Add an example to the description and update docs

Author: zaphar

Diff for: README.md

@@ -27,6 +27,15 @@ fn main() {
     let service = ServiceBuilder::new()
         // Make a trace layer where the chunks are bytes::Bytes
         .layer(make_layer(|b: &bytes::Bytes| b.len() as u64));
-    // ... Use this service in a Tower Middleware stack.
+    // ... Use this service in a Tower middleware stack.
 }
-```
+```
+
+## Recorded Metrics
+
+* http_request_counter The total count of all requests
+* http_request_failure_counter The total count of all request failures
+* http_request_size_bytes_hist A histogram of request size in bytes
+* http_request_request_time_micros_hist A histogram of request time in microseconds
+
+Each metric is faceted by `path`, `method`, and `host` for the request.

Diff for: src/lib.rs

@@ -58,7 +58,7 @@ where
     pub labels: Arc<Mutex<Vec<Label>>>,
     /// The accumulator for the number of bytes on this request.
     pub size: Arc<AtomicU64>,
-    /// The mapper function to extract the size from a chunk in [OnBodyChunk<B>],
+    /// The mapper function to extract the size in bytes from a chunk in [OnBodyChunk<B>],
     pub chunk_len: Arc<F>,
     _phantom: PhantomData<B>,
 }
@@ -82,7 +82,7 @@ where
     F: Fn(&B) -> u64,
 {
     /// Construct a new [MetricsRecorder] using the installed [metrics::Recorder].
-    /// The function passed in is used to extract the size from the chunks in a
+    /// The function passed in is used to extract the size in bytes from the chunks in a
     /// response for all [OnBodyChunk] calls.
     pub fn new(f: F) -> Self {
         Self {
@@ -169,7 +169,7 @@ where
 }
 
 /// Construct a [TraceLayer] that will use an installed [metrics::Recorder] to record metrics per request.
-/// The provided [Fn] is used to extract the size from the chunks in a
+/// The provided [Fn] is used to extract the size in bytes from the chunks in a
 /// response for all [OnBodyChunk] calls.
 pub fn make_layer<B, F>(f: F) -> MetricsTraceLayer<B, F>
 where