Attachment behavior fix for Firefox

util/peek.go

@@ -0,0 +1,61 @@
+package util
+
+import (
+	"bytes"
+	"io"
+	"strings"
+)
+
+// PeekedReadCloser is a ReadCloser that allows peeking into a stream and buffering it in memory.
+// It can be instantiated using the Peek function. After a stream has been peeked, it can still be fully
+// read by reading the PeekedReadCloser. It first drained from the memory buffer, and then from the remaining
+// underlying reader.
+type PeekedReadCloser struct {
+	PeekedBytes  []byte
+	LimitReached bool
+	peeked       io.Reader
+	underlying   io.ReadCloser
+	closed       bool
+}
+
+// Peek reads the underlying ReadCloser into memory up until the limit and returns a PeekedReadCloser
+func Peek(underlying io.ReadCloser, limit int) (*PeekedReadCloser, error) {
+	if underlying == nil {
+		underlying = io.NopCloser(strings.NewReader(""))
+	}
+	peeked := make([]byte, limit)
+	read, err := io.ReadFull(underlying, peeked)
+	if err != nil && err != io.ErrUnexpectedEOF && err != io.EOF {
+		return nil, err
+	}
+	return &PeekedReadCloser{
+		PeekedBytes:  peeked[:read],
+		LimitReached: read == limit,
+		underlying:   underlying,
+		peeked:       bytes.NewReader(peeked[:read]),
+		closed:       false,
+	}, nil
+}
+
+// Read reads from the peeked bytes and then from the underlying stream
+func (r *PeekedReadCloser) Read(p []byte) (n int, err error) {
+	if r.closed {
+		return 0, io.EOF
+	}
+	n, err = r.peeked.Read(p)
+	if err == io.EOF {
+		return r.underlying.Read(p)
+	} else if err != nil {
+		return 0, err
+	}
+	return
+}
+
+// Close closes the underlying stream
+func (r *PeekedReadCloser) Close() error {
+	if r.closed {
+		return io.EOF
+	}
+	r.closed = true
+	return r.underlying.Close()
+}