api: Stop adding Content-Type to requests without any fields

crates/ruma-api-macros/src/request/outgoing.rs

@@ -97,9 +97,22 @@ impl Request {
             quote! { "" }
         };
 
-        let mut header_kvs: TokenStream = self
-            .header_fields()
-            .map(|request_field| {
+        // If there are no body fields, the request body will be empty (not `{}`), so the
+        // `application/json` content-type would be wrong. It may also cause problems with CORS
+        // policies that don't allow the `Content-Type` header (for things such as `.well-known`
+        // that are commonly handled by something else than a homeserver).
+        let mut header_kvs = if self.raw_body_field().is_some() || self.has_body_fields() {
+            TokenStream::new()
+        } else {
+            quote! {
+                req_headers.insert(
+                    #http::header::CONTENT_TYPE,
+                    #http::header::HeaderValue::from_static("application/json"),
+                );
+            }
+        };
+
+        header_kvs.extend(self.header_fields().map(|request_field| {
             let (field, header_name) = match request_field {
                 RequestField::Header(field, header_name) => (field, header_name),
                 _ => unreachable!("expected request field to be header variant"),
@@ -127,10 +140,9 @@ impl Request {
                     );
                 },
             }
-            })
-            .collect();
+        }));
 
-        let hdr_kv = match self.authentication {
+        header_kvs.extend(match self.authentication {
             AuthScheme::AccessToken(_) => quote! {
                 req_headers.insert(
                     #http::header::AUTHORIZATION,
@@ -153,8 +165,7 @@ impl Request {
                 }
             },
             AuthScheme::QueryOnlyAccessToken(_) | AuthScheme::ServerSignatures(_) => quote! {},
-        };
-        header_kvs.extend(hdr_kv);
+        });
 
         let request_body = if let Some(field) = self.raw_body_field() {
             let field_name = field.ident.as_ref().expect("expected field to have an identifier");
@@ -203,11 +214,7 @@ impl Request {
                             base_url.strip_suffix('/').unwrap_or(base_url),
                             #request_path_string,
                             #request_query_string,
-                        ))
-                        .header(
-                            #ruma_api::exports::http::header::CONTENT_TYPE,
-                            "application/json",
-                        );
+                        ));
 
                     if let Some(mut req_headers) = req_builder.headers_mut() {
                         #header_kvs

crates/ruma-api/CHANGELOG.md

@@ -1,5 +1,12 @@
 # [unreleased]
 
+Bug fixes:
+
+* Stop adding a `Content-Type` header to requests without any fields
+  * This fixes usage of the `.well-known` endpoints in a browser WASM
+    environment if the server isn't configured to allow that header for
+    cross-origin requests
+
 # 0.18.3
 
 Improvements: