Set default user agent for external requests

Many servers will return errors (e.g. 400/403) to requests that do not
set a User-Agent header. This results in issues in both the link_checker
and load_data components. With the link_checker these are false positive
dead links. In load_data, remote data fails to be fetched. To mitigate
this issue, this sets a default User-Agent of

    $CARGO_PKG_NAME/$CARGO_PKG_VERSION

Note that the root cause of this regression from zola v0.9.0 is that
reqwest 0.10 changed their default behavior and no longer sets a
User-Agent by default:

    https://github.com/seanmonstar/reqwest/pull/751

Fixes #950.

components/link_checker/src/lib.rs

@@ -58,7 +58,10 @@ pub fn check_url(url: &str, config: &LinkChecker) -> LinkResult {
     headers.insert(ACCEPT, "text/html".parse().unwrap());
     headers.append(ACCEPT, "*/*".parse().unwrap());
 
-    let client = Client::new();
+    let client = Client::builder()
+        .user_agent(concat!(env!("CARGO_PKG_NAME"), "/", env!("CARGO_PKG_VERSION")))
+        .build()
+        .expect("reqwest client build");
 
     let check_anchor = !config.skip_anchor_prefixes.iter().any(|prefix| url.starts_with(prefix));
 
@@ -185,6 +188,22 @@ mod tests {
         assert!(res.error.is_none());
     }
 
+    #[test]
+    fn set_default_user_agent() {
+        let user_agent = concat!(env!("CARGO_PKG_NAME"), "/", env!("CARGO_PKG_VERSION"));
+        let _m1 = mock("GET", "/C4Szbfnvj6M0LoPk")
+            .match_header("User-Agent", user_agent)
+            .with_status(200)
+            .with_body("Test")
+            .create();
+
+        let url = format!("{}{}", mockito::server_url(), "/C4Szbfnvj6M0LoPk");
+        let res = check_url(&url, &LinkChecker::default());
+        assert!(res.is_valid());
+        assert!(res.code.is_some());
+        assert!(res.error.is_none());
+    }
+
     #[test]
     fn can_fail_301_to_404_links() {
         let _m1 = mock("GET", "/cav9vibhsc")

components/templates/src/global_fns/load_data.rs

@@ -178,7 +178,12 @@ pub struct LoadData {
 }
 impl LoadData {
     pub fn new(base_path: PathBuf) -> Self {
-        let client = Arc::new(Mutex::new(Client::builder().build().expect("reqwest client build")));
+        let client = Arc::new(Mutex::new(
+            Client::builder()
+                .user_agent(concat!(env!("CARGO_PKG_NAME"), "/", env!("CARGO_PKG_VERSION")))
+                .build()
+                .expect("reqwest client build"),
+        ));
         let result_cache = Arc::new(Mutex::new(HashMap::new()));
         Self { base_path, client, result_cache }
     }
@@ -443,6 +448,31 @@ mod tests {
         );
     }
 
+    #[test]
+    fn set_default_user_agent() {
+        let user_agent = concat!(env!("CARGO_PKG_NAME"), "/", env!("CARGO_PKG_VERSION"));
+        let _m = mock("GET", "/chu8aizahBiy")
+            .match_header("User-Agent", user_agent)
+            .with_header("content-type", "application/json")
+            .with_body(
+                r#"{
+  "test": {
+    "foo": "bar"
+  }
+}
+"#,
+            )
+            .create();
+
+        let url = format!("{}{}", mockito::server_url(), "/chu8aizahBiy");
+        let static_fn = LoadData::new(PathBuf::new());
+        let mut args = HashMap::new();
+        args.insert("url".to_string(), to_value(&url).unwrap());
+        args.insert("format".to_string(), to_value("json").unwrap());
+        let result = static_fn.call(&args).unwrap();
+        assert_eq!(result.get("test").unwrap().get("foo").unwrap(), &to_value("bar").unwrap());
+    }
+
     #[test]
     fn can_load_toml() {
         let static_fn = LoadData::new(PathBuf::from("../utils/test-files"));