cURL: Malformed encoding found in chunked-encoding, why? - ruby

Question

I am experimenting with CGI and the chunked encoding ("Transfer-Encoding: chunked" HTTP header field.) This way files can be sent without a content-length header. I wrote a minimalistic CGI application in Ruby, to try it out. My code is the following (chunked.rb):
#!/usr/bin/ruby
puts "Date: Fri, 28 Nov 2015 09:59:59 GMT"
puts "Content-Type: application/octet-stream; charset=\"ASCII-8BIT\""
puts "Content-Disposition: attachment; filename=image.jpg"
puts "Transfer-Encoding: chunked"
puts
File.open("image.jpg","rb"){|f|
while data=f.read(32)
STDOUT.puts data.size.to_s(16)
STDOUT.puts data
end
STDOUT.puts "0"
STDOUT.puts
}
I took the idea and chunked format example from here: https://www.jmarshall.com/easy/http/
HTTP/1.1 200 OK
Date: Fri, 31 Dec 1999 23:59:59 GMT
Content-Type: text/plain
Transfer-Encoding: chunked
1a; ignore-stuff-here
abcdefghijklmnopqrstuvwxyz
10
1234567890abcdef
0
some-footer: some-value
another-footer: another-value
[blank line here]
As my CGI app resides in Apache cgi-bin directory, I can issue cURL:
curl http://example.com/cgi-bin/chunked.rb -O -J
cURL should reassamble the original image.jpg file from the chunks, but unfortunately the saved file isn't complete, it is smaller than the original, and I get an error message too from cURL:
curl: (56) Malformed encoding found in chunked-encoding
However when I change line data=f.read(32) to something like data=f.read(1024*50), then file is saved correctly. Using another, bigger file from the server make the CGI app useless again, I got the same error message again. What can I do to make my CGI app working, and to send the file correctly?

Answer 1

So the working example:
puts "Date: Fri, 28 Nov 2015 09:59:59 GMT"
puts "Content-Type: application/octet-stream; charset=\"ASCII-8BIT\""
puts "Content-Disposition: attachment; filename=image.jpg"
puts "Transfer-Encoding: chunked"
puts
File.open("image.jpg","rb"){|f|
while data=f.read(32)
STDOUT.puts data.size.to_s(16)
STDOUT.print data
STDOUT.puts
end
STDOUT.puts "0"
STDOUT.puts
}