Add support for ASCII tags

src/decoder/ifd.rs

@@ -6,7 +6,7 @@ use std::collections::{HashMap};
 use super::stream::{ByteOrder, SmartReader, EndianReader};
 use ::{TiffError, TiffResult};
 
-use self::Value::{Unsigned, List, Rational};
+use self::Value::{Unsigned, List, Rational, Ascii};
 
 macro_rules! tags {
     {$(
@@ -33,7 +33,7 @@ macro_rules! tags {
 // Note: These tags appear in the order they are mentioned in the TIFF reference
 tags!{
     // Baseline tags:
-    Artist 315; // TODO add support
+    Artist 315;
     // grayscale images PhotometricInterpretation 1 or 3
     BitsPerSample 258;
     CellLength 265; // TODO add support
@@ -41,22 +41,22 @@ tags!{
     // palette-color images (PhotometricInterpretation 3)
     ColorMap 320; // TODO add support
     Compression 259; // TODO add support for 2 and 32773
-    Copyright 33_432; // TODO add support
-    DateTime 306; // TODO add support
+    Copyright 33_432;
+    DateTime 306;
     ExtraSamples 338; // TODO add support
     FillOrder 266; // TODO add support
     FreeByteCounts 289; // TODO add support
     FreeOffsets 288; // TODO add support
     GrayResponseCurve 291; // TODO add support
     GrayResponseUnit 290; // TODO add support
-    HostComputer 316; // TODO add support
-    ImageDescription 270; // TODO add support
+    HostComputer 316;
+    ImageDescription 270;
     ImageLength 257;
     ImageWidth 256;
-    Make 271; // TODO add support
+    Make 271;
     MaxSampleValue 281; // TODO add support
     MinSampleValue 280; // TODO add support
-    Model 272; // TODO add support
+    Model 272;
     NewSubfileType 254; // TODO add support
     Orientation 274; // TODO add support
     PhotometricInterpretation 262;
@@ -91,7 +91,8 @@ pub enum Value {
     //Signed(i32),
     Unsigned(u32),
     List(Vec<Value>),
-    Rational(u32, u32)
+    Rational(u32, u32),
+    Ascii(String)
 }
 
 impl Value {
@@ -113,8 +114,8 @@ impl Value {
                 Ok(new_vec)
             },
             Unsigned(val) => Ok(vec![val]),
-            Rational(numerator, denominator) => Ok(vec![numerator, denominator])
-            //_ => Err(::image::FormatError("Tag data malformed.".to_string()))
+            Rational(numerator, denominator) => Ok(vec![numerator, denominator]),
+            Ascii(val) => Ok(val.chars().map(|x| x as u32).collect())
         }
     }
 }
@@ -196,6 +197,11 @@ impl Entry {
                 }
                 Ok(List(v))
             },
+            (Type::ASCII, n) => {
+                try!(decoder.goto_offset(try!(self.r(bo).read_u32())));
+                let string = try!(decoder.read_string(n as usize));
+                Ok(Ascii(string))
+            }
             _ => Err(TiffError::UnsupportedError("Unsupported data type.".to_string()))
         }
     }

src/decoder/mod.rs

@@ -2,6 +2,7 @@ use std::io::{self, Read, Seek};
 use std::mem;
 use num_traits::{FromPrimitive, Num};
 use std::collections::HashMap;
+use std::string::FromUtf8Error;
 
 use ::{ColorType, TiffError, TiffResult};
 
@@ -279,6 +280,16 @@ impl<R: Read + Seek> Decoder<R> {
         self.reader.read_u32()
     }
 
+    /// Reads a string
+    #[inline]
+    pub fn read_string(&mut self, length: usize) -> Result<String, FromUtf8Error> {
+        let mut out = String::with_capacity(length);
+        self.reader.read_to_string(&mut out);
+        // Strings may be null-terminated, so we trim anything downstream of the null byte
+        let trimmed = out.bytes().take_while(|&n| n != 0).collect::<Vec<u8>>();
+        String::from_utf8(trimmed)
+    }
+
     /// Reads a TIFF IFA offset/value field
     #[inline]
     pub fn read_offset(&mut self) -> Result<[u8; 4], io::Error> {

src/error.rs

@@ -1,6 +1,7 @@
 use std::error::Error;
 use std::fmt;
 use std::io;
+use std::string;
 
 /// Tiff error kinds.
 #[derive(Debug)]
@@ -49,5 +50,11 @@ impl From<io::Error> for TiffError {
     }
 }
 
+impl From<string::FromUtf8Error> for TiffError {
+    fn from(err: string::FromUtf8Error) -> TiffError {
+        TiffError::FormatError(String::from("Image contains invalid tag."))
+    }
+}
+
 /// Result of an image decoding/encoding process
 pub type TiffResult<T> = Result<T, TiffError>;

tests/decode_images.rs

@@ -1,7 +1,7 @@
 extern crate tiff;
 
 use tiff::ColorType;
-use tiff::decoder::{Decoder, DecodingResult};
+use tiff::decoder::{Decoder, DecodingResult, ifd::Tag, ifd::Value};
 
 use std::fs::File;
 
@@ -45,6 +45,24 @@ fn test_rgb_u16()
     assert!(img_res.is_ok());
 }
 
+#[test]
+fn test_string_tags()
+{
+    // these files have null-terminated strings for their Software tag. One has extra bytes after
+    // the null byte, so we check both to ensure that we're truncating properly
+    let filenames = vec!["minisblack-1c-16b.tiff", "rgb-3c-16b.tiff"];
+    for filename in filenames.iter() {
+        let path = format!("./tests/images/{}", filename);
+        let img_file = File::open(path).expect("can't open file");
+        let mut decoder = Decoder::new(img_file).expect("Cannot create decoder");
+        let software= decoder.get_tag(Tag::Software).unwrap();
+        match software {
+            Value::Ascii(s) => assert_eq!(s, String::from("GraphicsMagick 1.2 unreleased Q16 http://www.GraphicsMagick.org/")),
+            _ => assert!(false)
+        };
+    }
+}
+
 // TODO: GrayA support
 //#[test]
 //fn test_gray_alpha_u8()