IO.popen behaving strangely within SU

[draftomatic]

Hi all -

I am trying to run a subprocess from a shell command using IO.popen (have also tried Kernel#system with identical results), and I'm getting odd behavior. Here's my code:

curl = "curl "
curl += "--cookie \"JSESSIONID=#{@sessionid}\" "
curl += "-H \"Content-type;application/octet-stream\" "
curl += "-X POST "
curl += "-o \"#{responseFile}\" "
curl += "--data-binary \"@#{filename}\" "
curl += "\"#{url}\""

puts "command; #{curl}"

IO.popen(curl, "r") { |out|
  out.readlines
}
# Script never makes it to here

It's a streaming file upload using curl. Curl starts uploading, sends about 100kb, which is received by my server, and suddenly the stream ends ("unexpected end of stream error" on the server-side). Curl keeps running endlessly, sending zero data after that. Since I'm blocking with readlines, SU is forever frozen from then on...

I have tried this same code in a standalone script as well as running the command directly from a shell, and both work fine.

Anyone encountered this before? SU doesn't seem to like subprocesses...

EDIT: I should note this is on OSX.