Add an i/o error label to http metrics (#512)

This change modifies HTTP error-labeling to detect I/O errors
and label them explicitly. Previously all I/O errors were reported as
`unexpected`.

Additionally, an `errno` label is included when possible.

Fixes linkerd/linkerd2#4364

Author: olix0r

Cargo.lock

@@ -641,6 +641,7 @@ dependencies = [
  "linkerd2-dns",
  "linkerd2-drain",
  "linkerd2-duplex",
+ "linkerd2-errno",
  "linkerd2-error",
  "linkerd2-error-metrics",
  "linkerd2-error-respond",
@@ -856,6 +857,10 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "linkerd2-errno"
+version = "0.1.0"
+
 [[package]]
 name = "linkerd2-error"
 version = "0.1.0"
@@ -1197,6 +1202,7 @@ dependencies = [
  "libc",
  "linkerd2-conditional",
  "linkerd2-dns-name",
+ "linkerd2-errno",
  "linkerd2-error",
  "linkerd2-identity",
  "linkerd2-io",

Cargo.toml

@@ -19,6 +19,7 @@ members = [
     "linkerd/drain",
     "linkerd/duplex",
     "linkerd/error",
+    "linkerd/errno",
     "linkerd/error-metrics",
     "linkerd/error-respond",
     "linkerd/exp-backoff",

linkerd/app/core/Cargo.toml

@@ -29,6 +29,7 @@ linkerd2-conditional = { path = "../../conditional" }
 linkerd2-dns = { path = "../../dns" }
 linkerd2-drain = { path = "../../drain" }
 linkerd2-duplex = { path = "../../duplex" }
+linkerd2-errno = { path = "../../errno" }
 linkerd2-error = { path = "../../error" }
 linkerd2-error-metrics = { path = "../../error-metrics" }
 linkerd2-error-respond = { path = "../../error-respond" }

linkerd/app/core/src/errors.rs

@@ -1,6 +1,7 @@
 use crate::proxy::identity;
 use futures::{Async, Poll};
 use http::{header::HeaderValue, StatusCode};
+use linkerd2_errno::Errno;
 use linkerd2_error::Error;
 use linkerd2_error_metrics as metrics;
 use linkerd2_error_respond as respond;
@@ -30,6 +31,7 @@ pub enum Reason {
     DispatchTimeout,
     ResponseTimeout,
     IdentityRequired,
+    Io(Option<Errno>),
     FailFast,
     Unexpected,
 }
@@ -295,23 +297,31 @@ impl std::fmt::Display for IdentityRequired {
 
 impl std::error::Error for IdentityRequired {}
 
-impl metrics::LabelError<Error> for LabelError {
-    type Labels = Label;
-
-    fn label_error(&self, err: &Error) -> Self::Labels {
-        let reason = if err.is::<ResponseTimeout>() {
+impl LabelError {
+    fn reason(err: &(dyn std::error::Error + 'static)) -> Reason {
+        if err.is::<ResponseTimeout>() {
             Reason::ResponseTimeout
         } else if err.is::<FailFastError>() {
             Reason::FailFast
         } else if err.is::<tower::timeout::error::Elapsed>() {
             Reason::DispatchTimeout
         } else if err.is::<IdentityRequired>() {
             Reason::IdentityRequired
+        } else if let Some(e) = err.downcast_ref::<std::io::Error>() {
+            Reason::Io(e.raw_os_error().map(Errno::from))
+        } else if let Some(e) = err.source() {
+            Self::reason(e)
         } else {
             Reason::Unexpected
-        };
+        }
+    }
+}
 
-        (self.0, reason)
+impl metrics::LabelError<Error> for LabelError {
+    type Labels = Label;
+
+    fn label_error(&self, err: &Error) -> Self::Labels {
+        (self.0, Self::reason(err.as_ref()))
     }
 }
 
@@ -325,9 +335,16 @@ impl metrics::FmtLabels for Reason {
                 Reason::DispatchTimeout => "dispatch timeout",
                 Reason::ResponseTimeout => "response timeout",
                 Reason::IdentityRequired => "identity required",
+                Reason::Io(_) => "i/o",
                 Reason::Unexpected => "unexpected",
             }
-        )
+        )?;
+
+        if let Reason::Io(Some(errno)) = self {
+            write!(f, ",errno=\"{}\"", errno)?;
+        }
+
+        Ok(())
     }
 }
 

linkerd/errno/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "linkerd2-errno"
+version = "0.1.0"
+authors = ["Linkerd Developers <[email protected]>"]
+edition = "2018"
+publish = false

linkerd/proxy/transport/src/metrics/errno.rs renamed to linkerd/errno/src/lib.rs

@@ -1,3 +1,5 @@
+#![deny(warnings, rust_2018_idioms)]
+
 use std::fmt;
 
 /// Represents a platform-agnostic system error for metrics labels.

linkerd/proxy/transport/Cargo.toml

@@ -19,6 +19,7 @@ futures = "0.1"
 indexmap = "1.0.0"
 linkerd2-conditional = { path = "../../conditional" }
 linkerd2-dns-name = { path = "../../dns/name" }
+linkerd2-errno = { path = "../../errno" }
 linkerd2-error = { path = "../../error" }
 linkerd2-identity = { path = "../../identity" }
 linkerd2-io = { path = "../../io" }

linkerd/proxy/transport/src/metrics/mod.rs

@@ -1,5 +1,6 @@
 use futures::{try_ready, Future, Poll};
 use indexmap::IndexMap;
+use linkerd2_errno::Errno;
 use linkerd2_metrics::{
     latency, metrics, Counter, FmtLabels, FmtMetric, FmtMetrics, Gauge, Histogram, Metric,
 };
@@ -10,10 +11,9 @@ use std::time::Instant;
 use tokio::io::{AsyncRead, AsyncWrite};
 use tracing::debug;
 
-mod errno;
 mod io;
 
-pub use self::{errno::Errno, io::Io};
+pub use self::io::Io;
 
 metrics! {
     tcp_open_total: Counter { "Total count of opened connections" },