re-pull-request allow tokens and hotwords be loaded from buffered string driectly (#1339)

Co-authored-by: xiao <shawl336@163.com>

+name: c-api-test-loading-tokens-hotwords-from-memory
+
+on:
+  push:
+    branches:
+      - master
+    tags:
+      - 'v[0-9]+.[0-9]+.[0-9]+*'
+    paths:
+      - '.github/workflows/c-api.yaml'
+      - 'CMakeLists.txt'
+      - 'cmake/**'
+      - 'sherpa-onnx/csrc/*'
+      - 'sherpa-onnx/c-api/*'
+      - 'c-api-examples/**'
+      - 'ffmpeg-examples/**'
+  pull_request:
+    branches:
+      - master
+    paths:
+      - '.github/workflows/c-api.yaml'
+      - 'CMakeLists.txt'
+      - 'cmake/**'
+      - 'sherpa-onnx/csrc/*'
+      - 'sherpa-onnx/c-api/*'
+      - 'c-api-examples/**'
+      - 'ffmpeg-examples/**'
+
+  workflow_dispatch:
+
+concurrency:
+  group: c-api-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  c_api:
+    name: ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: ccache
+        uses: hendrikmuhs/ccache-action@v1.2
+        with:
+          key: ${{ matrix.os }}-c-api-shared
+
+      - name: Build sherpa-onnx
+        shell: bash
+        run: |
+          export CMAKE_CXX_COMPILER_LAUNCHER=ccache
+          export PATH="/usr/lib/ccache:/usr/local/opt/ccache/libexec:$PATH"
+          cmake --version
+
+          mkdir build
+          cd build
+
+          cmake \
+            -D CMAKE_BUILD_TYPE=Release \
+            -D BUILD_SHARED_LIBS=ON \
+            -D CMAKE_INSTALL_PREFIX=./install \
+            -D SHERPA_ONNX_ENABLE_BINARY=OFF \
+            ..
+
+          make -j2 install
+
+          ls -lh install/lib
+          ls -lh install/include
+
+          if [[ ${{ matrix.os }} == ubuntu-latest ]]; then
+            ldd ./install/lib/libsherpa-onnx-c-api.so
+            echo "---"
+            readelf -d ./install/lib/libsherpa-onnx-c-api.so
+          fi
+
+          if [[ ${{ matrix.os }} == macos-latest ]]; then
+            otool -L ./install/lib/libsherpa-onnx-c-api.dylib
+          fi
+
+      - name: Test streaming zipformer with tokens and hotwords loaded from buffers
+        shell: bash
+        run: |
+          gcc -o streaming-zipformer-buffered-tokens-hotwords-c-api ./c-api-examples/streaming-zipformer-buffered-tokens-hotwords-c-api.c \
+            -I ./build/install/include \
+            -L ./build/install/lib/ \
+            -l sherpa-onnx-c-api \
+            -l onnxruntime
+
+          ls -lh streaming-zipformer-buffered-tokens-hotwords-c-api
+
+          if [[ ${{ matrix.os }} == ubuntu-latest ]]; then
+            ldd ./streaming-zipformer-buffered-tokens-hotwords-c-api
+            echo "----"
+            readelf -d ./streaming-zipformer-buffered-tokens-hotwords-c-api
+          fi
+
+          curl -SL -O https://github.com/k2-fsa/sherpa-onnx/releases/download/asr-models/sherpa-onnx-streaming-zipformer-en-20M-2023-02-17.tar.bz2
+          tar xvf sherpa-onnx-streaming-zipformer-en-20M-2023-02-17.tar.bz2
+          rm sherpa-onnx-streaming-zipformer-en-20M-2023-02-17.tar.bz2
+          curl -SL -O https://huggingface.co/desh2608/icefall-asr-librispeech-pruned-transducer-stateless7-streaming-small/blob/main/data/lang_bpe_500/bpe.model
+          cp bpe.model sherpa-onnx-streaming-zipformer-en-20M-2023-02-17/
+          rm bpe.model
+          
+          printf "▁A ▁T ▁P :1.5\n▁A ▁B ▁C :3.0" > hotwords.txt
+
+          ls -lh sherpa-onnx-streaming-zipformer-en-20M-2023-02-17
+          echo "---"
+          ls -lh sherpa-onnx-streaming-zipformer-en-20M-2023-02-17/test_wavs
+
+          export LD_LIBRARY_PATH=$PWD/build/install/lib:$LD_LIBRARY_PATH
+          export DYLD_LIBRARY_PATH=$PWD/build/install/lib:$DYLD_LIBRARY_PATH
+          
+          ./streaming-zipformer-buffered-tokens-hotwords-c-api
+          
+          rm -rf sherpa-onnx-streaming-zipformer-*

@@ -48,6 +48,10 @@ target_link_libraries(telespeech-c-api sherpa-onnx-c-api)
 add_executable(vad-sense-voice-c-api vad-sense-voice-c-api.c)
 add_executable(vad-sense-voice-c-api vad-sense-voice-c-api.c)
 target_link_libraries(vad-sense-voice-c-api sherpa-onnx-c-api)
 target_link_libraries(vad-sense-voice-c-api sherpa-onnx-c-api)
 
 
+add_executable(streaming-zipformer-buffered-tokens-hotwords-c-api
+               streaming-zipformer-buffered-tokens-hotwords-c-api.c)
+target_link_libraries(streaming-zipformer-buffered-tokens-hotwords-c-api sherpa-onnx-c-api)
+
 if(SHERPA_ONNX_HAS_ALSA)
 if(SHERPA_ONNX_HAS_ALSA)
   add_subdirectory(./asr-microphone-example)
   add_subdirectory(./asr-microphone-example)
 elseif((UNIX AND NOT APPLE) OR LINUX)
 elseif((UNIX AND NOT APPLE) OR LINUX)

+// c-api-examples/streaming-zipformer-buffered-tokens-hotwords-c-api.c
+//
+// Copyright (c)  2024  Xiaomi Corporation
+// Copyright (c)  2024  Luo Xiao
+
+//
+// This file demonstrates how to use streaming Zipformer with sherpa-onnx's C
+// and with tokens and hotwords loaded from buffered strings instead of from external
+// files API.
+// clang-format off
+// 
+// wget https://github.com/k2-fsa/sherpa-onnx/releases/download/asr-models/sherpa-onnx-streaming-zipformer-en-20M-2023-02-17.tar.bz2
+// tar xvf sherpa-onnx-streaming-zipformer-en-20M-2023-02-17.tar.bz2
+// rm sherpa-onnx-streaming-zipformer-en-20M-2023-02-17.tar.bz2
+//
+// clang-format on
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "sherpa-onnx/c-api/c-api.h"
+
+static size_t ReadFile(const char *filename, const char **buffer_out) {
+  FILE *file = fopen(filename, "rb");
+  if (file == NULL) {
+    fprintf(stderr, "Failed to open %s\n", filename);
+    return -1;
+  }
+  fseek(file, 0L, SEEK_END);
+  long size = ftell(file);
+  rewind(file);
+  *buffer_out = malloc(size);
+  if (*buffer_out == NULL) {
+    fclose(file);
+    fprintf(stderr, "Memory error\n");
+    return -1;
+  }
+  size_t read_bytes = fread(*buffer_out, 1, size, file);
+  if (read_bytes != size) {
+    printf("Errors occured in reading the file %s\n", filename);
+    free(*buffer_out);
+    *buffer_out = NULL;
+    fclose(file);
+    return -1;
+  }
+  fclose(file);
+  return read_bytes;
+}
+
+int32_t main() {
+  const char *wav_filename =
+      "sherpa-onnx-streaming-zipformer-en-20M-2023-02-17/test_wavs/0.wav";
+  const char *encoder_filename =
+      "sherpa-onnx-streaming-zipformer-en-20M-2023-02-17/"
+      "encoder-epoch-99-avg-1.onnx";
+  const char *decoder_filename =
+      "sherpa-onnx-streaming-zipformer-en-20M-2023-02-17/"
+      "decoder-epoch-99-avg-1.onnx";
+  const char *joiner_filename =
+      "sherpa-onnx-streaming-zipformer-en-20M-2023-02-17/"
+      "joiner-epoch-99-avg-1.onnx";
+  const char *provider = "cpu";
+  const char *modeling_unit = "bpe";
+  const char *tokens_filename =
+      "sherpa-onnx-streaming-zipformer-en-20M-2023-02-17/tokens.txt";
+  const char *hotwords_filename =
+      "sherpa-onnx-streaming-zipformer-en-20M-2023-02-17/hotwords.txt";
+  const char *bpe_vocab =
+      "sherpa-onnx-streaming-zipformer-en-20M-2023-02-17/"
+      "bpe.vocab";
+  const SherpaOnnxWave *wave = SherpaOnnxReadWave(wav_filename);
+  if (wave == NULL) {
+    fprintf(stderr, "Failed to read %s\n", wav_filename);
+    return -1;
+  }
+
+  // reading tokens and hotwords to buffers
+  const char *tokens_buf;
+  size_t token_buf_size = ReadFile(tokens_filename, &tokens_buf);
+  if (token_buf_size < 1) {
+    fprintf(stderr, "Please check your tokens.txt!\n");
+    free(tokens_buf);
+    return -1;
+  }
+  const char *hotwords_buf;
+  size_t hotwords_buf_size = ReadFile(hotwords_filename, &hotwords_buf);
+  if (hotwords_buf_size < 1) {
+    fprintf(stderr, "Please check your hotwords.txt!\n");
+    free(hotwords_buf);
+    return -1;
+  }
+
+  // Zipformer config
+  SherpaOnnxOnlineTransducerModelConfig zipformer_config;
+  memset(&zipformer_config, 0, sizeof(zipformer_config));
+  zipformer_config.encoder = encoder_filename;
+  zipformer_config.decoder = decoder_filename;
+  zipformer_config.joiner = joiner_filename;
+
+  // Online model config
+  SherpaOnnxOnlineModelConfig online_model_config;
+  memset(&online_model_config, 0, sizeof(online_model_config));
+  online_model_config.debug = 1;
+  online_model_config.num_threads = 1;
+  online_model_config.provider = provider;
+  online_model_config.tokens_buf = tokens_buf;
+  online_model_config.tokens_buf_size = token_buf_size;
+  online_model_config.transducer = zipformer_config;
+
+  // Recognizer config
+  SherpaOnnxOnlineRecognizerConfig recognizer_config;
+  memset(&recognizer_config, 0, sizeof(recognizer_config));
+  recognizer_config.decoding_method = "modified_beam_search";
+  recognizer_config.model_config = online_model_config;
+  recognizer_config.hotwords_buf = hotwords_buf;
+  recognizer_config.hotwords_buf_size = hotwords_buf_size;
+
+  SherpaOnnxOnlineRecognizer *recognizer =
+      SherpaOnnxCreateOnlineRecognizer(&recognizer_config);
+
+  free(tokens_buf);
+  tokens_buf = NULL;
+  free(hotwords_buf);
+  hotwords_buf = NULL;
+
+  if (recognizer == NULL) {
+    fprintf(stderr, "Please check your config!\n");
+    SherpaOnnxFreeWave(wave);
+    return -1;
+  }
+
+  SherpaOnnxOnlineStream *stream = SherpaOnnxCreateOnlineStream(recognizer);
+
+  const SherpaOnnxDisplay *display = SherpaOnnxCreateDisplay(50);
+  int32_t segment_id = 0;
+
+// simulate streaming. You can choose an arbitrary N
+#define N 3200
+
+  fprintf(stderr, "sample rate: %d, num samples: %d, duration: %.2f s\n",
+          wave->sample_rate, wave->num_samples,
+          (float)wave->num_samples / wave->sample_rate);
+
+  int32_t k = 0;
+  while (k < wave->num_samples) {
+    int32_t start = k;
+    int32_t end =
+        (start + N > wave->num_samples) ? wave->num_samples : (start + N);
+    k += N;
+
+    SherpaOnnxOnlineStreamAcceptWaveform(stream, wave->sample_rate,
+                                         wave->samples + start, end - start);
+    while (SherpaOnnxIsOnlineStreamReady(recognizer, stream)) {
+      SherpaOnnxDecodeOnlineStream(recognizer, stream);
+    }
+
+    const SherpaOnnxOnlineRecognizerResult *r =
+        SherpaOnnxGetOnlineStreamResult(recognizer, stream);
+
+    if (strlen(r->text)) {
+      SherpaOnnxPrint(display, segment_id, r->text);
+    }
+
+    if (SherpaOnnxOnlineStreamIsEndpoint(recognizer, stream)) {
+      if (strlen(r->text)) {
+        ++segment_id;
+      }
+      SherpaOnnxOnlineStreamReset(recognizer, stream);
+    }
+
+    SherpaOnnxDestroyOnlineRecognizerResult(r);
+  }
+
+  // add some tail padding
+  float tail_paddings[4800] = {0};  // 0.3 seconds at 16 kHz sample rate
+  SherpaOnnxOnlineStreamAcceptWaveform(stream, wave->sample_rate, tail_paddings,
+                                       4800);
+
+  SherpaOnnxFreeWave(wave);
+
+  SherpaOnnxOnlineStreamInputFinished(stream);
+  while (SherpaOnnxIsOnlineStreamReady(recognizer, stream)) {
+    SherpaOnnxDecodeOnlineStream(recognizer, stream);
+  }
+
+  const SherpaOnnxOnlineRecognizerResult *r =
+      SherpaOnnxGetOnlineStreamResult(recognizer, stream);
+
+  if (strlen(r->text)) {
+    SherpaOnnxPrint(display, segment_id, r->text);
+  }
+
+  SherpaOnnxDestroyOnlineRecognizerResult(r);
+
+  SherpaOnnxDestroyDisplay(display);
+  SherpaOnnxDestroyOnlineStream(stream);
+  SherpaOnnxDestroyOnlineRecognizer(recognizer);
+  fprintf(stderr, "\n");
+
+  return 0;
+}

@@ -73,6 +73,12 @@ SherpaOnnxOnlineRecognizer *SherpaOnnxCreateOnlineRecognizer(
 
 
   recognizer_config.model_config.tokens =
   recognizer_config.model_config.tokens =
       SHERPA_ONNX_OR(config->model_config.tokens, "");
       SHERPA_ONNX_OR(config->model_config.tokens, "");
+  if (config->model_config.tokens_buf &&
+      config->model_config.tokens_buf_size > 0) {
+    recognizer_config.model_config.tokens_buf = std::string(
+        config->model_config.tokens_buf, config->model_config.tokens_buf_size);
+  }
+
   recognizer_config.model_config.num_threads =
   recognizer_config.model_config.num_threads =
       SHERPA_ONNX_OR(config->model_config.num_threads, 1);
       SHERPA_ONNX_OR(config->model_config.num_threads, 1);
   recognizer_config.model_config.provider_config.provider =
   recognizer_config.model_config.provider_config.provider =
@@ -120,6 +126,10 @@ SherpaOnnxOnlineRecognizer *SherpaOnnxCreateOnlineRecognizer(
   recognizer_config.hotwords_file = SHERPA_ONNX_OR(config->hotwords_file, "");
   recognizer_config.hotwords_file = SHERPA_ONNX_OR(config->hotwords_file, "");
   recognizer_config.hotwords_score =
   recognizer_config.hotwords_score =
       SHERPA_ONNX_OR(config->hotwords_score, 1.5);
       SHERPA_ONNX_OR(config->hotwords_score, 1.5);
+  if (config->hotwords_buf && config->hotwords_buf_size > 0) {
+    recognizer_config.hotwords_buf =
+        std::string(config->hotwords_buf, config->hotwords_buf_size);
+  }
 
 
   recognizer_config.blank_penalty = config->blank_penalty;
   recognizer_config.blank_penalty = config->blank_penalty;
 
 

@@ -88,6 +88,11 @@ SHERPA_ONNX_API typedef struct SherpaOnnxOnlineModelConfig {
   //  - cjkchar+bpe
   //  - cjkchar+bpe
   const char *modeling_unit;
   const char *modeling_unit;
   const char *bpe_vocab;
   const char *bpe_vocab;
+  /// if non-null, loading the tokens from the buffered string directly in
+  /// prioriy
+  const char *tokens_buf;
+  /// byte size excluding the tailing '\0'
+  int32_t tokens_buf_size;
 } SherpaOnnxOnlineModelConfig;
 } SherpaOnnxOnlineModelConfig;
 
 
 /// It expects 16 kHz 16-bit single channel wave format.
 /// It expects 16 kHz 16-bit single channel wave format.
@@ -147,6 +152,11 @@ SHERPA_ONNX_API typedef struct SherpaOnnxOnlineRecognizerConfig {
   const char *rule_fsts;
   const char *rule_fsts;
   const char *rule_fars;
   const char *rule_fars;
   float blank_penalty;
   float blank_penalty;
+
+  /// if non-nullptr, loading the hotwords from the buffered string directly in
+  const char *hotwords_buf;
+  /// byte size excluding the tailing '\0'
+  int32_t hotwords_buf_size;
 } SherpaOnnxOnlineRecognizerConfig;
 } SherpaOnnxOnlineRecognizerConfig;
 
 
 SHERPA_ONNX_API typedef struct SherpaOnnxOnlineRecognizerResult {
 SHERPA_ONNX_API typedef struct SherpaOnnxOnlineRecognizerResult {

@@ -56,8 +56,19 @@ bool OnlineModelConfig::Validate() const {
     return false;
     return false;
   }
   }
 
 
-  if (!FileExists(tokens)) {
-    SHERPA_ONNX_LOGE("tokens: '%s' does not exist", tokens.c_str());
+  if (!tokens_buf.empty() && FileExists(tokens)) {
+    SHERPA_ONNX_LOGE(
+        "you can not provide a tokens_buf and a tokens file: '%s', "
+        "at the same time, which is confusing",
+        tokens.c_str());
+    return false;
+  }
+
+  if (tokens_buf.empty() && !FileExists(tokens)) {
+    SHERPA_ONNX_LOGE(
+        "tokens: '%s' does not exist, you should provide "
+        "either a tokens buffer or a tokens file",
+        tokens.c_str());
     return false;
     return false;
   }
   }
 
 

@@ -45,6 +45,11 @@ struct OnlineModelConfig {
   std::string modeling_unit = "cjkchar";
   std::string modeling_unit = "cjkchar";
   std::string bpe_vocab;
   std::string bpe_vocab;
 
 
+  /// if tokens_buf is non-empty,
+  /// the tokens will be loaded from the buffered string instead of from the
+  /// ${tokens} file
+  std::string tokens_buf;
+
   OnlineModelConfig() = default;
   OnlineModelConfig() = default;
   OnlineModelConfig(const OnlineTransducerModelConfig &transducer,
   OnlineModelConfig(const OnlineTransducerModelConfig &transducer,
                     const OnlineParaformerModelConfig &paraformer,
                     const OnlineParaformerModelConfig &paraformer,
@@ -53,8 +58,7 @@ struct OnlineModelConfig {
                     const OnlineNeMoCtcModelConfig &nemo_ctc,
                     const OnlineNeMoCtcModelConfig &nemo_ctc,
                     const ProviderConfig &provider_config,
                     const ProviderConfig &provider_config,
                     const std::string &tokens, int32_t num_threads,
                     const std::string &tokens, int32_t num_threads,
-                    int32_t warm_up, bool debug,
-                    const std::string &model_type,
+                    int32_t warm_up, bool debug, const std::string &model_type,
                     const std::string &modeling_unit,
                     const std::string &modeling_unit,
                     const std::string &bpe_vocab)
                     const std::string &bpe_vocab)
       : transducer(transducer),
       : transducer(transducer),

@@ -83,8 +83,14 @@ class OnlineRecognizerTransducerImpl : public OnlineRecognizerImpl {
       : OnlineRecognizerImpl(config),
       : OnlineRecognizerImpl(config),
         config_(config),
         config_(config),
         model_(OnlineTransducerModel::Create(config.model_config)),
         model_(OnlineTransducerModel::Create(config.model_config)),
-        sym_(config.model_config.tokens),
         endpoint_(config_.endpoint_config) {
         endpoint_(config_.endpoint_config) {
+    if (!config.model_config.tokens_buf.empty()) {
+      sym_ = SymbolTable(config.model_config.tokens_buf, false);
+    } else {
+      /// assuming tokens_buf and tokens are guaranteed not being both empty
+      sym_ = SymbolTable(config.model_config.tokens, true);
+    }
+
     if (sym_.Contains("<unk>")) {
     if (sym_.Contains("<unk>")) {
       unk_id_ = sym_["<unk>"];
       unk_id_ = sym_["<unk>"];
     }
     }
@@ -97,7 +103,9 @@ class OnlineRecognizerTransducerImpl : public OnlineRecognizerImpl {
             config_.model_config.bpe_vocab);
             config_.model_config.bpe_vocab);
       }
       }
 
 
-      if (!config_.hotwords_file.empty()) {
+      if (!config_.hotwords_buf.empty()) {
+        InitHotwordsFromBufStr();
+      } else if (!config_.hotwords_file.empty()) {
         InitHotwords();
         InitHotwords();
       }
       }
 
 
@@ -108,8 +116,7 @@ class OnlineRecognizerTransducerImpl : public OnlineRecognizerImpl {
       decoder_ = std::make_unique<OnlineTransducerModifiedBeamSearchDecoder>(
       decoder_ = std::make_unique<OnlineTransducerModifiedBeamSearchDecoder>(
           model_.get(), lm_.get(), config_.max_active_paths,
           model_.get(), lm_.get(), config_.max_active_paths,
           config_.lm_config.scale, config_.lm_config.shallow_fusion, unk_id_,
           config_.lm_config.scale, config_.lm_config.shallow_fusion, unk_id_,
-          config_.blank_penalty,
-          config_.temperature_scale);
+          config_.blank_penalty, config_.temperature_scale);
 
 
     } else if (config.decoding_method == "greedy_search") {
     } else if (config.decoding_method == "greedy_search") {
       decoder_ = std::make_unique<OnlineTransducerGreedySearchDecoder>(
       decoder_ = std::make_unique<OnlineTransducerGreedySearchDecoder>(
@@ -158,8 +165,7 @@ class OnlineRecognizerTransducerImpl : public OnlineRecognizerImpl {
       decoder_ = std::make_unique<OnlineTransducerModifiedBeamSearchDecoder>(
       decoder_ = std::make_unique<OnlineTransducerModifiedBeamSearchDecoder>(
           model_.get(), lm_.get(), config_.max_active_paths,
           model_.get(), lm_.get(), config_.max_active_paths,
           config_.lm_config.scale, config_.lm_config.shallow_fusion, unk_id_,
           config_.lm_config.scale, config_.lm_config.shallow_fusion, unk_id_,
-          config_.blank_penalty,
-          config_.temperature_scale);
+          config_.blank_penalty, config_.temperature_scale);
 
 
     } else if (config.decoding_method == "greedy_search") {
     } else if (config.decoding_method == "greedy_search") {
       decoder_ = std::make_unique<OnlineTransducerGreedySearchDecoder>(
       decoder_ = std::make_unique<OnlineTransducerGreedySearchDecoder>(
@@ -446,6 +452,20 @@ class OnlineRecognizerTransducerImpl : public OnlineRecognizerImpl {
   }
   }
 #endif
 #endif
 
 
+  void InitHotwordsFromBufStr() {
+    // each line in hotwords_file contains space-separated words
+
+    std::istringstream iss(config_.hotwords_buf);
+    if (!EncodeHotwords(iss, config_.model_config.modeling_unit, sym_,
+                        bpe_encoder_.get(), &hotwords_, &boost_scores_)) {
+      SHERPA_ONNX_LOGE(
+          "Failed to encode some hotwords, skip them already, see logs above "
+          "for details.");
+    }
+    hotwords_graph_ = std::make_shared<ContextGraph>(
+        hotwords_, config_.hotwords_score, boost_scores_);
+  }
+
   void InitOnlineStream(OnlineStream *stream) const {
   void InitOnlineStream(OnlineStream *stream) const {
     auto r = decoder_->GetEmptyResult();
     auto r = decoder_->GetEmptyResult();
 
 

@@ -44,10 +44,16 @@ class OnlineRecognizerTransducerNeMoImpl : public OnlineRecognizerImpl {
       const OnlineRecognizerConfig &config)
       const OnlineRecognizerConfig &config)
       : OnlineRecognizerImpl(config),
       : OnlineRecognizerImpl(config),
         config_(config),
         config_(config),
-        symbol_table_(config.model_config.tokens),
         endpoint_(config_.endpoint_config),
         endpoint_(config_.endpoint_config),
         model_(
         model_(
             std::make_unique<OnlineTransducerNeMoModel>(config.model_config)) {
             std::make_unique<OnlineTransducerNeMoModel>(config.model_config)) {
+    if (!config.model_config.tokens_buf.empty()) {
+      symbol_table_ = SymbolTable(config.model_config.tokens_buf, false);
+    } else {
+      /// assuming tokens_buf and tokens are guaranteed not being both empty
+      symbol_table_ = SymbolTable(config.model_config.tokens, true);
+    }
+
     if (config.decoding_method == "greedy_search") {
     if (config.decoding_method == "greedy_search") {
       decoder_ = std::make_unique<OnlineTransducerGreedySearchNeMoDecoder>(
       decoder_ = std::make_unique<OnlineTransducerGreedySearchNeMoDecoder>(
           model_.get(), config_.blank_penalty);
           model_.get(), config_.blank_penalty);

@@ -106,6 +106,11 @@ struct OnlineRecognizerConfig {
   // If there are multiple FST archives, they are applied from left to right.
   // If there are multiple FST archives, they are applied from left to right.
   std::string rule_fars;
   std::string rule_fars;
 
 
+  /// used only for modified_beam_search, if hotwords_buf is non-empty,
+  /// the hotwords will be loaded from the buffered string instead of from
+  /// ${hotwords_file}
+  std::string hotwords_buf;
+
   OnlineRecognizerConfig() = default;
   OnlineRecognizerConfig() = default;
 
 
   OnlineRecognizerConfig(
   OnlineRecognizerConfig(

@@ -20,9 +20,14 @@
 
 
 namespace sherpa_onnx {
 namespace sherpa_onnx {
 
 
-SymbolTable::SymbolTable(const std::string &filename) {
-  std::ifstream is(filename);
-  Init(is);
+SymbolTable::SymbolTable(const std::string &filename, bool is_file) {
+  if (is_file) {
+    std::ifstream is(filename);
+    Init(is);
+  } else {
+    std::istringstream iss(filename);
+    Init(iss);
+  }
 }
 }
 
 
 #if __ANDROID_API__ >= 9
 #if __ANDROID_API__ >= 9

@@ -19,13 +19,13 @@ namespace sherpa_onnx {
 class SymbolTable {
 class SymbolTable {
  public:
  public:
   SymbolTable() = default;
   SymbolTable() = default;
-  /// Construct a symbol table from a file.
+  /// Construct a symbol table from a file or from a buffered string.
   /// Each line in the file contains two fields:
   /// Each line in the file contains two fields:
   ///
   ///
   ///    sym ID
   ///    sym ID
   ///
   ///
   /// Fields are separated by space(s).
   /// Fields are separated by space(s).
-  explicit SymbolTable(const std::string &filename);
+  explicit SymbolTable(const std::string &filename, bool is_file = true);
 
 
 #if __ANDROID_API__ >= 9
 #if __ANDROID_API__ >= 9
   SymbolTable(AAssetManager *mgr, const std::string &filename);
   SymbolTable(AAssetManager *mgr, const std::string &filename);