[Chicken-janitors] #568: read-line produces inconsistent results on DOS-style line endings when buffer is cut off at an unfortunate point

[Chicken Trac]

#568: read-line produces inconsistent results on DOS-style line endings when
buffer is cut off at an unfortunate point
----------------------------+-----------------------------------------------
 Reporter:  sjamaan         |       Owner:  felix
     Type:  defect          |      Status:  new  
 Priority:  critical        |   Milestone:  4.7.0
Component:  core libraries  |     Version:  4.6.x
 Keywords:  tcp, read-line  |  
----------------------------+-----------------------------------------------
 This showed up when trying to use {{{chicken-install}}}, I got this:

 {{{
 % /tmp/chicken-snapshot/bin/chicken-install -test coops
 retrieving ...
 resolving alias `kitten-technologies' to: http://chicken.kitten-
 technologies.co.uk/henrietta.cgi
 connecting to host "chicken.kitten-technologies.co.uk", port 80 ...
 requesting "/henrietta.cgi?name=coops&mode=default&tests=yes" ...
 reading response ...
 HTTP/1.1 200 OK
 Date: Sun, 17 Apr 2011 13:07:39 GMT
 Server: Apache
 Connection: close
 Transfer-Encoding: chunked
 Content-Type: text/plain
 reading chunks SIZE: 1 line: "1"
 ...

 Error: (zero?) bad argument type: #f
 }}}

 Oddly, it worked when I omitted the {{{-test}}} or tried the call-cc
 server instead!

 It turned out that in {{{setup-download.scm}}} in {{{read-chunks}}} the
 value of {{{size}}} was {{{#f}}}.  After adding some debugging code I
 found out that {{{read-line}}} returned {{{"0\r"}}} instead of the
 expected {{{"0"}}}, and {{{string->number}}} failed on that.

 The actual problem is in an interaction between unit TCP's code for
 reading lines from a TCP port and {{{##sys#scan-buffer-line}}}, which it
 calls.  The attached code reproduces this issue 100% reliably for me and
 triggers what's happening in the kernel on Alaric's machine; it happens to
 buffer the output just in such a way that my machine reads only a few
 characters exactly in the middle of the \r and \n line ending markers.

 This causes ##sys#scan-buffer-line to be invoked like this:

 {{{
 ; read buffer, get two characters in it: "0\r"..
 (##sys#scan-buffer-line "0\r" 2 0 ...)
 ; read buffer, get one character in it: "\n"..
 (##sys#scan-buffer-line "\n" 1 0 ...)
 }}}

 At the first call, the one-character lookahead for a \n following the \r
 fails because it's not present in the buffer. At the next call, it forgot
 that it encountered the \r in the previous buffer and just returns the
 empty string. The \r is never discarded.

 This can theoretically happen with other types of buffered ports too, but
 so far I think it only happens with TCP ports.

-- 
Ticket URL: <http://makeabank.com/ticket/568>
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