Implement UserComment parsing

src/reader.rs

@@ -178,8 +178,27 @@ impl Exif {
         self.entry_map.get(&(ifd_num, tag))
             .map(|&i| self.entries[i].ref_field(&self.buf, self.little_endian))
     }
+
+    // Returns the content of the UserComment tag, converted to a String, if the tag
+    // saved in an Unicode format.
+    pub fn get_user_comment(&self, ifd_num: In) -> Option<String> {
+        self.get_field(Tag::UserComment, ifd_num)
+            .and_then(|field| match &field.value {
+                crate::Value::Undefined(buffer, _) if buffer.len() > 8 => {
+                    let unicode_prefix = "UNICODE\0".as_bytes();
+                    if &buffer[..8] == unicode_prefix {
+                        Some(crate::util::ucs2_to_string(&buffer[8..]))
+                    } else {
+                        None
+                    }
+                }
+                _ => None,
+            })
+    }
 }
 
+
+
 impl<'a> ProvideUnit<'a> for &'a Exif {
     fn get_field(self, tag: Tag, ifd_num: In) -> Option<&'a Field> {
         self.get_field(tag, ifd_num)

src/tiff.rs

@@ -247,6 +247,10 @@ impl Parser {
             return Err(Error::InvalidFormat("Truncated next IFD offset"));
         }
         let next_ifd_offset = E::loadu32(data, offset + 2 + count * 12);
+        if next_ifd_offset != 0 && ctx != Context::Tiff {
+            // Invalid Next IFD offset. ignored.
+            return Ok(0usize);
+        }
         Ok(next_ifd_offset as usize)
     }
 
@@ -584,8 +588,11 @@ mod tests {
                      \x00\x00\x00\x00\
                      \x00\x01\x90\x00\x00\x07\x00\x00\x00\x040231\
                      \x00\x00\x00\x08";
-        assert_err_pat!(parse_exif(data),
-                        Error::InvalidFormat("Unexpected next IFD"));
+        let (v, _le) = parse_exif(data).unwrap();
+        assert_eq!(v.len(), 1);
+        println!("result : {:?}", v);
+        let undef_data = Value::Undefined(b"30323331".to_vec(), 0x24);
+        assert_pat!(&v[0].value, undef_data);
     }
 
     #[test]

src/util.rs

@@ -126,6 +126,20 @@ pub fn ctou32(c: u8) -> Result<u32, Error> {
     Ok((c - ASCII_0) as u32)
 }
 
+pub fn ucs2_to_string(bytes: &[u8]) -> String {
+    let mut string = String::with_capacity(bytes.len() / 2);
+
+    let mut index = 0;
+    while index < bytes.len() {
+        let code_point = (bytes[index + 1] as u16) | ((bytes[index] as u16) << 8);
+        string.push(char::from_u32(code_point.into()).unwrap());
+
+        index += 2;
+    }
+
+    string
+}
+
 #[cfg(test)]
 mod tests {
     use std::io::ErrorKind;