ifd: Can now resolve its own tags' values.

- Adjustments to argument naming.

exif-read-tool/main.go

@@ -26,8 +26,8 @@ import (
 )
 
 var (
-    filepathArgument = ""
+    filepathArg = ""
-    printAsJsonArgument = false
+    printAsJsonArg = false
 )
 
 
@@ -52,17 +52,17 @@ func main() {
         }
     }()
 
-    flag.StringVar(&filepathArgument, "filepath", "", "File-path of image")
+    flag.StringVar(&filepathArg, "filepath", "", "File-path of image")
-    flag.BoolVar(&printAsJsonArgument, "json", false, "Print JSON")
+    flag.BoolVar(&printAsJsonArg, "json", false, "Print JSON")
 
     flag.Parse()
 
-    if filepathArgument == "" {
+    if filepathArg == "" {
         fmt.Printf("Please provide a file-path for an image.\n")
         os.Exit(1)
     }
 
-    f, err := os.Open(filepathArgument)
+    f, err := os.Open(filepathArg)
     log.PanicIf(err)
 
     data, err := ioutil.ReadAll(f)
@@ -146,7 +146,7 @@ func main() {
     _, err = e.Visit(data[foundAt:], visitor)
     log.PanicIf(err)
 
-    if printAsJsonArgument == true {
+    if printAsJsonArg == true {
         data, err := json.MarshalIndent(entries, "", "    ")
         log.PanicIf(err)
 

ifd_enumerate.go

@@ -271,6 +271,11 @@ func (ie *IfdEnumerate) Scan(ifdOffset uint32, visitor TagVisitor) (err error) {
 
 
 type Ifd struct {
+    // This is just for convenience, just so that we can easily get the values
+    // and not involve other projects in semantics that they won't otherwise
+    // need to know.
+    addressableData []byte
+
     ByteOrder binary.ByteOrder
 
     Ii IfdIdentity
@@ -289,6 +294,19 @@ type Ifd struct {
     NextIfd *Ifd
 }
 
+func (ifd *Ifd) TagValue(ite *IfdTagEntry) (value interface{}, err error) {
+    defer func() {
+        if state := recover(); state != nil {
+            err = log.Wrap(state.(error))
+        }
+    }()
+
+    value, err = ite.Value(ifd.addressableData, ifd.ByteOrder)
+    log.PanicIf(err)
+
+    return value, nil
+}
+
 // FindTagWithId returns a list of tags (usually just zero or one) that match
 // the given tag ID. This is efficient.
 func (ifd Ifd) FindTagWithId(tagId uint16) (results []*IfdTagEntry, err error) {
@@ -550,6 +568,8 @@ func (ie *IfdEnumerate) Collect(rootIfdOffset uint32) (index IfdIndex, err error
         }
 
         ifd := Ifd{
+            addressableData: ie.exifData[ExifAddressableAreaStart:],
+
             ByteOrder: ie.byteOrder,
             Ii: ii,
             Id: id,