utility.go: Add ExifFullTimestampString

- Added time examples.
- Added comments.

ifd_builder_test.go

@@ -1760,6 +1760,11 @@ func ExampleBuilderTag_SetValue() {
 	// Output:
 }
 
+// ExampleIfdBuilder_SetStandardWithName establishes a chain of `IfdBuilder`
+// structs from an existing chain of `Ifd` structs, navigates to the IB
+// representing IFD0, updates the ProcessingSoftware tag to a different value,
+// encodes down to a new EXIF block, reparses, and validates that the value for
+// that tag is what we set it to.
 func ExampleIfdBuilder_SetStandardWithName() {
 	filepath := path.Join(assetsPath, "NDM_8901.jpg")
 

utility.go

@@ -67,7 +67,8 @@ func DumpBytesClauseToString(data []byte) string {
     return b.String()
 }
 
-// ParseExifFullTimestamp parses dates like "2018:11:30 13:01:49".
+// ParseExifFullTimestamp parses dates like "2018:11:30 13:01:49" into a UTC
+// `time.Time` struct.
 func ParseExifFullTimestamp(fullTimestampPhrase string) (timestamp time.Time, err error) {
     defer func() {
         if state := recover(); state != nil {
@@ -115,3 +116,11 @@ func ParseExifFullTimestamp(fullTimestampPhrase string) (timestamp time.Time, er
     timestamp = time.Date(int(year), time.Month(month), int(day), int(hour), int(minute), int(second), 0, time.UTC)
     return timestamp, nil
 }
+
+// ExifFullTimestampString produces a string like "2018:11:30 13:01:49" from a
+// `time.Time` struct. It will attempt to convert to UTC first.
+func ExifFullTimestampString(t time.Time) (fullTimestampPhrase string) {
+    t = t.UTC()
+
+    return fmt.Sprintf("%04d:%02d:%02d %02d:%02d:%02d", t.Year(), t.Month(), t.Day(), t.Hour(), t.Minute(), t.Second())
+}

utility_test.go

@@ -3,8 +3,9 @@ package exif
 import (
     "io/ioutil"
 
-    "testing"
+    "fmt"
     "os"
+    "testing"
     "time"
 
     "github.com/dsoprea/go-logging"
@@ -19,7 +20,7 @@ func TestDumpBytes(t *testing.T) {
     originalStdout := os.Stdout
     os.Stdout = f
 
-    DumpBytes([]byte { 0x11, 0x22 })
+    DumpBytes([]byte{0x11, 0x22})
 
     os.Stdout = originalStdout
 
@@ -43,7 +44,7 @@ func TestDumpBytesClause(t *testing.T) {
     originalStdout := os.Stdout
     os.Stdout = f
 
-    DumpBytesClause([]byte { 0x11, 0x22 })
+    DumpBytesClause([]byte{0x11, 0x22})
 
     os.Stdout = originalStdout
 
@@ -59,7 +60,7 @@ func TestDumpBytesClause(t *testing.T) {
 }
 
 func TestDumpBytesToString(t *testing.T) {
-    s := DumpBytesToString([]byte { 0x12, 0x34, 0x56 })
+    s := DumpBytesToString([]byte{0x12, 0x34, 0x56})
 
     if s != "12 34 56" {
         t.Fatalf("result not expected")
@@ -67,7 +68,7 @@ func TestDumpBytesToString(t *testing.T) {
 }
 
 func TestDumpBytesClauseToString(t *testing.T) {
-    s := DumpBytesClauseToString([]byte { 0x12, 0x34, 0x56 })
+    s := DumpBytesClauseToString([]byte{0x12, 0x34, 0x56})
 
     if s != "0x12, 0x34, 0x56" {
         t.Fatalf("result not expected")
@@ -85,3 +86,40 @@ func TestParseExifFullTimestamp(t *testing.T) {
         t.Fatalf("time not formatted correctly: [%s] != [%s]", actual, expected)
     }
 }
+
+func TestExifFullTimestampString(t *testing.T) {
+    originalPhrase := "2018:11:30 13:01:49"
+
+    timestamp, err := ParseExifFullTimestamp(originalPhrase)
+    log.PanicIf(err)
+
+    restoredPhrase := ExifFullTimestampString(timestamp)
+    if restoredPhrase != originalPhrase {
+        t.Fatalf("Final phrase [%s] does not equal original phrase [%s]", restoredPhrase, originalPhrase)
+    }
+}
+
+func ExampleParseExifFullTimestamp() {
+    originalPhrase := "2018:11:30 13:01:49"
+
+    timestamp, err := ParseExifFullTimestamp(originalPhrase)
+    log.PanicIf(err)
+
+    fmt.Printf("To Go timestamp: [%s]\n", timestamp.Format(time.RFC3339))
+
+    // Output:
+    // To Go timestamp: [2018-11-30T13:01:49Z]
+}
+
+func ExampleExifFullTimestampString() {
+    originalPhrase := "2018:11:30 13:01:49"
+
+    timestamp, err := ParseExifFullTimestamp(originalPhrase)
+    log.PanicIf(err)
+
+    restoredPhrase := ExifFullTimestampString(timestamp)
+    fmt.Printf("To EXIF timestamp: [%s]\n", restoredPhrase)
+
+    // Output:
+    // To EXIF timestamp: [2018:11:30 13:01:49]
+}