Don't cancel context on SIGPIPE in "zed serve" (#4587)

On Linux (but not macOS), "zed serve" exits if it writes to a closed
socket (i.e., a broken network connection) because that raises SIGPIPE,
canceling the context created by cmd/zed/serve.Command.Init due to the
change in #4180.  Fix this by removing SIGPIPE from the list of
signal.NotifyContext signals for "zed serve".

Closes #4498.

cli/cli.go

@@ -30,7 +30,15 @@ type Initializer interface {
 	Init() error
 }
 
+// Init is equivalent to InitWithSignals with SIGINT, SIGPIPE, and SIGTERM.
 func (f *Flags) Init(all ...Initializer) (context.Context, context.CancelFunc, error) {
+	return f.InitWithSignals(all, syscall.SIGINT, syscall.SIGPIPE, syscall.SIGTERM)
+}
+
+// InitWithSignals handles the flags defined in SetFlags, calls the Init method
+// for each element of all, and returns a context canceled when any signal in
+// signals is raised.
+func (f *Flags) InitWithSignals(all []Initializer, signals ...os.Signal) (context.Context, context.CancelFunc, error) {
 	if f.showVersion {
 		fmt.Printf("Version: %s\n", Version())
 		os.Exit(0)
@@ -47,8 +55,7 @@ func (f *Flags) Init(all ...Initializer) (context.Context, context.CancelFunc, e
 	if f.cpuprofile != "" {
 		f.runCPUProfile(f.cpuprofile)
 	}
-	ctx, cancel := signal.NotifyContext(
-		context.Background(), syscall.SIGINT, syscall.SIGPIPE, syscall.SIGTERM)
+	ctx, cancel := signal.NotifyContext(context.Background(), signals...)
 	cleanup := func() {
 		cancel()
 		f.cleanup()

cmd/zed/root/command.go

@@ -1,7 +1,6 @@
 package root
 
 import (
-	"context"
 	"flag"
 
 	"github.com/brimdata/zed/cli"
@@ -21,23 +20,19 @@ querying, and orchestrating Zed data lakes.`,
 
 type Command struct {
 	charm.Command
+	cli.Flags
 	LakeFlags lakeflags.Flags
-	cli       cli.Flags
 }
 
 func New(parent charm.Command, f *flag.FlagSet) (charm.Command, error) {
 	c := &Command{}
-	c.cli.SetFlags(f)
+	c.SetFlags(f)
 	c.LakeFlags.SetFlags(f)
 	return c, nil
 }
 
-func (c *Command) Init(all ...cli.Initializer) (context.Context, func(), error) {
-	return c.cli.Init(all...)
-}
-
 func (c *Command) Run(args []string) error {
-	_, cancel, err := c.cli.Init()
+	_, cancel, err := c.Init()
 	if err != nil {
 		return err
 	}

cmd/zed/serve/command.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"os/signal"
 	"runtime"
+	"syscall"
 
 	"github.com/brimdata/zed/cli"
 	"github.com/brimdata/zed/cli/logflags"
@@ -65,7 +66,9 @@ func New(parent charm.Command, f *flag.FlagSet) (charm.Command, error) {
 }
 
 func (c *Command) Run(args []string) error {
-	ctx, cleanup, err := c.Init()
+	// Don't include SIGPIPE here or else a write to a closed socket (i.e.,
+	// a broken network connection) will cancel the context on Linux.
+	ctx, cleanup, err := c.InitWithSignals(nil, syscall.SIGINT, syscall.SIGTERM)
 	if err != nil {
 		return err
 	}