Extend BaseClient to accept extra middleware (#8807)

This PR is a revival of #3502, albeit in a much simpler form.

This would allow for different middlewares like authentication and such,
useful for if you want to deviate from the keychain authentication
methods when using uv as a library.

@zanieb I hope I made the changes as you noted you wanted to see them :)

Happy to add/change anything you need.

crates/uv-client/src/base_client.rs

@@ -1,6 +1,6 @@
 use itertools::Itertools;
 use reqwest::{Client, ClientBuilder, Response};
-use reqwest_middleware::ClientWithMiddleware;
+use reqwest_middleware::{ClientWithMiddleware, Middleware};
 use reqwest_retry::policies::ExponentialBackoff;
 use reqwest_retry::{
     DefaultRetryableStrategy, RetryTransientMiddleware, Retryable, RetryableStrategy,
@@ -8,6 +8,7 @@ use reqwest_retry::{
 use std::error::Error;
 use std::fmt::Debug;
 use std::path::Path;
+use std::sync::Arc;
 use std::time::Duration;
 use std::{env, iter};
 use tracing::debug;
@@ -54,6 +55,19 @@ pub struct BaseClientBuilder<'a> {
     platform: Option<&'a Platform>,
     auth_integration: AuthIntegration,
     default_timeout: Duration,
+    extra_middleware: Option<ExtraMiddleware>,
+}
+
+/// A list of user-defined middlewares to be applied to the client.
+#[derive(Clone)]
+pub struct ExtraMiddleware(pub Vec<Arc<dyn Middleware>>);
+
+impl Debug for ExtraMiddleware {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("ExtraMiddleware")
+            .field("0", &format!("{} middlewares", self.0.len()))
+            .finish()
+    }
 }
 
 impl Default for BaseClientBuilder<'_> {
@@ -75,6 +89,7 @@ impl BaseClientBuilder<'_> {
             platform: None,
             auth_integration: AuthIntegration::default(),
             default_timeout: Duration::from_secs(30),
+            extra_middleware: None,
         }
     }
 }
@@ -140,6 +155,12 @@ impl<'a> BaseClientBuilder<'a> {
         self
     }
 
+    #[must_use]
+    pub fn extra_middleware(mut self, middleware: ExtraMiddleware) -> Self {
+        self.extra_middleware = Some(middleware);
+        self
+    }
+
     pub fn is_offline(&self) -> bool {
         matches!(self.connectivity, Connectivity::Offline)
     }
@@ -313,6 +334,13 @@ impl<'a> BaseClientBuilder<'a> {
                     }
                 }
 
+                // When supplied add the extra middleware
+                if let Some(extra_middleware) = &self.extra_middleware {
+                    for middleware in &extra_middleware.0 {
+                        client = client.with_arc(middleware.clone());
+                    }
+                }
+
                 client.build()
             }
             Connectivity::Offline => reqwest_middleware::ClientBuilder::new(client)

crates/uv-client/src/registry_client.rs

@@ -26,7 +26,7 @@ use uv_pep508::MarkerEnvironment;
 use uv_platform_tags::Platform;
 use uv_pypi_types::{ResolutionMetadata, SimpleJson};
 
-use crate::base_client::BaseClientBuilder;
+use crate::base_client::{BaseClientBuilder, ExtraMiddleware};
 use crate::cached_client::CacheControl;
 use crate::html::SimpleHtml;
 use crate::remote_metadata::wheel_metadata_from_remote_zip;
@@ -110,6 +110,12 @@ impl<'a> RegistryClientBuilder<'a> {
         self
     }
 
+    #[must_use]
+    pub fn extra_middleware(mut self, middleware: ExtraMiddleware) -> Self {
+        self.base_client_builder = self.base_client_builder.extra_middleware(middleware);
+        self
+    }
+
     #[must_use]
     pub fn markers(mut self, markers: &'a MarkerEnvironment) -> Self {
         self.base_client_builder = self.base_client_builder.markers(markers);