feat: BACK-2316 add a simple method to detect TDFs (#111)

* just validate that we have a zip file with the right entries
* add `InvalidZipException` so that we can catch it

Author: mkleene

sdk/src/main/java/io/opentdf/platform/sdk/InvalidZipException.java

@@ -0,0 +1,7 @@
+package io.opentdf.platform.sdk;
+
+public class InvalidZipException extends RuntimeException {
+    public InvalidZipException(String message) {
+        super(message);
+    }
+}

sdk/src/main/java/io/opentdf/platform/sdk/SDK.java

@@ -13,8 +13,12 @@
 import io.opentdf.platform.policy.subjectmapping.SubjectMappingServiceGrpc;
 import io.opentdf.platform.policy.subjectmapping.SubjectMappingServiceGrpc.SubjectMappingServiceFutureStub;
 import io.opentdf.platform.sdk.nanotdf.NanoTDFType;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import javax.net.ssl.TrustManager;
+import java.io.IOException;
+import java.nio.channels.SeekableByteChannel;
 import java.util.Optional;
 
 /**
@@ -26,6 +30,8 @@ public class SDK implements AutoCloseable {
     private final TrustManager trustManager;
     private final ClientInterceptor authInterceptor;
 
+    private static final Logger log = LoggerFactory.getLogger(SDK.class);
+
     @Override
     public void close() throws Exception {
         services.close();
@@ -112,4 +118,25 @@ public Optional<ClientInterceptor> getAuthInterceptor() {
     public Services getServices() {
         return this.services;
     }
+
+    /**
+     * Checks to see if this has the structure of a Z-TDF in that it is a zip file containing
+     * a `manifest.json` and a `0.payload`
+     * @param channel A channel containing the bytes of the potential Z-TDF
+     * @return `true` if
+     */
+    public static boolean isTDF(SeekableByteChannel channel) {
+        ZipReader zipReader;
+        try {
+            zipReader = new ZipReader(channel);
+        } catch (IOException | InvalidZipException e) {
+            return false;
+        }
+        var entries = zipReader.getEntries();
+        if (entries.size() != 2) {
+            return false;
+        }
+        return entries.stream().anyMatch(e -> "0.manifest.json".equals(e.getName()))
+                && entries.stream().anyMatch(e -> "0.payload".equals(e.getName()));
+    }
 }

sdk/src/main/java/io/opentdf/platform/sdk/ZipReader.java

@@ -84,7 +84,7 @@ CentralDirectoryRecord readEndOfCentralDirectory() throws IOException {
         }
 
         if (eoCDRStart < 0) {
-            throw new RuntimeException("Didn't find the end of central directory");
+            throw new InvalidZipException("Didn't find the end of central directory");
         }
 
         short diskNumber = readShort();
@@ -109,7 +109,7 @@ private CentralDirectoryRecord extractZIP64CentralDirectoryInfo() throws IOExcep
         // buffer's position at the start of the Central Directory
         int signature = readInt();
         if (signature != ZIP64_END_OF_CENTRAL_DIRECTORY_LOCATOR_SIGNATURE) {
-            throw new RuntimeException("Invalid Zip64 End of Central Directory Record Signature");
+            throw new InvalidZipException("Invalid Zip64 End of Central Directory Record Signature");
         }
 
         int centralDirectoryDiskNumber = readInt();
@@ -119,7 +119,7 @@ private CentralDirectoryRecord extractZIP64CentralDirectoryInfo() throws IOExcep
         zipChannel.position(offsetToEndOfCentralDirectory);
         int sig = readInt();
         if (sig != ZIP_64_END_OF_CENTRAL_DIRECTORY_SIGNATURE) {
-            throw new RuntimeException("Invalid");
+            throw new InvalidZipException("Invalid");
         }
         long sizeOfEndOfCentralDirectoryRecord = readLong();
         short versionMadeBy = readShort();
@@ -152,7 +152,7 @@ public String getName() {
         public InputStream getData() throws IOException {
             zipChannel.position(offsetToLocalHeader);
             if (readInt() != LOCAL_FILE_HEADER_SIGNATURE) {
-                throw new RuntimeException("Invalid Local Header Signature");
+                throw new InvalidZipException("Invalid Local Header Signature");
             }
             zipChannel.position(zipChannel.position()
                     + Short.BYTES
@@ -218,7 +218,7 @@ public int read(byte[] b, int off, int len) throws IOException {
     public Entry readCentralDirectoryFileHeader() throws IOException {
         int signature = readInt();
         if (signature != CENTRAL_FILE_HEADER_SIGNATURE) {
-            throw new RuntimeException("Invalid Central Directory File Header Signature");
+            throw new InvalidZipException("Invalid Central Directory File Header Signature");
         }
         short versionMadeBy = readShort();
         short versionNeededToExtract = readShort();

sdk/src/test/java/io/opentdf/platform/sdk/SDKTest.java

@@ -0,0 +1,78 @@
+package io.opentdf.platform.sdk;
+
+import org.apache.commons.compress.utils.SeekableInMemoryByteChannel;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.channels.SeekableByteChannel;
+import java.util.Random;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class SDKTest {
+
+    @Test
+    void testExaminingValidZTDF() throws IOException {
+        try (var ztdf = SDKTest.class.getClassLoader().getResourceAsStream("sample.txt.tdf")) {
+            assert ztdf != null;
+            var chan = new SeekableInMemoryByteChannel(ztdf.readAllBytes());
+            assertThat(SDK.isTDF(chan)).isTrue();
+        }
+    }
+
+    @Test
+    void testExaminingInvalidFile() {
+        var chan = new SeekableByteChannel() {
+            @Override
+            public boolean isOpen() {
+                return false;
+            }
+
+            @Override
+            public void close() {
+
+            }
+
+            @Override
+            public int read(ByteBuffer dst) {
+                return 0;
+            }
+
+            @Override
+            public int write(ByteBuffer src) {
+                return 0;
+            }
+
+            @Override
+            public long position() {
+                return 0;
+            }
+
+            @Override
+            public SeekableByteChannel position(long newPosition) {
+                return this;
+            }
+
+            @Override
+            public long size() {
+                return 0;
+            }
+
+            @Override
+            public SeekableByteChannel truncate(long size) {
+                return null;
+            }
+        };
+
+        assertThat(SDK.isTDF(chan)).isFalse();
+    }
+
+    @Test
+    void testReadingRandomBytes() {
+        var tdf = new byte[2023];
+        new Random().nextBytes(tdf);
+
+        assertThat(SDK.isTDF(new SeekableInMemoryByteChannel(tdf))).isFalse();
+    }
+}