From d6d19b3a8f66f27f78fd2c6fa02b32fb2a88e9ad Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@lukeshu.com>
Date: Wed, 25 Jan 2023 17:41:28 -0700
Subject: Move btrfs-rec's logging RuneScanner to a new `streamio` package

---
 cmd/btrfs-rec/util.go       | 61 +-----------------------------
 lib/streamio/runescanner.go | 90 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+), 59 deletions(-)
 create mode 100644 lib/streamio/runescanner.go

diff --git a/cmd/btrfs-rec/util.go b/cmd/btrfs-rec/util.go
index 9a0d60c..b2497b2 100644
--- a/cmd/btrfs-rec/util.go
+++ b/cmd/btrfs-rec/util.go
@@ -9,77 +9,20 @@ import (
 	"context"
 	"io"
 	"os"
-	"time"
 
 	"git.lukeshu.com/go/lowmemjson"
 	"github.com/datawire/dlib/dlog"
 
-	"git.lukeshu.com/btrfs-progs-ng/lib/textui"
+	"git.lukeshu.com/btrfs-progs-ng/lib/streamio"
 )
 
-type runeScanner struct {
-	ctx            context.Context //nolint:containedctx // For detecting shutdown from methods
-	progress       textui.Portion[int64]
-	progressWriter *textui.Progress[textui.Portion[int64]]
-	unreadCnt      uint64
-	reader         *bufio.Reader
-	closer         io.Closer
-}
-
-func newRuneScanner(ctx context.Context, fh *os.File) (*runeScanner, error) {
-	fi, err := fh.Stat()
-	if err != nil {
-		return nil, err
-	}
-	ret := &runeScanner{
-		ctx: ctx,
-		progress: textui.Portion[int64]{
-			D: fi.Size(),
-		},
-		progressWriter: textui.NewProgress[textui.Portion[int64]](ctx, dlog.LogLevelInfo, textui.Tunable(1*time.Second)),
-		reader:         bufio.NewReader(fh),
-		closer:         fh,
-	}
-	return ret, nil
-}
-
-func (rs *runeScanner) ReadRune() (r rune, size int, err error) {
-	if err := rs.ctx.Err(); err != nil {
-		return 0, 0, err
-	}
-	r, size, err = rs.reader.ReadRune()
-	if rs.unreadCnt > 0 {
-		rs.unreadCnt--
-	} else {
-		rs.progress.N += int64(size)
-		rs.progressWriter.Set(rs.progress)
-	}
-	return
-}
-
-func (rs *runeScanner) UnreadRune() error {
-	if err := rs.ctx.Err(); err != nil {
-		return err
-	}
-	if err := rs.reader.UnreadRune(); err != nil {
-		return err
-	}
-	rs.unreadCnt++
-	return nil
-}
-
-func (rs *runeScanner) Close() error {
-	rs.progressWriter.Done()
-	return rs.closer.Close()
-}
-
 func readJSONFile[T any](ctx context.Context, filename string) (T, error) {
 	fh, err := os.Open(filename)
 	if err != nil {
 		var zero T
 		return zero, err
 	}
-	buf, err := newRuneScanner(dlog.WithField(ctx, "btrfs.read-json-file", filename), fh)
+	buf, err := streamio.NewRuneScanner(dlog.WithField(ctx, "btrfs.read-json-file", filename), fh)
 	defer func() {
 		_ = buf.Close()
 	}()
diff --git a/lib/streamio/runescanner.go b/lib/streamio/runescanner.go
new file mode 100644
index 0000000..421859d
--- /dev/null
+++ b/lib/streamio/runescanner.go
@@ -0,0 +1,90 @@
+// Copyright (C) 2022-2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package streamio
+
+import (
+	"bufio"
+	"context"
+	"io"
+	"os"
+	"time"
+
+	"github.com/datawire/dlib/dlog"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/textui"
+)
+
+type RuneScanner interface {
+	io.RuneScanner
+	io.Closer
+}
+
+type runeScanner struct {
+	ctx            context.Context //nolint:containedctx // For detecting shutdown from methods
+	progress       textui.Portion[int64]
+	progressWriter *textui.Progress[textui.Portion[int64]]
+	unreadCnt      uint64
+	reader         *bufio.Reader
+	closer         io.Closer
+}
+
+// NewRuneScanner returns an io.RuneScanner (and io.Closer) that
+// bufferes a file, similar to bufio.NewReader.  There are two
+// advantages over bufio.NewReader:
+//
+//   - It takes a Context, and causes reads to fail once the Context is
+//     canceled; allowing large parse operations to be gracefully cut
+//     short.
+//
+//   - It logs the progress of reading the file via textui.Progress.
+func NewRuneScanner(ctx context.Context, fh *os.File) (RuneScanner, error) {
+	fi, err := fh.Stat()
+	if err != nil {
+		return nil, err
+	}
+	ret := &runeScanner{
+		ctx: ctx,
+		progress: textui.Portion[int64]{
+			D: fi.Size(),
+		},
+		progressWriter: textui.NewProgress[textui.Portion[int64]](ctx, dlog.LogLevelInfo, textui.Tunable(1*time.Second)),
+		reader:         bufio.NewReader(fh),
+		closer:         fh,
+	}
+	return ret, nil
+}
+
+// ReadRune implements io.RuneReader.
+func (rs *runeScanner) ReadRune() (r rune, size int, err error) {
+	if err := rs.ctx.Err(); err != nil {
+		return 0, 0, err
+	}
+	r, size, err = rs.reader.ReadRune()
+	if rs.unreadCnt > 0 {
+		rs.unreadCnt--
+	} else {
+		rs.progress.N += int64(size)
+		rs.progressWriter.Set(rs.progress)
+	}
+	return
+}
+
+// ReadRune implements io.RuneScanner.
+func (rs *runeScanner) UnreadRune() error {
+	if err := rs.ctx.Err(); err != nil {
+		return err
+	}
+	if err := rs.reader.UnreadRune(); err != nil {
+		return err
+	}
+	rs.unreadCnt++
+	return nil
+}
+
+// ReadRune implements io.Closer.
+func (rs *runeScanner) Close() error {
+	rs.progressWriter.Done()
+	return rs.closer.Close()
+}
-- 
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