Encode transformed properties files with specified Charset

Currently, the content from any properties file that is passed through
the `PropertiesFileTransformer` will have its output written into the
jar encoded as `ISO_8859_1`. If the source file contains UTF-8 content,
the output becomes corrupted.

This commit allows the buildscript to define the Charset to perform the
transformation with.

src/main/groovy/com/github/jengelman/gradle/plugins/shadow/transformers/PropertiesFileTransformer.groovy

@@ -131,6 +131,9 @@ class PropertiesFileTransformer implements Transformer {
     @Input
     String mergeSeparator = ','
 
+    @Input
+    String charset = 'ISO_8859_1'
+
     @Internal
     Closure<String> keyTransformer = IDENTITY
 
@@ -180,7 +183,8 @@ class PropertiesFileTransformer implements Transformer {
 
     private Properties loadAndTransformKeys(InputStream is) {
         Properties props = new Properties()
-        props.load(is)
+        // InputStream closed by caller, so we don't do it here.
+        props.load(new InputStreamReader(is, charset))
         return transformKeys(props)
     }
 
@@ -227,18 +231,23 @@ class PropertiesFileTransformer implements Transformer {
 
     @Override
     void modifyOutputStream(ZipOutputStream os, boolean preserveFileTimestamps) {
+        // cannot close the writer as the OutputStream needs to remain open
+        def zipWriter = new OutputStreamWriter(os, charset)
         propertiesEntries.each { String path, Properties props ->
             ZipEntry entry = new ZipEntry(path)
             entry.time = TransformerContext.getEntryTimestamp(preserveFileTimestamps, entry.time)
             os.putNextEntry(entry)
-            IOUtil.copy(toInputStream(props), os)
+            IOUtil.copy(readerFor(props, charset), zipWriter)
+            zipWriter.flush()
             os.closeEntry()
         }
     }
 
-    private static InputStream toInputStream(Properties props) {
+    private static InputStreamReader readerFor(Properties props, String charset) {
         ByteArrayOutputStream baos = new ByteArrayOutputStream()
-        props.store(baos, '')
-        new ByteArrayInputStream(baos.toByteArray())
+        baos.withWriter(charset) { w ->
+            props.store(w, '')
+        }
+        new InputStreamReader(new ByteArrayInputStream(baos.toByteArray()), charset)
     }
 }

src/test/groovy/com/github/jengelman/gradle/plugins/shadow/transformers/PropertiesFileTransformerSpec.groovy

@@ -142,4 +142,23 @@ class PropertiesFileTransformerSpec extends TransformerSpecSupport {
         'foo.properties' | { key -> 'bar.' + key.toLowerCase() }         | ['foo': 'bar'] | ['FOO': 'baz'] || ['bar.foo': 'bar,baz']
         'foo.properties' | { key -> key.replaceAll('^(foo)', 'bar.$1') } | ['foo': 'bar'] | ['FOO': 'baz'] || ['bar.foo': 'bar', 'FOO': 'baz']
     }
+
+    void appliesCharset() {
+        given:
+        def element = getFileElement(path)
+        def transformer = new PropertiesFileTransformer()
+        transformer.charset = charset
+
+        when:
+        if (transformer.canTransformResource(element)) {
+            transformer.transform(context(path, input, charset))
+        }
+
+        then:
+        output == toMap(transformer.propertiesEntries[path])
+
+        where:
+        path                    | charset      | input                 || output
+        'utf8.properties'       | 'utf-8'      | ['foo': '传傳磨宿说説'] || ['foo': '传傳磨宿说説']
+    }
 }

src/test/groovy/com/github/jengelman/gradle/plugins/shadow/transformers/TransformerSpecSupport.groovy

@@ -24,9 +24,11 @@ class TransformerSpecSupport extends Specification {
         return new ByteArrayInputStream(str.bytes)
     }
 
-    protected static InputStream toInputStream(Properties props) {
+    protected static InputStream toInputStream(Properties props, String charset) {
         ByteArrayOutputStream baos = new ByteArrayOutputStream()
-        props.store(baos, '')
+        baos.withWriter(charset) { w ->
+            props.store(w, '')
+        }
         new ByteArrayInputStream(baos.toByteArray())
     }
 
@@ -44,8 +46,8 @@ class TransformerSpecSupport extends Specification {
         }
     }
 
-    protected TransformerContext context(String path, Map input) {
-        TransformerContext.builder().path(path).is(toInputStream(toProperties(input))).relocators([]).stats(stats).build()
+    protected TransformerContext context(String path, Map input, String charset = 'ISO_8859_1') {
+        TransformerContext.builder().path(path).is(toInputStream(toProperties(input), charset)).relocators([]).stats(stats).build()
     }
 
     protected TransformerContext context(String path, String input) {