feat(http2): add http2_max_send_buf_size option to client and server

This value is like a high-water mark. It applies per stream. Once a
stream has buffered that amount of bytes to send, it won't poll more
data from the `HttpBody` until the stream has been able to flush under
it.

Cargo.toml

@@ -31,7 +31,7 @@ http = "0.2"
 http-body = "0.4"
 httpdate = "1.0"
 httparse = "1.5.1"
-h2 = { version = "0.3.3", optional = true }
+h2 = { version = "0.3.9", optional = true }
 itoa = "0.4.1"
 tracing = { version = "0.1", default-features = false, features = ["std"] }
 pin-project-lite = "0.2.4"

src/client/client.rs

@@ -1223,6 +1223,20 @@ impl Builder {
         self
     }
 
+    /// Set the maximum write buffer size for each HTTP/2 stream.
+    ///
+    /// Default is currently 1MB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// The value must be no larger than `u32::MAX`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_send_buf_size(&mut self, max: usize) -> &mut Self {
+        self.conn_builder.http2_max_send_buf_size(max);
+        self
+    }
+
     /// Set whether to retry requests that get disrupted before ever starting
     /// to write.
     ///

src/client/conn.rs

@@ -837,6 +837,21 @@ impl Builder {
         self
     }
 
+    /// Set the maximum write buffer size for each HTTP/2 stream.
+    ///
+    /// Default is currently 1MB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// The value must be no larger than `u32::MAX`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_send_buf_size(&mut self, max: usize) -> &mut Self {
+        assert!(max <= std::u32::MAX as usize);
+        self.h2_builder.max_send_buffer_size = max;
+        self
+    }
+
     /// Constructs a connection with the configured options and IO.
     /// See [`client::conn`](crate::client::conn) for more.
     ///

src/proto/h2/client.rs

@@ -36,6 +36,7 @@ type ConnEof = oneshot::Receiver<Never>;
 const DEFAULT_CONN_WINDOW: u32 = 1024 * 1024 * 5; // 5mb
 const DEFAULT_STREAM_WINDOW: u32 = 1024 * 1024 * 2; // 2mb
 const DEFAULT_MAX_FRAME_SIZE: u32 = 1024 * 16; // 16kb
+const DEFAULT_MAX_SEND_BUF_SIZE: usize = 1024 * 1024; // 1mb
 
 #[derive(Clone, Debug)]
 pub(crate) struct Config {
@@ -50,6 +51,7 @@ pub(crate) struct Config {
     #[cfg(feature = "runtime")]
     pub(crate) keep_alive_while_idle: bool,
     pub(crate) max_concurrent_reset_streams: Option<usize>,
+    pub(crate) max_send_buffer_size: usize,
 }
 
 impl Default for Config {
@@ -66,6 +68,7 @@ impl Default for Config {
             #[cfg(feature = "runtime")]
             keep_alive_while_idle: false,
             max_concurrent_reset_streams: None,
+            max_send_buffer_size: DEFAULT_MAX_SEND_BUF_SIZE,
         }
     }
 }
@@ -76,6 +79,7 @@ fn new_builder(config: &Config) -> Builder {
         .initial_window_size(config.initial_stream_window_size)
         .initial_connection_window_size(config.initial_conn_window_size)
         .max_frame_size(config.max_frame_size)
+        .max_send_buffer_size(config.max_send_buffer_size)
         .enable_push(false);
     if let Some(max) = config.max_concurrent_reset_streams {
         builder.max_concurrent_reset_streams(max);

src/proto/h2/server.rs

@@ -33,6 +33,7 @@ use crate::{Body, Response};
 const DEFAULT_CONN_WINDOW: u32 = 1024 * 1024; // 1mb
 const DEFAULT_STREAM_WINDOW: u32 = 1024 * 1024; // 1mb
 const DEFAULT_MAX_FRAME_SIZE: u32 = 1024 * 16; // 16kb
+const DEFAULT_MAX_SEND_BUF_SIZE: usize = 1024 * 400; // 400kb
 
 #[derive(Clone, Debug)]
 pub(crate) struct Config {
@@ -45,6 +46,7 @@ pub(crate) struct Config {
     pub(crate) keep_alive_interval: Option<Duration>,
     #[cfg(feature = "runtime")]
     pub(crate) keep_alive_timeout: Duration,
+    pub(crate) max_send_buffer_size: usize,
 }
 
 impl Default for Config {
@@ -59,6 +61,7 @@ impl Default for Config {
             keep_alive_interval: None,
             #[cfg(feature = "runtime")]
             keep_alive_timeout: Duration::from_secs(20),
+            max_send_buffer_size: DEFAULT_MAX_SEND_BUF_SIZE,
         }
     }
 }
@@ -109,7 +112,8 @@ where
         builder
             .initial_window_size(config.initial_stream_window_size)
             .initial_connection_window_size(config.initial_conn_window_size)
-            .max_frame_size(config.max_frame_size);
+            .max_frame_size(config.max_frame_size)
+            .max_send_buffer_size(config.max_send_buffer_size);
         if let Some(max) = config.max_concurrent_streams {
             builder.max_concurrent_streams(max);
         }

src/server/conn.rs

@@ -543,6 +543,21 @@ impl<E> Http<E> {
         self
     }
 
+    /// Set the maximum write buffer size for each HTTP/2 stream.
+    ///
+    /// Default is currently ~400KB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// The value must be no larger than `u32::MAX`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_send_buf_size(&mut self, max: usize) -> &mut Self {
+        assert!(max <= std::u32::MAX as usize);
+        self.h2_builder.max_send_buffer_size = max;
+        self
+    }
+
     /// Set the maximum buffer size for the connection.
     ///
     /// Default is ~400kb.

src/server/server.rs

@@ -439,6 +439,20 @@ impl<I, E> Builder<I, E> {
         self
     }
 
+    /// Set the maximum write buffer size for each HTTP/2 stream.
+    ///
+    /// Default is currently ~400KB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// The value must be no larger than `u32::MAX`.
+    #[cfg(feature = "http2")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
+    pub fn http2_max_send_buf_size(mut self, max: usize) -> Self {
+        self.protocol.http2_max_send_buf_size(max);
+        self
+    }
+
     /// Sets the `Executor` to deal with connection tasks.
     ///
     /// Default is `tokio::spawn`.