perf(headers): switch from fmt to itoa when writing content-length header

src/headers.rs

@@ -1,5 +1,3 @@
-use std::fmt::Write;
-
 use bytes::BytesMut;
 use http::HeaderMap;
 use http::header::{CONTENT_LENGTH, TRANSFER_ENCODING};
@@ -70,7 +68,7 @@ pub fn content_length_parse_all_values(values: ValueIter<HeaderValue>) -> Option
 
 pub fn content_length_value(len: u64) -> HeaderValue {
     let mut len_buf = BytesMut::with_capacity(MAX_DECIMAL_U64_BYTES);
-    write!(len_buf, "{}", len)
+    ::itoa::fmt(&mut len_buf, len)
         .expect("BytesMut can hold a decimal u64");
     // safe because u64 Display is ascii numerals
     unsafe {
@@ -141,6 +139,10 @@ fn eq_ascii(left: &str, right: &str) -> bool {
 
 #[cfg(test)]
 mod tests {
+
+    #[cfg(feature = "nightly")]
+    use test::Bencher;
+
     #[test]
     fn assert_max_decimal_u64_bytes() {
         assert_eq!(
@@ -148,4 +150,32 @@ mod tests {
             ::std::u64::MAX.to_string().len()
         );
     }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn bench_content_length_fmt_small(b: &mut Bencher) {
+        let n = 13;
+        let s = n.to_string();
+        b.bytes = s.len() as u64;
+
+        b.iter(|| {
+            let val = super::content_length_value(n);
+            debug_assert_eq!(val, s);
+            ::test::black_box(&val);
+        })
+    }
+
+    #[cfg(feature = "nightly")]
+    #[bench]
+    fn bench_content_length_fmt_big(b: &mut Bencher) {
+        let n = 326_893_010;
+        let s = n.to_string();
+        b.bytes = s.len() as u64;
+
+        b.iter(|| {
+            let val = super::content_length_value(n);
+            debug_assert_eq!(val, s);
+            ::test::black_box(&val);
+        })
+    }
 }

src/lib.rs

@@ -21,6 +21,7 @@ extern crate h2;
 extern crate http;
 extern crate httparse;
 extern crate iovec;
+extern crate itoa;
 #[macro_use] extern crate log;
 #[cfg(feature = "runtime")] extern crate net2;
 extern crate time;

src/proto/h1/role.rs

@@ -190,7 +190,7 @@ impl Http1Transaction for Server {
         }))
     }
 
-    fn encode(mut msg: Encode<Self::Outgoing>, dst: &mut Vec<u8>) -> ::Result<Encoder> {
+    fn encode(mut msg: Encode<Self::Outgoing>, mut dst: &mut Vec<u8>) -> ::Result<Encoder> {
         trace!(
             "Server::encode status={:?}, body={:?}, req_method={:?}",
             msg.head.subject,
@@ -439,7 +439,9 @@ impl Http1Transaction for Server {
                     Encoder::length(0)
                 },
                 Some(BodyLength::Known(len)) => {
-                    let _ = write!(FastWrite(dst), "content-length: {}\r\n", len);
+                    extend(dst, b"content-length: ");
+                    let _ = ::itoa::write(&mut dst, len);
+                    extend(dst, b"\r\n");
                     Encoder::length(len)
                 },
             };
@@ -1444,9 +1446,9 @@ mod tests {
         b.bytes = len as u64;
 
         let mut head = MessageHead::default();
+        let mut vec = Vec::with_capacity(128);
 
         b.iter(|| {
-            let mut vec = Vec::new();
             Server::encode(Encode {
                 head: &mut head,
                 body: Some(BodyLength::Known(10)),
@@ -1455,7 +1457,12 @@ mod tests {
                 title_case_headers: false,
             }, &mut vec).unwrap();
             assert_eq!(vec.len(), len);
-            ::test::black_box(vec);
+            ::test::black_box(&vec);
+
+            // reset Vec<u8> to 0 (always safe)
+            unsafe {
+                vec.set_len(0);
+            }
         })
     }
 }