From 6feea82d618499b42f480d7b68bf7398ab99016e Mon Sep 17 00:00:00 2001
From: Kai Jewson <kai.jewson@gmail.com>
Date: Sun, 12 Dec 2021 16:03:20 +0000
Subject: [PATCH] Enforce stronger validation of SSE values (#599)

* Enforce stronger validation of SSE values

* Mention `sse::Event` strictness in changelog

Co-authored-by: David Pedersen <david.pdrsn@gmail.com>
---
 axum/CHANGELOG.md        |  3 +++
 axum/Cargo.toml          |  1 +
 axum/src/response/sse.rs | 49 ++++++++++++++++++++++++++++++++++++----
 3 files changed, 49 insertions(+), 4 deletions(-)

diff --git a/axum/CHANGELOG.md b/axum/CHANGELOG.md
index a25e226c..f9d0db4c 100644
--- a/axum/CHANGELOG.md
+++ b/axum/CHANGELOG.md
@@ -7,8 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 # Unreleased
 
+- **fixed:** `sse::Event` is more strict about what field values it supports, disallowing any SSE
+  events that break the specification (such as field values containing carriage returns) ([#599])
 - **added:** `axum::AddExtension::layer` ([#607])
 
+[#599]: https://github.com/tokio-rs/axum/pull/599
 [#607]: https://github.com/tokio-rs/axum/pull/607
 
 # 0.4.2 (06. December, 2021)
diff --git a/axum/Cargo.toml b/axum/Cargo.toml
index 51651b7c..5795104e 100644
--- a/axum/Cargo.toml
+++ b/axum/Cargo.toml
@@ -30,6 +30,7 @@ http-body = "0.4.4"
 mime = "0.3.16"
 hyper = { version = "0.14.14", features = ["server", "tcp", "stream"] }
 matchit = "0.4.4"
+memchr = "2.4.1"
 percent-encoding = "2.1"
 pin-project-lite = "0.2.7"
 serde = "1.0"
diff --git a/axum/src/response/sse.rs b/axum/src/response/sse.rs
index 8a37d00b..b8dbe23b 100644
--- a/axum/src/response/sse.rs
+++ b/axum/src/response/sse.rs
@@ -188,11 +188,21 @@ impl Event {
     /// This corresponds to [`MessageEvent`'s data field].
     ///
     /// [`MessageEvent`'s data field]: https://developer.mozilla.org/en-US/docs/Web/API/MessageEvent/data
+    ///
+    /// # Panics
+    ///
+    /// Panics if `data` contains any carriage returns, as they cannot be transmitted over SSE.
     pub fn data<T>(mut self, data: T) -> Event
     where
         T: Into<String>,
     {
-        self.data = Some(DataType::Text(data.into()));
+        let data = data.into();
+        assert_eq!(
+            memchr::memchr(b'\r', data.as_bytes()),
+            None,
+            "SSE data cannot contain carriage returns",
+        );
+        self.data = Some(DataType::Text(data));
         self
     }
 
@@ -214,11 +224,22 @@ impl Event {
     /// Set the event's comment field (`:<comment-text>`).
     ///
     /// This field will be ignored by most SSE clients.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `comment` contains any newlines or carriage returns, as they are not allowed in
+    /// comments.
     pub fn comment<T>(mut self, comment: T) -> Event
     where
         T: Into<String>,
     {
-        self.comment = Some(comment.into());
+        let comment = comment.into();
+        assert_eq!(
+            memchr::memchr2(b'\r', b'\n', comment.as_bytes()),
+            None,
+            "SSE comment cannot contain newlines or carriage returns"
+        );
+        self.comment = Some(comment);
         self
     }
 
@@ -231,11 +252,21 @@ impl Event {
     ///
     /// [`EventSource`]: https://developer.mozilla.org/en-US/docs/Web/API/EventSource
     /// [`message` event]: https://developer.mozilla.org/en-US/docs/Web/API/EventSource/message_event
+    ///
+    /// # Panics
+    ///
+    /// Panics if `event` contains any newlines or carriage returns.
     pub fn event<T>(mut self, event: T) -> Event
     where
         T: Into<String>,
     {
-        self.event = Some(event.into());
+        let event = event.into();
+        assert_eq!(
+            memchr::memchr2(b'\r', b'\n', event.as_bytes()),
+            None,
+            "SSE event name cannot contain newlines or carriage returns"
+        );
+        self.event = Some(event);
         self
     }
 
@@ -256,11 +287,21 @@ impl Event {
     /// string.
     ///
     /// [`MessageEvent`'s `lastEventId` field]: https://developer.mozilla.org/en-US/docs/Web/API/MessageEvent/lastEventId
+    ///
+    /// # Panics
+    ///
+    /// Panics if `id` contains any newlines, carriage returns or null characters.
     pub fn id<T>(mut self, id: T) -> Event
     where
         T: Into<String>,
     {
-        self.id = Some(id.into());
+        let id = id.into();
+        assert_eq!(
+            memchr::memchr3(b'\r', b'\n', b'\0', id.as_bytes()),
+            None,
+            "Event ID cannot contain newlines, carriage returns or null characters",
+        );
+        self.id = Some(id);
         self
     }
 }