Fix the EOFException when MSIFile.isFile() is used on a file smaller than 8 bytes (Fixes ebourg#160)

Author: paolodenti

jsign-core/src/main/java/net/jsign/msi/MSIFile.java

@@ -107,6 +107,9 @@ public class MSIFile implements Signable {
      * @throws IOException if an I/O error occurs
      */
     public static boolean isMSIFile(File file) throws IOException {
+        if (file.length() < 8) {
+            return false;
+        }
         try (DataInputStream in = new DataInputStream(new FileInputStream(file))) {
             return in.readLong() == MSI_HEADER;
         }

jsign-core/src/test/java/net/jsign/msi/MSIFileTest.java

@@ -18,6 +18,7 @@
 
 import java.io.File;
 
+import org.apache.commons.io.FileUtils;
 import org.junit.Test;
 
 import static org.junit.Assert.*;
@@ -28,6 +29,11 @@ public class MSIFileTest {
     public void testIsMSIFile() throws Exception {
         assertFalse(MSIFile.isMSIFile(new File("pom.xml")));
         assertTrue(MSIFile.isMSIFile(new File("target/test-classes/minimal.msi")));
+
+        // small file
+        File file = File.createTempFile("small", ".msi");
+        FileUtils.writeByteArrayToFile(file, new byte[3]);
+        assertFalse(MSIFile.isMSIFile(file));
     }
 
     @Test