#764 Do not reject attempts to read blob id 0

jaybird-native/src/main/java/org/firebirdsql/gds/ng/jna/JnaBlob.java

@@ -53,15 +53,42 @@ public class JnaBlob extends AbstractFbBlob implements FbBlob, DatabaseListener
     private final FbClientLibrary clientLibrary;
     private ByteBuffer byteBuffer;
 
+    /**
+     * Creates a blob for output (writing to the database).
+     *
+     * @param database
+     *         database
+     * @param transaction
+     *         transaction
+     * @param blobParameterBuffer
+     *         blob parameter buffer
+     */
     public JnaBlob(JnaDatabase database, JnaTransaction transaction, BlobParameterBuffer blobParameterBuffer) {
-        this(database, transaction, blobParameterBuffer, NO_BLOB_ID);
+        this(database, transaction, blobParameterBuffer, NO_BLOB_ID, true);
     }
 
+    /**
+     * Creates a blob for input (reading from the database).
+     *
+     * @param database
+     *         database
+     * @param transaction
+     *         transaction
+     * @param blobParameterBuffer
+     *         blob parameter buffer
+     * @param blobId
+     *         blob id
+     */
     public JnaBlob(JnaDatabase database, JnaTransaction transaction, BlobParameterBuffer blobParameterBuffer,
             long blobId) {
+        this(database, transaction, blobParameterBuffer, blobId, false);
+    }
+
+    private JnaBlob(JnaDatabase database, JnaTransaction transaction, BlobParameterBuffer blobParameterBuffer,
+            long blobId, boolean outputBlob) {
         super(database, transaction, blobParameterBuffer);
         this.blobId = new LongByReference(blobId);
-        outputBlob = blobId == NO_BLOB_ID;
+        this.outputBlob = outputBlob;
         clientLibrary = database.getClientLibrary();
     }
 

src/docs/asciidoc/release_notes.adoc

@@ -812,6 +812,14 @@ Previously almost all types returned `true` (including -- for example -- `BOOLEA
 * Added methods `List<String> getTypeAliasList()` and `List<String> getSupportedProtocolList()` to `GDSFactoryPlugin`, and deprecated `String[] getTypeAliases()` and `String[] getSupportedProtocols()` for removal in Jaybird 7 or later
 * Fixed formatting of `isc_formatted_exception` to not repeat the original parameters of the exception (https://github.com/FirebirdSQL/jaybird/issues/749[jaybird#749])
 * Added aliases `ApplicationName` and `applicationName` for connection property `processName` (https://github.com/FirebirdSQL/jaybird/issues/751[jaybird#751])
+* Improvement: Do not reject attempts to read blob id 0 (https://github.com/FirebirdSQL/jaybird/issues/764[jaybird#764])
++
+Previously, Jaybird rejected attempts to read blobs with blob id `0` (not on all code paths, for some only when assertions are enabled).
+Formally, blob id `0` is not a valid blob id, but in practice they can occur (e.g. due to bugs, or access components/drivers explicitly setting a blob column to id `0`).
+Other drivers and tools simply send the requests for blob id `0` to the server, which then treats it as an empty blob.
+For consistency, we decided to let Jaybird handle it the same.
++
+This change was also backported to Jaybird 5.0.3.
 
 [#removal-of-deprecated-classes-and-packages]
 === Removal of deprecated classes and packages

src/jna-test/org/firebirdsql/gds/ng/jna/JnaBlobTest.java

@@ -420,6 +420,22 @@ void testOutputBlobDoubleOpen() throws Exception {
         }
     }
 
+    @Test
+    void readBlobIdZero() throws Exception {
+        try (JnaDatabase db = createDatabaseConnection()) {
+            try {
+                transaction = getTransaction(db);
+                FbBlob blob = db.createBlobForInput(transaction, 0);
+                blob.open();
+                assertEquals(0, blob.length());
+                byte[] segment = blob.getSegment(500);
+                assertEquals(0, segment.length, "expected empty segment");
+            } finally {
+                if (transaction != null) transaction.commit();
+            }
+        }
+    }
+
     @Override
     protected JnaDatabase createFbDatabase(FbConnectionProperties connectionInfo) throws SQLException {
         final JnaDatabase db = factory.connect(connectionInfo);

src/main/org/firebirdsql/gds/ng/AbstractFbBlob.java

@@ -353,10 +353,10 @@ public <T> T getBlobInfo(final byte[] requestItems, final int bufferLength, fina
     public long length() throws SQLException {
         try (LockCloseable ignored = withLock()) {
             checkDatabaseAttached();
-            if (getBlobId() == FbBlob.NO_BLOB_ID) {
+            if (isOutput() && getBlobId() == FbBlob.NO_BLOB_ID) {
                 throw FbExceptionBuilder.forException(ISCConstants.isc_bad_segstr_id).toSQLException();
             }
-            final BlobLengthProcessor blobLengthProcessor = createBlobLengthProcessor();
+            BlobLengthProcessor blobLengthProcessor = createBlobLengthProcessor();
             return getBlobInfo(blobLengthProcessor.getBlobLengthItems(), 20, blobLengthProcessor);
         } catch (SQLException e) {
             exceptionListenerDispatcher.errorOccurred(e);

src/main/org/firebirdsql/gds/ng/wire/AbstractFbWireInputBlob.java

@@ -20,7 +20,6 @@
 
 import org.firebirdsql.gds.BlobParameterBuffer;
 import org.firebirdsql.gds.ISCConstants;
-import org.firebirdsql.gds.ng.FbBlob;
 import org.firebirdsql.gds.ng.FbExceptionBuilder;
 
 import java.sql.SQLException;
@@ -34,9 +33,8 @@ public abstract class AbstractFbWireInputBlob extends AbstractFbWireBlob {
     private final long blobId;
 
     protected AbstractFbWireInputBlob(FbWireDatabase database, FbWireTransaction transaction,
-                                      BlobParameterBuffer blobParameterBuffer, long blobId) {
+            BlobParameterBuffer blobParameterBuffer, long blobId) {
         super(database, transaction, blobParameterBuffer);
-        assert blobId != FbBlob.NO_BLOB_ID : "blobId must be non-zero for an input blob";
         this.blobId = blobId;
     }
 

src/test/org/firebirdsql/gds/ng/wire/version10/V10InputBlobTest.java

@@ -226,4 +226,21 @@ public void testDoubleOpen() throws Exception {
             }
         }
     }
+
+    @Test
+    public void readBlobIdZero() throws Exception {
+        try (FbWireDatabase db = createDatabaseConnection()) {
+            try {
+                transaction = getTransaction(db);
+                FbBlob blob = db.createBlobForInput(transaction, 0);
+                blob.open();
+                assertEquals(0, blob.length());
+                byte[] segment = blob.getSegment(500);
+                assertEquals(0, segment.length, "expected empty segment");
+            } finally {
+                if (transaction != null) transaction.commit();
+            }
+        }
+    }
+
 }