Auto detect proxy from environments

src/agent.rs

@@ -37,6 +37,7 @@ pub enum RedirectAuthHeaders {
 /// Accumulates options towards building an [Agent].
 pub struct AgentBuilder {
     config: AgentConfig,
+    try_proxy_from_env: bool,
     max_idle_connections: usize,
     max_idle_connections_per_host: usize,
     /// Cookies saved between requests.
@@ -263,6 +264,7 @@ impl AgentBuilder {
                 user_agent: format!("ureq/{}", env!("CARGO_PKG_VERSION")),
                 tls_config: TlsConfig(crate::default_tls_config()),
             },
+            try_proxy_from_env: false,
             max_idle_connections: DEFAULT_MAX_IDLE_CONNECTIONS,
             max_idle_connections_per_host: DEFAULT_MAX_IDLE_CONNECTIONS_PER_HOST,
             resolver: StdResolver.into(),
@@ -277,7 +279,12 @@ impl AgentBuilder {
     // AgentBuilder to be used multiple times, except CookieStore does
     // not implement clone, so we have to give ownership to the newly
     // built Agent.
-    pub fn build(self) -> Agent {
+    pub fn build(mut self) -> Agent {
+        if self.config.proxy.is_none() && self.try_proxy_from_env {
+            if let Some(proxy) = Proxy::try_from_system() {
+                self.config.proxy = Some(proxy);
+            }
+        }
         Agent {
             config: Arc::new(self.config),
             state: Arc::new(AgentState {
@@ -306,11 +313,24 @@ impl AgentBuilder {
     /// # Ok(())
     /// # }
     /// ```
+    ///
+    /// Adding a proxy will disable `try_proxy_from_env`.
     pub fn proxy(mut self, proxy: Proxy) -> Self {
         self.config.proxy = Some(proxy);
         self
     }
 
+    /// Attempt to detect proxy settings from the environment, i.e. HTTP_PROXY
+    ///
+    /// The default is `false`, i.e. not detecting proxy from env since this is
+    /// a potential security risk.
+    ///
+    /// If the `proxy` is set on the builder, this setting has no effect.
+    pub fn try_proxy_from_env(mut self, do_try: bool) -> Self {
+        self.try_proxy_from_env = do_try;
+        self
+    }
+
     /// Enforce the client to only perform HTTPS requests.
     /// This setting also makes the client refuse HTTPS to HTTP redirects.
     /// Default is false

src/proxy.rs

@@ -67,6 +67,30 @@ impl Proxy {
         self.user.is_some() && self.password.is_some()
     }
 
+    pub(crate) fn try_from_system() -> Option<Self> {
+        macro_rules! try_env {
+            ($($env:literal),+) => {
+                $(
+                    if let Ok(env) = std::env::var($env) {
+                        if let Ok(proxy) = Self::new(env) {
+                            return Some(proxy);
+                        }
+                    }
+                )+
+            };
+        }
+
+        try_env!(
+            "ALL_PROXY",
+            "all_proxy",
+            "HTTPS_PROXY",
+            "https_proxy",
+            "HTTP_PROXY",
+            "http_proxy"
+        );
+        None
+    }
+
     /// Create a proxy from a format string.
     /// # Arguments:
     /// * `proxy` - a str of format `<protocol>://<user>:<password>@<host>:port` . All parts except host are optional.