kernel32: Fix GetComputerNameA to not count trailing NULL, with test.

dlls/kernel32/computername.c

@@ -371,7 +371,7 @@ out:
 BOOL WINAPI GetComputerNameA(LPSTR name, LPDWORD size)
 {
     WCHAR nameW[ MAX_COMPUTERNAME_LENGTH + 1 ];
-    DWORD sizeW = MAX_COMPUTERNAME_LENGTH;
+    DWORD sizeW = MAX_COMPUTERNAME_LENGTH + 1;
     unsigned int len;
     BOOL ret;
 
@@ -381,17 +381,16 @@ BOOL WINAPI GetComputerNameA(LPSTR name, LPDWORD size)
     /* for compatibility with Win9x */
     __TRY
     {
-        if ( *size < len + 1 )
+        if ( *size < len )
         {
-            *size = len + 1;
+            *size = len;
             SetLastError( ERROR_MORE_DATA );
             ret = FALSE;
         }
-        else 
+        else
         {
             WideCharToMultiByte ( CP_ACP, 0, nameW, -1, name, len, NULL, 0 );
-            name[len] = 0;
-            *size = len;
+            *size = len - 1;
             ret = TRUE;
         }
     }

dlls/kernel32/tests/environ.c

@@ -239,6 +239,7 @@ static void test_GetComputerName(void)
     LPSTR name;
     LPWSTR nameW;
     DWORD error;
+    int name_len;
 
     size = 0;
     ret = GetComputerNameA((LPSTR)0xdeadbeef, &size);
@@ -250,6 +251,16 @@ static void test_GetComputerName(void)
     ok(ret, "GetComputerNameA failed with error %d\n", GetLastError());
     HeapFree(GetProcessHeap(), 0, name);
 
+    size = MAX_COMPUTERNAME_LENGTH + 1;
+    name = HeapAlloc(GetProcessHeap(), 0, size * sizeof(name[0]));
+    ok(name != NULL, "HeapAlloc failed with error %d\n", GetLastError());
+    ret = GetComputerNameA(name, &size);
+    ok(ret, "GetComputerNameA failed with error %d\n", GetLastError());
+    trace("computer name is \"%s\"\n", name);
+    name_len = strlen(name);
+    ok(size == name_len, "size should be same as length, name_len=%d, size=%d\n", name_len, size);
+    HeapFree(GetProcessHeap(), 0, name);
+
     size = 0;
     ret = GetComputerNameW((LPWSTR)0xdeadbeef, &size);
     error = GetLastError();