Show descriptive error messages when FileCommit fails

Only raw errno codes are logged if FileCommit fails. These are
implementation-specific, so it makes it harder to debug based on
user reports. Instead, use SysErrorString to display both the
raw int value and the descriptive message.

src/util/fs_helpers.cpp

@@ -14,6 +14,7 @@
 #include <tinyformat.h>
 #include <util/fs.h>
 #include <util/getuniquepath.h>
+#include <util/syserror.h>
 
 #include <cerrno>
 #include <filesystem>
@@ -120,28 +121,28 @@ std::streampos GetFileSize(const char* path, std::streamsize max)
 bool FileCommit(FILE* file)
 {
     if (fflush(file) != 0) { // harmless if redundantly called
-        LogPrintf("%s: fflush failed: %d\n", __func__, errno);
+        LogPrintf("fflush failed: %s\n", SysErrorString(errno));
         return false;
     }
 #ifdef WIN32
     HANDLE hFile = (HANDLE)_get_osfhandle(_fileno(file));
     if (FlushFileBuffers(hFile) == 0) {
-        LogPrintf("%s: FlushFileBuffers failed: %d\n", __func__, GetLastError());
+        LogPrintf("FlushFileBuffers failed: %s\n", Win32ErrorString(GetLastError()));
         return false;
     }
 #elif defined(MAC_OSX) && defined(F_FULLFSYNC)
     if (fcntl(fileno(file), F_FULLFSYNC, 0) == -1) { // Manpage says "value other than -1" is returned on success
-        LogPrintf("%s: fcntl F_FULLFSYNC failed: %d\n", __func__, errno);
+        LogPrintf("fcntl F_FULLFSYNC failed: %s\n", SysErrorString(errno));
         return false;
     }
 #elif HAVE_FDATASYNC
     if (fdatasync(fileno(file)) != 0 && errno != EINVAL) { // Ignore EINVAL for filesystems that don't support sync
-        LogPrintf("%s: fdatasync failed: %d\n", __func__, errno);
+        LogPrintf("fdatasync failed: %s\n", SysErrorString(errno));
         return false;
     }
 #else
     if (fsync(fileno(file)) != 0 && errno != EINVAL) {
-        LogPrintf("%s: fsync failed: %d\n", __func__, errno);
+        LogPrintf("fsync failed: %s\n", SysErrorString(errno));
         return false;
     }
 #endif

src/util/sock.cpp

@@ -419,18 +419,7 @@ void Sock::Close()
 #ifdef WIN32
 std::string NetworkErrorString(int err)
 {
-    wchar_t buf[256];
-    buf[0] = 0;
-    if(FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS | FORMAT_MESSAGE_MAX_WIDTH_MASK,
-            nullptr, err, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
-            buf, ARRAYSIZE(buf), nullptr))
-    {
-        return strprintf("%s (%d)", std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>,wchar_t>().to_bytes(buf), err);
-    }
-    else
-    {
-        return strprintf("Unknown error (%d)", err);
-    }
+    return Win32ErrorString(err);
 }
 #else
 std::string NetworkErrorString(int err)

src/util/syserror.cpp

@@ -12,6 +12,12 @@
 #include <cstring>
 #include <string>
 
+#if defined(WIN32)
+#include <windows.h>
+#include <locale>
+#include <codecvt>
+#endif
+
 std::string SysErrorString(int err)
 {
     char buf[1024];
@@ -33,3 +39,21 @@ std::string SysErrorString(int err)
         return strprintf("Unknown error (%d)", err);
     }
 }
+
+#if defined(WIN32)
+std::string Win32ErrorString(int err)
+{
+    wchar_t buf[256];
+    buf[0] = 0;
+    if(FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS | FORMAT_MESSAGE_MAX_WIDTH_MASK,
+                       nullptr, err, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+                       buf, ARRAYSIZE(buf), nullptr))
+    {
+        return strprintf("%s (%d)", std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>,wchar_t>().to_bytes(buf), err);
+    }
+    else
+    {
+        return strprintf("Unknown error (%d)", err);
+    }
+}
+#endif

src/util/syserror.h

@@ -13,4 +13,8 @@
  */
 std::string SysErrorString(int err);
 
+#if defined(WIN32)
+std::string Win32ErrorString(int err);
+#endif
+
 #endif // BITCOIN_UTIL_SYSERROR_H