Session,
+        upstream_request: &mut RequestHeader,
+        _ctx: &mut Self::CTX,
+    ) -> Result<()>
+    where
+        Self::CTX: Send + Sync,
+    {
+        upstream_request
+            .insert_header("Host", "one.one.one.one")
+            .unwrap();
+        Ok(())
+    }
+
+    async fn request_filter(&self, session: &mut Session, _ctx: &mut Self::CTX) -> Result<bool>
+    where
+        Self::CTX: Send + Sync,
+    {
+        let appid = match self.get_request_appid(session) {
+            None => return Ok(false), // no client appid found, skip rate limiting
+            Some(addr) => addr,
+        };
+
+        // retrieve the current window requests
+        let curr_window_requests = RATE_LIMITER.observe(&appid, 1);
+        if curr_window_requests > MAX_REQ_PER_SEC {
+            // rate limited, return 429
+            let mut header = ResponseHeader::build(429, None).unwrap();
+            header
+                .insert_header("X-Rate-Limit-Limit", MAX_REQ_PER_SEC.to_string())
+                .unwrap();
+            header.insert_header("X-Rate-Limit-Remaining", "0").unwrap();
+            header.insert_header("X-Rate-Limit-Reset", "1").unwrap();
+            session.set_keepalive(None);
+            session
+                .write_response_header(Box::new(header), true)
+                .await?;
+            return Ok(true);
+        }
+        Ok(false)
+    }
+}
+```
+
+## Testing
+To use the example above, 
+
+1. Run your program with `cargo run`. 
+2. Verify the program is working with a few executions of ` curl localhost:6188 -H "appid:1" -v`
+   - The first request should work and any later requests that arrive within 1s of a previous request should fail with: 
+     ```
+     *   Trying 127.0.0.1:6188...
+     * Connected to localhost (127.0.0.1) port 6188 (#0)
+     > GET / HTTP/1.1
+     > Host: localhost:6188
+     > User-Agent: curl/7.88.1
+     > Accept: */*
+     > appid:1
+     > 
+     < HTTP/1.1 429 Too Many Requests
+     < X-Rate-Limit-Limit: 1
+     < X-Rate-Limit-Remaining: 0
+     < X-Rate-Limit-Reset: 1
+     < Date: Sun, 14 Jul 2024 20:29:02 GMT
+     < Connection: close
+     < 
+     * Closing connection 0
+     ```
+
+## Complete Example
+You can run the pre-made example code in the [`pingora-proxy` examples folder](https://github.com/cloudflare/pingora/tree/main/pingora-proxy/examples/rate_limiter.rs) with 
+
+```
+cargo run --example rate_limiter
+```
\ No newline at end of file
diff --git a/docs/user_guide/ratelimiter.md b/docs/user_guide/ratelimiter.md
deleted file mode 100644
index 3bb36c3..0000000
--- a/docs/user_guide/ratelimiter.md
+++ /dev/null
@@ -1,116 +0,0 @@
-# **RateLimiter quickstart**
-Pingora provides a crate `pingora-limits` which provides a simple and easy to use rate limiter for your application.
-
-## Steps
-1. Add the following dependencies to your `Cargo.toml`:
-   ```toml
-   pingora-limits = "0.1.0"
-   lazy_static = "1.4.0"
-   ```
-2. Declare a global rate limiter map to store the rate limiter for each client. In this example, we use `appid`.
-3. Override the `request_filter` method in the `ProxyHttp` trait to implement rate limiting.
-   1. Retrieve the client appid from header.
-   2. Retrieve the current window requests from the rate limiter map. If there is no rate limiter for the client, create a new one and insert it into the map.
-   3. If the current window requests exceed the limit, return 429 and set RateLimiter associated headers.
-   4. If the request is not rate limited, return `Ok(false)` to continue the request.
-
-## Example
-```rust
-use std::collections::HashMap;
-use std::sync::{Arc, Mutex};
-use std::time::Duration;
-use async_trait::async_trait;
-use lazy_static::lazy_static;
-use pingora::http::ResponseHeader;
-use pingora::prelude::*;
-use pingora_limits::rate::Rate;
-
-fn main() {
-   let mut server = Server::new(Some(Opt::default())).unwrap();
-   server.bootstrap();
-   let mut upstreams = LoadBalancer::try_from_iter(["1.1.1.1:443", "1.0.0.1:443"]).unwrap();
-   // Set health check
-   let hc = TcpHealthCheck::new();
-   upstreams.set_health_check(hc);
-   upstreams.health_check_frequency = Some(Duration::from_secs(1));
-   // Set background service
-   let background = background_service("health check", upstreams);
-   let upstreams = background.task();
-   // Set load balancer
-   let mut lb = http_proxy_service(&server.configuration, LB(upstreams));
-   lb.add_tcp("0.0.0.0:6188");
-
-   // let rate = Rate
-   server.add_service(background);
-   server.add_service(lb);
-   server.run_forever();
-}
-
-pub struct LB(Arc<LoadBalancer<RoundRobin>>);
-
-impl LB {
-   pub fn get_request_appid(&self, session: &mut Session) -> Option<String> {
-      match session.req_header().headers.get("appid").map(|v| v.to_str()) {
-         None => None,
-         Some(v) => match v {
-            Ok(v) => Some(v.to_string()),
-            Err(_) => None
-         }
-      }
-   }
-}
-
-
-// global limiter
-lazy_static! {
-    static ref RATE_LIMITER_MAP: Arc<Mutex<HashMap<String, Rate>>> = {
-       Arc::new(Mutex::new(HashMap::new()))
-    };
-}
-// max request per second per client
-static MAX_REQ_PER_SEC: isize = 1;
-
-#[async_trait]
-impl ProxyHttp for LB {
-   type CTX = ();
-
-   fn new_ctx(&self) -> Self::CTX {
-      ()
-   }
-   async fn upstream_peer(&self, _session: &mut Session, _ctx: &mut Self::CTX) -> Result<Box<HttpPeer>> {
-      let upstream = self.0
-              .select(b"", 256)
-              .unwrap();
-      // Set SNI
-      let peer = Box::new(HttpPeer::new(upstream, true, "one.one.one.one".to_string()));
-      Ok(peer)
-   }
-   async fn upstream_request_filter(&self, _session: &mut Session, upstream_request: &mut RequestHeader, _ctx: &mut Self::CTX) -> Result<()> where Self::CTX: Send + Sync {
-      upstream_request.insert_header("Host", "one.one.one.one").unwrap();
-      Ok(())
-   }
-   async fn request_filter(&self, session: &mut Session, _ctx: &mut Self::CTX) -> Result<bool> where Self::CTX: Send + Sync {
-      let appid = match self.get_request_appid(session) {
-         None => return Ok(false), // no client appid found, skip rate limiting
-         Some(addr) => addr
-      };
-
-      // retrieve the current window requests
-      let curr_window_requests = {
-         let mut rate_limiter_map = RATE_LIMITER_MAP.lock().unwrap();
-         let rate_limiter = rate_limiter_map.entry(appid.clone()).insert_or_with(|| Rate::new(Duration::from_secs(1)));
-         rate_limiter.observe(&appid, 1)
-      };
-      if curr_window_requests > MAX_REQ_PER_SEC { // rate limited, return 429
-         let mut header = ResponseHeader::build(429, None).unwrap();
-         header.insert_header("X-Rate-Limit-Limit", MAX_REQ_PER_SEC.to_string()).unwrap();
-         header.insert_header("X-Rate-Limit-Remaining", "0").unwrap();
-         header.insert_header("X-Rate-Limit-Reset", "1").unwrap();
-         session.set_keepalive(None);
-         session.write_response_header(Box::new(header)).await?;
-         return Ok(true);
-      }
-      Ok(false)
-   }
-}
-```