attic: Split out stream feature

Right now it just depends on tokio, but the goal is to support
alternative async runtimes.

attic/Cargo.toml

@@ -50,14 +50,19 @@ tempfile = "3"
 version-compare = "0.2.0"
 
 [features]
-default = [ "nix_store", "tokio" ]
+default = [
+	"nix_store",
+	"stream",
+	"tokio",
+]
 
 # Native libnixstore bindings.
 #
 # When disabled, the native Rust portions of nix_store can still be used.
-nix_store = [ "dep:cxx", "dep:cxx-build", "tokio/rt" ]
+nix_store = ["tokio", "dep:cxx", "dep:cxx-build"]
 
-# Tokio.
-#
-# When disabled, any part depending on tokio is unavailable.
-tokio = [ "dep:tokio", "dep:async-stream" ]
+# Stream utilities.
+stream = ["tokio", "dep:async-stream"]
+
+# Tokio runtime.
+tokio = ["dep:tokio", "tokio/rt"]

attic/src/lib.rs

@@ -22,7 +22,7 @@ pub mod hash;
 pub mod mime;
 pub mod nix_store;
 pub mod signing;
-#[cfg(feature = "tokio")]
+#[cfg(feature = "stream")]
 pub mod stream;
 #[cfg(target_family = "unix")]
 pub mod testing;

server/Cargo.toml

@@ -19,7 +19,7 @@ path = "src/adm/main.rs"
 doc = false
 
 [dependencies]
-attic = { path = "../attic", default-features = false, features = [ "tokio" ] }
+attic = { path = "../attic", default-features = false, features = ["stream", "tokio"] }
 attic-token = { path = "../token" }
 
 anyhow = "1.0.71"