fix(server): panic on max_buf_size too small

src/proto/h1/io.rs

@@ -13,6 +13,9 @@ use proto::{Http1Transaction, MessageHead};
 /// The initial buffer size allocated before trying to read from IO.
 pub(crate) const INIT_BUFFER_SIZE: usize = 8192;
 
+/// The minimum value that can be set to max buffer size.
+pub const MINIMUM_MAX_BUFFER_SIZE: usize = INIT_BUFFER_SIZE;
+
 /// The default maximum read buffer size. If the buffer gets this big and
 /// a message is still not complete, a `TooLarge` error is triggered.
 // Note: if this changes, update server::conn::Http::max_buf_size docs.
@@ -72,6 +75,10 @@ where
     }
 
     pub fn set_max_buf_size(&mut self, max: usize) {
+        assert!(
+            max >= MINIMUM_MAX_BUFFER_SIZE,
+            "The max_buf_size cannot be smaller than the initial buffer size."
+        );
         self.max_buf_size = max;
         self.write_buf.max_buf_size = max;
     }

src/proto/h1/mod.rs

@@ -3,6 +3,7 @@ pub(crate) use self::dispatch::Dispatcher;
 pub use self::decode::Decoder;
 pub use self::encode::{EncodedBuf, Encoder};
 pub use self::io::Cursor; //TODO: move out of h1::io
+pub use self::io::MINIMUM_MAX_BUFFER_SIZE;
 
 mod conn;
 mod date;

src/server/conn.rs

@@ -148,7 +148,15 @@ impl Http {
     /// Set the maximum buffer size for the connection.
     ///
     /// Default is ~400kb.
+    ///
+    /// # Panics
+    ///
+    /// The minimum value allowed is 8192. This method panics if the passed `max` is less than the minimum.
     pub fn max_buf_size(&mut self, max: usize) -> &mut Self {
+        assert!(
+            max >= proto::h1::MINIMUM_MAX_BUFFER_SIZE,
+            "the max_buf_size cannot be smaller than the minimum that h1 specifies."
+        );
         self.max_buf_size = Some(max);
         self
     }

tests/server.rs

@@ -1055,6 +1055,18 @@ fn illegal_request_length_returns_400_response() {
     fut.wait().unwrap_err();
 }
 
+#[test]
+#[should_panic]
+fn max_buf_size_panic_too_small() {
+    const MAX: usize = 8191;
+    Http::new().max_buf_size(MAX);
+}
+#[test]
+fn max_buf_size_no_panic() {
+    const MAX: usize = 8193;
+    Http::new().max_buf_size(MAX);
+}
+
 #[test]
 fn max_buf_size() {
     let _ = pretty_env_logger::try_init();