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 v0.51.1
 	golang.org/x/crypto v0.21.0
 	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 v1.19.0 // indirect
 	github.com/prometheus/client_model v0.6.0 // indirect

go.sum

@@ -30,6 +30,10 @@ github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
 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/kingpinflag/flag.go

@@ -33,7 +33,7 @@ func AddFlags(a *kingpin.Application, defaultAddress string) *web.FlagConfig {
 	flags := web.FlagConfig{
 		WebListenAddresses: a.Flag(
 			"web.listen-address",
-			"Addresses on which to expose metrics and web interface. Repeatable for multiple addresses.",
+			"Addresses on which to expose metrics and web interface. Repeatable for multiple addresses. Examples: `:9100` or `127.0.0.1:9100` for http, `vsock://:9100` for vsock",
 		).Default(defaultAddress).HintOptions(defaultAddress).Strings(),
 		WebSystemdSocket: systemdSocket,
 		WebConfigFile: a.Flag(

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"
@@ -275,9 +279,11 @@ func ServeMultiple(listeners []net.Listener, server *http.Server, flags *FlagCon
 }
 
 // ListenAndServe starts the server on addresses given in WebListenAddresses in
-// the FlagConfig or instead uses systemd socket activated listeners if
-// WebSystemdSocket in the FlagConfig is true. The FlagConfig is also passed on
-// to ServeMultiple.
+// the FlagConfig. When address starts looks like vsock://:{port}, it listens on
+// vsock. More info check https://wiki.qemu.org/Features/VirtioVsock .
+// Or instead uses systemd socket activated listeners if WebSystemdSocket in the
+// FlagConfig is true.
+// The FlagConfig is also passed on to ServeMultiple.
 func ListenAndServe(server *http.Server, flags *FlagConfig, logger log.Logger) error {
 	if flags.WebSystemdSocket == nil && (flags.WebListenAddresses == nil || len(*flags.WebListenAddresses) == 0) {
 		return ErrNoListeners
@@ -297,16 +303,45 @@ 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)
-		if err != nil {
-			return err
+		var err error
+		var listener net.Listener
+		if strings.HasPrefix(address, "vsock://") {
+			port, err := parseVsockPort(address)
+			if err != nil {
+				return err
+			}
+			listener, err = vsock.Listen(port, nil)
+			if err != nil {
+				return err
+			}
+		} else {
+			listener, err = net.Listen("tcp", address)
+			if err != nil {
+				return nil
+			}
 		}
 		defer listener.Close()
 		listeners = append(listeners, listener)
 	}
 	return ServeMultiple(listeners, server, flags, logger)
 }
 
+func parseVsockPort(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 {