From e028438a8b80b08471d76df3ae6b2973f23eb230 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jo=C3=ABl=20G=C3=A4hwiler?= <joel.gaehwiler@gmail.com>
Date: Sun, 22 Oct 2017 18:59:06 +0300
Subject: [PATCH] made string helpers NULL-safe

---
 CMakeLists.txt   |  1 +
 src/string.c     | 27 +++++++++++++++++++++------
 tests/string.cpp | 36 ++++++++++++++++++++++++++++++++++++
 3 files changed, 58 insertions(+), 6 deletions(-)
 create mode 100644 tests/string.cpp

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2138597..6810db1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -40,6 +40,7 @@ set(TEST_FILES
         tests/client.cpp
         tests/helpers.cpp
         tests/packet.cpp
+        tests/string.cpp
         tests/tests.cpp)
 
 add_executable(tests ${TEST_FILES})
diff --git a/src/string.c b/src/string.c
index fe32bab..9117c00 100644
--- a/src/string.c
+++ b/src/string.c
@@ -3,21 +3,36 @@
 #include <lwmqtt.h>
 
 lwmqtt_string_t lwmqtt_string(const char *str) {
+  // check for null
+  if (str == NULL) {
+    return (lwmqtt_string_t){0, NULL};
+  }
+
   // get length
   uint16_t len = (uint16_t)strlen(str);
 
+  // check zero length
+  if (len == 0) {
+    return (lwmqtt_string_t){0, NULL};
+  }
+
   return (lwmqtt_string_t){len, (char *)str};
 }
 
 int lwmqtt_strcmp(lwmqtt_string_t a, const char *b) {
-  // get length of b
-  size_t len = strlen(b);
+  // get string of b
+  lwmqtt_string_t b_str = lwmqtt_string(b);
+
+  // return if both are zero length
+  if (a.len == 0 && b_str.len == 0) {
+    return 0;
+  }
 
-  // otherwise check if length matches
-  if (len != a.len) {
+  // return if lengths are different
+  if (a.len != b_str.len) {
     return -1;
   }
 
-  // compare memory
-  return strncmp(a.data, b, len);
+  // compare memory of same length
+  return strncmp(a.data, b_str.data, a.len);
 }
diff --git a/tests/string.cpp b/tests/string.cpp
new file mode 100644
index 0000000..66c6310
--- /dev/null
+++ b/tests/string.cpp
@@ -0,0 +1,36 @@
+#include <gtest/gtest.h>
+
+extern "C" {
+#include <lwmqtt.h>
+}
+
+TEST(StringConstructor, Valid) {
+  lwmqtt_string_t null_str = lwmqtt_string(nullptr);
+  EXPECT_EQ(null_str.len, 0);
+  EXPECT_TRUE(null_str.data == nullptr);
+
+  lwmqtt_string_t empty_str = lwmqtt_string("");
+  EXPECT_EQ(empty_str.len, 0);
+  EXPECT_TRUE(empty_str.data == nullptr);
+
+  lwmqtt_string_t hello_str = lwmqtt_string("hello");
+  EXPECT_EQ(hello_str.len, 5);
+  EXPECT_TRUE(hello_str.data != nullptr);
+}
+
+TEST(StringCompare, Valid) {
+  lwmqtt_string_t null_str = lwmqtt_string(nullptr);
+  EXPECT_TRUE(lwmqtt_strcmp(null_str, nullptr) == 0);
+  EXPECT_TRUE(lwmqtt_strcmp(null_str, "") == 0);
+  EXPECT_TRUE(lwmqtt_strcmp(null_str, "hello") != 0);
+
+  lwmqtt_string_t empty_str = lwmqtt_string("");
+  EXPECT_TRUE(lwmqtt_strcmp(empty_str, nullptr) == 0);
+  EXPECT_TRUE(lwmqtt_strcmp(empty_str, "") == 0);
+  EXPECT_TRUE(lwmqtt_strcmp(empty_str, "hello") != 0);
+
+  lwmqtt_string_t hello_str = lwmqtt_string("hello");
+  EXPECT_TRUE(lwmqtt_strcmp(hello_str, nullptr) != 0);
+  EXPECT_TRUE(lwmqtt_strcmp(hello_str, "") != 0);
+  EXPECT_TRUE(lwmqtt_strcmp(hello_str, "hello") == 0);
+}