Pseudo-io writes fail for >= 256kB writes

[RootTJNII]

When attempting to write >= 256kB of data I'm consistently seeing the connection hang. For the following code:

Net::SFTP.start(args) do |sftp|
  1024.times do |c|
    puts "Length: #{c}"
    sftp.file.open("test.file", "w") do |f|
      f.write(Random.new.bytes(c * 1024))
    end
  end
end

I see the following output:

[Snip <250]
Length: 250
Length: 251
Length: 252
Length: 253
Length: 254
Length: 255
Length: 256
[Upload hangs here, until killed with ctrl-c]
^CNoMethodError: undefined method `send_data' for nil:NilClass
from /home/tom/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/net-sftp-2.1.2/lib/net/sftp/session.rb:814:in `send_packet'
Caused by Interrupt:
from /home/tom/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/net-ssh-5.2.0/lib/net/ssh/connection/event_loop.rb:110:in `select'

The exception appears to be the same as #94.

[RootTJNII]

upload! doesn't have this problem, working around it with a tempfile.

[dawidof]

@RootTJNII actually I got problem with upload!, it can be tempfile or stringIO

[dawidof]

Issue solved, connection was in class method, which was cached, moved the connection to instance method.

[mayuresh-srivastava]

I found the workaround as mentioned here

[acuster77]

Ran into the same issue today.

Using ruby 3.1.3p185 with [email protected] and [email protected]. I'm using OpenSSH, which has a max packet size of 256kb which I suspect is the culprit:

https://github.com/openssh/openssh-portable/blob/2709809fd616a0991dc18e3a58dea10fb383c3f0/packet.c#LL106C1-L106C1

It doesn't seem like there is any logic for checking the size of the payload within the packet to be delivered to the server when using the write method.

I really wanted to avoid writing anything to disk and using upload as I needed to upload partial chunks of data at a time. This code is working for me:

string_io = StringIO.new(file_data)

Net::SFTP.start(*args) do |sftp|
  file_handle = sftp.open!("foo.bin", "wb+")
  # utilizes the configured max packet size, by default it's 32768 bytes
  max_packet_size = sftp.channel.local_maximum_packet_size
  offset = 0
  until string_io.eof?
    datum = string_io.read(max_packet_size)
    sftp.write!(file_handle, offset, datum)
    offset += datum.bytesize
  end
end

[prcongithub]

@acuster77 Your solution worked in my case. Thanks for this.