Pick the checkout for the right host, too

Ref: #107

src/main.rs

@@ -68,7 +68,8 @@ fn actual_main() -> Result<(), i32> {
         (false, false) => packages = cargo_update::ops::intersect_packages(&packages, &opts.to_update, opts.install),
     }
 
-    let registry = cargo_update::ops::get_index_path(&opts.cargo_dir.1).map_err(|e| {
+    let registry_url = cargo_update::ops::get_index_url(&crates_file);
+    let registry = cargo_update::ops::get_index_path(&opts.cargo_dir.1, Some(&registry_url)).map_err(|e| {
             println!("Couldn't get package repository: {}.", e);
             2
         })?;
@@ -77,7 +78,7 @@ fn actual_main() -> Result<(), i32> {
             2
         })?;
     cargo_update::ops::update_index(&mut registry_repo,
-                                    &cargo_update::ops::get_index_url(&crates_file),
+                                    &registry_url,
                                     http_proxy.as_ref().map(String::as_str),
                                     &mut stdout()).map_err(|e| {
             println!("Failed to update index repository: {}.", e);

src/ops/mod.rs

@@ -658,7 +658,8 @@ fn crate_versions_impl(buf: String) -> Vec<Semver> {
         .collect()
 }
 
-/// Get the location of the latest registry index in the specified cargo directory.
+/// Get the location of the latest registry index whose name optionally starts with the registry URL's domain name in the
+/// specified cargo directory.
 ///
 /// If no indices exist, an appropriate `Err` is returned.
 ///
@@ -676,15 +677,23 @@ fn crate_versions_impl(buf: String) -> Vec<Semver> {
 /// # let _ = fs::create_dir(&cargo_dir);
 /// # let idx_dir = cargo_dir.join("registry").join("index").join("github.com-1ecc6299db9ec823");
 /// # let _ = fs::create_dir_all(&idx_dir);
-/// let index = get_index_path(&cargo_dir).unwrap();
+/// // These are equivalent for most users,
+/// // but you might need to specify the URL to find the right checkout if you use more than one registry
+/// let index = get_index_path(&cargo_dir, None).unwrap();
+/// let index = get_index_path(&cargo_dir, Some("https://github.com/rust-lang/crates.io-index")).unwrap();
+///
 /// // Use find_package_data() to look for packages
 /// # assert_eq!(index, idx_dir);
 /// ```
-pub fn get_index_path(cargo_dir: &Path) -> Result<PathBuf, &'static str> {
+pub fn get_index_path(cargo_dir: &Path, registry_url: Option<&str>) -> Result<PathBuf, &'static str> {
+    let registry_url = registry_url.map(|u| Url::parse(u).map_err(|_| "registry URL not an URL")).transpose()?;
+    let registry_host = registry_url.as_ref().and_then(|u| u.host_str());
+
     Ok(fs::read_dir(cargo_dir.join("registry").join("index"))
         .map_err(|_| "index directory nonexistant")?
         .map(Result::unwrap)
         .filter(|i| i.file_type().unwrap().is_dir())
+        .filter(|i| registry_host.map(|rh| i.file_name().to_string_lossy().starts_with(rh)).unwrap_or(true))
         .max_by_key(latest_modified)
         .ok_or("empty index directory")?
         .path())