fix: Make content_length optional

To make it possible to distinguish whether the response has no content
or contains an empty content, wraps `content_length` with `Option`.
Without having 'Content-Length: 0' for an empty content, a client may
wait for the server to close the connection or for a timeout to occur.

Signed-off-by: Takahiro Itazuri <itazur@amazon.com>

CHANGELOG.md

@@ -11,6 +11,7 @@
 
 - Mark `HttpServer::new_from_fd` as `unsafe` as the correctness of the unsafe code
   in this method relies on an invariant the caller has to uphold
+- Set `Content-Length: 0` when setting an empty body in the response.
 
 # v0.1.0
 

src/response.rs

@@ -86,7 +86,7 @@ impl StatusLine {
 /// The content type can be updated with a call to `set_content_type`.
 #[derive(Debug, PartialEq, Eq)]
 pub struct ResponseHeaders {
-    content_length: i32,
+    content_length: Option<i32>,
     content_type: MediaType,
     deprecation: bool,
     server: String,
@@ -151,15 +151,15 @@ impl ResponseHeaders {
         self.write_allow_header(buf)?;
         self.write_deprecation_header(buf)?;
 
-        if self.content_length != 0 {
+        if let Some(content_length) = self.content_length {
             buf.write_all(Header::ContentType.raw())?;
             buf.write_all(&[COLON, SP])?;
             buf.write_all(self.content_type.as_str().as_bytes())?;
             buf.write_all(&[CR, LF])?;
 
             buf.write_all(Header::ContentLength.raw())?;
             buf.write_all(&[COLON, SP])?;
-            buf.write_all(self.content_length.to_string().as_bytes())?;
+            buf.write_all(content_length.to_string().as_bytes())?;
             buf.write_all(&[CR, LF])?;
 
             if self.accept_encoding {
@@ -175,7 +175,7 @@ impl ResponseHeaders {
 
     // Sets the content length to be written in the HTTP response.
     fn set_content_length(&mut self, content_length: i32) {
-        self.content_length = content_length;
+        self.content_length = Some(content_length);
     }
 
     /// Sets the HTTP response header server.
@@ -296,7 +296,7 @@ impl Response {
 
     /// Returns the Content Length of the response.
     pub fn content_length(&self) -> i32 {
-        self.headers.content_length
+        self.headers.content_length.unwrap_or(0)
     }
 
     /// Returns the Content Type of the response.
@@ -480,4 +480,20 @@ mod tests {
         let another_response = Response::new(Version::Http10, StatusCode::BadRequest);
         assert_ne!(response, another_response);
     }
+
+    #[test]
+    fn test_content_length() {
+        let mut response = Response::new(Version::Http10, StatusCode::OK);
+
+        // When not calling `set_body()`, the content_length must be 0 and the body must be None.
+        assert_eq!(response.content_length(), 0);
+        assert_eq!(response.body(), None);
+
+        // When calling `set_body()` with an empty content, the content_length must also be 0
+        // and the body is an empty content.
+        let body = Body::new("");
+        response.set_body(body.clone());
+        assert_eq!(response.content_length(), 0);
+        assert_eq!(response.body(), Some(body));
+    }
 }