Add default headers as request is built in Client::request

src/async_impl/client.rs

@@ -2442,7 +2442,14 @@ impl Client {
     ///
     /// This method fails whenever the supplied `Url` cannot be parsed.
     pub fn request<U: IntoUrl>(&self, method: Method, url: U) -> RequestBuilder {
-        let req = url.into_url().map(move |url| Request::new(method, url));
+        let req = url.into_url().map(move |url| {
+            let mut req = Request::new(method, url);
+            let headers = req.headers_mut();
+            for (key, value) in &self.inner.headers {
+                headers.insert(key, value.clone());
+            }
+            req
+        });
         RequestBuilder::new(self.clone(), req)
     }
 

src/blocking/client.rs

@@ -1289,7 +1289,14 @@ impl Client {
     ///
     /// This method fails whenever supplied `Url` cannot be parsed.
     pub fn request<U: IntoUrl>(&self, method: Method, url: U) -> RequestBuilder {
-        let req = url.into_url().map(move |url| Request::new(method, url));
+        let req = url.into_url().map(move |url| {
+            let mut req = Request::new(method, url);
+            let headers = req.headers_mut();
+            for (key, value) in &self.inner.headers {
+                headers.insert(key, value.clone());
+            }
+            req
+        });
         RequestBuilder::new(self.clone(), req)
     }
 

tests/client.rs

@@ -4,7 +4,10 @@ mod support;
 
 use support::server;
 
-use http::header::{CONTENT_LENGTH, CONTENT_TYPE, TRANSFER_ENCODING};
+use http::{
+    header::{CONTENT_LENGTH, CONTENT_TYPE, TRANSFER_ENCODING},
+    HeaderMap, HeaderValue,
+};
 #[cfg(feature = "json")]
 use std::collections::HashMap;
 
@@ -528,3 +531,21 @@ async fn error_has_url() {
     let err = reqwest::get(u).await.unwrap_err();
     assert_eq!(err.url().map(AsRef::as_ref), Some(u), "{err:?}");
 }
+
+#[test]
+fn client_request_builder_includes_default_headers() {
+    let mut headers = HeaderMap::new();
+    headers.insert("X-MY-HEADER", HeaderValue::from_static("value"));
+    let client = Client::builder()
+        .default_headers(headers)
+        .build()
+        .expect("build client");
+    let req = client
+        .get("http://google.com")
+        .build()
+        .expect("build request");
+    assert!(req
+        .headers()
+        .get("X-MY-HEADER")
+        .is_some_and(|v| v == HeaderValue::from_static("value")));
+}