Draft: Java API to use tf.function available on SavedModel.

Python models that contain tf.function is inconvenient to be consumed by Java clients.
This proposal provides an API to
(a) Invoke a tf.function, given the signature name
(b) Retrieve the node name in the graph corresponding to a tf.function

Author: shajandasan

tensorflow-framework/src/main/java/org/tensorflow/framework/utils/SignatureToNodeName.java

@@ -0,0 +1,99 @@
+/*
+ * Copyright 2020 The TensorFlow Authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.tensorflow.framework.utils;
+
+import com.google.protobuf.InvalidProtocolBufferException;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import org.tensorflow.proto.framework.MetaGraphDef;
+import org.tensorflow.proto.framework.SignatureDef;
+import org.tensorflow.SavedModelBundle;
+
+public class SignatureToNodeName {
+
+  public SignatureToNodeName(SavedModelBundle savedModelBundle) {
+    loadSignatures(savedModelBundle);
+  }
+
+  public Map<String, String> inputNameToNode(String functionSignatureName) {
+    NameContainer nc = this.functionMap.get(functionSignatureName);
+    return (nc == null) ? null : nc.inputNameToNode();
+  }
+
+  public Map<String, String> outputNameToNode(String functionSignatureName) {
+    NameContainer nc = this.functionMap.get(functionSignatureName);
+    return (nc == null) ? null : nc.outputNameToNode();
+  }
+
+  public String methodName(String functionSignatureName) {
+    NameContainer nc = this.functionMap.get(functionSignatureName);
+    return (nc == null) ? null : nc.methodName();
+  }
+
+  private void loadSignatures(SavedModelBundle savedModelBundle) {
+    MetaGraphDef metaGraph = savedModelBundle.metaGraphDef();
+    Map<String, SignatureDef> signatureMap = metaGraph.getSignatureDefMap();
+
+    // A saved model can contain multiple SignatureDef
+    for (Map.Entry<String, SignatureDef> entry : signatureMap.entrySet()) {
+      NameContainer nc = new NameContainer(entry.getValue());
+      this.functionMap.put(entry.getKey(), nc);
+    }
+  }
+
+  private Map<String, NameContainer> functionMap = new HashMap<>();
+
+  private static final class NameContainer {
+     NameContainer(SignatureDef sd) {
+       this.inputNameToNodeName = sd.getInputsMap()
+         .entrySet()
+         .stream()
+         .collect(Collectors.toMap(
+            e -> e.getKey(),
+            e -> e.getValue().getName()
+        ));
+
+       this.outputNameToNodeName = sd.getOutputsMap()
+         .entrySet()
+         .stream()
+         .collect(Collectors.toMap(
+            e -> e.getKey(),
+            e -> e.getValue().getName()
+        ));
+
+       this.method = sd.getMethodName();
+     }
+
+     public Map<String, String> inputNameToNode() {
+       return this.inputNameToNodeName;
+     }
+
+     public Map<String, String> outputNameToNode() {
+       return this.outputNameToNodeName;
+     }
+
+     public String methodName() {
+       return this.method;
+     }
+
+     private Map<String, String> inputNameToNodeName;
+     private Map<String, String> outputNameToNodeName;
+     private String method;
+  }
+}

tensorflow-framework/src/main/java/org/tensorflow/framework/utils/TfFunction.java

@@ -0,0 +1,91 @@
+/*
+ * Copyright 2020 The TensorFlow Authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.tensorflow.framework.utils;
+
+import com.google.protobuf.InvalidProtocolBufferException;
+
+import java.util.List;
+import java.util.ListIterator;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.tensorflow.SavedModelBundle;
+import org.tensorflow.Session;
+import org.tensorflow.Tensor;
+
+public class TfFunction {
+
+  public TfFunction(SavedModelBundle savedModelBundle) {
+    this.nameToNode = new SignatureToNodeName(savedModelBundle);
+    this.session = savedModelBundle.session();
+  }
+
+  /**
+   * Caller is responsible for closing all Tensors
+   */
+  public Map<String, Tensor<?>> call(
+    String functionSignatureName,
+    Map<String, Tensor<?>> arguments) throws IllegalArgumentException {
+
+    Session.Runner runner = this.session.runner();
+
+    Map<String, String> inputToNode = this.nameToNode.inputNameToNode(functionSignatureName);
+
+    if (inputToNode == null) {
+      throw new IllegalArgumentException(
+        String.format("Function [%s] is missing input", functionSignatureName));
+    }
+
+    // Join arguments.key, inputToNodeName.key
+    for (Map.Entry<String, String> entry: inputToNode.entrySet()) {
+      String argName = entry.getKey();
+      Tensor<?> tensor = arguments.get(argName);
+
+      if (tensor == null) {
+        throw new IllegalArgumentException(String.format("Missing argument [%s]", argName));
+      }
+
+      // Node name in the tensorflow graph, corresponding to the tf.function argument
+      runner = runner.feed(entry.getValue(), tensor);
+    }
+
+    Map<String, String> outputToNode = this.nameToNode.outputNameToNode(functionSignatureName);
+    if (outputToNode == null) {
+      throw new IllegalArgumentException(
+        String.format("Function [%] is missing output", functionSignatureName));
+    }
+
+    for (String nodeName: outputToNode.values()) {
+      // Node names corresponding to the return value
+      runner = runner.fetch(nodeName);
+    }
+
+    List<Tensor<?>> resultTensors = runner.run();
+    ListIterator<Tensor<?>> resultTensorIter = resultTensors.listIterator();
+
+    Map<String, Tensor<?>> returnMap = new HashMap<String, Tensor<?>>();
+
+    // Use the output names as present in the signature definition
+    for (String nodeName: outputToNode.keySet()) {
+      returnMap.put(nodeName, resultTensorIter.next());
+    }
+
+    return returnMap;
+  }
+
+  private Session session;
+  private SignatureToNodeName nameToNode;
+}