On 04/21/2017 01:36 PM, Vasiliy Tolstov wrote:
2017-04-21 14:14 GMT+03:00 Michal Privoznik <mprivozn@xxxxxxxxxx>:
That's how strings are encoded in RPC. the first four bytes say how long the
string is followed by N bytes (padded to 4 bytes boundary) of the actual
string.
I know, I'm use https://godoc.org/github.com/davecgh/go-xdr/xdr2 and
as i see EncodeString already to that. And all other functions what
operates on strings works fine. Fow example LookupDomainByName. Or
StoragePool functions
Bad payload from own prog:
0x0000: 6001 2a87 006c 0640 2a04 ac00 0006 0001 `.*..l.@*.......
0x0010: 0000 0000 0000 0001 2a04 ac00 0004 0010 ........*.......
0x0020: 0ec4 7aff fe54 cb0a e8b2 407d e44c 1249 ..z..T....@}.L.I
0x0030: eafc 4a72 8018 00e1 ffba 0000 0101 080a ..Jr............
0x0040: 2ef0 9ea7 02ad afcb 0000 004c 2000 8086 ...........L....
0x0050: 0000 0001 0000 00c9 0000 0000 0000 0009 ................
0x0060: 0000 0000 0000 0006 3134 3331 3737 0000 ........143177..
0x0070: 49bf 97e1 4bda 5749 ca89 0000 7db6 2f02 I...K.WI....}./.
0x0080: 0000 0001 0000 0007 7365 7269 616c 3000 ........serial0.
0x0090: 0000 0001 ....
Good payload from virsh:
0x0000: 6009 09de 0070 0640 2a04 ac00 0006 0001 `....p.@*.......
0x0010: 0000 0000 0000 0001 2a04 ac00 0004 0010 ........*.......
0x0020: 0ec4 7aff fe54 cb0a e8a8 407d e159 1a3e ..z..T....@}.Y.>
0x0030: 2e25 4a72 8018 00ea ffbe 0000 0101 080a .%Jr............
0x0040: 2eed 6e7c 02ac e3be 0000 0050 2000 8086 ..n|.......P....
0x0050: 0000 0001 0000 00c9 0000 0000 0000 0009 ................
0x0060: 0000 0000 0000 0006 3134 3331 3737 0000 ........143177..
0x0070: 49bf 97e1 4bda 5749 ca89 0000 7db6 2f02 I...K.WI....}./.
0x0080: 0000 0001 0000 0001 0000 0007 7365 7269 ............seri
So the extra "byte" (in fact 4 bytes) are at 0x0084-0x0087. So this is
how strings are encoded. There are basically two types of strings when
it comes to XDR. The first one is nonnull_string, which are encoded
[length][string]. With just this it would be impossible to differentiate
between NULL and an empty string "" as both would be encoded in the same
way. Therefore, there is remote_string (libvirt terminology) or
xdr_pointer (XDR terminology) which encodes a pointer as [bool][pointer]
where bool is either 00 00 00 00 meaning the pointer is NULL or
something else (e.g. 00 00 00 01) meaning the pointer has a non-NULL
value. So long story short, what you can see here is:
00 00 00 01 00 00 00 07 73 65 72 69 61 6c 30
which is the same as (regroup)
[00 00 00 01] [00 00 00 07] [73 65 72 69 61 6c 30]
which means: the following pointer is a non-NULL pointer, and it is a
string of the length 7 and the string is "serial0".
0x0090: 616c 3000 0000 0000 al0.....
Michal
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