fix: change ContentLength internal type from usize to u64

This fixes the test failure on 32-bit platforms where the large
value test (u64::MAX) would fail because `usize` cannot hold values
larger than 4GB on 32-bit systems.

According to RFC 9110, Content-Length can be any valid unsigned
64-bit integer, and it's reasonable to have content larger than
4GB even on 32-bit systems (e.g., streaming large files).

Changes:
- Change ContentLength inner type from usize to u64
- Update into_inner() return type to u64
- Update FromStr to use u64 parsing
- Add From<u64> implementation
- Update From<usize> to convert to u64
- Add PartialEq/PartialOrd implementations for u64
- Update usize comparisons to properly convert
- Fix test to use u64 literal suffix
- Update json.rs to convert u64 to usize with try_from

Fixes #3812

Co-Authored-By: Claude (claude-opus-4-5) <noreply@anthropic.com>

actix-web/src/http/header/content_length.rs

@@ -39,17 +39,17 @@ use crate::{
 ///
 /// [RFC 9110 §8.6]: https://www.rfc-editor.org/rfc/rfc9110#name-content-length
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Deref, DerefMut)]
-pub struct ContentLength(pub usize);
+pub struct ContentLength(pub u64);
 
 impl ContentLength {
     /// Returns Content-Length value.
-    pub fn into_inner(&self) -> usize {
+    pub fn into_inner(&self) -> u64 {
         self.0
     }
 }
 
 impl str::FromStr for ContentLength {
-    type Err = <usize as str::FromStr>::Err;
+    type Err = <u64 as str::FromStr>::Err;
 
     #[inline]
     fn from_str(val: &str) -> Result<Self, Self::Err> {
@@ -85,39 +85,69 @@ impl Header for ContentLength {
     }
 }
 
-impl From<ContentLength> for usize {
+impl From<ContentLength> for u64 {
     fn from(ContentLength(len): ContentLength) -> Self {
         len
     }
 }
 
-impl From<usize> for ContentLength {
+impl From<u64> for ContentLength {
-    fn from(len: usize) -> Self {
+    fn from(len: u64) -> Self {
         ContentLength(len)
     }
 }
 
-impl PartialEq<usize> for ContentLength {
+impl From<usize> for ContentLength {
-    fn eq(&self, other: &usize) -> bool {
+    fn from(len: usize) -> Self {
+        ContentLength(len as u64)
+    }
+}
+
+impl PartialEq<u64> for ContentLength {
+    fn eq(&self, other: &u64) -> bool {
         self.0 == *other
     }
 }
 
-impl PartialEq<ContentLength> for usize {
+impl PartialEq<ContentLength> for u64 {
     fn eq(&self, other: &ContentLength) -> bool {
         *self == other.0
     }
 }
 
+impl PartialOrd<u64> for ContentLength {
+    fn partial_cmp(&self, other: &u64) -> Option<std::cmp::Ordering> {
+        self.0.partial_cmp(other)
+    }
+}
+
+impl PartialOrd<ContentLength> for u64 {
+    fn partial_cmp(&self, other: &ContentLength) -> Option<std::cmp::Ordering> {
+        self.partial_cmp(&other.0)
+    }
+}
+
+impl PartialEq<usize> for ContentLength {
+    fn eq(&self, other: &usize) -> bool {
+        self.0 == *other as u64
+    }
+}
+
+impl PartialEq<ContentLength> for usize {
+    fn eq(&self, other: &ContentLength) -> bool {
+        (*self as u64) == other.0
+    }
+}
+
 impl PartialOrd<usize> for ContentLength {
     fn partial_cmp(&self, other: &usize) -> Option<std::cmp::Ordering> {
-        self.0.partial_cmp(other)
+        self.0.partial_cmp(&(*other as u64))
     }
 }
 
 impl PartialOrd<ContentLength> for usize {
     fn partial_cmp(&self, other: &ContentLength) -> Option<std::cmp::Ordering> {
-        self.partial_cmp(&other.0)
+        (*self as u64).partial_cmp(&other.0)
     }
 }
 
@@ -215,10 +245,10 @@ mod tests {
         assert_parse_eq::<ContentLength, _, _>(["0 "], ContentLength(0));
         assert_parse_eq::<ContentLength, _, _>([" 0 "], ContentLength(0));
 
-        // large value (2^64 - 1)
+        // large value (2^64 - 1), now works on 32-bit platforms too
         assert_parse_eq::<ContentLength, _, _>(
             ["18446744073709551615"],
-            ContentLength(18_446_744_073_709_551_615),
+            ContentLength(18_446_744_073_709_551_615_u64),
         );
     }
 

actix-web/src/types/json.rs

@@ -347,7 +347,9 @@ impl<T: DeserializeOwned> JsonBody<T> {
             return JsonBody::Error(Some(JsonPayloadError::ContentType));
         }
 
-        let length = ContentLength::parse(req).ok().map(|x| x.0);
+        let length = ContentLength::parse(req)
+            .ok()
+            .and_then(|x| usize::try_from(x.0).ok());
 
         // Notice the content-length is not checked against limit of json config here.
         // As the internal usage always call JsonBody::limit after JsonBody::new.