Increase URI MAX_LEN

**This Commit**
Increases the max length of URIs

**Why?**
STEM can receive requests > u16::MAX. When it tries to forward these
requests to Impeller, `reqwest` crashes when parsing the URL into a URI
because `http` returns a `Result::Err`.

This is currently being tracked
[here](seanmonstar/reqwest#668).

src/header/map.rs

@@ -629,7 +629,7 @@ impl<T> HeaderMap<T> {
     /// ```
     pub fn reserve(&mut self, additional: usize) {
         // TODO: This can't overflow if done properly... since the max # of
-        // elements is u16::MAX.
+        // elements is u16::MAX
         let cap = self.entries.len()
             .checked_add(additional)
             .expect("reserve overflow");

src/uri/mod.rs

@@ -147,8 +147,8 @@ enum ErrorKind {
     SchemeTooLong,
 }
 
-// u16::MAX is reserved for None
-const MAX_LEN: usize = (u16::MAX - 1) as usize;
+// 256 * 1024 is reserved for NONE
+const MAX_LEN: usize = 256 * 1024 - 1;
 
 const URI_CHARS: [u8; 256] = [
     //  0      1      2      3      4      5      6      7      8      9

src/uri/path.rs

@@ -11,10 +11,10 @@ use super::{ErrorKind, InvalidUri, InvalidUriBytes};
 #[derive(Clone)]
 pub struct PathAndQuery {
     pub(super) data: ByteStr,
-    pub(super) query: u16,
+    pub(super) query: u32,
 }
 
-const NONE: u16 = ::std::u16::MAX;
+const NONE: u32 = 1024 * 256;
 
 impl PathAndQuery {
     /// Attempt to convert a `PathAndQuery` from `Bytes`.
@@ -57,7 +57,7 @@ impl PathAndQuery {
                 match b {
                     b'?' => {
                         debug_assert_eq!(query, NONE);
-                        query = i as u16;
+                        query = i as u32;
                         break;
                     }
                     b'#' => {

src/uri/tests.rs

@@ -445,7 +445,7 @@ fn test_uri_parse_error() {
 fn test_max_uri_len() {
     let mut uri = vec![];
     uri.extend(b"http://localhost/");
-    uri.extend(vec![b'a'; 70 * 1024]);
+    uri.extend(vec![b'a';256 * 1024 - uri.len()]);
 
     let uri = String::from_utf8(uri).unwrap();
     let res: Result<Uri, InvalidUri> = uri.parse();