Provide optional features on tokio crate (#808)

Disabling all features means the only dependency is `futures`.

Relevant pieces of the API can then be enabled with the following features:

- `codec`
- `fs`
- `io`
- `reactor`
- `tcp`
- `timer`
- `udp`
- `uds`

This also introduces the beginnings of enabling only certain pieces of the `Runtime`. As a start, the entire default runtime API is enabled via the `rt-full` feature.

.travis.yml

@@ -22,6 +22,22 @@ matrix:
   - env: TARGET=i686-unknown-freebsd
   - env: TARGET=i686-unknown-linux-gnu
 
+  # Test combinations of enabled features.
+  - rust: stable
+    script: |
+      shopt -s expand_aliases
+      alias check="cargo check --no-default-features"
+      check
+      check --features codec
+      check --features fs
+      check --features io
+      check --features reactor
+      check --features rt-full
+      check --features tcp
+      check --features timer
+      check --features udp
+      check --features uds
+
   # Test the async / await preview. We don't want to block PRs on this failing
   # though.
   - rust: nightly

Cargo.toml

@@ -43,6 +43,35 @@ members = [
 ]
 
 [features]
+default = [
+  "codec",
+  "fs",
+  "io",
+  "reactor",
+  "rt-full",
+  "tcp",
+  "timer",
+  "udp",
+  "uds",
+]
+
+codec = ["tokio-codec"]
+fs = ["tokio-fs"]
+io = ["bytes", "tokio-io"]
+reactor = ["io", "mio", "tokio-reactor"]
+rt-full = [
+  "num_cpus",
+  "reactor",
+  "timer",
+  "tokio-current-thread",
+  "tokio-executor",
+  "tokio-threadpool",
+]
+tcp = ["tokio-tcp"]
+timer = ["tokio-timer"]
+udp = ["tokio-udp"]
+uds = ["tokio-uds"]
+
 # This feature comes with no promise of stability. Things will
 # break with each patch release. Use at your own risk.
 async-await-preview = [
@@ -54,29 +83,31 @@ travis-ci = { repository = "tokio-rs/tokio" }
 appveyor = { repository = "carllerche/tokio", id = "s83yxhy9qeb58va7" }
 
 [dependencies]
-bytes = "0.4"
-num_cpus = "1.8.0"
-tokio-codec = { version = "0.1.0", path = "tokio-codec" }
-tokio-current-thread = { version = "0.1.3", path = "tokio-current-thread" }
-tokio-io = { version = "0.1.6", path = "tokio-io" }
-tokio-executor = { version = "0.1.5", path = "tokio-executor" }
-tokio-reactor = { version = "0.1.1", path = "tokio-reactor" }
-tokio-threadpool = { version = "0.1.4", path = "tokio-threadpool" }
-tokio-tcp = { version = "0.1.0", path = "tokio-tcp" }
-tokio-udp = { version = "0.1.0", path = "tokio-udp" }
-tokio-timer = { version = "0.2.8", path = "tokio-timer" }
-tokio-fs = { version = "0.1.3", path = "tokio-fs" }
-
+# Only non-optional dependency...
 futures = "0.1.20"
 
+# Everything else is optional...
+bytes = { version = "0.4", optional = true }
+num_cpus = { version = "1.8.0", optional = true }
+tokio-codec = { version = "0.1.0", path = "tokio-codec", optional = true }
+tokio-current-thread = { version = "0.1.3", path = "tokio-current-thread", optional = true }
+tokio-fs = { version = "0.1.3", path = "tokio-fs", optional = true }
+tokio-io = { version = "0.1.6", path = "tokio-io", optional = true }
+tokio-executor = { version = "0.1.5", path = "tokio-executor", optional = true }
+tokio-reactor = { version = "0.1.1", path = "tokio-reactor", optional = true }
+tokio-threadpool = { version = "0.1.4", path = "tokio-threadpool", optional = true }
+tokio-tcp = { version = "0.1.0", path = "tokio-tcp", optional = true }
+tokio-udp = { version = "0.1.0", path = "tokio-udp", optional = true }
+tokio-timer = { version = "0.2.8", path = "tokio-timer", optional = true }
+
 # Needed until `reactor` is removed from `tokio`.
-mio = "0.6.14"
+mio = { version = "0.6.14", optional = true }
 
 # Needed for async/await preview support
 tokio-async-await = { version = "0.1.0", path = "tokio-async-await", optional = true }
 
 [target.'cfg(unix)'.dependencies]
-tokio-uds = { version = "0.2.1", path = "tokio-uds" }
+tokio-uds = { version = "0.2.1", path = "tokio-uds", optional = true }
 
 [dev-dependencies]
 env_logger = { version = "0.5", default-features = false }
@@ -92,18 +123,18 @@ serde_json = "1.0"
 time = "0.1"
 
 [patch.crates-io]
-tokio = { path = "." }
-tokio-async-await  = { path = "./tokio-async-await" }
-tokio-codec = { path = "./tokio-codec" }
-tokio-current-thread = { path = "./tokio-current-thread" }
-tokio-executor = { path = "./tokio-executor" }
-tokio-fs = { path = "./tokio-fs" }
-tokio-io = { path = "./tokio-io" }
-tokio-reactor = { path = "./tokio-reactor" }
-tokio-signal = { path = "./tokio-signal" }
-tokio-tcp = { path = "./tokio-tcp" }
-tokio-threadpool = { path = "./tokio-threadpool" }
-tokio-timer = { path = "./tokio-timer" }
-tokio-tls = { path = "./tokio-tls" }
-tokio-udp = { path = "./tokio-udp" }
-tokio-uds = { path = "./tokio-uds" }
+#tokio = { path = "." }
+#tokio-async-await  = { path = "./tokio-async-await" }
+#tokio-codec = { path = "./tokio-codec" }
+#tokio-current-thread = { path = "./tokio-current-thread" }
+#tokio-executor = { path = "./tokio-executor" }
+#tokio-fs = { path = "./tokio-fs" }
+#tokio-io = { path = "./tokio-io" }
+#tokio-reactor = { path = "./tokio-reactor" }
+#tokio-signal = { path = "./tokio-signal" }
+#tokio-tcp = { path = "./tokio-tcp" }
+#tokio-threadpool = { path = "./tokio-threadpool" }
+#tokio-timer = { path = "./tokio-timer" }
+#tokio-tls = { path = "./tokio-tls" }
+#tokio-udp = { path = "./tokio-udp" }
+#tokio-uds = { path = "./tokio-uds" }

src/io.rs

@@ -51,6 +51,7 @@ pub use tokio_io::{
 };
 
 // standard input, output, and error
+#[cfg(feature = "fs")]
 pub use tokio_fs::{
     stdin,
     Stdin,

src/lib.rs

@@ -72,42 +72,72 @@
 //! }
 //! ```
 
-extern crate bytes;
-#[macro_use]
+macro_rules! if_runtime {
+    ($($i:item)*) => ($(
+        #[cfg(any(feature = "rt-full"))]
+        $i
+    )*)
+}
+
+#[cfg_attr(feature = "rt-full", macro_use)]
 extern crate futures;
+
+#[cfg(feature = "io")]
+extern crate bytes;
+#[cfg(feature = "reactor")]
 extern crate mio;
+#[cfg(feature = "rt-full")]
 extern crate num_cpus;
+#[cfg(feature = "rt-full")]
 extern crate tokio_current_thread;
+#[cfg(feature = "io")]
 extern crate tokio_io;
-extern crate tokio_executor;
+#[cfg(feature = "codec")]
 extern crate tokio_codec;
+#[cfg(feature = "fs")]
 extern crate tokio_fs;
+#[cfg(feature = "reactor")]
 extern crate tokio_reactor;
+#[cfg(feature = "rt-full")]
 extern crate tokio_threadpool;
+#[cfg(feature = "timer")]
 extern crate tokio_timer;
+#[cfg(feature = "tcp")]
 extern crate tokio_tcp;
+#[cfg(feature = "udp")]
 extern crate tokio_udp;
 
 #[cfg(feature = "async-await-preview")]
 extern crate tokio_async_await;
 
-#[cfg(unix)]
+#[cfg(all(unix, feature = "uds"))]
 extern crate tokio_uds;
 
+#[cfg(feature = "timer")]
 pub mod clock;
+#[cfg(feature = "codec")]
 pub mod codec;
-pub mod executor;
+#[cfg(feature = "fs")]
 pub mod fs;
+#[cfg(feature = "io")]
 pub mod io;
+#[cfg(any(feature = "tcp", feature = "udp", feature = "uds"))]
 pub mod net;
 pub mod prelude;
+#[cfg(feature = "reactor")]
 pub mod reactor;
-pub mod runtime;
+#[cfg(feature = "timer")]
 pub mod timer;
 pub mod util;
 
-pub use executor::spawn;
-pub use runtime::run;
+if_runtime! {
+    extern crate tokio_executor;
+    pub mod executor;
+    pub mod runtime;
+
+    pub use executor::spawn;
+    pub use runtime::run;
+}
 
 // ===== Experimental async/await support =====
 

src/net.rs

@@ -22,6 +22,7 @@
 //! [`UnixDatagram`]: struct.UnixDatagram.html
 //! [`UnixDatagramFramed`]: struct.UnixDatagramFramed.html
 
+#[cfg(feature = "tcp")]
 pub mod tcp {
     //! TCP bindings for `tokio`.
     //!
@@ -42,15 +43,19 @@ pub mod tcp {
     //! [`Incoming`]: struct.Incoming.html
     pub use tokio_tcp::{ConnectFuture, Incoming, TcpListener, TcpStream};
 }
+#[cfg(feature = "tcp")]
 pub use self::tcp::{TcpListener, TcpStream};
 
+#[cfg(feature = "tcp")]
 #[deprecated(note = "use `tokio::net::tcp::ConnectFuture` instead")]
 #[doc(hidden)]
 pub type ConnectFuture = self::tcp::ConnectFuture;
+#[cfg(feature = "tcp")]
 #[deprecated(note = "use `tokio::net::tcp::Incoming` instead")]
 #[doc(hidden)]
 pub type Incoming = self::tcp::Incoming;
 
+#[cfg(feature = "udp")]
 pub mod udp {
     //! UDP bindings for `tokio`.
     //!
@@ -68,16 +73,19 @@ pub mod udp {
     //! [`framed`]: struct.UdpSocket.html#method.framed
     pub use tokio_udp::{RecvDgram, SendDgram, UdpFramed, UdpSocket};
 }
+#[cfg(feature = "udp")]
 pub use self::udp::{UdpFramed, UdpSocket};
 
+#[cfg(feature = "udp")]
 #[deprecated(note = "use `tokio::net::udp::RecvDgram` instead")]
 #[doc(hidden)]
 pub type RecvDgram<T> = self::udp::RecvDgram<T>;
+#[cfg(feature = "udp")]
 #[deprecated(note = "use `tokio::net::udp::SendDgram` instead")]
 #[doc(hidden)]
 pub type SendDgram<T> = self::udp::SendDgram<T>;
 
-#[cfg(unix)]
+#[cfg(all(unix, feature = "uds"))]
 pub mod unix {
     //! Unix domain socket bindings for `tokio` (only available on unix systems).
 
@@ -86,5 +94,5 @@ pub mod unix {
         UnixListener, UnixStream,
     };
 }
-#[cfg(unix)]
+#[cfg(all(unix, feature = "uds"))]
 pub use self::unix::{UnixDatagram, UnixDatagramFramed, UnixListener, UnixStream};

src/prelude.rs

@@ -10,6 +10,7 @@
 //!
 //! The prelude may grow over time as additional items see ubiquitous use.
 
+#[cfg(feature = "io")]
 pub use tokio_io::{
     AsyncRead,
     AsyncWrite,

src/runtime/current_thread/mod.rs

@@ -90,3 +90,18 @@ where
     r.run().expect("failed to resolve remaining futures");
     Ok(v)
 }
+
+/// Start a current-thread runtime using the supplied future to bootstrap execution.
+///
+/// # Panics
+///
+/// This function panics if called from the context of an executor.
+pub fn run<F>(future: F)
+where
+    F: Future<Item = (), Error = ()> + 'static,
+{
+
+    let mut r = Runtime::new().expect("failed to start runtime on current thread");
+    r.spawn(future);
+    r.run().expect("failed to resolve remaining futures");
+}