Looking for ideas on how to generate a Name Resolution request and specify to which server to dispatch the request.
I'm working on Linux.
Up until now, I found two options:
Use an external library which can be hooked for achieving this.
Anyone knows a reliable DNS library that can be used for a production system?
Use Network Namespaces to virtualize the stack and use mounting to link the name resolution server files per namespace (see iproute2 latest version). Requests issued from each namespace may have different servers.
please share your thoughts...
Linux actually comes with a resolver API. See the man(3) page for 'resolver', and link your application with -lresolv.
The libsres library (dnsval) from the DNSSEC-Tools project definitely lets you send queries to a particular server. I know because I've done just that inside the DNSSEC-Check application, which is also part of the DNSSEC-Tools project.
Related
IBM offer an installable MQSeries Client software that allows you to access queue managers on remote hosts. They also offer some C-callable libraries that let you do messaging from a C application.
My problem is that I don't have admin access on the hosts I plan to test-deploy on, and getting an application installed comes with bigtime Enterprise hassle. IBM, meanwhile, acts as if there's no alternative to installing their whole client package. Assuming I'm willing to forgo their support, can I get around this? i.e. is there some set of objects/libraries I can link with to produce a standalone client?
From v8.0.0.4 onwards, IBM provides set of libraries as a zip/tar and you don't need to install whole client package. See here: http://www.ibm.com/support/knowledgecenter/SSFKSJ_8.0.0/com.ibm.mq.ins.doc/q122882_.htm.
But you still need queue manager running somewhere to test your application.
Once I've written a sort of a driver for Windows, which had to intercept the interaction of the native display driver with the OS. The native display driver consists of a miniport driver and a DLL loaded by win32k.sys into the session space. My goal was to meddle between the win32k.sys and that DLL. Moreover, the system might have several display drivers, I had to hook them all.
I created a standard WDM driver, which was configured to load at system boot (i.e. before win32k). During its initialization it hooked the ZwSetSystemInformation, by patching the SSDT. This function is called by the OS whenever it loads/unloads a DLL into the session space, which is exactly what I need.
When ZwSetSystemInformation is invoked with SystemLoadImage parameter - one of its parameters is the pointer to a SYSTEM_LOAD_IMAGE structure, and its ModuleBase is the module base mapping address. Then I analyze the mapped image, patch its entry point with my function, and the rest is straightforward.
Now I need to port this driver to a 64-bit Windows. Needless to say it's not a trivial task at all. So far I found the following obstacles:
All drivers must be signed
PatchGuard
SSDT is not directly exported.
If I understand correctly, PatchGuard and driver signing verification may be turned off, the driver should be installed on a dedicated machine, and we may torture it the way we want.
There're tricks to locate the SSDT as well, according to online sources.
However recently I've discovered there exists a function called PsSetLoadImageNotifyRoutine. It may simplify the task considerably, and help avoid dirty tricks.
My question are:
If I use PsSetLoadImageNotifyRoutine, will I receive notifications about DLLs loaded into the session space? The official documentation talks about "system space or user space", but does "system space" also includes the session space?
Do I need to disable the PatchGuard if I'm going to patch the mapped DLL image after it was mapped?
Are there any more potential problems I didn't think about?
Are there any other ways to achieve what I want?
Thanks in advance.
Do I need to disable the PatchGuard if I'm going to patch the mapped DLL image after it was mapped?
To load any driver on x64 it must be signed. With admin rights you can disabled PatchGuard and I personally recommend using DSEO, a GUI application made for this. Or you can bypass PatchGuard by overwriting the MBR (or BIOS), although this is typically considered a bootkit - malware.
I'd like my application to be able to show a directory listing from a remote FTP (or SFTP etc) location. When a file/directory changes in the remote directory tree, the application should update its view with the relevant changes.
Because traversing the entire tree is slow and wasteful, I'd like to use something along the lines of FSEvents (inotify/kqueues on Linux), but obviously these libraries are filesystem-based, and a connection to an FTP server is not the same as a mounted filesystem.
In order to make these libraries work, I'd need to actually mount a filesystem backed by FTP/SFTP on the local machine, then attach an FSEventStream (or kqueue etc) to this local mount. I know FUSE can do this, but is there any way I can use FUSE without the user having to first install it? I mean, can I bundle it with my (Mac) application and create mounts without having to put the user through the process of actually running an installer package to copy libfuse and the kernel modules into the system? Does it assume /dev/fuse exists, or can this live outside the /dev/ path, inside my application directory?
Nice Mac applications are installed with a simple drag & drop and I'd like to keep mine this way if possible. I'm unclear on if it's possible to use libfuse directly (provided the files are included with the app), without installing it in the system paths.
Alternatively, does anyone have any other suggestions for monitoring for changes over FTP, without polling?
Unfortunately FTP and SFTP do not support any form of client notification.
Much like HTTP they are based on a request/response scheme, where each data transfer is initiated by the client. What makes things worse is that, contrary to HTTP, there is no way to ask the server to inform the client of any changes since a specific date.
This means that not only you have to use polling, but also that said polling will by no means be lightweight.
As far as FUSE is related, most FTP and SFTP modules that are available only update their view of the filesystem when the userspace applications ask for a directory listing (e.g. hitting Refresh in a file browser window). They do not perform polling on their own. Your userspace application will have to initiate the refresh by polling the directory itself.
EDIT:
To clarify a couple of things, recent versions of FUSE do support notification events. They
simply pass through the events from the modules to the kernel. The modules still have to generate them and in the case of an FTP/SFTP client module that is impossible without polling the server.
Also keep in mind that many current NFS implementations do not support change notifications either, despite the fact that NFSv4.1 has the necessary provisions. Many SMB/CIFS servers (esp. those in cheap Network-Attached-Storage embedded systems) also have limited to no support.
I am currently using libproxy to get the proxy information (if any) on RedHat and Debian Linux. It doesn't work all that well, but it's the only way I know I can use to get the proxy information from my code.
I need to stop using the lib since in most cases it doesn't recognize the proxy.
Is there any way to acquire the proxy information? What i mean is, is there a file (or group of files) i can read, or an env variable or an API or system call that i can use to get the information?
Gnome based code is OK, KDE might help as well but i am looking for something more generic.
The code is C.
Now, before anyone asks, I don't want to use libproxy anymore. Period. I don't want to start investigating why it doesn't work. I don't really want to know whether there is a new version of that lib. I know it might work, I just don't want to use it. i can't use it (just because). So please don't point me that way.
Code is appreciated.
thanks.
In linux, the "global proxy setting" is typically just environment variables that are usually set in /etc/profile. You can examine those variables to see what proxy is set.
The variables are:
http_proxy - the proxy for HTTP connections
ftp_proxy - the proxy for FTP connections
Using the Network Proxy Preferences tool under Gnome saves information in the GConf database. The path to the keys are /system/http_proxy and /system/proxy. You can read about the detail in those trees at this page.
You can access the GConf database using the library API. Note that GConf is based on GObject. To examine the contents of this tree using the command line, try the following:
gconftool-2 -R /system/http_proxy
This will provide a "name = value" listing of the tree, which may be usable in your application. Note that this requires a system() call, so it's not recommended for a deployed application, but it might help you get started.
GNOME has its own place to store the Proxy settings, and I am sure KDE or any other DE has its own place too. May be you can look for any mention of where Proxy settings should be store in the Linux Standard Base. That could hint you a standard of doing it irrespective of Distro or DE.
DE -> Desktop Environment
char* proxy = getenv("all_proxy");
This statement puts the value of the environment variable called all_proxy, which is used by the system as a global proxy, in your C variable.
To print it in bash, try env | grep 'all_proxy' | cut -d= -f 2.
Is there any way to have something that looks just like a file on a Windows file share, but is really a resource served up over HTTP?
For context, I'm working with an old app that can only deal with files on a Windows file share, I want to create a simple HTTP-based service to serve the content of the files dynamically to pick up real time changes to the underlying data on request.
WebDAV (basically) takes an existing directory, and shares it over HTTP - which sounds like the opposite of what you want.
You need something that speaks SMB/CIFS on one end, and your own code on the other. The easiest way to do that is with a userspace file system.
To that end, here's a couple of links:
WinFUSE, which is kind of a barebones CIFS/SMB server that can host your own filesystem. I've done a couple of small samples with it - and the docs are terrible, but it more or less worked.
Dokan, a userspace file driver with .NET bindings. I haven't used this one, but it looks promising. It has both .NET and Ruby bindings, so you should be able to get a POC up pretty quickly.
Callback File System - yet another userspace file system. Again, I have no experience with this one.
A Linux box with SAMBA and FUSE that shares the drive out to the Windows box.
This won't answer your question in any meaningful way, but maybe it will get you pointed in the right direction. Look into serving the "file(s)" via WebDAV--SharePoint uses this and its files can be accessed exactly as you want, as a file share where the transport mechanism is HTTP. Unfortunately I can't give any more detailed info, as I've only worked on the client end of WebDAV and not the server side of things.
I think serving up files from WebDAV might be what you're looking for.