Support listen on vsock

With this patch, node_exporter can run with `--web.listen-address=vsock:
//:9100` to listen on vsock in qemu guest. Then host can get the
metrics.

Signed-off-by: Jeffrey Zhang <zhang.lei.fly@gmail.com>

go.mod

@@ -6,6 +6,7 @@ require (
 	github.com/alecthomas/kingpin/v2 v2.4.0
 	github.com/coreos/go-systemd/v22 v22.5.0
 	github.com/go-kit/log v0.2.1
+	github.com/mdlayher/vsock v1.2.1
 	github.com/prometheus/common v0.46.0
 	golang.org/x/crypto v0.18.0
 	golang.org/x/sync v0.6.0
@@ -20,6 +21,7 @@ require (
 	github.com/golang/protobuf v1.5.3 // indirect
 	github.com/jpillora/backoff v1.0.0 // indirect
 	github.com/kr/text v0.2.0 // indirect
+	github.com/mdlayher/socket v0.4.1 // indirect
 	github.com/mwitkow/go-conntrack v0.0.0-20190716064945-2f068394615f // indirect
 	github.com/prometheus/client_golang v1.18.0 // indirect
 	github.com/prometheus/client_model v0.5.0 // indirect

go.sum

@@ -27,6 +27,10 @@ github.com/jpillora/backoff v1.0.0/go.mod h1:J/6gKK9jxlEcS3zixgDgUAsiuZ7yrSoa/FX
 github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
+github.com/mdlayher/socket v0.4.1 h1:eM9y2/jlbs1M615oshPQOHZzj6R6wMT7bX5NPiQvn2U=
+github.com/mdlayher/socket v0.4.1/go.mod h1:cAqeGjoufqdxWkD7DkpyS+wcefOtmu5OQ8KuoJGIReA=
+github.com/mdlayher/vsock v1.2.1 h1:pC1mTJTvjo1r9n9fbm7S1j04rCgCzhCOS5DY0zqHlnQ=
+github.com/mdlayher/vsock v1.2.1/go.mod h1:NRfCibel++DgeMD8z/hP+PPTjlNJsdPOmxcnENvE+SE=
 github.com/mwitkow/go-conntrack v0.0.0-20190716064945-2f068394615f h1:KUppIJq7/+SVif2QVs3tOP0zanoHgBEVAwHxUSIzRqU=
 github.com/mwitkow/go-conntrack v0.0.0-20190716064945-2f068394615f/go.mod h1:qRWi+5nqEBWmkhHvq77mSJWrCKwh8bxhgT7d/eI7P4U=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=

web/tls_config.go

@@ -20,12 +20,16 @@ import (
 	"fmt"
 	"net"
 	"net/http"
+	"net/url"
 	"os"
 	"path/filepath"
+	"strconv"
+	"strings"
 
 	"github.com/coreos/go-systemd/v22/activation"
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
+	"github.com/mdlayher/vsock"
 	config_util "github.com/prometheus/common/config"
 	"golang.org/x/sync/errgroup"
 	"gopkg.in/yaml.v2"
@@ -297,7 +301,17 @@ func ListenAndServe(server *http.Server, flags *FlagConfig, logger log.Logger) e
 
 	listeners := make([]net.Listener, 0, len(*flags.WebListenAddresses))
 	for _, address := range *flags.WebListenAddresses {
-		listener, err := net.Listen("tcp", address)
+		var err error
+		var listener net.Listener
+		if strings.HasPrefix(address, "vsock://") {
+			var port uint32
+			port, err = parseVsockAddress(address)
+			if err == nil {
+				listener, err = vsock.Listen(port, nil)
+			}
+		} else {
+			listener, err = net.Listen("tcp", address)
+		}
 		if err != nil {
 			return err
 		}
@@ -307,6 +321,23 @@ func ListenAndServe(server *http.Server, flags *FlagConfig, logger log.Logger) e
 	return ServeMultiple(listeners, server, flags, logger)
 }
 
+func parseVsockAddress(address string) (uint32, error) {
+		uri, err := url.Parse(address)
+		if err != nil {
+			return 0, err
+		}
+		_, portStr, err := net.SplitHostPort(uri.Host)
+		if err != nil {
+			return 0, err
+		}
+		port, err := strconv.ParseUint(portStr, 10, 32)
+		if err != nil {
+			return 0, err
+		}
+		return uint32(port), nil
+}
+
+
 // Server starts the server on the given listener. Based on the file path
 // WebConfigFile in the FlagConfig, TLS or basic auth could be enabled.
 func Serve(l net.Listener, server *http.Server, flags *FlagConfig, logger log.Logger) error {