types/result, util/lineread: add package for a result type, use it

This adds a new generic result type (motivated by golang/go#70084) to try it out, and uses it in the lineread package, changing that package to return iterators: sometimes over []byte (when the input is all in memory), but sometimes iterators over results of []byte, if errors might happen at runtime. Updates #12912 Updates golang/go#70084 Change-Id: Iacdc1070e661b5fb163907b1e8b07ac7d51d3f83 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
tailscale · Nov 5, 2024 · 3a78ec4 · 3a78ec4
1 parent 809a6eb
commit 3a78ec4
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Showing 14 changed files with 173 additions and 52 deletions.
diff --git a/cmd/derper/depaware.txt b/cmd/derper/depaware.txt
@@ -140,6 +140,7 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa
         tailscale.com/types/persist                                  from tailscale.com/ipn
         tailscale.com/types/preftype                                 from tailscale.com/ipn
         tailscale.com/types/ptr                                      from tailscale.com/hostinfo+
+        tailscale.com/types/result                                   from tailscale.com/util/lineread
         tailscale.com/types/structs                                  from tailscale.com/ipn+
         tailscale.com/types/tkatype                                  from tailscale.com/client/tailscale+
         tailscale.com/types/views                                    from tailscale.com/ipn+

diff --git a/cmd/k8s-operator/depaware.txt b/cmd/k8s-operator/depaware.txt
@@ -775,6 +775,7 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
         tailscale.com/types/persist                                  from tailscale.com/control/controlclient+
         tailscale.com/types/preftype                                 from tailscale.com/ipn+
         tailscale.com/types/ptr                                      from tailscale.com/cmd/k8s-operator+
+        tailscale.com/types/result                                   from tailscale.com/util/lineread
         tailscale.com/types/structs                                  from tailscale.com/control/controlclient+
         tailscale.com/types/tkatype                                  from tailscale.com/client/tailscale+
         tailscale.com/types/views                                    from tailscale.com/appc+

diff --git a/cmd/stund/depaware.txt b/cmd/stund/depaware.txt
@@ -67,6 +67,7 @@ tailscale.com/cmd/stund dependencies: (generated by github.com/tailscale/depawar
         tailscale.com/types/logger                                   from tailscale.com/tsweb
         tailscale.com/types/opt                                      from tailscale.com/envknob+
         tailscale.com/types/ptr                                      from tailscale.com/tailcfg+
+        tailscale.com/types/result                                   from tailscale.com/util/lineread
         tailscale.com/types/structs                                  from tailscale.com/tailcfg+
         tailscale.com/types/tkatype                                  from tailscale.com/tailcfg+
         tailscale.com/types/views                                    from tailscale.com/net/tsaddr+

diff --git a/cmd/tailscale/depaware.txt b/cmd/tailscale/depaware.txt
@@ -148,6 +148,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/types/persist                                  from tailscale.com/ipn
         tailscale.com/types/preftype                                 from tailscale.com/cmd/tailscale/cli+
         tailscale.com/types/ptr                                      from tailscale.com/hostinfo+
+        tailscale.com/types/result                                   from tailscale.com/util/lineread
         tailscale.com/types/structs                                  from tailscale.com/ipn+
         tailscale.com/types/tkatype                                  from tailscale.com/types/key+
         tailscale.com/types/views                                    from tailscale.com/tailcfg+

diff --git a/cmd/tailscaled/depaware.txt b/cmd/tailscaled/depaware.txt
@@ -364,6 +364,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/types/persist                                  from tailscale.com/control/controlclient+
         tailscale.com/types/preftype                                 from tailscale.com/ipn+
         tailscale.com/types/ptr                                      from tailscale.com/control/controlclient+
+        tailscale.com/types/result                                   from tailscale.com/util/lineread
         tailscale.com/types/structs                                  from tailscale.com/control/controlclient+
         tailscale.com/types/tkatype                                  from tailscale.com/tka+
         tailscale.com/types/views                                    from tailscale.com/ipn/ipnlocal+

diff --git a/hostinfo/hostinfo.go b/hostinfo/hostinfo.go
@@ -231,12 +231,12 @@ func desktop() (ret opt.Bool) {
 	}
 
 	seenDesktop := false
-	lineread.File("/proc/net/unix", func(line []byte) error {
+	for lr := range lineread.File("/proc/net/unix") {
+		line, _ := lr.Value()
 		seenDesktop = seenDesktop || mem.Contains(mem.B(line), mem.S(" @/tmp/dbus-"))
 		seenDesktop = seenDesktop || mem.Contains(mem.B(line), mem.S(".X11-unix"))
 		seenDesktop = seenDesktop || mem.Contains(mem.B(line), mem.S("/wayland-1"))
-		return nil
-	})
+	}
 	ret.Set(seenDesktop)
 
 	// Only cache after a minute - compositors might not have started yet.
@@ -305,21 +305,21 @@ func inContainer() opt.Bool {
 		ret.Set(true)
 		return ret
 	}
-	lineread.File("/proc/1/cgroup", func(line []byte) error {
+	for lr := range lineread.File("/proc/1/cgroup") {
+		line, _ := lr.Value()
 		if mem.Contains(mem.B(line), mem.S("/docker/")) ||
 			mem.Contains(mem.B(line), mem.S("/lxc/")) {
 			ret.Set(true)
-			return io.EOF // arbitrary non-nil error to stop loop
+			break
 		}
-		return nil
-	})
-	lineread.File("/proc/mounts", func(line []byte) error {
+	}
+	for lr := range lineread.File("/proc/mounts") {
+		line, _ := lr.Value()
 		if mem.Contains(mem.B(line), mem.S("lxcfs /proc/cpuinfo fuse.lxcfs")) {
 			ret.Set(true)
-			return io.EOF
+			break
 		}
-		return nil
-	})
+	}
 	return ret
 }
 

diff --git a/hostinfo/hostinfo_linux.go b/hostinfo/hostinfo_linux.go
@@ -106,15 +106,18 @@ func linuxVersionMeta() (meta versionMeta) {
 	}
 
 	m := map[string]string{}
-	lineread.File(propFile, func(line []byte) error {
+	for lr := range lineread.File(propFile) {
+		line, err := lr.Value()
+		if err != nil {
+			break
+		}
 		eq := bytes.IndexByte(line, '=')
 		if eq == -1 {
-			return nil
+			continue
 		}
 		k, v := string(line[:eq]), strings.Trim(string(line[eq+1:]), `"'`)
 		m[k] = v
-		return nil
-	})
+	}
 
 	if v := m["VERSION_CODENAME"]; v != "" {
 		meta.DistroCodeName = v

diff --git a/ipn/ipnlocal/ssh.go b/ipn/ipnlocal/ssh.go
@@ -80,30 +80,32 @@ func (b *LocalBackend) getSSHUsernames(req *tailcfg.C2NSSHUsernamesRequest) (*ta
 		if err != nil {
 			return nil, err
 		}
-		lineread.Reader(bytes.NewReader(out), func(line []byte) error {
+		for line := range lineread.Bytes(out) {
 			line = bytes.TrimSpace(line)
 			if len(line) == 0 || line[0] == '_' {
-				return nil
+				continue
 			}
 			add(string(line))
-			return nil
-		})
+		}
 	default:
-		lineread.File("/etc/passwd", func(line []byte) error {
+		for lr := range lineread.File("/etc/passwd") {
+			line, err := lr.Value()
+			if err != nil {
+				break
+			}
 			line = bytes.TrimSpace(line)
 			if len(line) == 0 || line[0] == '#' || line[0] == '_' {
-				return nil
+				continue
 			}
 			if mem.HasSuffix(mem.B(line), mem.S("/nologin")) ||
 				mem.HasSuffix(mem.B(line), mem.S("/false")) {
-				return nil
+				continue
 			}
 			colon := bytes.IndexByte(line, ':')
 			if colon != -1 {
 				add(string(line[:colon]))
 			}
-			return nil
-		})
+		}
 	}
 	return res, nil
 }

diff --git a/ssh/tailssh/tailssh_test.go b/ssh/tailssh/tailssh_test.go
@@ -1123,14 +1123,11 @@ func TestSSH(t *testing.T) {
 
 func parseEnv(out []byte) map[string]string {
 	e := map[string]string{}
-	lineread.Reader(bytes.NewReader(out), func(line []byte) error {
-		i := bytes.IndexByte(line, '=')
-		if i == -1 {
-			return nil
+	for line := range lineread.Bytes(out) {
+		if i := bytes.IndexByte(line, '='); i != -1 {
+			e[string(line[:i])] = string(line[i+1:])
 		}
-		e[string(line[:i])] = string(line[i+1:])
-		return nil
-	})
+	}
 	return e
 }
 

diff --git a/ssh/tailssh/user.go b/ssh/tailssh/user.go
@@ -6,7 +6,6 @@
 package tailssh
 
 import (
-	"io"
 	"os"
 	"os/exec"
 	"os/user"
@@ -110,15 +109,16 @@ func defaultPathForUser(u *user.User) string {
 }
 
 func defaultPathForUserOnNixOS(u *user.User) string {
-	var path string
-	lineread.File("/etc/pam/environment", func(lineb []byte) error {
+	for lr := range lineread.File("/etc/pam/environment") {
+		lineb, err := lr.Value()
+		if err != nil {
+			return ""
+		}
 		if v := pathFromPAMEnvLine(lineb, u); v != "" {
-			path = v
-			return io.EOF // stop iteration
+			return v
 		}
-		return nil
-	})
-	return path
+	}
+	return ""
 }
 
 func pathFromPAMEnvLine(line []byte, u *user.User) (path string) {

diff --git a/types/result/result.go b/types/result/result.go
@@ -0,0 +1,49 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package result contains the Of result type, which is
+// either a value or an error.
+package result
+
+// Of is either a T value or an error.
+//
+// Think of it like Rust or Swift's result types.
+// It's named "Of" because the fully qualified name
+// for callers reads result.Of[T].
+type Of[T any] struct {
+	v   T // valid if Err is nil; invalid if Err is non-nil
+	err error
+}
+
+// Value returns a new result with value v,
+// without an error.
+func Value[T any](v T) Of[T] {
+	return Of[T]{v: v}
+}
+
+// Error returns a new result with error err.
+// If err is nil, the returned result is equivalent
+// to calling Value with T's zero value.
+func Error[T any](err error) Of[T] {
+	return Of[T]{err: err}
+}
+
+// MustValue returns r's result value.
+// It panics if r.Err returns non-nil.
+func (r Of[T]) MustValue() T {
+	if r.err != nil {
+		panic(r.err)
+	}
+	return r.v
+}
+
+// Value returns r's result value and error.
+func (r Of[T]) Value() (T, error) {
+	return r.v, r.err
+}
+
+// Err returns r's error, if any.
+// When r.Err returns nil, it's safe to call r.MustValue without it panicking.
+func (r Of[T]) Err() error {
+	return r.err
+}
diff --git a/util/lineread/lineread.go b/util/lineread/lineread.go
@@ -6,19 +6,52 @@ package lineread
 
 import (
 	"bufio"
+	"bytes"
 	"io"
+	"iter"
 	"os"
+
+	"tailscale.com/types/result"
 )
 
-// File opens name and calls fn for each line. It returns an error if the Open failed
-// or once fn returns an error.
-func File(name string, fn func(line []byte) error) error {
+// File returns an iterator that reads lines from the named file.
+func File(name string) iter.Seq[result.Of[[]byte]] {
 	f, err := os.Open(name)
-	if err != nil {
-		return err
+	return func(yield func(result.Of[[]byte]) bool) {
+		if err != nil {
+			yield(result.Error[[]byte](err))
+			return
+		}
+		defer f.Close()
+		bs := bufio.NewScanner(f)
+		for bs.Scan() {
+			if !yield(result.Value(bs.Bytes())) {
+				return
+			}
+		}
+		if err := bs.Err(); err != nil {
+			yield(result.Error[[]byte](err))
+		}
+	}
+}
+
+// Bytes returns an iterator over the lines in bs.
+// The returned substrings don't include the trailing newline.
+// Lines may be empty.
+func Bytes(bs []byte) iter.Seq[[]byte] {
+	return func(yield func([]byte) bool) {
+		for len(bs) > 0 {
+			i := bytes.IndexByte(bs, '\n')
+			if i < 0 {
+				yield(bs)
+				return
+			}
+			if !yield(bs[:i]) {
+				return
+			}
+			bs = bs[i+1:]
+		}
 	}
-	defer f.Close()
-	return Reader(f, fn)
 }
 
 // Reader calls fn for each line.

diff --git a/util/lineread/lineread_test.go b/util/lineread/lineread_test.go
@@ -0,0 +1,30 @@
+package lineread
+
+import (
+	"slices"
+	"strings"
+	"testing"
+)
+
+func TestBytesLines(t *testing.T) {
+	var got []string
+	for line := range Bytes([]byte("foo\n\nbar\nbaz")) {
+		got = append(got, string(line))
+	}
+	want := []string{"foo", "", "bar", "baz"}
+	if !slices.Equal(got, want) {
+		t.Errorf("got %q; want %q", got, want)
+	}
+}
+
+func TestReader(t *testing.T) {
+	var got []string
+	Reader(strings.NewReader("foo\n\nbar\nbaz"), func(line []byte) error {
+		got = append(got, string(line))
+		return nil
+	})
+	want := []string{"foo", "", "bar", "baz"}
+	if !slices.Equal(got, want) {
+		t.Errorf("got %q; want %q", got, want)
+	}
+}
diff --git a/version/distro/distro.go b/version/distro/distro.go
@@ -6,7 +6,6 @@ package distro
 
 import (
 	"bytes"
-	"io"
 	"os"
 	"runtime"
 	"strconv"
@@ -132,18 +131,21 @@ func DSMVersion() int {
 			return v
 		}
 		// But when run from the command line, we have to read it from the file:
-		lineread.File("/etc/VERSION", func(line []byte) error {
+		for lr := range lineread.File("/etc/VERSION") {
+			line, err := lr.Value()
+			if err != nil {
+				break // but otherwise ignore
+			}
 			line = bytes.TrimSpace(line)
 			if string(line) == `majorversion="7"` {
 				v = 7
-				return io.EOF
+				break
 			}
 			if string(line) == `majorversion="6"` {
 				v = 6
-				return io.EOF
+				break
 			}
-			return nil
-		})
+		}
 		return v
 	})
 }