Use .strip_prefix in place of .starts_with

The route! macro gets expanded into library consumer code, which is then
evaluated by Clippy, as such we need to fix these lints so downstream
users don't need to add exceptions.

Fix the same lint elsewhere in this codebase for consistency.

src/input/priority_header.rs

@@ -130,8 +130,8 @@ impl<'a> Iterator for PriorityHeaderIter<'a> {
 
             for p in params {
                 let trimmed_p = p.trim_start();
-                if trimmed_p.starts_with("q=") {
-                    if let Ok(val) = FromStr::from_str(trimmed_p[2..].trim()) {
+                if let Some(stripped) = trimmed_p.strip_prefix("q=") {
+                    if let Ok(val) = FromStr::from_str(stripped.trim()) {
                         value = val;
                         break;
                     }

src/router.rs

@@ -174,8 +174,7 @@ macro_rules! router {
                 let url_params = (|| {
                     let mut url_params = RouilleUrlParams::new();
                     for (actual, desired) in request_url.iter().zip(url_pattern.iter()) {
-                        if desired.starts_with("{") && desired.ends_with("}") {
-                            let key = &desired[1..desired.len()-1];
+                        if let Some(key) = desired.strip_prefix("{").and_then(|d| d.strip_suffix("}")) {
                             $crate::router!(__insert_param $request_url_str, url_params, key, actual ; $($param: $param_type)*)
                         } else if actual != desired {
                             return None
@@ -276,9 +275,7 @@ macro_rules! router {
     };
 
     (__check_pattern $url:ident $value:block /{$p:ident} $($rest:tt)*) => (
-        if !$url.starts_with('/') {
-            None
-        } else {
+        if let Some(url) = $url.strip_prefix('/') {
             let url = &$url[1..];
             let pat_end = url.find('/').unwrap_or(url.len());
             let rest_url = &url[pat_end..];
@@ -288,13 +285,13 @@ macro_rules! router {
             } else {
                 None
             }
+        } else {
+            None
         }
     );
 
     (__check_pattern $url:ident $value:block /{$p:ident: $t:ty} $($rest:tt)*) => (
-        if !$url.starts_with('/') {
-            None
-        } else {
+        if let Some(url) = $url.strip_prefix('/') {
             let url = &$url[1..];
             let pat_end = url.find('/').unwrap_or(url.len());
             let rest_url = &url[pat_end..];
@@ -306,14 +303,15 @@ macro_rules! router {
             } else {
                 None
             }
+        } else {
+            None
         }
     );
 
     (__check_pattern $url:ident $value:block /$p:ident $($rest:tt)*) => (
         {
             let required = concat!("/", stringify!($p));
-            if $url.starts_with(required) {
-                let rest_url = &$url[required.len()..];
+            if let Some(rest_url) = $url.strip_prefix(required) {
                 $crate::router!(__check_pattern rest_url $value $($rest)*)
             } else {
                 None
@@ -323,8 +321,7 @@ macro_rules! router {
 
     (__check_pattern $url:ident $value:block - $($rest:tt)*) => (
         {
-            if $url.starts_with('-') {
-                let rest_url = &$url[1..];
+            if let Some(rest_url) = $url.strip_prefix('-') {
                 $crate::router!(__check_pattern rest_url $value $($rest)*)
             } else {
                 None
@@ -343,8 +340,7 @@ macro_rules! router {
     (__check_pattern $url:ident $value:block $p:ident $($rest:tt)*) => (
         {
             let required = stringify!($p);
-            if $url.starts_with(required) {
-                let rest_url = &$url[required.len()..];
+            if let Some(rest_url) = $url.strip_prefix(required) {
                 $crate::router!(__check_pattern rest_url $value $($rest)*)
             } else {
                 None