Add the 2nd member to Value::Undefined to keep the offset of the value.

src/lib.rs

@@ -48,6 +48,7 @@
 //! Major changes between 0.2.3 and 0.3 are listed below.
 //!
 //! * Enum Error has two new variants: TooBig and NotSupported.
+//! * Value::Undefined has the 2nd member to keep the offset of the value.
 
 pub use error::Error;
 pub use jpeg::get_exif_attr as get_exif_attr_from_jpeg;

src/reader.rs

@@ -186,6 +186,6 @@ mod tests {
         let file = File::open("tests/exif.jpg").unwrap();
         let reader = Reader::new(&mut BufReader::new(&file)).unwrap();
         assert_pat!(reader.get_field(tag::ExifVersion, false).unwrap().value,
-                    Value::Undefined(b"0230"));
+                    Value::Undefined(b"0230", _));
     }
 }

src/tag.rs

@@ -670,7 +670,7 @@ fn d_sensitivitytype(w: &mut fmt::Write, value: &Value) -> fmt::Result {
 
 // ExifVersion (Exif 0x9000), FlashpixVersion (Exif 0xa000)
 fn d_exifver(w: &mut fmt::Write, value: &Value) -> fmt::Result {
-    if let Value::Undefined(u) = *value {
+    if let Value::Undefined(u, _) = *value {
         if u.len() == 4 {
             if let Ok(major) = atou16(&u[0..2]) {
                 if let Ok(minor) = atou16(&u[2..4]) {
@@ -688,7 +688,7 @@ fn d_exifver(w: &mut fmt::Write, value: &Value) -> fmt::Result {
 
 // ComponentsConfiguration (Exif 0x9101)
 fn d_cpntcfg(w: &mut fmt::Write, value: &Value) -> fmt::Result {
-    if let Value::Undefined(u) = *value {
+    if let Value::Undefined(u, _) = *value {
         for &x in u {
             try!(match x {
                 0 => w.write_char('_'),
@@ -859,7 +859,7 @@ fn d_sensingmethod(w: &mut fmt::Write, value: &Value) -> fmt::Result {
 // FileSource (Exif 0xa300)
 fn d_filesrc(w: &mut fmt::Write, value: &Value) -> fmt::Result {
     let s = match match *value {
-        Value::Undefined(s) => s.first().map(|&x| x),
+        Value::Undefined(s, _) => s.first().map(|&x| x),
         _ => None,
     } {
         Some(0) => "others",
@@ -874,7 +874,7 @@ fn d_filesrc(w: &mut fmt::Write, value: &Value) -> fmt::Result {
 // SceneType (Exif 0xa301)
 fn d_scenetype(w: &mut fmt::Write, value: &Value) -> fmt::Result {
     let s = match match *value {
-        Value::Undefined(s) => s.first().map(|&x| x),
+        Value::Undefined(s, _) => s.first().map(|&x| x),
         _ => None,
     } {
         Some(1) => "directly photographed image",
@@ -1168,7 +1168,7 @@ fn d_gpsdifferential(w: &mut fmt::Write, value: &Value) -> fmt::Result {
 
 fn d_ascii_in_undef(w: &mut fmt::Write, value: &Value) -> fmt::Result {
     match *value {
-        Value::Undefined(s) => d_sub_ascii(w, s),
+        Value::Undefined(s, _) => d_sub_ascii(w, s),
         _ => d_default(w, value),
     }
 }
@@ -1205,7 +1205,7 @@ fn d_default(w: &mut fmt::Write, value: &Value) -> fmt::Result {
         Value::Long(ref v) => d_sub_comma(w, v),
         Value::Rational(ref v) => d_sub_comma(w, v),
         Value::SByte(ref v) => d_sub_comma(w, v),
-        Value::Undefined(ref s) => d_sub_hex(w, s),
+        Value::Undefined(ref s, _) => d_sub_hex(w, s),
         Value::SShort(ref v) => d_sub_comma(w, v),
         Value::SLong(ref v) => d_sub_comma(w, v),
         Value::SRational(ref v) => d_sub_comma(w, v),
@@ -1304,7 +1304,7 @@ mod tests {
             _ => panic!(),
         }
         match tag::FileSource.default_value() {
-            Some(Value::Undefined(v)) => assert_eq!(v, &[3]),
+            Some(Value::Undefined(v, _)) => assert_eq!(v, &[3]),
             _ => panic!(),
         }
         match tag::GPSAltitudeRef.default_value() {

src/value.rs

@@ -48,7 +48,12 @@ pub enum Value<'a> {
     /// Vector of 8-bit signed integers.  Unused in the Exif specification.
     SByte(Vec<i8>),
     /// Slice of 8-bit bytes.
-    Undefined(&'a [u8]),
+    ///
+    /// The second member keeps the offset of the value in the Exif data.
+    /// The interpretation of the value does not generally depend on
+    /// the location, but if it does, the offset information helps.
+    /// When encoding Exif, it is ignored.
+    Undefined(&'a [u8], u32),
     /// Vector of 16-bit signed integers.  Unused in the Exif specification.
     SShort(Vec<i16>),
     /// Vector of 32-bit signed integers.
@@ -77,7 +82,7 @@ impl<'a> Value<'a> {
     ///
     /// ```
     /// use exif::{Value, tag};
-    /// let val = Value::Undefined(b"0231");
+    /// let val = Value::Undefined(b"0231", 0);
     /// assert_eq!(format!("{}", val.display_as(tag::ExifVersion)),
     ///            "2.31");
     /// let val = Value::Short(vec![2]);
@@ -177,7 +182,7 @@ impl<'a> From<&'a DefaultValue> for Option<Value<'a>> {
             DefaultValue::Short(s) => Some(Value::Short(s.to_vec())),
             DefaultValue::Rational(s) => Some(Value::Rational(
                 s.iter().map(|&t| tuple2rational(t)).collect())),
-            DefaultValue::Undefined(s) => Some(Value::Undefined(s)),
+            DefaultValue::Undefined(s) => Some(Value::Undefined(s, 0)),
             DefaultValue::ContextDependent => None,
             DefaultValue::Unspecified => None,
         }
@@ -361,7 +366,7 @@ fn parse_sbyte<'a>(data: &'a [u8], offset: usize, count: usize)
 
 fn parse_undefined<'a>(data: &'a [u8], offset: usize, count: usize)
                        -> Value<'a> {
-    Value::Undefined(&data[offset .. offset + count])
+    Value::Undefined(&data[offset .. offset + count], offset as u32)
 }
 
 fn parse_sshort<'a, E>(data: &'a [u8], offset: usize, count: usize)
@@ -546,7 +551,10 @@ mod tests {
         for &(data, ans) in sets {
             assert!((data.len() - 1) % unitlen == 0);
             match parser(data, 1, (data.len() - 1) / unitlen) {
-                Value::Undefined(v) => assert_eq!(v, ans),
+                Value::Undefined(v, o) => {
+                    assert_eq!(v, ans);
+                    assert_eq!(o, 1);
+                },
                 v => panic!("wrong variant {:?}", v),
             }
         }

src/writer.rs

@@ -509,7 +509,7 @@ fn compose_value<E>(value: &Value)
                 vec.as_ptr() as *const u8, vec.len()) };
             Ok((6, vec.len(), uslice.to_vec()))
         },
-        Value::Undefined(ref s) =>
+        Value::Undefined(ref s, _) =>
             Ok((7, s.len(), s.to_vec())),
         Value::SShort(ref vec) => {
             let mut buf = Vec::new();
@@ -614,7 +614,7 @@ mod tests {
         let exif_ver = Field {
             tag: tag::ExifVersion,
             thumbnail: false,
-            value: Value::Undefined(b"0231"),
+            value: Value::Undefined(b"0231", 0),
         };
         let mut writer = Writer::new();
         let mut buf = Cursor::new(Vec::new());
@@ -692,7 +692,7 @@ mod tests {
         let exif_ver = Field {
             tag: tag::ExifVersion,
             thumbnail: false,
-            value: Value::Undefined(b"0231"),
+            value: Value::Undefined(b"0231", 0),
         };
         let gps_ver = Field {
             tag: tag::GPSVersionID,
@@ -772,7 +772,7 @@ mod tests {
             (Value::SByte(vec![-2, -128]),
              (6, 2, b"\xfe\x80".to_vec()),
              (6, 2, b"\xfe\x80".to_vec())),
-            (Value::Undefined(b"abc"),
+            (Value::Undefined(b"abc", 0),
              (7, 3, b"abc".to_vec()),
              (7, 3, b"abc".to_vec())),
             (Value::SShort(vec![-2, -0x8000]),

tests/rwrcmp.rs

@@ -155,7 +155,7 @@ fn compare_field_value(value1: &Value, value2: &Value) {
         },
         (&Value::SByte(ref v1), &Value::SByte(ref v2)) =>
             assert_eq!(v1, v2),
-        (&Value::Undefined(ref v1), &Value::Undefined(ref v2)) =>
+        (&Value::Undefined(ref v1, _), &Value::Undefined(ref v2, _)) =>
             assert_eq!(v1, v2),
         (&Value::SShort(ref v1), &Value::SShort(ref v2)) =>
             assert_eq!(v1, v2),