This adds a new generic result type (motivated by golang/go#70084) to try it out, and uses it in the new lineutil package (replacing the old 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>main
Brad Fitzpatrick
1 year ago
committed by
Brad Fitzpatrick
parent
809a6eba80
commit
01185e436f
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// Package result contains the Of result type, which is
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// either a value or an error.
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package result |
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// Of is either a T value or an error.
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//
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// Think of it like Rust or Swift's result types.
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// It's named "Of" because the fully qualified name
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// for callers reads result.Of[T].
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type Of[T any] struct { |
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v T // valid if Err is nil; invalid if Err is non-nil
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err error |
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} |
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// Value returns a new result with value v,
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// without an error.
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func Value[T any](v T) Of[T] { |
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return Of[T]{v: v} |
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} |
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// Error returns a new result with error err.
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// If err is nil, the returned result is equivalent
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// to calling Value with T's zero value.
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func Error[T any](err error) Of[T] { |
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return Of[T]{err: err} |
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} |
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// MustValue returns r's result value.
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// It panics if r.Err returns non-nil.
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func (r Of[T]) MustValue() T { |
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if r.err != nil { |
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panic(r.err) |
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} |
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return r.v |
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} |
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// Value returns r's result value and error.
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func (r Of[T]) Value() (T, error) { |
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return r.v, r.err |
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} |
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// Err returns r's error, if any.
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// When r.Err returns nil, it's safe to call r.MustValue without it panicking.
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func (r Of[T]) Err() error { |
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return r.err |
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} |
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// Package lineiter iterates over lines in things.
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package lineiter |
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import ( |
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"bufio" |
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"bytes" |
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"io" |
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"iter" |
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"os" |
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"tailscale.com/types/result" |
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) |
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// File returns an iterator that reads lines from the named file.
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//
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// The returned substrings don't include the trailing newline.
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// Lines may be empty.
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func File(name string) iter.Seq[result.Of[[]byte]] { |
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f, err := os.Open(name) |
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return reader(f, f, err) |
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} |
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// Bytes returns an iterator over the lines in bs.
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// The returned substrings don't include the trailing newline.
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// Lines may be empty.
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func Bytes(bs []byte) iter.Seq[[]byte] { |
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return func(yield func([]byte) bool) { |
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for len(bs) > 0 { |
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i := bytes.IndexByte(bs, '\n') |
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if i < 0 { |
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yield(bs) |
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return |
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} |
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if !yield(bs[:i]) { |
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return |
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} |
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bs = bs[i+1:] |
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} |
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} |
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} |
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// Reader returns an iterator over the lines in r.
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//
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// The returned substrings don't include the trailing newline.
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// Lines may be empty.
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func Reader(r io.Reader) iter.Seq[result.Of[[]byte]] { |
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return reader(r, nil, nil) |
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} |
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func reader(r io.Reader, c io.Closer, err error) iter.Seq[result.Of[[]byte]] { |
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return func(yield func(result.Of[[]byte]) bool) { |
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if err != nil { |
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yield(result.Error[[]byte](err)) |
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return |
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} |
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if c != nil { |
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defer c.Close() |
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} |
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bs := bufio.NewScanner(r) |
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for bs.Scan() { |
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if !yield(result.Value(bs.Bytes())) { |
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return |
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} |
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} |
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if err := bs.Err(); err != nil { |
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yield(result.Error[[]byte](err)) |
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} |
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} |
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} |
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@ -0,0 +1,32 @@ |
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package lineiter |
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import ( |
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"slices" |
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"strings" |
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"testing" |
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) |
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func TestBytesLines(t *testing.T) { |
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var got []string |
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for line := range Bytes([]byte("foo\n\nbar\nbaz")) { |
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got = append(got, string(line)) |
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} |
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want := []string{"foo", "", "bar", "baz"} |
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if !slices.Equal(got, want) { |
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t.Errorf("got %q; want %q", got, want) |
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} |
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} |
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func TestReader(t *testing.T) { |
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var got []string |
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for line := range Reader(strings.NewReader("foo\n\nbar\nbaz")) { |
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got = append(got, string(line.MustValue())) |
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} |
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want := []string{"foo", "", "bar", "baz"} |
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if !slices.Equal(got, want) { |
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t.Errorf("got %q; want %q", got, want) |
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} |
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} |
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