Don't set User-Agent header by default

src/async_impl/client.rs

@@ -1,3 +1,4 @@
+use std::convert::TryInto;
 use std::net::IpAddr;
 use std::sync::Arc;
 #[cfg(feature = "cookies")]
@@ -36,8 +37,6 @@ use crate::tls::TlsBackend;
 use crate::{Certificate, Identity};
 use crate::{IntoUrl, Method, Proxy, StatusCode, Url};
 
-static DEFAULT_USER_AGENT: &str = concat!(env!("CARGO_PKG_NAME"), "/", env!("CARGO_PKG_VERSION"));
-
 /// An asynchronous `Client` to make Requests with.
 ///
 /// The Client has various configuration values to tweak, but the defaults
@@ -85,6 +84,7 @@ struct Config {
     nodelay: bool,
     #[cfg(feature = "cookies")]
     cookie_store: Option<cookie::CookieStore>,
+    error: Option<crate::Error>,
 }
 
 impl Default for ClientBuilder {
@@ -99,11 +99,11 @@ impl ClientBuilder {
     /// This is the same as `Client::builder()`.
     pub fn new() -> ClientBuilder {
         let mut headers: HeaderMap<HeaderValue> = HeaderMap::with_capacity(2);
-        headers.insert(USER_AGENT, HeaderValue::from_static(DEFAULT_USER_AGENT));
         headers.insert(ACCEPT, HeaderValue::from_static("*/*"));
 
         ClientBuilder {
             config: Config {
+                error: None,
                 gzip: cfg!(feature = "gzip"),
                 headers,
                 #[cfg(feature = "native-tls")]
@@ -143,6 +143,11 @@ impl ClientBuilder {
     /// cannot load the system configuration.
     pub fn build(self) -> crate::Result<Client> {
         let config = self.config;
+
+        if let Some(err) = config.error {
+            return Err(err);
+        }
+
         let mut proxies = config.proxies;
         if config.auto_sys_proxy {
             proxies.push(Proxy::system());
@@ -151,8 +156,8 @@ impl ClientBuilder {
 
         let mut connector = {
             #[cfg(feature = "__tls")]
-            fn user_agent(headers: &HeaderMap) -> HeaderValue {
-                headers[USER_AGENT].clone()
+            fn user_agent(headers: &HeaderMap) -> Option<HeaderValue> {
+                headers.get(USER_AGENT).cloned()
             }
 
             #[cfg(feature = "__tls")]
@@ -270,6 +275,42 @@ impl ClientBuilder {
 
     // Higher-level options
 
+
+    /// Sets the `User-Agent` header to be used by this client.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # async fn doc() -> Result<(), reqwest::Error> {
+    /// // Name your user agent after your app?
+    /// static APP_USER_AGENT: &str = concat!(
+    ///     env!("CARGO_PKG_NAME"),
+    ///     "/",
+    ///     env!("CARGO_PKG_VERSION"),
+    /// );
+    ///
+    /// let client = reqwest::Client::builder()
+    ///     .user_agent(APP_USER_AGENT)
+    ///     .build()?;
+    /// let res = client.get("https://www.rust-lang.org").send().await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn user_agent<V>(mut self, value: V) -> ClientBuilder
+    where
+        V: TryInto<HeaderValue>,
+        V::Error: Into<http::Error>,
+    {
+        match value.try_into() {
+            Ok(value) => {
+                self.config.headers.insert(USER_AGENT, value);
+            }
+            Err(e) => {
+                self.config.error = Some(crate::error::builder(e.into()));
+            }
+        };
+        self
+    }
     /// Sets the default headers for every request.
     ///
     /// # Example

src/blocking/client.rs

@@ -1,3 +1,4 @@
+use std::convert::TryInto;
 use std::fmt;
 use std::future::Future;
 use std::net::IpAddr;
@@ -7,7 +8,7 @@ use std::time::Duration;
 
 use futures_channel::{mpsc, oneshot};
 use futures_util::{StreamExt, TryFutureExt};
-
+use http::header::HeaderValue;
 use log::{error, trace};
 
 use super::request::{Request, RequestBuilder};
@@ -87,6 +88,35 @@ impl ClientBuilder {
 
     // Higher-level options
 
+
+    /// Sets the `User-Agent` header to be used by this client.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # fn doc() -> Result<(), reqwest::Error> {
+    /// // Name your user agent after your app?
+    /// static APP_USER_AGENT: &str = concat!(
+    ///     env!("CARGO_PKG_NAME"),
+    ///     "/",
+    ///     env!("CARGO_PKG_VERSION"),
+    /// );
+    ///
+    /// let client = reqwest::blocking::Client::builder()
+    ///     .user_agent(APP_USER_AGENT)
+    ///     .build()?;
+    /// let res = client.get("https://www.rust-lang.org").send()?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn user_agent<V>(mut self, value: V) -> ClientBuilder
+    where
+        V: TryInto<HeaderValue>,
+        V::Error: Into<http::Error>,
+    {
+        self.with_inner(move |inner| inner.user_agent(value))
+    }
+
     /// Sets the default headers for every request.
     ///
     /// # Example

src/connect.rs

@@ -41,7 +41,7 @@ pub(crate) struct Connector {
     #[cfg(feature = "__tls")]
     nodelay: bool,
     #[cfg(feature = "__tls")]
-    user_agent: HeaderValue,
+    user_agent: Option<HeaderValue>,
 }
 
 #[derive(Clone)]
@@ -82,7 +82,7 @@ impl Connector {
     pub(crate) fn new_default_tls<T>(
         tls: TlsConnectorBuilder,
         proxies: Arc<Vec<Proxy>>,
-        user_agent: HeaderValue,
+        user_agent: Option<HeaderValue>,
         local_addr: T,
         nodelay: bool,
     ) -> crate::Result<Connector>
@@ -108,7 +108,7 @@ impl Connector {
     pub(crate) fn new_rustls_tls<T>(
         tls: rustls::ClientConfig,
         proxies: Arc<Vec<Proxy>>,
-        user_agent: HeaderValue,
+        user_agent: Option<HeaderValue>,
         local_addr: T,
         nodelay: bool,
     ) -> crate::Result<Connector>
@@ -515,7 +515,7 @@ async fn tunnel<T>(
     mut conn: T,
     host: String,
     port: u16,
-    user_agent: HeaderValue,
+    user_agent: Option<HeaderValue>,
     auth: Option<HeaderValue>,
 ) -> Result<T, io::Error>
 where
@@ -534,9 +534,11 @@ where
 
 
     // user-agent
-    buf.extend_from_slice(b"User-Agent: ");
-    buf.extend_from_slice(user_agent.as_bytes());
-    buf.extend_from_slice(b"\r\n");
+    if let Some(user_agent) = user_agent {
+        buf.extend_from_slice(b"User-Agent: ");
+        buf.extend_from_slice(user_agent.as_bytes());
+        buf.extend_from_slice(b"\r\n");
+    }
 
 
     // proxy-authorization
@@ -888,8 +890,8 @@ mod tests {
         }};
     }
 
-    fn ua() -> http::header::HeaderValue {
-        http::header::HeaderValue::from_static(TUNNEL_UA)
+    fn ua() -> Option<http::header::HeaderValue> {
+        Some(http::header::HeaderValue::from_static(TUNNEL_UA))
     }
 
     #[test]

tests/client.rs

@@ -11,7 +11,7 @@ async fn auto_headers() {
             assert_eq!(req.method(), "GET");
 
             assert_eq!(req.headers()["accept"], "*/*");
-            assert_eq!(req.headers()["user-agent"], DEFAULT_USER_AGENT);
+            assert_eq!(req.headers().get("user-agent"), None);
             if cfg!(feature = "gzip") {
                 assert_eq!(req.headers()["accept-encoding"], "gzip");
             }
@@ -28,6 +28,27 @@ async fn auto_headers() {
     assert_eq!(res.remote_addr(), Some(server.addr()));
 }
 
+#[tokio::test]
+async fn user_agent() {
+    let server = server::http(move |req| {
+        async move {
+            assert_eq!(req.headers()["user-agent"], "reqwest-test-agent");
+            http::Response::default()
+        }
+    });
+
+    let url = format!("http://{}/ua", server.addr());
+    let res = reqwest::Client::builder()
+        .user_agent("reqwest-test-agent")
+        .build()
+        .expect("client builder")
+        .get(&url)
+        .await
+        .expect("request");
+
+    assert_eq!(res.status(), reqwest::StatusCode::OK);
+}
+
 #[tokio::test]
 async fn response_text() {
     let _ = env_logger::try_init();