lstmtraining: Check write permission for output model

This is done by creating a temporary file.
Report an error and terminate if that fails.

Use also EXIT_SUCCESS and EXIT_FAILURE for the return values of main().

Signed-off-by: Stefan Weil <sw@weilnetz.de>

src/training/lstmtraining.cpp

@@ -76,11 +76,11 @@ int main(int argc, char **argv) {
   // Purify the model name in case it is based on the network string.
   if (FLAGS_model_output.empty()) {
     tprintf("Must provide a --model_output!\n");
-    return 1;
+    return EXIT_FAILURE;
   }
   if (FLAGS_traineddata.empty()) {
     tprintf("Must provide a --traineddata see training wiki\n");
-    return 1;
+    return EXIT_FAILURE;
   }
   STRING model_output = FLAGS_model_output.c_str();
   for (int i = 0; i < model_output.length(); ++i) {
@@ -89,6 +89,19 @@ int main(int argc, char **argv) {
     if (model_output[i] == '(' || model_output[i] == ')')
       model_output[i] = '_';
   }
+
+  // Check write permissions.
+  STRING test_file = FLAGS_model_output.c_str();
+  test_file += "_wtest";
+  FILE* f = fopen(test_file.c_str(), "wb");
+  if (f != nullptr) {
+    fclose(f);
+    remove(test_file.c_str());
+  } else {
+    tprintf("Error, model output cannot be written: %s\n", strerror(errno));
+    return EXIT_FAILURE;
+  }
+
   // Setup the trainer.
   STRING checkpoint_file = FLAGS_model_output.c_str();
   checkpoint_file += "_checkpoint";
@@ -105,7 +118,7 @@ int main(int argc, char **argv) {
     if (!trainer.TryLoadingCheckpoint(FLAGS_continue_from.c_str(), nullptr)) {
       tprintf("Failed to read continue from: %s\n",
               FLAGS_continue_from.c_str());
-      return 1;
+      return EXIT_FAILURE;
     }
     if (FLAGS_debug_network) {
       trainer.DebugNetwork();
@@ -116,20 +129,20 @@ int main(int argc, char **argv) {
                 FLAGS_model_output.c_str());
       }
     }
-    return 0;
+    return EXIT_SUCCESS;
   }
 
   // Get the list of files to process.
   if (FLAGS_train_listfile.empty()) {
     tprintf("Must supply a list of training filenames! --train_listfile\n");
-    return 1;
+    return EXIT_FAILURE;
   }
   GenericVector<STRING> filenames;
   if (!tesseract::LoadFileLinesToStrings(FLAGS_train_listfile.c_str(),
                                          &filenames)) {
     tprintf("Failed to load list of training filenames from %s\n",
             FLAGS_train_listfile.c_str());
-    return 1;
+    return EXIT_FAILURE;
   }
 
   // Checkpoints always take priority if they are available.
@@ -145,7 +158,7 @@ int main(int argc, char **argv) {
                                             ? FLAGS_continue_from.c_str()
                                             : FLAGS_old_traineddata.c_str())) {
         tprintf("Failed to continue from: %s\n", FLAGS_continue_from.c_str());
-        return 1;
+        return EXIT_FAILURE;
       }
       tprintf("Continuing from %s\n", FLAGS_continue_from.c_str());
       trainer.InitIterations();
@@ -155,7 +168,7 @@ int main(int argc, char **argv) {
         tprintf("Appending a new network to an old one!!");
         if (FLAGS_continue_from.empty()) {
           tprintf("Must set --continue_from for appending!\n");
-          return 1;
+          return EXIT_FAILURE;
         }
       }
       // We are initializing from scratch.
@@ -165,7 +178,7 @@ int main(int argc, char **argv) {
                                FLAGS_adam_beta)) {
         tprintf("Failed to create network from spec: %s\n",
                 FLAGS_net_spec.c_str());
-        return 1;
+        return EXIT_FAILURE;
       }
       trainer.set_perfect_delay(FLAGS_perfect_sample_delay);
     }
@@ -176,7 +189,7 @@ int main(int argc, char **argv) {
                                        : tesseract::CS_ROUND_ROBIN,
                                    FLAGS_randomly_rotate)) {
     tprintf("Load of images failed!!\n");
-    return 1;
+    return EXIT_FAILURE;
   }
 
   tesseract::LSTMTester tester(static_cast<int64_t>(FLAGS_max_image_MB) *
@@ -186,7 +199,7 @@ int main(int argc, char **argv) {
     if (!tester.LoadAllEvalData(FLAGS_eval_listfile.c_str())) {
       tprintf("Failed to load eval data from: %s\n",
               FLAGS_eval_listfile.c_str());
-      return 1;
+      return EXIT_FAILURE;
     }
     tester_callback =
         NewPermanentTessCallback(&tester, &tesseract::LSTMTester::RunEvalAsync);
@@ -208,5 +221,5 @@ int main(int argc, char **argv) {
             FLAGS_max_iterations == 0));
   delete tester_callback;
   tprintf("Finished! Error rate = %g\n", trainer.best_error_rate());
-  return 0;
+  return EXIT_SUCCESS;
 } /* main */