cmd/btrfs-rec: Add a utility function for reading JSON files with progress

1 files changed, 83 insertions, 0 deletions

diff --git a/cmd/btrfs-rec/util.go b/cmd/btrfs-rec/util.go
new file mode 100644
index 0000000..adfe97e
--- /dev/null
+++ b/cmd/btrfs-rec/util.go
@@ -0,0 +1,83 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package main
+
+import (
+	"bufio"
+	"context"
+	"io"
+	"os"
+	"time"
+
+	"git.lukeshu.com/go/lowmemjson"
+	"github.com/datawire/dlib/dlog"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/textui"
+)
+
+type runeScanner struct {
+	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{
+		progress: textui.Portion[int64]{
+			D: fi.Size(),
+		},
+		progressWriter: textui.NewProgress[textui.Portion[int64]](ctx, dlog.LogLevelInfo, 1*time.Second),
+		reader:         bufio.NewReader(fh),
+		closer:         fh,
+	}
+	return ret, nil
+}
+
+func (rs *runeScanner) ReadRune() (r rune, size int, err error) {
+	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 {
+	rs.unreadCnt++
+	return rs.reader.UnreadRune()
+}
+
+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)
+	if err != nil {
+		var zero T
+		return zero, err
+	}
+	var ret T
+	if err := lowmemjson.DecodeThenEOF(buf, &ret); err != nil {
+		var zero T
+		return zero, err
+	}
+	_ = buf.Close()
+	return ret, nil
+}