[bugfix] Parse video metadata more accurately; allow Range in fileserver (#1342)

* don't serve unused fields for video attachments

* parse video bitrate + duration more accurately

* use ServeContent where appropriate to respect Range

* abstract temp file seeker into its own function

internal/iotools/io.go

@@ -20,6 +20,7 @@ package iotools
 
 import (
 	"io"
+	"os"
 )
 
 // ReadFnCloser takes an io.Reader and wraps it to use the provided function to implement io.Closer.
@@ -157,3 +158,35 @@ func StreamWriteFunc(write func(io.Writer) error) io.Reader {
 
 	return pr
 }
+
+type tempFileSeeker struct {
+	io.Reader
+	io.Seeker
+	tmp *os.File
+}
+
+func (tfs *tempFileSeeker) Close() error {
+	tfs.tmp.Close()
+	return os.Remove(tfs.tmp.Name())
+}
+
+// TempFileSeeker converts the provided Reader into a ReadSeekCloser
+// by using an underlying temporary file. Callers should call the Close
+// function when they're done with the TempFileSeeker, to release +
+// clean up the temporary file.
+func TempFileSeeker(r io.Reader) (io.ReadSeekCloser, error) {
+	tmp, err := os.CreateTemp(os.TempDir(), "gotosocial-")
+	if err != nil {
+		return nil, err
+	}
+
+	if _, err := io.Copy(tmp, r); err != nil {
+		return nil, err
+	}
+
+	return &tempFileSeeker{
+		Reader: tmp,
+		Seeker: tmp,
+		tmp:    tmp,
+	}, nil
+}