fix: clamp range end to file size instead of returning 416

RFC 7233 Section 2.1 states that if the last-byte-pos is greater than
or equal to the current length of the representation, the byte range
should be interpreted as the remainder of the representation, not
rejected as unsatisfiable.

`bytes=0-999` on a 500-byte file now returns `bytes 0-499/500` (206)
instead of 416.

Author: mi-caren

src/headers/tests.rs

@@ -428,15 +428,29 @@ mod file_range {
     }
 
     #[test]
-    fn range_end_at_size() {
+    fn range_end_at_size_is_clamped() {
         let range = HttpRange::Range(OrderedRange::new(0..=10).unwrap());
+        let result = file_range(size(10), Some(range)).unwrap();
+        assert_eq!(result.range(), &(0..=9));
+    }
+
+    #[test]
+    fn range_beyond_size_is_clamped() {
+        let range = HttpRange::Range(OrderedRange::new(0..=50).unwrap());
+        let result = file_range(size(10), Some(range)).unwrap();
+        assert_eq!(result.range(), &(0..=9));
+    }
+
+    #[test]
+    fn range_start_at_size_is_unsatisfiable() {
+        let range = HttpRange::Range(OrderedRange::new(10..=20).unwrap());
         let result = file_range(size(10), Some(range));
         assert!(result.is_err());
     }
 
     #[test]
-    fn range_beyond_size() {
-        let range = HttpRange::Range(OrderedRange::new(0..=50).unwrap());
+    fn range_start_beyond_size_is_unsatisfiable() {
+        let range = HttpRange::Range(OrderedRange::new(50..=100).unwrap());
         let result = file_range(size(10), Some(range));
         assert!(result.is_err());
     }

src/lib.rs

@@ -55,7 +55,9 @@ pub fn file_range(
 
     let range = match http_range {
         HttpRange::StartingPoint(start) if start < size => start..=size - 1,
-        HttpRange::Range(range) if range.end() < size => range.start()..=range.end(),
+        HttpRange::Range(range) if range.start() < size => {
+            range.start()..=range.end().min(size - 1)
+        }
         HttpRange::Suffix(suffix) if suffix > 0 && suffix <= size => size - suffix..=size - 1,
         _ => {
             let content_range = HttpContentRange::Unsatisfiable(Unsatisfiable::new(size));