[NaCl SDK] nacl_io example: Check ferror() after reading/writing.

native_client_sdk/src/examples/demo/nacl_io/handlers.c

Index: native_client_sdk/src/examples/demo/nacl_io/handlers.c
diff --git a/native_client_sdk/src/examples/demo/nacl_io/handlers.c b/native_client_sdk/src/examples/demo/nacl_io/handlers.c
index 062a41fb341343b7a4a2034da55d0e86254c44aa..5c2a6ab85ef725e6301fb55d795e30136c2dc493 100644
--- a/native_client_sdk/src/examples/demo/nacl_io/handlers.c
+++ b/native_client_sdk/src/examples/demo/nacl_io/handlers.c
@@ -164,6 +164,12 @@ int HandleFwrite(int num_params, char** params, char** output) {
 
   bytes_written = fwrite(data, 1, data_len, file);
 
+  if (ferror(file)) {
+    *output = PrintfToNewString(
+        "Error: Wrote %d bytes, but ferror() returns true.", bytes_written);
+    return 3;
+  }
+
   *output = PrintfToNewString("fwrite\1%s\1%d", file_index_string,
                               bytes_written);
   return 0;
@@ -211,6 +217,12 @@ int HandleFread(int num_params, char** params, char** output) {
   bytes_read = fread(buffer, 1, data_len, file);
   buffer[bytes_read] = 0;
 
+  if (ferror(file)) {
+    *output = PrintfToNewString(
+        "Error: Read %d bytes, but ferror() returns true.", bytes_read);
+    return 3;
+  }
+
   *output = PrintfToNewString("fread\1%s\1%s", file_index_string, buffer);
   free(buffer);
   return 0;