Author Topic: Server Protocol  (Read 4048 times)

DivinityArcane

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Server Protocol
« on: June 27, 2014, 05:26:24 AM »
Hi there.


I was thinking of writing a custom server for the game (to add random features for myself and some friends), so I was wondering if there is any public info (or any plans for there to be) on the actual protocol the server<->client uses.

I could write up a proxy and figure it out manually, of course. But it's always easier if it exists already.  :)

Also, kudos on the game, it's great. I even managed to get the wife playing it.

Myran

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Re: Server Protocol
« Reply #1 on: June 27, 2014, 02:21:22 PM »
Oh wow, that is quite the project. So the game doesn't really have a well defined protocol for communication, but we use the lidgren network library for all messages, which you can take a look at for the protocol for reliable messages and heartbeat and all that. Then we have a whole bunch of messages with their parameters defined in an xml file, you can extract the assets.bin to take a look at network.xml, or just look at this one.
You're probably still going to have to do a bit of packet analyzing for more details though :\

DivinityArcane

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Re: Server Protocol
« Reply #2 on: June 27, 2014, 10:36:41 PM »
Oh, awesome. I've actually heard of that framework before, and since I'm working mainly with C#, I can use that if I don't want to port it.

A proxy to find the rest shouldn't be hard. It looks like the game uses a pretty straight-forward way of doing things, unlike games I've worked with before (Conquer Online being one of them)

Thanks for the reply!

DivinityArcane

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Re: Server Protocol
« Reply #3 on: June 27, 2014, 11:12:54 PM »
Quick question.

I see it's not possible to change the port the via the client, and I haven't found it hard-coded in the client (by normal means. Hex search returns 20+ results for 270B, which is 9995)

I checked the hex dump of assets.bin, and it did have an occurrence there, but it was just the string that says "Port: 9995", and did not affect the client or server aspect at all. I assume [unless I'm missing something here] that the port should be in either the main binary (Hammerwatch.exe) or the assets file. Any pointers on which file I should look to, to modify that? Modifying a hex value is easy enough, I just don't want to go on a wild goose chase, modifying every occurrence of the value, only to find that I was changing values in the wrong file.

Myran

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Re: Server Protocol
« Reply #4 on: June 28, 2014, 01:15:48 AM »
Sure, it should be in the Hammerwatch.exe, more specifically in the class LobbyMenu if you use a decompiler.

DivinityArcane

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Re: Server Protocol
« Reply #5 on: June 28, 2014, 02:10:20 AM »
Alrighty, thanks. Since it's a const int (32bit integer) I know that for little-endian I'm searching for 0B270000 (9995 stored in a little-endian 4byte integer). I was able to find 7 occurrences at these offsets: 23E0B, 2B1B0, 2B21D, 2B2BD, 2D06D, 2D191, 6F310

Since I'm only looking to change the client port so I can add a middle-man proxy to log packets, I simply changed it to 0C270000 (9996), but it can be changed to any port needed. Did the changes using a hex editor and saved the new Hammerwatch.exe, and it works like a charm.

Thanks for all the help so far Myran :)


EDIT: Something to note for the devs. In LobbyMenu.cs, though this.port is defined as a const int, the port is hardcoded in various spots in the file. Not a big issue, but it's less of a hassle to have those hardcoded numbers just refer to this.port. Not that it matters at the moment, since the client doesn't provide a way to change it.)
« Last Edit: June 28, 2014, 08:36:03 AM by DivinityArcane »

DivinityArcane

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Re: Server Protocol
« Reply #6 on: June 30, 2014, 07:21:53 AM »
Well, after looking over the source of the game binary and all the networking tidbits involved, it's safe to say that a private server would be a bit.. impractical at the moment. As it stands, HW's "server" aspect is simply a relay, so clients can tell eachother what they're doing. The problem with this is that basically all the logic is left up to the individual clients, making a dedicated server a bit of a "waste", short of writing some sort of server to just relay the packets and select one of the clients to be the actual "host", which would be a bit pointless. It also creates a bit of a problem, since HW utilizes UDP mainly as opposed to TCP, so a middle-man would be more of a harm than good. HW also doesn't really _have_ a protocol, but rather just passes around objects via packets and the clients just pull the objects from the packets.

So, well, I guess my hopes are dashed. While I slightly dislike the method used for multiplayer in the game (for reasons like the fact that each client can give themselves unlimited mana/hp/etc, as well as send false packets to gain things like unlimited lives or keys, which would reflect on _all_ clients), it does do its job as intended.

I'll just wait around to see where the game goes from here :) I enjoy playing it as-is, so that's fine in the long run.