From 379e4d7e4d2539f35d559d4b0752531e546238a9 Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@lukeshu.com>
Date: Mon, 18 Dec 2017 15:07:24 -0500
Subject: nslcd_{server,systemd}: BREAKING CHANGE: use contexts

---
 nslcd_server/ctx.go                    | 46 ++++++++++++++++++++++++++++++++++
 nslcd_server/func_handlerequest.go.gen | 26 +++++++++++++++----
 nslcd_server/interface_backend.go.gen  |  9 ++++---
 nslcd_server/type_nilbackend.go.gen    |  7 +++---
 nslcd_systemd/misc_test.go             |  7 +++---
 nslcd_systemd/nslcd_systemd.go         | 23 +++++++++++++----
 6 files changed, 98 insertions(+), 20 deletions(-)
 create mode 100644 nslcd_server/ctx.go

diff --git a/nslcd_server/ctx.go b/nslcd_server/ctx.go
new file mode 100644
index 0000000..5214adc
--- /dev/null
+++ b/nslcd_server/ctx.go
@@ -0,0 +1,46 @@
+// Copyright (C) 2017 Luke Shumaker <lukeshu@sbcglobal.net>
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+// 02110-1301 USA
+
+package nslcd_server
+
+import (
+	"context"
+
+	"golang.org/x/sys/unix"
+)
+
+// contextKey is a value for use with context.WithValue.  It's used as
+// a pointer so it fits in an interface{} without allocation.
+type contextKey struct {
+	name string
+}
+
+var (
+	// PeerCredKey is a context key.  It can be used in backend
+	// methods to access the credentials of the client process.
+	// The associated value will be of type
+	// "golang.org/x/sys/unix".Ucred
+	PeerCredKey = &contextKey{"peercred"}
+)
+
+// PeerCredFromContext is a convenience function for
+//
+//     cred, ok := ctx.Value(nslcd_server.PeerCredKey).(unix.Ucred)
+func PeerCredFromContext(ctx context.Context) (unix.Ucred, bool) {
+	cred, ok := ctx.Value(PeerCredKey).(unix.Ucred)
+	return cred, ok
+}
diff --git a/nslcd_server/func_handlerequest.go.gen b/nslcd_server/func_handlerequest.go.gen
index 00e9663..750a7b0 100755
--- a/nslcd_server/func_handlerequest.go.gen
+++ b/nslcd_server/func_handlerequest.go.gen
@@ -25,12 +25,12 @@ cat <<EOF | gofmt
 package nslcd_server
 
 import (
+	"context"
 	"fmt"
 	"io"
 	"os"
 	"time"
 
-	"golang.org/x/sys/unix"
 	p "git.lukeshu.com/go/libnslcd/nslcd_proto"
 )
 
@@ -70,8 +70,9 @@ type Conn interface {
 	SetWriteDeadline(t time.Time) error
 }
 
-// Handle a request to nslcd
-func HandleRequest(backend Backend, limits Limits, conn Conn, cred unix.Ucred) (err error) {
+// Handle a request to nslcd.  The caller is responsible for
+// initializing the context with PeerCredKey.
+func HandleRequest(backend Backend, limits Limits, conn Conn, ctx context.Context) (err error) {
 	defer func() {
 		if r := recover(); r != nil {
 			switch r := r.(type) {
@@ -89,6 +90,11 @@ func HandleRequest(backend Backend, limits Limits, conn Conn, cred unix.Ucred) (
 	if limits.Timeout != 0 {
 		deadlineAll = now.Add(limits.Timeout)
 	}
+	if deadline, ok := ctx.Deadline(); ok {
+		if deadlineAll.IsZero() || deadline.Before(deadlineAll) {
+			deadlineAll = deadline
+		}
+	}
 	if limits.ReadTimeout != 0 {
 		deadlineRead = now.Add(limits.ReadTimeout)
 		if !deadlineAll.IsZero() && deadlineAll.Before(deadlineRead) {
@@ -149,6 +155,7 @@ while read -r request; do
 				;;
 		esac
 		)
+
 		if limits.WriteTimeout != 0 {
 			deadlineWrite = time.Now().Add(limits.WriteTimeout)
 			if !deadlineAll.IsZero() && deadlineAll.Before(deadlineWrite) {
@@ -161,9 +168,18 @@ while read -r request; do
 				return err
 			}
 		}
+
+		var cancel context.CancelFunc
+		if deadline, ok := ctx.Deadline(); !ok || (!deadlineWrite.IsZero() && deadline.After(deadlineWrite)) {
+			ctx, cancel = context.WithDeadline(ctx, deadlineWrite)
+		} else {
+			ctx, cancel = context.WithCancel(ctx)
+		}
+		defer cancel()
+
 		maybePanic(p.Write(out, p.NSLCD_VERSION))
 		maybePanic(p.Write(out, action))
-		ch := backend.${request}(cred, req)
+		ch := backend.${request}(ctx, req)
 		for result := range ch {
 			if err == nil {
 				err = p.Write(out, p.NSLCD_RESULT_BEGIN)
@@ -174,7 +190,7 @@ while read -r request; do
 		}
 		maybePanic(err)
 		maybePanic(p.Write(out, p.NSLCD_RESULT_END))
-		return nil
+		return ctx.Err() // probably nil
 EOT
 done < "$requests"
 )
diff --git a/nslcd_server/interface_backend.go.gen b/nslcd_server/interface_backend.go.gen
index 4749d0c..4ced5e7 100755
--- a/nslcd_server/interface_backend.go.gen
+++ b/nslcd_server/interface_backend.go.gen
@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# Copyright (C) 2015 Luke Shumaker <lukeshu@sbcglobal.net>
+# Copyright (C) 2015, 2017 Luke Shumaker <lukeshu@sbcglobal.net>
 #
 # This library is free software; you can redistribute it and/or
 # modify it under the terms of the GNU Lesser General Public
@@ -24,7 +24,8 @@ cat <<EOF | gofmt
 package nslcd_server
 
 import (
-	"golang.org/x/sys/unix"
+	"context"
+
 	p "git.lukeshu.com/go/libnslcd/nslcd_proto"
 )
 
@@ -33,7 +34,7 @@ import (
 // that the nslcd server may reply to is implemented simply as a
 // method that returns a channel of the resulting values.
 type Backend interface {
-	$(sed -rn 's/([^_]+)(.*)/\1\2(unix.Ucred, p.Request_\1\2) <-chan p.\1/p' "$requests" | grep -v PAM)
-	$(sed -rn 's/(PAM)(.*)/\1\2(unix.Ucred, p.Request_\1\2) <-chan p.\1\2/p' "$requests")
+	$(sed -rn 's/([^_]+)(.*)/\1\2(context.Context, p.Request_\1\2) <-chan p.\1/p' "$requests" | grep -v PAM)
+	$(sed -rn 's/(PAM)(.*)/\1\2(context.Context, p.Request_\1\2) <-chan p.\1\2/p' "$requests")
 }
 EOF
diff --git a/nslcd_server/type_nilbackend.go.gen b/nslcd_server/type_nilbackend.go.gen
index 0c6f4b5..b7ea372 100755
--- a/nslcd_server/type_nilbackend.go.gen
+++ b/nslcd_server/type_nilbackend.go.gen
@@ -24,7 +24,8 @@ cat <<EOF | gofmt
 package nslcd_server
 
 import (
-	"golang.org/x/sys/unix"
+	"context"
+
 	p "git.lukeshu.com/go/libnslcd/nslcd_proto"
 )
 
@@ -35,8 +36,8 @@ import (
 type NilBackend struct{}
 
 $(
-	re_in='^\t([^(]+)\(unix\.Ucred, ([^)]+)\) <-chan (\S+)$'
-	re_out='func (o NilBackend) \1(unix.Ucred, \2) <-chan \3 { r := make(chan \3); close(r); return r }'
+	re_in='^\t([^(]+)\(context\.Context, ([^)]+)\) <-chan (\S+)$'
+	re_out='func (o NilBackend) \1(context.Context, \2) <-chan \3 { r := make(chan \3); close(r); return r }'
 	< "$interface" sed -rn "s/$re_in/$re_out/p"
 )
 
diff --git a/nslcd_systemd/misc_test.go b/nslcd_systemd/misc_test.go
index a75083d..bc7ace6 100644
--- a/nslcd_systemd/misc_test.go
+++ b/nslcd_systemd/misc_test.go
@@ -18,6 +18,7 @@
 package nslcd_systemd_test
 
 import (
+	"context"
 	"fmt"
 	"io/ioutil"
 	"net"
@@ -89,7 +90,7 @@ func testDriver(
 	// server //////////////////////////////////////////////////////////////
 	errfatal(sdActivatedStream(t.tmpdir + "/nslcd.sock"))
 	go func() {
-		evExitServer <- nslcd_systemd.Main(backend, limits)
+		evExitServer <- nslcd_systemd.Main(backend, limits, context.Background())
 	}()
 
 	// client/driver ///////////////////////////////////////////////////////
@@ -133,7 +134,7 @@ func (o *NonLockingBackend) Init() error   { return nil }
 func (o *NonLockingBackend) Reload() error { return nil }
 func (o *NonLockingBackend) Close()        {}
 
-func (o *NonLockingBackend) Passwd_All(cred unix.Ucred, req nslcd_proto.Request_Passwd_All) <-chan nslcd_proto.Passwd {
+func (o *NonLockingBackend) Passwd_All(ctx context.Context, req nslcd_proto.Request_Passwd_All) <-chan nslcd_proto.Passwd {
 	ret := make(chan nslcd_proto.Passwd)
 	go func() {
 		defer close(ret)
@@ -170,7 +171,7 @@ func (o *LockingBackend) Close() {
 	o.NonLockingBackend.Close()
 }
 
-func (o *LockingBackend) Passwd_All(cred unix.Ucred, req nslcd_proto.Request_Passwd_All) <-chan nslcd_proto.Passwd {
+func (o *LockingBackend) Passwd_All(ctx context.Context, req nslcd_proto.Request_Passwd_All) <-chan nslcd_proto.Passwd {
 	o.lock.RLock()
 	ret := make(chan nslcd_proto.Passwd)
 	go func() {
diff --git a/nslcd_systemd/nslcd_systemd.go b/nslcd_systemd/nslcd_systemd.go
index 0999106..b2f8e28 100644
--- a/nslcd_systemd/nslcd_systemd.go
+++ b/nslcd_systemd/nslcd_systemd.go
@@ -25,6 +25,7 @@
 // 	package main
 //
 // 	import (
+// 		"context"
 // 		"os"
 //
 // 		"git.lukeshu.com/go/libnslcd/nslcd_server"
@@ -34,11 +35,13 @@
 // 	func main() {
 // 		backend := ...
 // 		limits := nslcd_server.Limits{ ... }
-// 		os.Exit(int(nslcd_systemd.Main(backend, limits)))
+// 		ctx := context.Background()
+// 		os.Exit(int(nslcd_systemd.Main(backend, limits, ctx)))
 // 	}
 package nslcd_systemd // import "git.lukeshu.com/go/libnslcd/nslcd_systemd"
 
 import (
+	"context"
 	"fmt"
 	"net"
 	"os"
@@ -94,22 +97,26 @@ func getpeercred(conn *net.UnixConn) (cred unix.Ucred, err error) {
 	return
 }
 
-func handler(backend nslcd_server.Backend, limits nslcd_server.Limits, conn *net.UnixConn) {
+func handler(backend nslcd_server.Backend, limits nslcd_server.Limits, conn *net.UnixConn, ctx context.Context) {
 	defer conn.Close()
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
 	cred, err := getpeercred(conn)
 	if err != nil {
 		sd_daemon.Log.Debug("Connection from unknown client")
 	} else {
 		sd_daemon.Log.Debug(fmt.Sprintf("Connection from pid=%v uid=%v gid=%v",
 			cred.Pid, cred.Uid, cred.Gid))
+		ctx = context.WithValue(ctx, nslcd_server.PeerCredKey, cred)
 	}
-	err = nslcd_server.HandleRequest(backend, limits, conn, cred)
+	err = nslcd_server.HandleRequest(backend, limits, conn, ctx)
 	if err != nil {
 		sd_daemon.Log.Notice(fmt.Sprintf("Error while handling request: %v", err))
 	}
 }
 
-func Main(backend Backend, limits nslcd_server.Limits) uint8 {
+func Main(backend Backend, limits nslcd_server.Limits, ctx context.Context) uint8 {
 	defer sd_daemon.Recover()
 	var err error = nil
 
@@ -137,6 +144,9 @@ func Main(backend Backend, limits nslcd_server.Limits) uint8 {
 	}
 	defer func() { socket.(*net.UnixListener).SetDeadline(time.Now()) }()
 
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
 	socket_error := make(chan error)
 	wg.Add(1)
 	go func() {
@@ -171,7 +181,7 @@ func Main(backend Backend, limits nslcd_server.Limits) uint8 {
 				go func() {
 					defer sd_daemon.Recover()
 					defer wg.Done()
-					handler(backend, limits, conn.(*net.UnixConn))
+					handler(backend, limits, conn.(*net.UnixConn), ctx)
 				}()
 			}
 		}
@@ -196,6 +206,9 @@ func Main(backend Backend, limits nslcd_server.Limits) uint8 {
 				}
 				sd_daemon.Notification{State: "READY=1"}.Send(false)
 			}
+		case <-ctx.Done():
+			sd_daemon.Log.Err(fmt.Sprintf("Context was canceled, shutting down: %v", ctx.Err()))
+			return sd_daemon.EXIT_FAILURE
 		case err = <-socket_error:
 			sd_daemon.Log.Err(fmt.Sprintf("%v", err))
 			return sd_daemon.EXIT_NETWORK
-- 
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