call strerror before errno gets clobbered

3 files changed, 52 insertions, 13 deletions

diff --git a/serialize/json-helper.cpp b/serialize/json-helper.cpp
index 5504ff52..325d4d12 100644
--- a/serialize/json-helper.cpp
+++ b/serialize/json-helper.cpp
@@ -1,4 +1,6 @@
 #include "json-helper.hpp"
+#include <cerrno>
+#include <cstring>
 #include <fstream>
 
 namespace floormat {
@@ -7,8 +9,23 @@ template<typename T, std::ios_base::openmode mode>
 static T open_stream(StringView filename)
 {
     T s;
-    s.exceptions(s.exceptions() | std::ios::failbit | std::ios::badbit);
     s.open(filename.data(), mode);
+    if (!s.good())
+    {
+        char errbuf[128];
+        constexpr auto get_error_string = []<std::size_t N> (char (&buf)[N])
+        {
+            buf[0] = '\0';
+#ifndef _WIN32
+            (void)::strerror_r(errno, errbuf, std::size(errbuf));
+#else
+            (void)::strerror_s(buf, std::size(buf), errno);
+#endif
+        };
+        const char* mode_str = mode & std::ios_base::out ? "writing" : "reading";
+        (void)get_error_string(errbuf);
+        fm_error("can't open file '%s' for %s: %s", filename.data(), mode_str, errbuf);
+    }
     return s;
 }
 
diff --git a/serialize/world-reader.cpp b/serialize/world-reader.cpp
index 615aba0d..602eabf5 100644
--- a/serialize/world-reader.cpp
+++ b/serialize/world-reader.cpp
@@ -117,32 +117,46 @@ namespace floormat {
 world world::deserialize(StringView filename)
 {
     char errbuf[128];
-    constexpr auto strerror = []<std::size_t N> (char (&buf)[N]) -> const char* {
+    constexpr auto get_error_string = []<std::size_t N> (char (&buf)[N]) {
         buf[0] = '\0';
 #ifndef _WIN32
         (void)::strerror_r(errno, buf, std::size(buf));
 #else
         (void)::strerror_s(buf, std::size(buf), errno);
 #endif
-        return buf;
     };
     fm_assert(filename.flags() & StringViewFlag::NullTerminated);
     FILE_raii f = ::fopen(filename.data(), "rb");
     if (!f)
-        fm_abort("fopen(\"%s\", \"r\"): %s", filename.data(), strerror(errbuf));
+    {
+        get_error_string(errbuf);
+        fm_abort("fopen(\"%s\", \"r\"): %s", filename.data(), errbuf);
+    }
     if (int ret = ::fseek(f, 0, SEEK_END); ret != 0)
-        fm_abort("fseek(SEEK_END): %s", strerror(errbuf));
+    {
+        get_error_string(errbuf);
+        fm_abort("fseek(SEEK_END): %s", errbuf);
+    }
     std::size_t len;
     if (auto len_ = ::ftell(f); len_ >= 0)
         len = (std::size_t)len_;
     else
-        fm_abort("ftell: %s", strerror(errbuf));
+    {
+        get_error_string(errbuf);
+        fm_abort("ftell: %s", errbuf);
+    }
     if (int ret = ::fseek(f, 0, SEEK_SET); ret != 0)
-        fm_abort("fseek(SEEK_SET): %s", strerror(errbuf));
+    {
+        get_error_string(errbuf);
+        fm_abort("fseek(SEEK_SET): %s", errbuf);
+    }
     auto buf_ = std::make_unique<char[]>(len);
 
     if (auto ret = ::fread(&buf_[0], 1, len, f); ret != len)
-        fm_abort("fread short read: %s", strerror(errbuf));
+    {
+        get_error_string(errbuf);
+        fm_abort("fread short read: %s", errbuf);
+    }
 
     world w;
     Serialize::reader_state s{w};
diff --git a/serialize/world-writer.cpp b/serialize/world-writer.cpp
index 5e6c07fe..747610c1 100644
--- a/serialize/world-writer.cpp
+++ b/serialize/world-writer.cpp
@@ -252,27 +252,35 @@ void world::serialize(StringView filename)
 {
     collect(true);
     char errbuf[128];
-    constexpr auto strerror = []<std::size_t N> (char (&buf)[N]) -> const char* {
+    constexpr auto get_error_string = []<std::size_t N> (char (&buf)[N]) {
         buf[0] = '\0';
 #ifndef _WIN32
         (void)::strerror_r(errno, buf, std::size(buf));
 #else
         (void)::strerror_s(buf, std::size(buf), errno);
 #endif
-        return buf;
     };
     fm_assert(filename.flags() & StringViewFlag::NullTerminated);
     if (Path::exists(filename))
         Path::remove(filename);
     FILE_raii file = ::fopen(filename.data(), "wb");
     if (!file)
-        fm_abort("fopen(\"%s\", \"w\"): %s", filename.data(), strerror(errbuf));
+    {
+        get_error_string(errbuf);
+        fm_abort("fopen(\"%s\", \"w\"): %s", filename.data(), errbuf);
+    }
     Serialize::writer_state s{*this};
     const auto array = s.serialize_world();
     if (auto len = ::fwrite(array.data(), array.size(), 1, file); len != 1)
-        fm_abort("fwrite: %s", strerror(errbuf));
+    {
+        get_error_string(errbuf);
+        fm_abort("fwrite: %s", errbuf);
+    }
     if (int ret = ::fflush(file); ret != 0)
-        fm_abort("fflush: %s", strerror(errbuf));
+    {
+        get_error_string(errbuf);
+        fm_abort("fflush: %s", errbuf);
+    }
 }
 
 } // namespace floormat