Hypergrid
From OpenSimulator
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The OpenSim Hypergrid
What is the hypergrid?
The hypergrid is an extension to opensim that allows you to link your opensim to other opensims on the internet, and that supports seamless agent transfers among those opensims. It can be used both in standalone mode and in grid mode. The hypergrid is effectively supporting the emergence of a Web of virtual worlds.
The basic idea for the hypergrid is that region/grid administrations can place hyperlinks on their map to hypergrided regions run by others. Once those hyperlinks are established, users interact with those regions in exactly the same way as they interact with local regions. Specifically, users can choose to teleport there. Once the user reaches the region behind the hyperlink, she is automatically interacting with a different virtual world without having to logout from the world where she came from, and while still having access to her inventory.
The hypergrid is currently a GForge project. Technically, it's implemented as a thin layer on top of the OpenSim core facilities. It's very easy to install, and it is 100% compatible with the standard OpenSim distribution.
Virtual World Hyperlinks
We're all familiar with hypertext links on the Web. But what is a virtual world hyperlink?
In the hypergrid model, we consider the 2D map of the virtual world as the equivalent of a web page. As such, a VW hyperlink is simply a region on that map.
The default model of opensim-based virtual worlds already supports this concept of hyperlink, to some extent. When you teleport from one region to another via the map, chances are you are migrating your agent into a different opensim server. This migration is a glorified "agent transfer" that also exists, in rudimentary form, on the web when hypertext links are followed. The default model, however, imposes two very strong constraints on these hyperlinks:
- The entire map of regions is controlled by a central service known as the grid service, whose job is to provide a uniform view of the world to all of its regions.
- The only agents that can be transferred are those pertaining to users known to another central service, the user service; if the incoming user is not on that service's database, the agent transfer doesn't go through.
The hypergrid simply removes these two constraints.
First, it allows individual opensim instances to add "neighbors" to their local map, shifting the control of the map down from the grid server to individual opensim instances (although hyperlinks can also be served by grid servers if grid admins so wish). In doing so, the world becomes a lot more interesting and varied. The map that you see in one opensim instance may be completely different from the map that you see after you teleport via an hyperlink. As an opensim administrator, you are free to define what other opensims you want to see on your map.
Second, it allows the transfer of agents pertaining to foreigner users, i.e. users who are registered elsewhere. Instead of assuming one central user service, the hypergrid assumes an arbitrarily large number of such services distributed all over the world. As such, when agents are transferred among hypergrided opensims, a lot more information is passed about the corresponding user. That information includes the collection of servers that the transferring user needs.
Usage Scenarios
The following are some usage scenarios. There isn't a clear separation between these scenarios, there's a large overlap between them. This is also not an exhaustive list. The purpose of these descriptions is to give you some starting ideas for how to use the hypergrid in practice. Please feel free to add other interesting scenarios to this list.
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Personal Worlds This first scenario pertains to standalone opensims. Normally, standalones are completely disconnected from the internet. However, when run in hypergrid mode, standalones become network-able. As such, you can run your own world in your own computer, and link your world to whoever you want. For example, you can link to your friends' hypergrided opensims and to hypergrid gateways in open grids such as OSGrid. The great thing about this scenario is that all of your assets are stored on your computer, and not on somebody else's server. You can back them up using ordinary backend tools. The not so great thing about this scenario is that all of your assets are stored on your computer! If your disk goes berserk, you loose them. (so make sure you make external backups regularly) |
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Communities This second scenario is about communities, broadly construed. The idea here is that a group of people come together to support a small community grid, i.e. a common world where shared activities take place. But at the same time, the members of the community maintain their own standalone worlds. The standalones link to the community grid, and the community grid may link back to the individual members' worlds and other places of interest. The members' identities are probably the identities they have on their standalones, and their assets are also probably stored there. The assets present in the community regions, however, are stored on the grid asset server. |
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Grid Public Regions Walled-gardens are here to stay, and they serve many useful purposes. There is a hybrid mode for the hypergrid that some walled-garden grid operators may be interested in supporting. In this hybrid mode, most opensim instances on the grid run in normal, wall-garden mode, so no foreign visitors are allowed there - technically it is impossible to reach them. However, a few opensim instances on that grid can run in hypergrid mode, so that foreign visitors are allowed. This way, there is a gateway for grid-local users and arbitrary visitors to meet. This is also a good strategy for attracting new users to the grid, since random users are able to visit those gateway regions without having to sign up for an account upfront. This hybrid mode is very similar to what happens on the web. For example, anyone can visit Facebook's public pages without having to sign up for a Facebook account. However, only Facebook users can go further inside. |
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Level Games The normal version of OpenSim enforces a common map for all the regions on a grid. The hypergrid removes that constraint. As such, it becomes easy to design VW games where the world looks different depending of where the player is. |
Security Concerns
There is a wide-spread assumption that open grids such as OSGrid and new forms of grids such as the hypergrid are inherently insecure, and that it will be impossible to develop a "goods-based" economy on top of them; only walled-gardens can be secured. This is both true and false. While it is true with the current state of things, open grids, whatever their form, can be made as secure as the web. The first step towards that is to define exactly what the security threats are, and how they affect (or not) open and closed grids. So, let's spell them out, and face them head-on. This will help put our feet on the ground so that we start developing appropriate solutions.
Malicious Clients
CopyBots
Everyone knows about the infamous CopyBot. Using libraries such as LibSL (now known as OpenMetaverse) it is possible to develop clients for opensim servers that do unorthodox things such as bypassing the permissions system to copy people's assets. Bots written by griefers can do lots of other nasty things.
Malicious bots are a problem for all opensim administrators, including walled-garden grids. They can be prevented, to a certain extent, by exo-technical solutions such as Terms of Service and real-world lawsuits. Technically speaking, the only way to keep intruders out is to run opensim inside a firewall, pretty much like all other pieces of client/server software out there. If that's an acceptable solution for your case, you should do it.
Unfortunately firewalls also keep the public out, and most opensim operators, even the ones running walled-garden grids, want to reach out to the public. In this case, opensim operators may develop additional technical obstacles for bots, similar to those we see on the Web. For example, make sure agents are being run by real people by giving them a human-challenge during the login/TP process, etc.
Every obstacle to malicious clients lowers the risk of an intruder attack. However keep this in mind: no matter how many obstacles one builds, a sufficiently skilled and motivated attacker will be able to overcome them to penetrate opensims connected to the public internet. This affects hypergrid nodes as much as walled-garden grids. In fact, it's more pervasive than that: it affects all servers (opensim, web, etc.) connected to the public internet. Fighting malicious intruders is a fact of a connected world. Fortunately, those attacks don't happen very often, or the Web would have been dead by now.
Web Clients
CopyBots are the most well-known bots for opensim-based virtual worlds, but these virtual worlds are also susceptible to attacks by regular web clients. With the current state of things, it is actually easier to copy assets with a web-based client than with a libsl-based one. The weakness is that asset servers are connected to the public internet, and the protocol for interacting with them is public.
OpenSim has some minimal guards in place to fence against these kinds of attacks. Specifically, when the inventory server receives a request for an item, it checks the session identifier of the requester. Web clients aren't logged in, so they are refused service. I don't want to expand much more on this, so not to make life easy for attackers, but let's just say that opensim has the necessary mechanisms in place to fence off web-based attackers.
Malicious Hosts
Actively Malicious Hosts
The new security threat introduced by openness, one that does not exist in closed grids, is the possibility of a user to visit a region that is running malicious code. In the current state of opensim, a malicious host can do serious damage to the user's assets. Let's see how.
Assume you have your assets in your hypergrided-standalone opensim, and you go visit another opensim that happens to be running malicious code. Here is a non-exhaustive list of vulnerabilities that you are exposed to:
- The host has your session id, so it can request your inventory items on your behalf and store copies in its local asset server. To add insult to injury, a malicious host could simply wipe out your inventory after having copied it.
- Even if the malicious host doesn't access your items by itself, every time you access items in your inventory while you are in that region, those items are cached in the region's local cache, and can be stored persistently by the malicious host.
Malicious hosts can do a lot more damage, but those two are enough to illustrate this new kind of vulnerability affecting open grids. Note that this affects all open grids, i.e. those where arbitrary people can plug-in their opensims, and not just the hypergrid.
Fortunately, there is a family of simple solutions to this problem that can be summarized as "protecting you from yourself." That proposal is described here.
Piracy
A second new security threat affecting open grids is one pertaining to commerce of virtual goods. Suppose you put something out for sale on your hypergrided opensim. A foreign user comes and buys it. What that really means is that that user will physically get a copy of the assets moved to his/her asset server, which is different from your asset server. The permissions will be whatever you define them to be, and using the regular VW client, that user can only do what you defined he/she should could do with the object, as usual. However, if the user has direct backend access to the asset and inventory servers, that person can simply modify the permissions on his/her copy. This is commonly known as piracy.
This situation is the kernel of the belief that open grids are hopeless for a virtual-goods economy. DRM discussion aside, maybe they are hopeless. But then, everyone thought the web was hopeless for selling music, and look at the success of iTunes in spite of all the piracy that still exists out there. Who will be the equivalent of iTunes for virtual hair, skin and clothes?
Hypergrid Implementation
Hyperlinks and Agent Transfers
When you establish a link between your opensim and another, a message is sent out to that other opensim requesting information about it; the required information includes the network information of that opensim host, and the coordinates of its first region on its local grid in the form of a region handle. For example, suppose you are linking node X.com:9000, placing it in your local map at 900, 900. That opensim runs one or more regions that likely are not in 900, 900 on their own map; suppose the first region of that opensim is at 1100, 1100. From your point of view, it doesn't matter what those other coordinates are, and you don't need to know -- that's the key to being able to decentralize the "world" as given by a 2D map; you want to place it in your map at 900, 900. The "true" position of that simulator only matters for the LL viewer, when there are teleports between your world and that other opensim. This mapping between coordinate systems is the essence of hyperlinks for opensim; it's one simple but critical thing that the hypergrid implementation does. The mapping happens on the TeleportFinish event; instead of sending the local coordinates to the viewer, the hypergrid teleport wrapper sends the remote coordinates.
When an agent teleports through that hyperlink the following happens. First, before InformRegionOfChildAgent, the local opensim notifies the remote opensim of this foreign user via the "expect_hg_user" method. That message sends along the addresses of all the servers that this user uses, i.e. user, inventory and asset servers. The remote opensim places an entry for that user in its local user profile cache but not in its user database; the foreign user information is non-persistent. After that, the teleport process is exactly the same as the normal teleport process; the only difference is that the region handles are switched between the remote region's hyperlink position on the local grid and its actual position on its grid. Woosh! the viewer is tricked.
In summary, the two new concepts introduced by the hypergrid are the concept of an hyperlink and the concept of a "home user" vs. "foreign user".
Inventory Access
Inventory access from abroad is done by wrapping the existing scene-inventory interactions with additional code that gets or posts inventory assets from/to the user's asset server. When inventory is accessed, the hypergrid wrapper checks if the user is foreign and, if she is, the wrapper simply brings the necessary assets from the user's asset server to the local asset cache and server; from then on, the wrapper passes the control to the existing inventory access functions. When something is added to inventory, the hypergrid wrapper is notified via an event, and posts the assets to the user's asset server. A cache of the exchanged item identifiers is maintained so that they aren't brought back over and over again.
The result is that hypergrided opensim instances end up interacting with several asset servers, instead of just one. That interaction is implemented in a straightforward manner by instantiating several GridAssetClient objects, instead of just one.
The Hypergrid Namespace
Currently, the hypergrid is implemented outside of the OpenSim namespace, so that there is complete separation between what already exists and this new behavior. It has its own namespace, HyperGrid. In it, there are 4 sub-namespaces that follow directly the software architecture of OpenSim, namely:
- HyperGrid.Framework extends OpenSim.Framework in the following manner:
- HGUserProfileData extends UserProfileData by introducing information about the user's "home", namely the home address, port and remoting port. The user's home is not that user's user service; it's the opensim that the user has defined to be her home.
- HGNetworkServersInfo follows the spirit of NetworkServersInfo, although it neither extends it nor uses it. For now, it's a utility class whose two main functions are to convert domain names of servers to IP addresses, and to uniformly provide the answer to the question
bool IsLocalUser(...).
- HyperGrid.Environment extends OpenSim.Region.Environment.Scenes in the following manner:
- HGScene extends Scene, overriding TeleportClientHome(...). The only change to the base method is to stay away from the user server, for now, because the user service is still not completely wrapped up for foreign users. Once the user service is properly wrapped up, this class will become unnecessary.
- HGSceneCommunicationService extends SceneCommunicationService, overriding RequestTeleportToLocation. There are two very small but critical changes to the base method: (a) on the TeleportFinish event, we switch the region handles when the destination region is an hyperlink; (b) the connections at the end are always closed for hyperlink TPs.
Class Diagram
(Click on the image to enlarge)
The image on the left shows the fairly complete class diagram of the hypergrid implementation, and how it uses the OpenSim framework. A brief description of the classes is below.
OpenSimNode: this class extends OpenSim, so that it can redefine a couple of things. The first thing it redefines is the construction code for communications, so that the hypergrid classes (HGCommunicationsStandalone and HGCommunicationsGridMode) are instantiated instead of the default ones. The second thing it redefines is the creation of scenes, so that HGScene and HGSceneCommunicationServices are instantiated instead of the default ones.
HGScene: this class overrides the TeleportClientHome method. The only reason to do that is to avoid a lookup/store of user information on the user database. Foreigner users have no entries in the local user database, they're only in the cache.
HGSceneCommunicationService overrides the RequestTeleportToLocation method. The new method is almost an identical copy of the base method, but the region handle that is given to certain method calls inside is switched in some cases. (The trick with region handles is explained below.)
HGScene.Inventory: this is a partial class of HGScene, just like what happens in the OpenSim framework. This part of HGScene overrides some inventory-scene interaction methods, so that assets are fetched/posted from/to the user's asset server. Once that extra fetching/posting is done, these methods simply pass the ball to the base methods.
HGAssetMapper: this class manages the fetching and posting of assets between foreign regions where the user is and the user's asset server.
HGInventoryService: this class is a hybrid between LocalInventoryService for standalone inventory access and OSG1SecureInventoryService for accessing inventory remotely. (It should probably delegate to OSG1SecureInventoryService, needs revising.)
HGCommunicationsStandalone and HGCommunicationsGridMode: these are very thin classes, similar to their counter-parts in the framework, whose sole purpose is to create a bunch of communication-related service classes.
The HGGridServices cluster: the two subclasses are wrappers for the OpenSim framework classes for which they hold references. The pattern for these methods is very similar: check if the region to talk to is an hyperlink; if it's not, simply delegate the work; if it is, push the work to the base class HGGridServices. HGGridServices, in turn, does the management of hyperlink regions, and defines two additional pieces of inter-region protocol:
- region_uuid: for linking regions
- expect_hg_user: similar to the existing expect_user interface, but with a lot more information about the user being passed around, especially all the user's servers (inventory, asset, home, etc.)
The IRegionModule collection of classes is mainly for allowing access to inventory and assets on standalones when the users are out and about. They use the exact same REST interface as the Grid Asset/Inventory servers.
Installing and Running Hypergrid
Installing
- Checkout the hypergrid project: svn checkout http://forge.opensimulator.org/svn/hypergrid/trunk. Usually trunk is in a usable state. If it isn't, you can check the latest stable version from tags: svn checkout http://forge.opensimulator.org/svn/hypergrid/tags
- Read the README.txt file. It has important information about which version of opensim the hypergrid has been tested with. 'No guarantees of what will happen if you use the hypergrid extension with a different version of opensim'.
- Check out the version of opensim mentioned in the README file. Prebuild and build it as normal.
- Copy all the files under hypergrid/.../bin onto opensim/bin
- Make the following changes to your OpenSim.ini:
- The map: WorldMapModule = "HGWorldMap" If you didn't have this setting in your original OpenSim.ini, make sure yo place it under the [Startup] section.
- If you're running your opensim in grid mode, you're done. If you're running in standalone and you want it to be network-able, change all the [Network] server addresses to "http://<external_host_name>:<http_port>"
- Run opensim like this: [mono] OpenSim.exe -hypergrid=true. To make sure the hypergrid is running type this on your console: link-region. If you don't hear anything back, the hypergrid is not properly installed.
Linking regions
On the console, type for example:
link-region <Xloc> <Yloc> osl2.nac.uci.edu 9006 OSGrid Gateway
Use Xloc and Yloc that make sense to your world, i.e. close to your regions, but not adjacent.
Important Note
Due to a viewer bug, you can only TP between regions that are no more than 4096 cells apart in any dimension. What this means in practice is that if you want to link to OSGrid, you must have your own regions reachable from the (10,000; 10,000) point on the map, which is where OSGrid is centered. Place your regions somewhere in the 8,000s or the 12,000s.
Public Hypergrid Nodes
The following is a list of hypergrid-ready nodes that you can use for testing your installation and for linking your world. Please add your public node here if you wish to help build a web of opensims!
For the time being, and until the security concerns described above are addressed, we advise you to be careful about who you link to.
- osl2.nac.uci.edu 9006
The "UCI Welcome" region connected to OSGrid. It is run by Diva (Crista Lopes) on a machine owned by the University of California, Irvine. You can link to it as a way to link to OSGrid.
- ucigrid02.nacs.uci.edu 9000
A region in the UCI Grid. It is run by Diva (Crista Lopes) on a machine owned by the University of California, Irvine.
