Improve error handling around Scorer loading

native_client/ctcdecode/scorer.cpp

@@ -31,10 +31,8 @@ int
 Scorer::init(const std::string& lm_path,
              const Alphabet& alphabet)
 {
-  alphabet_ = alphabet;
-  setup_char_map();
-  load_lm(lm_path);
-  return 0;
+  set_alphabet(alphabet);
+  return load_lm(lm_path);
 }
 
 int
@@ -46,8 +44,7 @@ Scorer::init(const std::string& lm_path,
     return err;
   }
   setup_char_map();
-  load_lm(lm_path);
-  return 0;
+  return load_lm(lm_path);
 }
 
 void
@@ -72,15 +69,14 @@ void Scorer::setup_char_map()
   }
 }
 
-void Scorer::load_lm(const std::string& lm_path)
+int Scorer::load_lm(const std::string& lm_path)
 {
   // load language model
   const char* filename = lm_path.c_str();
-  VALID_CHECK_EQ(access(filename, R_OK), 0, "Invalid language model path");
-
   lm::ngram::Config config;
   config.load_method = util::LoadMethod::LAZY;
   language_model_.reset(lm::ngram::LoadVirtual(filename, config));
+  max_order_ = language_model_->Order();
 
   uint64_t package_size;
   {
@@ -88,26 +84,25 @@ void Scorer::load_lm(const std::string& lm_path)
     package_size = util::SizeFile(fd.get());
   }
   uint64_t trie_offset = language_model_->GetEndOfSearchOffset();
-  bool has_trie = package_size > trie_offset;
-
-  if (has_trie) {
-    // Read metadata and trie from file
-    std::ifstream fin(lm_path, std::ios::binary);
-    fin.seekg(trie_offset);
-    load_trie(fin, lm_path);
+  if (package_size <= trie_offset) {
+    // File ends without a trie structure
+    return 1;
   }
 
-  max_order_ = language_model_->Order();
+  // Read metadata and trie from file
+  std::ifstream fin(lm_path, std::ios::binary);
+  fin.seekg(trie_offset);
+  return load_trie(fin, lm_path);
 }
 
-void Scorer::load_trie(std::ifstream& fin, const std::string& file_path)
+int Scorer::load_trie(std::ifstream& fin, const std::string& file_path)
 {
   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;
+    return 1;
   }
 
   int version;
@@ -122,7 +117,7 @@ void Scorer::load_trie(std::ifstream& fin, const std::string& file_path)
       std::cerr << "Downgrade your trie file or update your version of DeepSpeech.";
     }
     std::cerr << std::endl;
-    throw 1;
+    return 1;
   }
 
   fin.read(reinterpret_cast<char*>(&is_utf8_mode_), sizeof(is_utf8_mode_));
@@ -137,6 +132,7 @@ void Scorer::load_trie(std::ifstream& fin, const std::string& file_path)
   opt.mode = fst::FstReadOptions::MAP;
   opt.source = file_path;
   dictionary.reset(FstType::Read(fin, opt));
+  return 0;
 }
 
 void Scorer::save_dictionary(const std::string& path, bool append_instead_of_overwrite)

native_client/ctcdecode/scorer.h

@@ -12,6 +12,7 @@
 
 #include "path_trie.h"
 #include "alphabet.h"
+#include "deepspeech.h"
 
 const double OOV_SCORE = -1000.0;
 const std::string START_TOKEN = "<s>";
@@ -85,7 +86,7 @@ public:
   void fill_dictionary(const std::vector<std::string> &vocabulary);
 
   // load language model from given path
-  void load_lm(const std::string &lm_path);
+  int load_lm(const std::string &lm_path);
 
   // language model weight
   double alpha = 0.;
@@ -99,7 +100,7 @@ protected:
   // necessary setup after setting alphabet
   void setup_char_map();
 
-  void load_trie(std::ifstream& fin, const std::string& file_path);
+  int load_trie(std::ifstream& fin, const std::string& file_path);
 
 private:
   std::unique_ptr<lm::base::Model> language_model_;