[SOLVED] Convert two 8 byte unsigned QWords to in6_addr (IPv6)
lazarus / 38-Networking and Web Programming

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Gizmo · 2016-10-28 16:09

Hi

I need to convert the binary representation of an IPv6 address into
the human readable and compressed format.

At the moment, the values are stored as two 8-byte unsigned QWord
values (the first 8 bytes, and the second 8 bytes, are two seperate
QWords, totalling a 16 byte range).

For example : 20 03 65 BC A0 C1 F4 10 38 8E 9C FF FE B6 D1 C0 is the
address as raw bytes.

QWordA : holds the 1st part 20 03 65 BC A0 C1 F4 10
QWordB : holds the 2nd part 38 8E 9C FF FE B6 D1 C0

I am aware of the sockets unit (http://www.freepascal.org/docs-
html/rtl/sockets/index-5.html) and specifically the function
NetAddrToStr6 (http://www.freepascal.org/docs-
html/rtl/sockets/netaddrtostr6.html) which I think is what I need to
use. But I am confused by how to get QWordA and QWordB to it using
type in6_addr (http://www.freepascal.org/docs-
html/rtl/sockets/in6_addr.html)

I cannot simply declare a variable of type in6_addr and assign QWordA
and QWordB to it, because it expects bytes. IN the short term I have
written a function that loops over the string representation of the
hex bytes, removes any consequitve zeroes (groups of 4) and replaces
with ':') but that is not ideal (slower and perhaps not even exactly
exactly correct)

Can anyone guide me on the issue?

Thanks

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Remy Lebeau · 2016-10-28 20:42

Quote from: Gizmo on October 28, 2016, 06:09:22 pmI need to convert
the binary representation of an IPv6 address into the human readable
and compressed format.

Use standard socket APIs for that, such as inet_ntop(), or
getnameinfo() with the NI_NUMERICHOST flag.

Quote from: Gizmo on October 28, 2016, 06:09:22 pmI cannot simply
declare a variable of type in6_addr and assign QWordA and QWordB to
it, because it expects bytes.

Sure, you can.

You can use Move() or similar function to move raw bytes from one
memory buffer to another.  Use your QWord variables as input buffers
and your in6_addr as an output buffer.

Or, you can simply type-cast the memory address of the in6_addr
variable to PQWord, and then access the in6_addr as if it were a
static 2-qword array using pointer arithmetic, then you can assign
your QWord variables directly to it.

Or, simply stop storing your IP addresses in QWord variables to begin
with.  Why are you doing that at all?  Why not use in6_addr or event
sockaddr_in6 to begin with?  Or at least a 16-byte array?  Where are
your IP addresses coming from?

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Gizmo · 2016-10-30 23:26

Thanks Remy!

I've not used "Move" before, so that was a very useful tip. Yes, it
worked perfectly, just passing 16 bytes from Position X to Move and
shifting them into a in6_addr declared variable worked first time!
You're a diamond.