crates-io: Set Content-Type: application/json only for requests wit…

…h a body payload

crates/crates-io/lib.rs

@@ -389,7 +389,9 @@ impl Registry {
         self.handle.url(&format!("{}/api/v1{}", self.host, path))?;
         let mut headers = List::new();
         headers.append("Accept: application/json")?;
-        headers.append("Content-Type: application/json")?;
+        if body.is_some() {
+            headers.append("Content-Type: application/json")?;
+        }
 
         if self.auth_required || authorized == Auth::Authorized {
             headers.append(&format!("Authorization: {}", self.token()?))?;

src/doc/src/reference/registry-web-api.md

@@ -40,7 +40,7 @@ be required in the future.
 
 Cargo sets the following headers for all requests:
 
-- `Content-Type`: `application/json`
+- `Content-Type`: `application/json` (for requests with a body payload)
 - `Accept`: `application/json`
 - `User-Agent`: The Cargo version such as `cargo 1.32.0 (8610973aa
   2019-01-02)`. This may be modified by the user in a configuration value.