Support pre-flight CORS check (#1772)

## Issue Addressed

- Resolves #1766 

## Proposed Changes

- Use the `warp::filters::cors` filter instead of our work-around.

## Additional Info

It's not trivial to enable/disable `cors` using `warp`, since using `routes.with(cors)` changes the type of `routes`.  This makes it difficult to apply/not apply cors at runtime. My solution has been to *always* use the `warp::filters::cors` wrapper but when cors should be disabled, just pass the HTTP server listen address as the only permissible origin.

common/warp_utils/Cargo.toml

@@ -7,7 +7,7 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-warp = "0.2.5"
+warp = { git = "https://github.com/paulhauner/warp", branch = "cors-wildcard" }
 eth2 = { path = "../eth2" }
 types = { path = "../../consensus/types" }
 beacon_chain = { path = "../../beacon_node/beacon_chain" }
@@ -15,3 +15,4 @@ state_processing = { path = "../../consensus/state_processing" }
 safe_arith = { path = "../../consensus/safe_arith" }
 serde = { version = "1.0.116", features = ["derive"] }
 tokio = { version = "0.2.22", features = ["sync"] }
+headers = "0.3.2"

common/warp_utils/src/cors.rs

@@ -0,0 +1,76 @@
+use std::net::Ipv4Addr;
+use warp::filters::cors::Builder;
+
+/// Configure a `cors::Builder`.
+///
+/// If `allow_origin.is_none()` the `default_origin` is used.
+pub fn set_builder_origins(
+    builder: Builder,
+    allow_origin: Option<&str>,
+    default_origin: (Ipv4Addr, u16),
+) -> Result<Builder, String> {
+    if let Some(allow_origin) = allow_origin {
+        let origins = allow_origin
+            .split(',')
+            .map(|s| verify_cors_origin_str(s).map(|_| s))
+            .collect::<Result<Vec<_>, _>>()?;
+        Ok(builder.allow_origins(origins))
+    } else {
+        let origin = format!("http://{}:{}", default_origin.0, default_origin.1);
+        verify_cors_origin_str(&origin)?;
+
+        Ok(builder.allow_origin(origin.as_str()))
+    }
+}
+
+/// Verify that `s` can be used as a CORS origin.
+///
+/// ## Notes
+///
+/// We need this function since `warp` will panic if provided an invalid origin. The verification
+/// code is taken from here:
+///
+/// https://github.com/seanmonstar/warp/blob/3d1760c6ca35ce2d03dee0562259d0320e9face3/src/filters/cors.rs#L616
+///
+/// Ideally we should make a PR to `warp` to expose this behaviour, however we defer this for a
+/// later time. The impact of a false-positive on this function is fairly limited, since only
+/// trusted users should be setting CORS origins.
+fn verify_cors_origin_str(s: &str) -> Result<(), String> {
+    // Always the wildcard origin.
+    if s == "*" {
+        return Ok(());
+    }
+
+    let mut parts = s.splitn(2, "://");
+    let scheme = parts
+        .next()
+        .ok_or_else(|| format!("{} is missing a scheme", s))?;
+    let rest = parts
+        .next()
+        .ok_or_else(|| format!("{} is missing the part following the scheme", s))?;
+
+    headers::Origin::try_from_parts(scheme, rest, None)
+        .map_err(|e| format!("Unable to parse {}: {}", s, e))
+        .map(|_| ())
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn valid_origins() {
+        verify_cors_origin_str("*").unwrap();
+        verify_cors_origin_str("http://127.0.0.1").unwrap();
+        verify_cors_origin_str("http://localhost").unwrap();
+        verify_cors_origin_str("http://127.0.0.1:8000").unwrap();
+        verify_cors_origin_str("http://localhost:8000").unwrap();
+    }
+
+    #[test]
+    fn invalid_origins() {
+        verify_cors_origin_str(".*").unwrap_err();
+        verify_cors_origin_str("127.0.0.1").unwrap_err();
+        verify_cors_origin_str("localhost").unwrap_err();
+    }
+}

common/warp_utils/src/lib.rs

@@ -1,6 +1,6 @@
 //! This crate contains functions that are common across multiple `warp` HTTP servers in the
 //! Lighthouse project. E.g., the `http_api` and `http_metrics` crates.
 
+pub mod cors;
 pub mod reject;
-pub mod reply;
 pub mod task;

common/warp_utils/src/reply.rs

@@ -1,15 +0,0 @@
-/// Add CORS headers to `reply` only if `allow_origin.is_some()`.
-pub fn maybe_cors<T: warp::Reply + 'static>(
-    reply: T,
-    allow_origin: Option<&String>,
-) -> Box<dyn warp::Reply> {
-    if let Some(allow_origin) = allow_origin {
-        Box::new(warp::reply::with_header(
-            reply,
-            "Access-Control-Allow-Origin",
-            allow_origin,
-        ))
-    } else {
-        Box::new(reply)
-    }
-}