transport/{TCP,TLS}: optional IP_FREEBIND / IP_BINDANY bind socketops

Allows to bind to an address even if it is not actually (yet or ever)
configured. Fixes #238

Rationale:
https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget/#whatdoesthismeanformeadeveloper

build/tools.go

@@ -3,9 +3,9 @@
 package main
 
 import (
-	_ "golang.org/x/tools/cmd/stringer"
-	_ "github.com/golang/protobuf/protoc-gen-go"
 	_ "github.com/alvaroloes/enumer"
-	_ "golang.org/x/tools/cmd/goimports"
+	_ "github.com/golang/protobuf/protoc-gen-go"
 	_ "github.com/golangci/golangci-lint/cmd/golangci-lint"
+	_ "golang.org/x/tools/cmd/goimports"
+	_ "golang.org/x/tools/cmd/stringer"
 )

config/config.go

@@ -245,14 +245,16 @@ type ServeCommon struct {
 }
 
 type TCPServe struct {
-	ServeCommon `yaml:",inline"`
-	Listen      string            `yaml:"listen,hostport"`
-	Clients     map[string]string `yaml:"clients"`
+	ServeCommon    `yaml:",inline"`
+	Listen         string            `yaml:"listen,hostport"`
+	ListenFreeBind bool              `yaml:"listen_freebind,default=false"`
+	Clients        map[string]string `yaml:"clients"`
 }
 
 type TLSServe struct {
 	ServeCommon      `yaml:",inline"`
 	Listen           string        `yaml:"listen,hostport"`
+	ListenFreeBind   bool          `yaml:"listen_freebind,default=false"`
 	Ca               string        `yaml:"ca"`
 	Cert             string        `yaml:"cert"`
 	Key              string        `yaml:"key"`
@@ -331,8 +333,9 @@ type MonitoringEnum struct {
 }
 
 type PrometheusMonitoring struct {
-	Type   string `yaml:"type"`
-	Listen string `yaml:"listen,hostport"`
+	Type           string `yaml:"type"`
+	Listen         string `yaml:"listen,hostport"`
+	ListenFreeBind bool   `yaml:"listen_freebind,default=false"`
 }
 
 type SyslogFacility syslog.Priority

daemon/prometheus.go

@@ -12,18 +12,20 @@ import (
 	"github.com/zrepl/zrepl/daemon/job"
 	"github.com/zrepl/zrepl/logger"
 	"github.com/zrepl/zrepl/rpc/dataconn/frameconn"
+	"github.com/zrepl/zrepl/util/tcpsock"
 	"github.com/zrepl/zrepl/zfs"
 )
 
 type prometheusJob struct {
-	listen string
+	listen   string
+	freeBind bool
 }
 
 func newPrometheusJobFromConfig(in *config.PrometheusMonitoring) (*prometheusJob, error) {
 	if _, _, err := net.SplitHostPort(in.Listen); err != nil {
 		return nil, err
 	}
-	return &prometheusJob{in.Listen}, nil
+	return &prometheusJob{in.Listen, in.ListenFreeBind}, nil
 }
 
 var prom struct {
@@ -60,7 +62,7 @@ func (j *prometheusJob) Run(ctx context.Context) {
 
 	log := job.GetLogger(ctx)
 
-	l, err := net.Listen("tcp", j.listen)
+	l, err := tcpsock.Listen(j.listen, j.freeBind)
 	if err != nil {
 		log.WithError(err).Error("cannot listen")
 		return

docs/changelog.rst

@@ -27,6 +27,11 @@ We use the following annotations for classifying changes:
 * |bugfix| Change that fixes a bug, no regressions or incompatibilities expected.
 * |docs| Change to the documentation.
 
+0.2.2 (unreleased)
+------------------
+
+* |feature| New option ``listen_freebind`` (tcp, tls, prometheus listener)
+
 0.2.1
 -----
 

docs/configuration/monitoring.rst

@@ -14,6 +14,7 @@ Prometheus & Grafana
 
 zrepl can expose `Prometheus metrics <https://prometheus.io/docs/instrumenting/exposition_formats/>`_ via HTTP.
 The ``listen`` attribute is a `net.Listen <https://golang.org/pkg/net/#Listen>`_  string for tcp, e.g. ``:9091`` or ``127.0.0.1:9091``.
+The ``listen_freebind`` attribute is :ref:`explained here <listen-freebind-explanation>`.
 The Prometheues monitoring job appears in the ``zrepl control`` job list and may be specified **at most once**.
 
 zrepl also ships with an importable `Grafana <https://grafana.com>`_ dashboard that consumes the Prometheus metrics:
@@ -30,6 +31,7 @@ The dashboard also contains some advice on which metrics are important to monito
       monitoring:
         - type: prometheus
           listen: ':9091'
+          listen_freebind: true # optional, default false
 
 
 

docs/configuration/transports.rst

@@ -50,12 +50,18 @@ Serve
       serve:
         type: tcp
         listen: ":8888"
+        listen_freebind: true # optional, default false
         clients: {
           "192.168.122.123" : "mysql01"
           "192.168.122.123" : "mx01"
         }
       ...
 
+.. _listen-freebind-explanation:
+
+``listen_freebind`` controls whether the socket is allowed to bind to non-local or unconfigured IP addresses (Linux ``IP_FREEBIND`` , FreeBSD ``IP_BINDANY``).
+Enable this option if you want to ``listen`` on a specific IP address that might not yet be configured when the zrepl daemon starts.
+
 Connect
 ~~~~~~~
 
@@ -101,6 +107,7 @@ Serve
         serve:
           type: tls
           listen: ":8888"
+          listen_freebind: true # optional, default false
           ca:   /etc/zrepl/ca.crt
           cert: /etc/zrepl/prod.fullchain
           key:  /etc/zrepl/prod.key
@@ -110,6 +117,7 @@ Serve
 
 The ``ca`` field specified the certificate authority used to validate client certificates.
 The ``client_cns`` list specifies a list of accepted client common names (which are also the client identities for this transport).
+The ``listen_freebind`` field is :ref:`explained here <listen-freebind-explanation>`.
 
 Connect
 ~~~~~~~

platformtest/harness/harness.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/fatih/color"
 	"github.com/pkg/errors"
+
 	"github.com/zrepl/zrepl/config"
 	"github.com/zrepl/zrepl/daemon/logging"
 	"github.com/zrepl/zrepl/logger"

platformtest/platformtest_zpool.go

@@ -6,6 +6,7 @@ import (
 	"path/filepath"
 
 	"github.com/pkg/errors"
+
 	"github.com/zrepl/zrepl/zfs"
 )
 

platformtest/tests/undestroyableSnapshotParsing.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	"github.com/stretchr/testify/require"
+
 	"github.com/zrepl/zrepl/platformtest"
 	"github.com/zrepl/zrepl/zfs"
 )

transport/tcp/serve_tcp.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/zrepl/zrepl/config"
 	"github.com/zrepl/zrepl/transport"
+	"github.com/zrepl/zrepl/util/tcpsock"
 )
 
 type ipMapEntry struct {
@@ -44,16 +45,12 @@ func (m *ipMap) Get(ip net.IP) (string, error) {
 }
 
 func TCPListenerFactoryFromConfig(c *config.Global, in *config.TCPServe) (transport.AuthenticatedListenerFactory, error) {
-	addr, err := net.ResolveTCPAddr("tcp", in.Listen)
-	if err != nil {
-		return nil, errors.Wrap(err, "cannot parse listen address")
-	}
 	clientMap, err := ipMapFromConfig(in.Clients)
 	if err != nil {
 		return nil, errors.Wrap(err, "cannot parse client IP map")
 	}
 	lf := func() (transport.AuthenticatedListener, error) {
-		l, err := net.ListenTCP("tcp", addr)
+		l, err := tcpsock.Listen(in.Listen, in.ListenFreeBind)
 		if err != nil {
 			return nil, err
 		}

transport/tls/serve_tls.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"crypto/tls"
 	"fmt"
-	"net"
 	"time"
 
 	"github.com/pkg/errors"
@@ -12,6 +11,7 @@ import (
 	"github.com/zrepl/zrepl/config"
 	"github.com/zrepl/zrepl/tlsconf"
 	"github.com/zrepl/zrepl/transport"
+	"github.com/zrepl/zrepl/util/tcpsock"
 )
 
 type TLSListenerFactory struct{}
@@ -45,12 +45,11 @@ func TLSListenerFactoryFromConfig(c *config.Global, in *config.TLSServe) (transp
 	}
 
 	lf := func() (transport.AuthenticatedListener, error) {
-		l, err := net.Listen("tcp", address)
+		l, err := tcpsock.Listen(address, in.ListenFreeBind)
 		if err != nil {
 			return nil, err
 		}
-		tcpL := l.(*net.TCPListener)
-		tl := tlsconf.NewClientAuthListener(tcpL, clientCA, serverCert, handshakeTimeout)
+		tl := tlsconf.NewClientAuthListener(l, clientCA, serverCert, handshakeTimeout)
 		return &tlsAuthListener{tl, clientCNs}, nil
 	}
 

util/tcpsock/tcpsock.go

@@ -0,0 +1,27 @@
+package tcpsock
+
+import (
+	"context"
+	"net"
+	"syscall"
+)
+
+func Listen(address string, tryFreeBind bool) (*net.TCPListener, error) {
+	control := func(network, address string, c syscall.RawConn) error {
+		if tryFreeBind {
+			if err := freeBind(network, address, c); err != nil {
+				return err
+			}
+		}
+		return nil
+	}
+	var listenConfig = net.ListenConfig{
+		Control: control,
+	}
+
+	l, err := listenConfig.Listen(context.Background(), "tcp", address)
+	if err != nil {
+		return nil, err
+	}
+	return l.(*net.TCPListener), nil
+}

util/tcpsock/tcpsock_freebind_freebsd.go

@@ -0,0 +1,25 @@
+// +build freebsd
+
+package tcpsock
+
+import (
+	"fmt"
+	"syscall"
+)
+
+func freeBind(network, address string, c syscall.RawConn) error {
+	var err, sockerr error
+	err = c.Control(func(fd uintptr) {
+		if network == "tcp6" {
+			sockerr = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IPV6, syscall.IPV6_BINDANY, 1)
+		} else if network == "tcp4" {
+			sockerr = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP, syscall.IP_BINDANY, 1)
+		} else {
+			sockerr = fmt.Errorf("expecting 'tcp6' or 'tcp4', got %q", network)
+		}
+	})
+	if err != nil {
+		return err
+	}
+	return sockerr
+}

util/tcpsock/tcpsock_freebind_linux.go

@@ -0,0 +1,19 @@
+// +build linux
+
+package tcpsock
+
+import (
+	"syscall"
+)
+
+func freeBind(network, address string, c syscall.RawConn) error {
+	var err, sockerr error
+	err = c.Control(func(fd uintptr) {
+		// apparently, this works for both IPv4 and IPv6
+		sockerr = syscall.SetsockoptInt(int(fd), syscall.SOL_IP, syscall.IP_FREEBIND, 1)
+	})
+	if err != nil {
+		return err
+	}
+	return sockerr
+}

util/tcpsock/tcpsock_freebind_unsupported.go

@@ -0,0 +1,12 @@
+// +build !linux,!freebsd
+
+package tcpsock
+
+import (
+	"fmt"
+	"syscall"
+)
+
+func freeBind(network, address string, c syscall.RawConn) error {
+	return fmt.Errorf("IP_FREEBIND equivalent functionality not supported  on this platform")
+}

zfs/zfs.go

@@ -20,6 +20,7 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 
 	"github.com/pkg/errors"
+
 	"github.com/zrepl/zrepl/util/envconst"
 )