#493 Allow adding content to empty files

Author: srikanth-lingala

src/main/java/net/lingala/zip4j/headers/HeaderReader.java

@@ -66,6 +66,10 @@ public class HeaderReader {
 
   public ZipModel readAllHeaders(RandomAccessFile zip4jRaf, Zip4jConfig zip4jConfig) throws IOException {
 
+    if (zip4jRaf.length() == 0) {
+      return new ZipModel();
+    }
+
     if (zip4jRaf.length() < ENDHDR) {
       throw new ZipException("Zip file size less than minimum expected zip file size. " +
           "Probably not a zip file or a corrupted zip file");

src/test/java/net/lingala/zip4j/AddFilesToZipIT.java

@@ -949,6 +949,22 @@ public void testAddStreamWithStoreCompressionAndAesEncryptionWorksFine() throws
     extractZipFileWithStream(generatedZipFile, PASSWORD);
   }
 
+  @Test
+  public void testAddStreamToAnEmptyFileDoesNotThrowException() throws IOException {
+    if (!generatedZipFile.createNewFile()) {
+      throw new RuntimeException("Cannot create an empty file to test");
+    }
+    File fileToAdd = TestUtils.getTestFileFromResources("sample.pdf");
+    try (ZipFile zipFile = new ZipFile(generatedZipFile);
+          InputStream inputStream = Files.newInputStream(fileToAdd.toPath())) {
+      ZipParameters zipParameters = new ZipParameters();
+      zipParameters.setFileNameInZip(fileToAdd.getName());
+      zipFile.addStream(inputStream, zipParameters);
+    }
+
+    ZipFileVerifier.verifyZipFileByExtractingAllFiles(generatedZipFile, outputFolder, 1);
+  }
+
   @Test
   public void testAddFolderWithCustomBufferSize() throws IOException {
     ZipFile zipFile = new ZipFile(generatedZipFile);