Refactor Scorer so model/trie package can be created by an external tool

native_client/ctcdecode/__init__.py

@@ -1,6 +1,7 @@
 from __future__ import absolute_import, division, print_function
 
 from . import swigwrapper # pylint: disable=import-self
+from .swigwrapper import Alphabet
 
 __version__ = swigwrapper.__version__
 
@@ -16,7 +17,6 @@ class Scorer(swigwrapper.Scorer):
     :alphabet: Alphabet
     :type model_path: basestring
     """
-
     def __init__(self, alpha, beta, model_path, trie_path, alphabet):
         super(Scorer, self).__init__()
         serialized = alphabet.serialize()
@@ -32,6 +32,15 @@ class Scorer(swigwrapper.Scorer):
         if err != 0:
             raise ValueError("Scorer initialization failed with error code {}".format(err), err)
 
+    def __init__(self):
+        super(Scorer, self).__init__()
+
+    def load_lm(self, lm_path, trie_path):
+        super(Scorer, self).load_lm(lm_path.encode('utf-8'), trie_path.encode('utf-8'))
+
+    def save_dictionary(self, save_path):
+        super(Scorer, self).save_dictionary(save_path.encode('utf-8'))
+
 
 def ctc_beam_search_decoder(probs_seq,
                             alphabet,

native_client/ctcdecode/ctc_beam_search_decoder.cpp

@@ -36,7 +36,7 @@ DecoderState::init(const Alphabet& alphabet,
   prefix_root_.reset(root);
   prefixes_.push_back(root);
 
-  if (ext_scorer != nullptr) {
+  if (ext_scorer != nullptr && (bool)ext_scorer_->dictionary) {
     // no need for std::make_shared<>() since Copy() does 'new' behind the doors
     auto dict_ptr = std::shared_ptr<PathTrie::FstType>(ext_scorer->dictionary->Copy(true));
     root->set_dictionary(dict_ptr);

native_client/ctcdecode/scorer.cpp

@@ -38,7 +38,8 @@ Scorer::init(double alpha,
 {
   reset_params(alpha, beta);
   alphabet_ = alphabet;
-  setup(lm_path, trie_path);
+  setup_char_map();
+  load_lm(lm_path, trie_path);
   return 0;
 }
 
@@ -54,11 +55,19 @@ Scorer::init(double alpha,
   if (err != 0) {
     return err;
   }
-  setup(lm_path, trie_path);
+  setup_char_map();
+  load_lm(lm_path, trie_path);
   return 0;
 }
 
-void Scorer::setup(const std::string& lm_path, const std::string& trie_path)
+void
+Scorer::set_alphabet(const Alphabet& alphabet)
+{
+  alphabet_ = alphabet;
+  setup_char_map();
+}
+
+void Scorer::setup_char_map()
 {
   // (Re-)Initialize character map
   char_map_.clear();
@@ -71,52 +80,57 @@ void Scorer::setup(const std::string& lm_path, const std::string& trie_path)
     // state, otherwise wrong decoding results would be given.
     char_map_[alphabet_.StringFromLabel(i)] = i + 1;
   }
+}
 
+void Scorer::load_lm(const std::string& lm_path, const std::string& trie_path)
+{
   // load language model
   const char* filename = lm_path.c_str();
   VALID_CHECK_EQ(access(filename, R_OK), 0, "Invalid language model path");
 
   bool has_trie = trie_path.size() && access(trie_path.c_str(), R_OK) == 0;
-  VALID_CHECK(has_trie, "Invalid trie path");
+  // VALID_CHECK(has_trie, "Invalid trie path");
 
   lm::ngram::Config config;
   config.load_method = util::LoadMethod::LAZY;
   language_model_.reset(lm::ngram::LoadVirtual(filename, config));
 
-  // Read metadata and trie from file
-  std::ifstream fin(trie_path, std::ios::binary);
+  if (has_trie) {
+    // Read metadata and trie from file
+    std::ifstream fin(trie_path, std::ios::binary);
 
-  int magic;
-  fin.read(reinterpret_cast<char*>(&magic), sizeof(magic));
-  if (magic != MAGIC) {
-    std::cerr << "Error: Can't parse trie file, invalid header. Try updating "
-                 "your trie file." << std::endl;
-    throw 1;
+    int magic;
+    fin.read(reinterpret_cast<char*>(&magic), sizeof(magic));
+    if (magic != MAGIC) {
+      std::cerr << "Error: Can't parse trie file, invalid header. Try updating "
+                   "your trie file." << std::endl;
+      throw 1;
+    }
+
+    int version;
+    fin.read(reinterpret_cast<char*>(&version), sizeof(version));
+    if (version != FILE_VERSION) {
+      std::cerr << "Error: Trie file version mismatch (" << version
+                << " instead of expected " << FILE_VERSION
+                << "). Update your trie file."
+                << std::endl;
+      throw 1;
+    }
+
+    fin.read(reinterpret_cast<char*>(&is_utf8_mode_), sizeof(is_utf8_mode_));
+
+    fst::FstReadOptions opt;
+    opt.mode = fst::FstReadOptions::MAP;
+    opt.source = trie_path;
+    dictionary.reset(FstType::Read(fin, opt));
   }
 
-  int version;
-  fin.read(reinterpret_cast<char*>(&version), sizeof(version));
-  if (version != FILE_VERSION) {
-    std::cerr << "Error: Trie file version mismatch (" << version
-              << " instead of expected " << FILE_VERSION
-              << "). Update your trie file."
-              << std::endl;
-    throw 1;
-  }
-
-  fin.read(reinterpret_cast<char*>(&is_utf8_mode_), sizeof(is_utf8_mode_));
-
-  fst::FstReadOptions opt;
-  opt.mode = fst::FstReadOptions::MAP;
-  opt.source = trie_path;
-  dictionary_.reset(FstType::Read(fin, opt));
-
   max_order_ = language_model_->Order();
 }
 
 void Scorer::save_dictionary(const std::string& path)
 {
-  std::ofstream fout(path, std::ios::binary);
+  std::fstream fout(path, std::ios::in|std::ios::out|std::ios::binary|std::ios::ate);
   fout.write(reinterpret_cast<const char*>(&MAGIC), sizeof(MAGIC));
   fout.write(reinterpret_cast<const char*>(&FILE_VERSION), sizeof(FILE_VERSION));
   fout.write(reinterpret_cast<const char*>(&is_utf8_mode_), sizeof(is_utf8_mode_));

native_client/ctcdecode/scorer.h

@@ -40,9 +40,9 @@ public:
  *     scorer.get_sent_log_prob({ "WORD1", "WORD2", "WORD3" });
  */
 class Scorer {
+public:
   using FstType = PathTrie::FstType;
 
-public:
   Scorer() = default;
   ~Scorer() = default;
 
@@ -76,12 +76,15 @@ public:
   // return the max order
   size_t get_max_order() const { return max_order_; }
 
-  // retrun true if the language model is character based
+  // return true if the language model is character based
   bool is_utf8_mode() const { return is_utf8_mode_; }
 
   // reset params alpha & beta
   void reset_params(float alpha, float beta);
 
+  // force set UTF-8 mode, ignore value read from file
+  void set_utf8_mode(bool utf8) { is_utf8_mode_ = utf8; }
+
   // make ngram for a given prefix
   std::vector<std::string> make_ngram(PathTrie *prefix);
 
@@ -89,12 +92,20 @@ public:
   // the vector of characters (character based lm)
   std::vector<std::string> split_labels_into_scored_units(const std::vector<int> &labels);
 
+  void set_alphabet(const Alphabet& alphabet);
+
   // save dictionary in file
   void save_dictionary(const std::string &path);
 
   // return weather this step represents a boundary where beam scoring should happen
   bool is_scoring_boundary(PathTrie* prefix, size_t new_label);
 
+  // fill dictionary FST from a vocabulary
+  void fill_dictionary(const std::vector<std::string> &vocabulary);
+
+  // load language model from given path
+  void load_lm(const std::string &lm_path, const std::string &trie_path);
+
   // language model weight
   double alpha = 0.;
   // word insertion weight
@@ -104,14 +115,8 @@ public:
   std::unique_ptr<FstType> dictionary;
 
 protected:
-  // necessary setup: load language model, fill FST's dictionary
-  void setup(const std::string &lm_path, const std::string &trie_path);
-
-  // load language model from given path
-  void load_lm(const std::string &lm_path);
-
-  // fill dictionary for FST
-  void fill_dictionary(const std::vector<std::string> &vocabulary);
+  // necessary setup after setting alphabet
+  void setup_char_map();
 
 private:
   std::unique_ptr<lm::base::Model> language_model_;

native_client/ctcdecode/swigwrapper.i

@@ -16,6 +16,10 @@
 import_array();
 %}
 
+namespace std {
+    %template(StringVector) vector<string>;
+}
+
 // Convert NumPy arrays to pointer+lengths
 %apply (double* IN_ARRAY2, int DIM1, int DIM2) {(const double *probs, int time_dim, int class_dim)};
 %apply (double* IN_ARRAY3, int DIM1, int DIM2, int DIM3) {(const double *probs, int batch_size, int time_dim, int class_dim)};