net: switch from `log` to `tracing` (#1455)

* net: switch from `log` to `tracing`.

Motivation:

The `tracing` crate implements scoped, structured, context-aware
diagnostics, which can add significant debugging value over unstructured
log messages. `tracing` is part of the Tokio project. As part of the
`tokio` 0.2 changes, I thought it would be good to move over from `log`
to `tracing` in the tokio runtime.

Solution:

This branch replaces the use of `log` in `tokio-net` with
`tracing`. I've tried to leave all the instrumentation points more or
less the same, but modified to use structured fields instead of string
interpolation.

Notes:

I removed the timing in `Reactor::poll` in favor of simply adding a
`#[tracing::instrument]` attribute. Since the generated `tracing` span
will have enter and exit events, a `tracing::Subscriber`
implemementation can use those to record timestamps, and process that
timing data in a much more sophisticated manner than including it in a
log line.

We can add the timestamps back if they're desired.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

1 files changed, 1 insertions, 0 deletions

diff --git a/tokio/Cargo.toml b/tokio/Cargo.toml
index 9e4b24ac..d8b585f7 100644
--- a/tokio/Cargo.toml
+++ b/tokio/Cargo.toml
@@ -75,6 +75,7 @@ tokio-timer = { version = "=0.3.0-alpha.2", optional = true, path = "../tokio-ti
 tracing-core = { version = "0.1", optional = true }
 
 [target.'cfg(feature = "tracing")'.dependencies]
+tokio-net = { version = "=0.2.0-alpha.2", optional = true, path = "../tokio-net", features = ["tracing", "async-traits"] }
 tokio-executor = { version = "=0.2.0-alpha.2", optional = true, path = "../tokio-executor", features = ["tracing"] }
 
 [dev-dependencies]