Fix token and uri parsers to disallow empty results (#111)

This fixes cases where the parser would accept non-compliant request lines including empty methods
and paths.

For the `token` grammar, [the spec][spec-token] is:

```
  token          = 1*tchar
```

`1*` is shorthand for one-or-more, so the empty string is not a valid `token`.

For the path component of the request line, [the spec][spec-path] we're concerned with the
`absolute-path` grammar:

```
  absolute-path = 1*( "/" segment )
```

While `segment` might be empty, there must be at least a `"/"` for it to be syntactically valid.

I've added tests for these cases and their combination, and had to update the expected error of one
of the existing URI tests which now fails sooner due to the empty path.

[spec-token]: https://httpwg.org/http-core/draft-ietf-httpbis-semantics-latest.html#tokens
[spec-path]: https://httpwg.org/http-core/draft-ietf-httpbis-semantics-latest.html#uri.references

src/lib.rs

@@ -660,6 +660,12 @@ fn parse_reason<'a>(bytes: &mut Bytes<'a>) -> Result<&'a str> {
 
 #[inline]
 fn parse_token<'a>(bytes: &mut Bytes<'a>) -> Result<&'a str> {
+    let b = next!(bytes);
+    if !is_token(b) {
+        // First char must be a token char, it can't be a space which would indicate an empty token.
+        return Err(Error::Token);
+    }
+
     loop {
         let b = next!(bytes);
         if b == b' ' {
@@ -675,6 +681,12 @@ fn parse_token<'a>(bytes: &mut Bytes<'a>) -> Result<&'a str> {
 
 #[inline]
 fn parse_uri<'a>(bytes: &mut Bytes<'a>) -> Result<&'a str> {
+    let b = next!(bytes);
+    if !is_uri_token(b) {
+        // First char must be a URI char, it can't be a space which would indicate an empty path.
+        return Err(Error::Token);
+    }
+
     simd::match_uri_vectored(bytes);
 
     loop {
@@ -1310,6 +1322,27 @@ mod tests {
         |_r| {}
     }
 
+    req! {
+        test_request_with_empty_method,
+        b" / HTTP/1.1\r\n\r\n",
+        Err(::Error::Token),
+        |_r| {}
+    }
+
+    req! {
+        test_request_with_empty_path,
+        b"GET  HTTP/1.1\r\n\r\n",
+        Err(::Error::Token),
+        |_r| {}
+    }
+
+    req! {
+        test_request_with_empty_method_and_path,
+        b"  HTTP/1.1\r\n\r\n",
+        Err(::Error::Token),
+        |_r| {}
+    }
+
     macro_rules! res {
         ($name:ident, $buf:expr, |$arg:ident| $body:expr) => (
             res! {$name, $buf, Ok(Status::Complete($buf.len())), |$arg| $body }

tests/uri.rs

@@ -111,7 +111,7 @@ req! {
 req! {
     urltest_007,
     b"GET  foo.com HTTP/1.1\r\nHost: \r\n\r\n",
-    Err(Error::Version),
+    Err(Error::Token),
     |_r| {}
 }