Caption support (#2462)

Co-authored-by: WithoutPants <53250216+WithoutPants@users.noreply.github.com>

vendor/github.com/asticode/go-astikit/io.go

@@ -0,0 +1,121 @@
+package astikit
+
+import (
+	"bytes"
+	"context"
+	"io"
+)
+
+// Copy is a copy with a context
+func Copy(ctx context.Context, dst io.Writer, src io.Reader) (int64, error) {
+	return io.Copy(dst, NewCtxReader(ctx, src))
+}
+
+type nopCloser struct {
+	io.Writer
+}
+
+func (nopCloser) Close() error { return nil }
+
+// NopCloser returns a WriteCloser with a no-op Close method wrapping
+// the provided Writer w.
+func NopCloser(w io.Writer) io.WriteCloser {
+	return nopCloser{w}
+}
+
+// CtxReader represents a reader with a context
+type CtxReader struct {
+	ctx    context.Context
+	reader io.Reader
+}
+
+// NewCtxReader creates a reader with a context
+func NewCtxReader(ctx context.Context, r io.Reader) *CtxReader {
+	return &CtxReader{
+		ctx:    ctx,
+		reader: r,
+	}
+}
+
+// Read implements the io.Reader interface
+func (r *CtxReader) Read(p []byte) (n int, err error) {
+	// Check context
+	if err = r.ctx.Err(); err != nil {
+		return
+	}
+
+	// Read
+	return r.reader.Read(p)
+}
+
+// WriterAdapter represents an object that can adapt a Writer
+type WriterAdapter struct {
+	buffer *bytes.Buffer
+	o      WriterAdapterOptions
+}
+
+// WriterAdapterOptions represents WriterAdapter options
+type WriterAdapterOptions struct {
+	Callback func(i []byte)
+	Split    []byte
+}
+
+// NewWriterAdapter creates a new WriterAdapter
+func NewWriterAdapter(o WriterAdapterOptions) *WriterAdapter {
+	return &WriterAdapter{
+		buffer: &bytes.Buffer{},
+		o:      o,
+	}
+}
+
+// Close closes the adapter properly
+func (w *WriterAdapter) Close() error {
+	if w.buffer.Len() > 0 {
+		w.write(w.buffer.Bytes())
+	}
+	return nil
+}
+
+// Write implements the io.Writer interface
+func (w *WriterAdapter) Write(i []byte) (n int, err error) {
+	// Update n to avoid broken pipe error
+	defer func() {
+		n = len(i)
+	}()
+
+	// Split
+	if len(w.o.Split) > 0 {
+		// Split bytes are not present, write in buffer
+		if !bytes.Contains(i, w.o.Split) {
+			w.buffer.Write(i)
+			return
+		}
+
+		// Loop in split items
+		items := bytes.Split(i, w.o.Split)
+		for i := 0; i < len(items)-1; i++ {
+			// If this is the first item, prepend the buffer
+			if i == 0 {
+				items[i] = append(w.buffer.Bytes(), items[i]...)
+				w.buffer.Reset()
+			}
+
+			// Write
+			w.write(items[i])
+		}
+
+		// Add remaining to buffer
+		w.buffer.Write(items[len(items)-1])
+		return
+	}
+
+	// By default, forward the bytes
+	w.write(i)
+	return
+}
+
+func (w *WriterAdapter) write(i []byte) {
+	if w.o.Callback != nil {
+		w.o.Callback(i)
+	}
+}