Add client, client codegen, helloworld and routeguide client examples

tonic/src/codec/encode.rs

@@ -0,0 +1,40 @@
+use crate::{body::BytesBuf, Status};
+use bytes::{BufMut, BytesMut, IntoBuf};
+use futures_core::{Stream, TryStream};
+use futures_util::StreamExt;
+use tokio_codec::Encoder;
+
+pub fn encode<T, U>(mut encoder: T, mut source: U) -> impl TryStream<Ok = BytesBuf, Error = Status>
+where
+    T: Encoder<Error = Status>,
+    U: Stream<Item = Result<T::Item, Status>> + Unpin,
+{
+    async_stream::stream! {
+        let mut buf = BytesMut::with_capacity(1024);
+
+        loop {
+            match source.next().await {
+                Some(Ok(item)) => {
+                    buf.reserve(5);
+                    unsafe {
+                        buf.advance_mut(5);
+                    }
+                    encoder.encode(item, &mut buf).map_err(drop).unwrap();
+
+                    // now that we know length, we can write the header
+                    let len = buf.len() - 5;
+                    assert!(len <= std::u32::MAX as usize);
+                    {
+                        let mut cursor = std::io::Cursor::new(&mut buf[..5]);
+                        cursor.put_u8(0); // byte must be 0, reserve doesn't auto-zero
+                        cursor.put_u32_be(len as u32);
+                    }
+
+                    yield Ok(buf.split_to(len + 5).freeze().into_buf());
+                },
+                Some(Err(status)) => yield Err(status),
+                None => break,
+            }
+        }
+    }
+}