Thanks for the prompt response, but this is your question, not mine. I
hardly need an RTFM for my trouble.
I drew my conclusions using a packet sniffer. And as far-fetched as my
answer may seem, it's more plausible than your theory that Apache or modperl
is decoding a raw socket stream.
The crux of your question seems to be how the request content gets
magically re-assembled. I don't think it was ever disassembled in the first
place. But if you don't like my answer, and you don't want to ignore it
either, then please restate the question. I can't find any definition for
unchunked, and Wiktionary's definition of de-chunk says to "break apart a
chunk", that is (counter-intuitively) chunk a chunk.
Second, if there's no Content-Length header then how
does one know how much
data to read using $r->read?
One answer is until $r->read returns zero bytes, of
course. But, is
that guaranteed to always be the case, even for,
say, pipelined requests?
My guess is yes because whatever is de-chunking the
read() is blocking. So it never returns 0, even in a pipeline request (if no
data is available, it simply waits). I don't wish to discuss the merits
here, but there is no technical imperative for a content-length request in
the request header.
-Jim
On Wed, 3 Jul 2013, Bill Moseley wrote:
Hi Jim,
This is the Transfer-Encoding: chunked I was writing about:
http://tools.ietf.org/html/rfc2616#section-3.6.1
On Wed, Jul 3, 2013 at 11:34 AM, Jim Schueler <jschue...@eloquency.com>
wrote:
I played around with chunking recently in the context of media
streaming: The client is only requesting a "chunk" of data.
"Chunking" is how media players perform a "seek". It was
originally implemented for FTP transfers: E.g, to transfer a
large file in (say 10K) chunks. In the case that you describe
below, if no Content-Length is specified, that indicates "send
the remainder".
>From what I know, a "chunk" request header is used this way to
specify the server response. It does not reflect anything about
the data included in the body of the request. So first, I would
ask if you're confused about this request information.
Hypothetically, some browsers might try to upload large files in
small chunks and the "chunk" header might reflect a push
transfer. I don't know if "chunk" is ever used for this
purpose. But it would require the following characteristics:
1. The browser would need to originally inquire if the server
is
capable of this type of request.
2. Each chunk of data will arrive in a separate and
independent HTTP
request. Not necessarily in the order they were sent.
3. Two or more requests may be handled by separate processes
simultaneously that can't be written into a single
destination.
4. Somehow the server needs to request a resend if a chunk is
missing.
Solving this problem requires an imaginitive use of HTTP.
Sounds messy. But might be appropriate for 100M+ sized uploads.
This *may* reflect your situation. Can you please confirm?
For a single process, the incoming content-length is
unnecessary. Buffered I/O automatically knows when transmission
is complete. The read() argument is the buffer size, not the
content length. Whether you spool the buffer to disk or simply
enlarge the buffer should be determined by your hardware
capabilities. This is standard IO behavior that has nothing to
do with HTTP chunk. Without a "Content-Length" header, after
looping your read() operation, determine the length of the
aggregate data and pass that to Catalyst.
But if you're confident that the complete request spans several
smaller (chunked) HTTP requests, you'll need to address all the
problems I've described above, plus the problem of re-assembling
the whole thing for Catalyst. I don't know anything about
Plack, maybe it can perform all this required magic.
Otherwise, if the whole purpose of the Plack temporary file is
to pass a file handle, you can pass a buffer as a file handle.
Used to be IO::String, but now that functionality is built into
the core.
By your last paragraph, I'm really lost. Since you're already
passing the request as a file handle, I'm guessing that Catalyst
creates the tempororary file for the *response* body. Can you
please clarify? Also, what do you mean by "de-chunking"? Is
> that the same think as re-assembling?
Wish I could give a better answer. Let me know if this helps.
-Jim
On Tue, 2 Jul 2013, Bill Moseley wrote:
For requests that are chunked (Transfer-Encoding:
chunked and no
Content-Length header) calling $r->read returns
unchunked data from the
socket.
That's indeed handy. Is that mod_perl doing that
un-chunking or is it
Apache?
But, it leads to some questions.
First, if $r->read reads unchunked data then why is
there a
Transfer-Encoding header saying that the content is
chunked? Shouldn't
that header be removed? How does one know if the
content is chunked or
not, otherwise?
Second, if there's no Content-Length header then how
does one know how much
data to read using $r->read?
One answer is until $r->read returns zero bytes, of
course. But, is
that guaranteed to always be the case, even for,
say, pipelined requests?
My guess is yes because whatever is de-chunking the
request knows to stop
after reading the last chunk, trailer and empty
line. Can anyone elaborate
on how Apache/mod_perl is doing this?
Perhaps I'm approaching this incorrectly, but this
is all a bit untidy.
I'm using Catalyst and Catalyst needs a
Content-Length. So, I have a Plack
Middleware component that creates a temporary file
writing the buffer from
$r->read( my $buffer, 64 * 1024 ) until that returns
zero bytes. I pass
this file handle onto Catalyst.
Then, for some content-types, Catalyst (via
HTTP::Body) writes the body to
another temp file. I don't know how
Apache/mod_perl does its de-chunking,
but I can call $r->read with a huge buffer length
and Apache returns that.
So, maybe Apache is buffering to disk, too.
In other words, for each tiny chunked JSON POST or
PUT I'm creating two (or
three?) temp files which doesn't seem ideal.
--
Bill Moseley
mose...@hank.org
--
Bill Moseley
mose...@hank.org
