Implement TXT record parsing for properties

[clairernovotny]

This is a pretty big PR, mainly because there was some strangeness in the parsing of TXT records. There weren't many pure C# DNS implementations around - most P/Invoked to dnsds.dll.

The DNS code included is a subset of the files here:
http://www.codeproject.com/Articles/23673/DNS-NET-Resolver-C

They're allowed to be used under the codeproject license. The author simply requests that the namespaces of the types not change.

The internals now correctly read the necessary DNS records and can now return the TXT properties as well.

I've also removed the dependency on Rx to make the package self-contained. It provides a configurable scan time and retry count/delay.

Most scanning is less than 1-2 seconds, so it's not generally necessary to keep an open stream.

[saldoukhov]

Not sure what "strangeness" in TXT parsing you noticed, but this PR is essentially a full replacement of the current code. Is such situation, you probably want to create your own project.
When creating this one, I have looked at DNS .Net resolver and decided to start from scratch to make the code simpler and easier to understand. This PR goes against this line. You're welcome to create a "targeted" PR addressing the exact issue you're observing or report it and I will take a look.

[clairernovotny]

Hi,

I know its alot if code, but I figured I'd offer it up to you as I did base it off of yours.

There are two issues with the txt records.

1 Mult values per record are not split.

2 Because of 1, mDNS properties can't be parsed.

Look at ichats messages to see the key/value properties.

You might want to look at how DNS.net parses the txt record. It reads the str Len as a short, then n chats. It repeats for the rest of the txt data segment. Then you have a list of txt values per record.

Up to you; I'm happy to keep the package separate and I'll be sure to give you credit.

Regards,
Oren

[saldoukhov]

Ok, I'll try to see what is happening with iChat. Do I understand correctly
that iChat is a sample program from the Bonjour SDK?

On Mon, Sep 2, 2013 at 3:47 PM, Oren Novotny notifications@github.comwrote:

Hi,

I know its alot if code, but I figured I'd offer it up to you as I did
base it off of yours.

There are two issues with the txt records.

1 Mult values per record are not split.

2 Because of 1, mDNS properties can't be parsed.

Look at ichats messages to see the key/value properties.

You might want to look at how DNS.net parses the txt record. It reads the
str Len as a short, then n chats. It repeats for the rest of the txt data
segment. Then you have a list of txt values per record.

Up to you; I'm happy to keep the package separate and I'll be sure to give
you credit.

Regards,
Oren

—
Reply to this email directly or view it on GitHubhttps://github.com//pull/3#issuecomment-23682133
.

[clairernovotny]

It's not just iChat - that's one example. Many/most mDNS/Bonjour reponses contain key/value pairs. You can see an example here:
http://upload.wikimedia.org/wikipedia/commons/e/e0/Bonjour_Browser_window.png

For example, I have a network printer on my LAN on Ethernet. Both _printer._tcp.local. and _pdl-datastream._tcp.local. return data with key value pairs.

According to the mDNS spec though, text record values may contain an =, or the values may be scalar. A txt record string cannot start with an =. Any other char is valid though.