From acb469ae2e18bf35a56f534e53a680890948bfbd Mon Sep 17 00:00:00 2001
From: Vasili Galka <vgalka@sealights.io>
Date: Mon, 12 Mar 2018 14:43:29 +0200
Subject: [PATCH] Fixed UTF8/16 converters to support empty string input

Previously an exception was thrown since Win32 WideCharToMultiByte API
returns error on zero-length input.
---
 include/fmt/format.cc | 14 ++++++++++++++
 test/util-test.cc     | 14 ++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/include/fmt/format.cc b/include/fmt/format.cc
index 429657fb..0b4f2d80 100644
--- a/include/fmt/format.cc
+++ b/include/fmt/format.cc
@@ -283,6 +283,13 @@ FMT_FUNC internal::utf8_to_utf16::utf8_to_utf16(string_view s) {
   if (s.size() > INT_MAX)
     FMT_THROW(windows_error(ERROR_INVALID_PARAMETER, ERROR_MSG));
   int s_size = static_cast<int>(s.size());
+  if (s_size == 0) {
+    // MultiByteToWideChar does not support zero length, handle separately.
+    buffer_.resize(1);
+    buffer_[0] = 0;
+    return;
+  }
+
   int length = MultiByteToWideChar(
       CP_UTF8, MB_ERR_INVALID_CHARS, s.data(), s_size, FMT_NULL, 0);
   if (length == 0)
@@ -306,6 +313,13 @@ FMT_FUNC int internal::utf16_to_utf8::convert(wstring_view s) {
   if (s.size() > INT_MAX)
     return ERROR_INVALID_PARAMETER;
   int s_size = static_cast<int>(s.size());
+  if (s_size == 0) {
+    // WideCharToMultiByte does not support zero length, handle separately.
+    buffer_.resize(1);
+    buffer_[0] = 0;
+    return 0;
+  }
+
   int length = WideCharToMultiByte(
         CP_UTF8, 0, s.data(), s_size, FMT_NULL, 0, FMT_NULL, FMT_NULL);
   if (length == 0)
diff --git a/test/util-test.cc b/test/util-test.cc
index 97dabfbb..11957655 100644
--- a/test/util-test.cc
+++ b/test/util-test.cc
@@ -665,6 +665,13 @@ TEST(UtilTest, UTF16ToUTF8) {
   EXPECT_EQ(s.size(), u.size());
 }
 
+TEST(UtilTest, UTF16ToUTF8EmptyString) {
+  std::string s = "";
+  fmt::internal::utf16_to_utf8 u(L"");
+  EXPECT_EQ(s, u.str());
+  EXPECT_EQ(s.size(), u.size());
+}
+
 TEST(UtilTest, UTF8ToUTF16) {
   std::string s = "лошадка";
   fmt::internal::utf8_to_utf16 u(s.c_str());
@@ -672,6 +679,13 @@ TEST(UtilTest, UTF8ToUTF16) {
   EXPECT_EQ(7, u.size());
 }
 
+TEST(UtilTest, UTF8ToUTF16EmptyString) {
+  std::string s = "";
+  fmt::internal::utf8_to_utf16 u(s.c_str());
+  EXPECT_EQ(L"", u.str());
+  EXPECT_EQ(s.size(), u.size());
+}
+
 template <typename Converter, typename Char>
 void check_utf_conversion_error(
         const char *message,