fixed support for multipage images, the IDF offset is added during the new and also at the end of the internal_finish. This should only be done once

src/encoder/mod.rs

@@ -1,6 +1,7 @@
 use byteorder::NativeEndian;
 use std::collections::BTreeMap;
 use std::io::{Seek, Write};
+use std::mem;
 
 use decoder::ifd::{self, Tag};
 use error::{TiffError, TiffFormatError, TiffResult};
@@ -351,6 +352,8 @@ impl<W: Write + Seek> TiffEncoder<W> {
         };
 
         NativeEndian::write_header(&mut encoder.writer)?;
+        // blank the IFD offset location
+        encoder.writer.write_u32(0)?;
 
         Ok(encoder)
     }
@@ -417,9 +420,9 @@ pub struct DirectoryEncoder<'a, W: 'a + Write + Seek> {
 
 impl<'a, W: 'a + Write + Seek> DirectoryEncoder<'a, W> {
     fn new(writer: &'a mut TiffWriter<W>) -> TiffResult<DirectoryEncoder<'a, W>> {
+        // the previous word is the IFD offset position
+        let ifd_pointer_pos = writer.offset() - mem::size_of::<u32>() as u64;
         writer.pad_word_boundary()?;
-        let ifd_pointer_pos = writer.offset();
-        writer.write_u32(0)?;
         Ok(DirectoryEncoder {
             writer,
             dropped: false,