fix(tonic): Sanitize custom metadata

tonic/src/metadata/map.rs

@@ -197,6 +197,18 @@ pub struct OccupiedEntry<'a, VE: ValueEncoding> {
 // ===== impl MetadataMap =====
 
 impl MetadataMap {
+    // Headers reserved by the gRPC protocol.
+    pub(crate) const GRPC_RESERVED_HEADERS: [&'static str; 8] = [
+        "te",
+        "user-agent",
+        "content-type",
+        "grpc-timeout",
+        "grpc-message",
+        "grpc-encoding",
+        "grpc-message-type",
+        "grpc-status",
+    ];
+
     /// Create an empty `MetadataMap`.
     ///
     /// The map will be created without any capacity. This function will not
@@ -237,6 +249,29 @@ impl MetadataMap {
         self.headers
     }
 
+    /// Convert a MetadataMap into a HTTP HeaderMap
+    ///
+    /// The returned map excludes headers reserved by the gRPC protocol.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tonic::metadata::*;
+    /// let mut map = MetadataMap::new();
+    /// map.insert("grpc-timeout", "1S".parse().unwrap());
+    /// map.insert("x-host", "example.com".parse().unwrap());
+    ///
+    /// let http_map = map.into_sanitized_headers();
+    ///
+    /// assert!(http_map.get("grpc-timeout").is_none());
+    /// ```
+    pub fn into_sanitized_headers(mut self) -> http::HeaderMap {
+        for r in &Self::GRPC_RESERVED_HEADERS {
+            self.headers.remove(*r);
+        }
+        self.headers
+    }
+
     /// Create an empty `MetadataMap` with the specified capacity.
     ///
     /// The returned map will allocate internal storage in order to hold about

tonic/src/request.rs

@@ -149,7 +149,7 @@ impl<T> Request<T> {
         *request.version_mut() = http::Version::HTTP_2;
         *request.method_mut() = http::Method::POST;
         *request.uri_mut() = uri;
-        *request.headers_mut() = self.metadata.into_headers();
+        *request.headers_mut() = self.metadata.into_sanitized_headers();
 
         request
     }
@@ -209,3 +209,23 @@ impl<T> sealed::Sealed for T {}
 mod sealed {
     pub trait Sealed {}
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::metadata::MetadataValue;
+    use http::Uri;
+
+    #[test]
+    fn reserved_headers_are_excluded() {
+        let mut r = Request::new(1);
+
+        for header in &MetadataMap::GRPC_RESERVED_HEADERS {
+            r.metadata_mut()
+                .insert(*header, MetadataValue::from_static("invalid"));
+        }
+
+        let http_request = r.into_http(Uri::default());
+        assert!(http_request.headers().is_empty());
+    }
+}

tonic/src/response.rs

@@ -72,7 +72,7 @@ impl<T> Response<T> {
         let mut res = http::Response::new(self.message);
 
         *res.version_mut() = http::Version::HTTP_2;
-        *res.headers_mut() = self.metadata.into_headers();
+        *res.headers_mut() = self.metadata.into_sanitized_headers();
 
         res
     }
@@ -89,3 +89,22 @@ impl<T> Response<T> {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::metadata::MetadataValue;
+
+    #[test]
+    fn reserved_headers_are_excluded() {
+        let mut r = Response::new(1);
+
+        for header in &MetadataMap::GRPC_RESERVED_HEADERS {
+            r.metadata_mut()
+                .insert(*header, MetadataValue::from_static("invalid"));
+        }
+
+        let http_response = r.into_http();
+        assert!(http_response.headers().is_empty());
+    }
+}