[fpc-pascal] Resolving a local hostnames to an IP address
I need to resolve a hostname to an IP address, to pass to a minimal telnet implementation that expects that as its parameter. The reason that I'm not using something "industrial grade" like Synapse is that I'm trying to restrict myself to standard libraries so that I can ship sources to people who have no FPC experience, making the program both useful and a good demonstration of the development tools. If I use THostResolver.NameLookup I find that it can convert a fully-qualified name but not one where the domain is omitted, I notice that the README specifically says that resolv.conf isn't fully parsed. Unfortunately I find (2.6 on Debian "Squeeze") that GetDomainName returns nothing useful- I've not yet investigated whether that's down to a particular development system but if it happens to me it might happen to others. In short, how best should I work around this? -- Mark Morgan Lloyd markMLl .AT. telemetry.co .DOT. uk [Opinions above are the author's, not those of his employers or colleagues] ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Resolving a local hostnames to an IP address
In our previous episode, Mark Morgan Lloyd said: > a particular development system but if it happens to me it might happen > to others. > > In short, how best should I work around this? Have a look at unit cnetdb.pp in fcl-net package. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Resolving a local hostnames to an IP address
Marco van de Voort wrote: In our previous episode, Mark Morgan Lloyd said: a particular development system but if it happens to me it might happen to others. In short, how best should I work around this? Have a look at unit cnetdb.pp in fcl-net package. Thanks Marco, now working. I see I've used that elsewhere in the past... I rather loathe those return structures :-) -- Mark Morgan Lloyd markMLl .AT. telemetry.co .DOT. uk [Opinions above are the author's, not those of his employers or colleagues] ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Resolving a local hostnames to an IP address
On 4/13/2012 04:54, Mark Morgan Lloyd wrote: If I use THostResolver.NameLookup I find that it can convert a fully-qualified name but not one where the domain is omitted, can you explain this a bit more, please? the reason i ask is because some code wants at least one dot separator... example: foo.bar -- .bar is the TLD and foo is the hostname foo.bar. -- the last dot says this is the end, do not look to other domains so... foo -- may result in other domains being automatically looked up by stuffing known TLDs after it ie: foo.com, foo.net, foo.org... *BUT* foo. -- says there is no more domains to look at... so effectively one is looking for only the LAN name which should be easily served up by the LAN DNS server or the HOSTS file... some systems need the trailing dot and others do not... i've seen this problem for years and it seems to be limited to some OS' to a certain extent... I notice that the README specifically says that resolv.conf isn't fully parsed. in the above, i'm speaking purely from a network admin/tech/specialist POV... i work with a FOS firewall product and this is quite a common problem IF what i'm thinking it is is correct... sadly i've not (yet!) the coding knowledge in this area to be able to be more specific or of more help :? the main point is that many do not know about the use of the trailing dot to denote that there are no other domains to append in an attempt to locate the given hostname... clarification: foo.bar -- foo is the hostname, bar is the TLD... foo.bar.com -- foo is the hostname, bar is a SLD, and com is a TLD... foo.-- says look up "foo" only... foo.bar -- says look up "foo.bar" first and maybe other TLDs behind... foo.bar.-- says look up "foo.bar" and don't look up more than that... i hope this makes sense and is of some assistance... ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Resolving a local hostnames to an IP address
waldo kitty wrote: On 4/13/2012 04:54, Mark Morgan Lloyd wrote: If I use THostResolver.NameLookup I find that it can convert a fully-qualified name but not one where the domain is omitted, can you explain this a bit more, please? the reason i ask is because some code wants at least one dot separator... example: foo.bar -- .bar is the TLD and foo is the hostname foo.bar. -- the last dot says this is the end, do not look to other domains so... foo -- may result in other domains being automatically looked up by stuffing known TLDs after it ie: foo.com, foo.net, foo.org... *BUT* foo. -- says there is no more domains to look at... so effectively one is looking for only the LAN name which should be easily served up by the LAN DNS server or the HOSTS file... some systems need the trailing dot and others do not... i've seen this problem for years and it seems to be limited to some OS' to a certain extent... That issue IME is specifically at the server, i.e. you've got to be careful with your DNS zone files. Cf the cricket book. I've not checked what the RFCs have to say about trailing dots at the client or in the client protocol, IMO strictly they're an error. I notice that the README specifically says that resolv.conf isn't fully parsed. in the above, i'm speaking purely from a network admin/tech/specialist POV... i work with a FOS firewall product and this is quite a common problem IF what i'm thinking it is is correct... sadly i've not (yet!) the coding knowledge in this area to be able to be more specific or of more help :? the main point is that many do not know about the use of the trailing dot to denote that there are no other domains to append in an attempt to locate the given hostname... clarification: foo.bar -- foo is the hostname, bar is the TLD... foo.bar.com -- foo is the hostname, bar is a SLD, and com is a TLD... foo.-- says look up "foo" only... foo.bar -- says look up "foo.bar" first and maybe other TLDs behind... foo.bar.-- says look up "foo.bar" and don't look up more than that... i hope this makes sense and is of some assistance... The point is that I was knocking together a demo terminal emulator (using non-standard coding etc.) that communicates using telnet, and I'd copied over the ltelnet library that requires (a string containing) an IP address as its parameter. Communicating with localhost worked, but rather late in the day I discovered that I was unable to set up a connection with named servers (i.e. DNS lookups were failing). This applies to Linux, I've not checked the Windows situation (there are other things that might not work such as keycodes, so porting isn't very high on my list). Connecting to pye-dev-07 failed, but its IP address (192.168.1.22) was OK. Qualifying the name manually so that it read pye-dev-07.telemetry.co.uk worked, but trying to get the domain name using GetDomainName didn't. The unix /etc/resolv.conf file (normally on each client) has a line for search paths, which are suffixes to be applied to a name if it doesn't immediately match. The libc lookup implementation, wrapped in cnetdb, uses this, while resolve.pas doesn't. The file can also specify a domain although this is rarely used, it might be that this is what GetDomainName refers to. I've ended up using a hybrid approach: first well-known names such as localhost and lo, then THostResolver, then cnetdb, with the possible fallback of parsing resolv.conf for cases where libc isn't available. If I look at porting to Windows I'll probably have to consult the registry in lieu of resolv.conf. -- Mark Morgan Lloyd markMLl .AT. telemetry.co .DOT. uk [Opinions above are the author's, not those of his employers or colleagues] ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
