Use free_usize instead of a u64::try_from in gif.rs

src/codecs/gif.rs

@@ -174,10 +174,7 @@ impl<'a, R: 'a + Read> ImageDecoder<'a> for GifDecoder<R> {
 
             let mut frame_buffer = vec![0; buffer_size];
 
-            self.limits.free(
-                u64::try_from(buffer_size)
-                    .expect("if buffer_size overflows a usize, we should have returned already"),
-            );
+            self.limits.free_usize(buffer_size);
 
             self.reader
                 .read_into_buffer(&mut frame_buffer[..])

src/io/mod.rs

@@ -1,5 +1,7 @@
 //! Input and output of images.
 
+use std::convert::TryFrom;
+
 use crate::{error, ImageError, ImageResult};
 
 pub(crate) mod free_functions;
@@ -124,8 +126,6 @@ impl Limits {
 
     /// This function acts identically to [`reserve`], but takes a `usize` for convenience.
     pub fn reserve_usize(&mut self, amount: usize) -> ImageResult<()> {
-        use std::convert::TryFrom;
-
         match u64::try_from(amount) {
             Ok(n) => self.reserve(n),
             Err(_) if self.max_alloc.is_some() => {
@@ -149,4 +149,17 @@ impl Limits {
             *max_alloc = max_alloc.saturating_add(amount);
         }
     }
+
+    /// This function acts identically to [`free`], but takes a `usize` for convenience.
+    pub fn free_usize(&mut self, amount: usize) {
+        match u64::try_from(amount) {
+            Ok(n) => self.free(n),
+            Err(_) if self.max_alloc.is_some() => {
+                panic!("max_alloc is set, we should have exited earlier when the reserve failed");
+            }
+            Err(_) => {
+                // Out of bounds, but we weren't asked to consider any limit.
+            }
+        }
+    }
 }

tests/regression.rs

@@ -71,7 +71,7 @@ fn bad_gif_oom() {
     // It then exits normally with an EOF when reading.
     //
     // So instead we look for a limits error (or an unsupported error, for the case that we're
-    // running these tests without bmp being actually supported)
+    // running these tests without gif being actually supported)
     let error = image::load_from_memory(&data).unwrap_err();
 
     assert!(