精简后的项目：仅保留 api/ui 源码、文档、构建依赖

api/scanner/externaltools/exiftool/mark_reader.go

@@ -0,0 +1,116 @@
+package exiftool
+
+import (
+	"bytes"
+	"errors"
+	"io"
+)
+
+// MarkReader reads from upstream and stops at marker boundaries.
+type MarkReader struct {
+	upstream io.Reader
+	buf      []byte
+	mark     []byte
+
+	// valid data: buf[start:pending]
+	// pending, need to check if contains mark: buf[pending:end]
+	start   int
+	pending int
+	end     int
+
+	// if true, mark begins from buf[pending]
+	hasMark bool
+	// if true, upstream is EOF
+	upstreamEOF bool
+	// if true, this reader returns EOF
+	paused bool
+}
+
+// NewMarkReader creates a reader that stops at each marker and requires Reset to continue.
+func NewMarkReader(upstream io.Reader, bufferSize int, mark string) (*MarkReader, error) {
+	if bufferSize < 2*len(mark) {
+		return nil, errors.New("buffer too small")
+	}
+
+	return &MarkReader{
+		upstream: upstream,
+		buf:      make([]byte, bufferSize),
+		mark:     []byte(mark),
+	}, nil
+}
+
+// Reset resumes reading after a previously encountered marker boundary.
+func (r *MarkReader) Reset() {
+	r.paused = false
+}
+
+// Read returns bytes up to (but excluding) the next marker, then reports EOF until Reset.
+func (r *MarkReader) Read(p []byte) (int, error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+
+	if r.paused {
+		return 0, io.EOF
+	}
+
+	if r.start == r.pending {
+		// compact buffer
+		copy(r.buf[0:], r.buf[r.start:r.end])
+		r.end -= r.start
+		r.pending -= r.start
+		r.start = 0
+
+		// fill buffer
+		n, err := io.ReadAtLeast(r.upstream, r.buf[r.end:], len(r.mark))
+		r.end += n
+		if err == io.EOF || err == io.ErrUnexpectedEOF {
+			r.upstreamEOF = true
+			err = nil
+		}
+		if err != nil {
+			return 0, err
+		}
+
+		r.checkMarkInPending()
+	}
+
+	// read from valid data
+	n := copy(p, r.buf[r.start:r.pending])
+	r.start += n
+
+	if r.start == r.pending {
+		switch {
+		case r.hasMark:
+			r.pending += len(r.mark)
+			r.start += len(r.mark)
+			r.hasMark = false
+			r.paused = true
+
+			r.checkMarkInPending()
+		case r.upstreamEOF:
+			r.paused = r.start == r.end
+		}
+	}
+
+	if r.paused {
+		return n, io.EOF
+	}
+
+	return n, nil
+}
+
+func (r *MarkReader) checkMarkInPending() {
+	if markAt := bytes.Index(r.buf[r.pending:r.end], r.mark); markAt >= 0 {
+		r.hasMark = true
+		r.pending = r.pending + markAt
+		return
+	}
+
+	if r.upstreamEOF {
+		r.pending = r.end
+		return
+	}
+
+	r.pending = max(r.pending, r.end-len(r.mark)+1)
+}