Checking why the packet length is to big I found that the 4 bytes received
from the server have the too big value.
line 156 in sftp.c
rc = libssh2_channel_read_ex(channel, 0, (char *) buffer, 4);
.....
packet_len = libssh2_ntohu32(buffer);
_libssh2_debug(session, LIBSSH2_DBG_SFTP,
"Data begin - Packet Length: %lu", packet_len);
if (packet_len > LIBSSH2_SFTP_PACKET_MAXLEN) {
libssh2_error(session, LIBSSH2_ERROR_CHANNEL_PACKET_EXCEEDED,
"SFTP packet too large", 0);
return -1;
}
The server can only answer with a size which was set before by the client
(otherwise it is a server bug). As far as I understand the buffer size is
send as part of the SSH_FXP_READ request which is set in sftp.c in line
1025. Here the max buffer is set to buffer_maxlen (the user set value), but
I think it can't be more than bytes_requested =
LIBSSH2_SFTP_PACKET_MAXLEN - 10
Markus
if (sftp->read_state == libssh2_NB_state_allocated) {
libssh2_htonu32(s, packet_len - 4);
s += 4;
*(s++) = SSH_FXP_READ;
request_id = sftp->request_id++;
libssh2_htonu32(s, request_id);
s += 4;
libssh2_htonu32(s, handle->handle_len);
s += 4;
memcpy(s, handle->handle, handle->handle_len);
s += handle->handle_len;
libssh2_htonu64(s, handle->u.file.offset);
s += 8;
libssh2_htonu32(s, buffer_maxlen);
s += 4;
sftp->read_state = libssh2_NB_state_created;
}
"Markus Moeller" <hua...@moeller.plus.com> wrote in
message news:gi0gi8$lk...@ger.gmane.org...
> Since I experienced a similar issue when using curl with sftp I run the
> sample with some debug and got to the point where in libssh2_sftp.h the
> maximal packet length is defined as 40000. Where does this maximum come
> from
> ? Is it an arbitrary value or somewhere defined in the ssh/sftp protocol
> ?
>
> Thank you
> Markus
>
> #define LIBSSH2_SFTP_VERSION 3
> #define LIBSSH2_SFTP_PACKET_MAXLEN 40000
>
>
> trying buffer size 39990
> [libssh2] SFTP Subsystem: Reading 39990 bytes from SFTP handle
> [libssh2] SFTP Subsystem: Requesting 39990 bytes from SFTP handle
> [libssh2] Connection: Writing 29 bytes on channel 0/0, stream #0
> [libssh2] Connection: Sending 29 bytes on channel 0/0, stream_id=0
> [libssh2] SFTP Subsystem: _requirev(): Initialize timeout
> [libssh2] SFTP Subsystem: Waiting for packet
> [libssh2] SFTP Subsystem: Asking for 103 packet
> [libssh2] SFTP Subsystem: Asking for 101 packet
> [libssh2] SFTP Subsystem: Waiting for packet
> [libssh2] Connection: Attempting to read 4 bytes from channel 0/0 stream
> #0
> [libssh2] Transport: Packet type 94 received, length=16393
> [libssh2] Connection: 16384 bytes received for channel 0/0 stream #0
> [libssh2] Connection: Reading 4 of buffered data from 0/0/0
> [libssh2] SFTP Subsystem: Data begin - Packet Length: 39999
> [libssh2] Connection: Attempting to read 39999 bytes from channel 0/0
> stream
> #0
> [libssh2] Transport: Packet type 94 received, length=16393
> [libssh2] Connection: 16384 bytes received for channel 0/0 stream #0
> [libssh2] Transport: Packet type 94 received, length=7244
> [libssh2] Connection: 7235 bytes received for channel 0/0 stream #0
> [libssh2] Connection: Reading 16380 of buffered data from 0/0/0
> [libssh2] Connection: Unlinking empty packet buffer from channel 0/0
> [libssh2] Connection: Adjusting window 16384 bytes for data flushed from
> channel 0/0
> [libssh2] Connection: Reading 16384 of buffered data from 0/0/0
> [libssh2] Connection: Unlinking empty packet buffer from channel 0/0
> [libssh2] Connection: Adjusting window 16384 bytes for data flushed from
> channel 0/0
> [libssh2] Connection: Reading 7235 of buffered data from 0/0/0
> [libssh2] Connection: Unlinking empty packet buffer from channel 0/0
> [libssh2] Connection: Adjusting window 7235 bytes for data flushed from
> channel 0/0
> [libssh2] SFTP Subsystem: Received packet 103
> [libssh2] SFTP Subsystem: Asking for 103 packet
> [libssh2] SFTP Subsystem: 39990 bytes returned
> trying buffer size 39991
> [libssh2] SFTP Subsystem: Reading 39991 bytes from SFTP handle
> [libssh2] SFTP Subsystem: Requesting 39990 bytes from SFTP handle
> [libssh2] Connection: Writing 29 bytes on channel 0/0, stream #0
> [libssh2] Connection: Sending 29 bytes on channel 0/0, stream_id=0
> [libssh2] SFTP Subsystem: _requirev(): Initialize timeout
> [libssh2] SFTP Subsystem: Waiting for packet
> [libssh2] SFTP Subsystem: Asking for 103 packet
> [libssh2] SFTP Subsystem: Asking for 101 packet
> [libssh2] SFTP Subsystem: Waiting for packet
> [libssh2] Connection: Attempting to read 4 bytes from channel 0/0 stream
> #0
> [libssh2] Transport: Packet type 94 received, length=16393
> [libssh2] Connection: 16384 bytes received for channel 0/0 stream #0
> [libssh2] Connection: Reading 4 of buffered data from 0/0/0
> [libssh2] SFTP Subsystem: Data begin - Packet Length: 40000
> [libssh2] Connection: Attempting to read 40000 bytes from channel 0/0
> stream
> #0
> [libssh2] Transport: Packet type 94 received, length=16393
> [libssh2] Connection: 16384 bytes received for channel 0/0 stream #0
> [libssh2] Transport: Packet type 94 received, length=7245
> [libssh2] Connection: 7236 bytes received for channel 0/0 stream #0
> [libssh2] Connection: Reading 16380 of buffered data from 0/0/0
> [libssh2] Connection: Unlinking empty packet buffer from channel 0/0
> [libssh2] Connection: Adjusting window 16384 bytes for data flushed from
> channel 0/0
> [libssh2] Connection: Reading 16384 of buffered data from 0/0/0
> [libssh2] Connection: Unlinking empty packet buffer from channel 0/0
> [libssh2] Connection: Adjusting window 16384 bytes for data flushed from
> channel 0/0
> [libssh2] Connection: Reading 7236 of buffered data from 0/0/0
> [libssh2] Connection: Unlinking empty packet buffer from channel 0/0
> [libssh2] Connection: Adjusting window 7236 bytes for data flushed from
> channel 0/0
> [libssh2] SFTP Subsystem: Received packet 103
> [libssh2] SFTP Subsystem: Asking for 103 packet
> [libssh2] SFTP Subsystem: 39991 bytes returned
> trying buffer size 39992
> [libssh2] SFTP Subsystem: Reading 39992 bytes from SFTP handle
> [libssh2] SFTP Subsystem: Requesting 39990 bytes from SFTP handle
> [libssh2] Connection: Writing 29 bytes on channel 0/0, stream #0
> [libssh2] Connection: Sending 29 bytes on channel 0/0, stream_id=0
> [libssh2] SFTP Subsystem: _requirev(): Initialize timeout
> [libssh2] SFTP Subsystem: Waiting for packet
> [libssh2] SFTP Subsystem: Asking for 103 packet
> [libssh2] SFTP Subsystem: Asking for 101 packet
> [libssh2] SFTP Subsystem: Waiting for packet
> [libssh2] Connection: Attempting to read 4 bytes from channel 0/0 stream
> #0
> [libssh2] Transport: Packet type 94 received, length=16393
> [libssh2] Connection: 16384 bytes received for channel 0/0 stream #0
> [libssh2] Connection: Reading 4 of buffered data from 0/0/0
> [libssh2] SFTP Subsystem: Data begin - Packet Length: 40001
> [libssh2] Failure Event: -25 - SFTP packet too large
> [libssh2] Failure Event: -30 - Timeout waiting for status message
> libssh2_sftp_read() failed
>
>
>
>
>
>
>
> "Alexander Lamaison" <sw...@lammy.co.uk> wrote
> in message
> news:9c3275a90811271540y2f601286w7ce0c089e6ed5...@mail.gmail.com...
>> 2008/11/27 Daniel Stenberg <dan...@haxx.se>:
>>>> Does anyone have any ideas what might be happening? I'm afraid I
>>>> haven't
>>>> got a clue where to start debugging this.
>>
>> Firstly, apologies for my stupidity. The part of my previous email
>> about the speed-up was because I forgot to call
>> libssh2_sftp_seek(handle, 0) inside the loop so eventually it ran off
>> the end of the file. However the overall question of why there is a
>> threshold for the buffer size of 39992, still applies.
>>
>>> Can you provide us with the source for a full app that reproduces the
>>> problem?
>>>
>>> Preferably as small as possible, and without too much windows-specific
>>> code...
>>
>> I have attached the code you ask. Most of the window-specific stuff
>> is gone but I may have missed something. Also, I'm not sure what
>> should be included in the place of Winsock for unix. Maybe nothing.
>>
>> Many thanks.
>>
>> Alex
>>
>
>
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