Add online LSTM transducer model (#25)

sherpa-onnx/csrc/online-transducer-model.cc

@@ -0,0 +1,64 @@
+// sherpa/csrc/online-transducer-model.cc
+//
+// Copyright (c)  2023  Xiaomi Corporation
+#include "sherpa-onnx/csrc/online-transducer-model.h"
+
+#include <memory>
+#include <sstream>
+#include <string>
+
+#include "sherpa-onnx/csrc/online-lstm-transducer-model.h"
+#include "sherpa-onnx/csrc/onnx-utils.h"
+namespace sherpa_onnx {
+
+enum class ModelType {
+  kLstm,
+  kUnkown,
+};
+
+static ModelType GetModelType(const OnlineTransducerModelConfig &config) {
+  Ort::Env env(ORT_LOGGING_LEVEL_WARNING);
+  Ort::SessionOptions sess_opts;
+
+  auto sess = std::make_unique<Ort::Session>(
+      env, SHERPA_MAYBE_WIDE(config.encoder_filename).c_str(), sess_opts);
+
+  Ort::ModelMetadata meta_data = sess->GetModelMetadata();
+  if (config.debug) {
+    std::ostringstream os;
+    PrintModelMetadata(os, meta_data);
+    fprintf(stderr, "%s\n", os.str().c_str());
+  }
+
+  Ort::AllocatorWithDefaultOptions allocator;
+  auto model_type =
+      meta_data.LookupCustomMetadataMapAllocated("model_type", allocator);
+  if (!model_type) {
+    fprintf(stderr, "No model_type in the metadata!\n");
+    return ModelType::kUnkown;
+  }
+
+  if (model_type.get() == std::string("lstm")) {
+    return ModelType::kLstm;
+  } else {
+    fprintf(stderr, "Unsupported model_type: %s\n", model_type.get());
+    return ModelType::kUnkown;
+  }
+}
+
+std::unique_ptr<OnlineTransducerModel> OnlineTransducerModel::Create(
+    const OnlineTransducerModelConfig &config) {
+  auto model_type = GetModelType(config);
+
+  switch (model_type) {
+    case ModelType::kLstm:
+      return std::make_unique<OnlineLstmTransducerModel>(config);
+    case ModelType::kUnkown:
+      return nullptr;
+  }
+
+  // unreachable code
+  return nullptr;
+}
+
+}  // namespace sherpa_onnx