Recv and send all bytes via network

[cerevra]

Describe the bug
libssh2 functions return error LIBSSH2_ERROR_AGENT_PROTOCOL for valid client-server protocol.
Reason: posix functions recv()/send() accept buffer_start_pointer and buffer_len. Theese functions return succeed len which could be less then buffer_len. libssh2 doesn't cover this case ( 1, 2 ): so only part of message could be finished.

It leads to operations with garbage at the end of buffer on recv().
For example in agent_list_identities() in my project:

=== agent_list_identities got len: 689
=== agent_list_identities got *s: 12
=== agent_list_identities got num_identities: 2
=== agent_list_identities === next identity
=== agent_list_identities got blob_len: 277
=== agent_list_identities got comment_len: 35
=== agent_list_identities === next identity
=== agent_list_identities got blob_len: 279
=== agent_list_identities got comment_len: 3486502863
=== agent_list_identities goto error #7: -42

To Reproduce
I can't provide real steps in client: it depends on network quality and server side.

Expected behavior
Functions should return success code if client-server protocol is correct.

Version (please complete the following information):

• OS: linux
• libssh2 version 1.8.0

Additional context
Duplicate: #511

[cerevra]

Sorry for several issues: I'm not very experienced in github

[cerevra]

Test in broken in master: #513

[cerevra]

@bagder
@mback2k
Could you please take a look at this issue? How can I move it forward?

[mback2k]

I like the proposed solution, but I am wondering why this issue is coming up now. Isn't it the callers responsibility to call the API until all data is available? @bagder @willco007

[willco007]

@mback2k I was just thinking the same thing. The solution seems good, but it seems odd this would be coming up now.

[pkittenis]

Indeed clients are currently handling this, and this code is also in examples.

[willco007]

Looking at the code further, I think @pkittenis is right. All the places in sftp.c I looked at all take into account the possibility of a partial reply.

[cerevra]

OK, let's fix only definitely broken function =). agent_transact_unix() encupsulates operation with network and doesn't check length - i.e. result of the first recv/send call. agent_transact_unix() is used only in internal functions agent_list_identities() and agent_sign().
The only solution I see is to handle case with incomplete buffer inside of agent_transact_unix().

As far as I see length is checked for other usages of LIBSSH2_SEND().

Could I ask you to review next iteration of this patch?
@bagder @mback2k @willco007 @pkittenis

[cerevra]

Are there any comments for patch? Could I provide any help here?

[cerevra]

Could you please take a look at this issue?
@bagder @mback2k @willco007 @pkittenis

[cerevra]

Could I provide any help to move forward this issue?

[torkve]

Hi all!

I have client based on libssh2, that suffers from this very issue since my ssh-agent yields chunked data.
This patch appears to fix it. Could you merge it or mark if any problems exist, please?