Make HeaderName::from_static const (#499)

... plus some clean-up.

It was only after I came up with the scheme using
`const fn from_bytes(&[u8]) -> Option<StandardHeader>`
that I noticed the debug+wasm32-wasi version of `parse_hdr`, which had
something very similar.

While cleaning up that function, I realized it still would still panic
if an attempted name was too long, which had been fixed for all other
targets and profiles in #433.  Then, I thought it would be worth seeing
if the use of `eq!` in the primary version of `parse_hdr` still made any
difference.

And, it would not appear so. At least not on x86_64, nor wasm32-wasi run
via wasmtime.  I've run the benchmarks a number of times now, and it
seems the only significant performance change anywhere is actually that
of `HeaderName::from_static` itself, which now seems to run in about 2/3
the time on average.

Unfortunately, `const fn` still cannot `panic!`, but I've followed the
lead from `HeaderValue::from_static`.  While that version required 1.46,
this new function requires 1.49.  That is almost 8 months old, so
hopefully this isn't too controversial!

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
           - nightly
           # When updating this value, don't forget to also adjust the
           # `rust-version` field in the `Cargo.toml` file.
-          - 1.46.0
+          - 1.49.0
 
         include:
           - rust: nightly

Cargo.toml

@@ -21,7 +21,7 @@ keywords = ["http"]
 categories = ["web-programming"]
 edition = "2018"
 # When updating this value, don't forget to also adjust the GitHub Actions config.
-rust-version = "1.46.0"
+rust-version = "1.49.0"
 
 [dependencies]
 bytes = "1"

benches/header_name.rs

@@ -130,6 +130,128 @@ fn make_all_known_headers() -> Vec<Vec<u8>> {
     ]
 }
 
+static ALL_KNOWN_HEADERS: &[&str] = &[
+    // Standard request headers
+    "a-im",
+    "accept",
+    "accept-charset",
+    "accept-datetime",
+    "accept-encoding",
+    "accept-language",
+    "access-control-request-method",
+    "authorization",
+    "cache-control",
+    "connection",
+    "permanent",
+    "content-length",
+    "content-md5",
+    "content-type",
+    "cookie",
+    "date",
+    "expect",
+    "forwarded",
+    "from",
+    "host",
+    "permanent",
+    "http2-settings",
+    "if-match",
+    "if-modified-since",
+    "if-none-match",
+    "if-range",
+    "if-unmodified-since",
+    "max-forwards",
+    "origin",
+    "pragma",
+    "proxy-authorization",
+    "range",
+    "referer",
+    "te",
+    "user-agent",
+    "upgrade",
+    "via",
+    "warning",
+    // common_non_standard
+    "upgrade-insecure-requests",
+    "upgrade-insecure-requests",
+    "x-requested-with",
+    "dnt",
+    "x-forwarded-for",
+    "x-forwarded-host",
+    "x-forwarded-proto",
+    "front-end-https",
+    "x-http-method-override",
+    "x-att-deviceid",
+    "x-wap-profile",
+    "proxy-connection",
+    "x-uidh",
+    "x-csrf-token",
+    "x-request-id",
+    "x-correlation-id",
+    "save-data",
+    // standard_response_headers
+    "accept-patch",
+    "accept-ranges",
+    "access-control-allow-credentials",
+    "access-control-allow-headers",
+    "access-control-allow-methods",
+    "access-control-allow-origin",
+    "access-control-expose-headers",
+    "access-control-max-age",
+    "age",
+    "allow",
+    "alt-svc",
+    "cache-control",
+    "connection",
+    "content-disposition",
+    "content-encoding",
+    "content-language",
+    "content-length",
+    "content-location",
+    "content-md5",
+    "content-range",
+    "content-type",
+    "date",
+    "delta-base",
+    "etag",
+    "expires",
+    "im",
+    "last-modified",
+    "link",
+    "location",
+    "p3p",
+    "permanent",
+    "pragma",
+    "proxy-authenticate",
+    "public-key-pins",
+    "retry-after",
+    "server",
+    "set-cookie",
+    "strict-transport-security",
+    "tk",
+    "trailer",
+    "transfer-encoding",
+    "upgrade",
+    "vary",
+    "via",
+    "warning",
+    "www-authenticate",
+    "x-frame-options",
+    // common_non_standard_response
+    "content-security-policy",
+    "refresh",
+    "status",
+    "timing-allow-origin",
+    "x-content-duration",
+    "x-content-security-policy",
+    "x-content-type-options",
+    "x-correlation-id",
+    "x-powered-by",
+    "x-request-id",
+    "x-ua-compatible",
+    "x-webkit-csp",
+    "x-xss-protection",
+];
+
 #[bench]
 fn header_name_easy(b: &mut Bencher) {
     let name = b"Content-type";
@@ -138,6 +260,14 @@ fn header_name_easy(b: &mut Bencher) {
     });
 }
 
+#[bench]
+fn header_name_custom(b: &mut Bencher) {
+    let name = b"Foo-Bar-Baz-Blah";
+    b.iter(|| {
+        HeaderName::from_bytes(&name[..]).unwrap();
+    });
+}
+
 #[bench]
 fn header_name_bad(b: &mut Bencher) {
     let name = b"bad header name";
@@ -155,3 +285,12 @@ fn header_name_various(b: &mut Bencher) {
         }
     });
 }
+
+#[bench]
+fn header_name_from_static(b: &mut Bencher) {
+    b.iter(|| {
+        for name in ALL_KNOWN_HEADERS {
+            HeaderName::from_static(name);
+        }
+    });
+}

src/byte_str.rs

@@ -18,7 +18,7 @@ impl ByteStr {
     }
 
     #[inline]
-    pub fn from_static(val: &'static str) -> ByteStr {
+    pub const fn from_static(val: &'static str) -> ByteStr {
         ByteStr {
             // Invariant: val is a str so contains vaid UTF-8.
             bytes: Bytes::from_static(val.as_bytes()),