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The Chunked input API

An API for managing HTTP chunked input requests has been added in uWSGI 1.9.13.

The API is very low-level to allow easy integration with standard apps.

There are only two functions exposed:

  • chunked_read([timeout])
  • chunked_read_nb()

This API is supported (from uWSGI 1.9.20) on CPython, PyPy and Perl.

Reading chunks

To read a chunk (blocking) just run

my $msg = uwsgi::chunked_read

If no timeout is specified, the default one will be used. If you do not get a chunk in time, the function will croak (or raise an exception when under Python).

Under non-blocking/async engines you may want to use

my $msg = uwsgi::chunked_read_nb

The function will soon return undef (or None on Python) if no chunks are available (and croak/raise an exception on error).

A full PSGI streaming echo example:

# simple PSGI echo app reading chunked input
sub streamer {
     $responder = shift;
     # generate the headers and start streaming the response
     my $writer = $responder->( [200, ['Content-Type' => 'text/plain']]);

     while(1) {
             my $msg = uwsgi::chunked_read;
             last unless $msg;
             $writer->write($msg);
     }

     $writer->close;
}

my $app = sub {
     return \&streamer;
};

Tuning the chunks buffer

Before starting to read chunks, uWSGI allocates a fixed buffer for storing chunks.

All of the messages are always stored in the same buffer. If a message bigger than the buffer is received, an exception will be raised.

By default the buffer is limited to 1 MB. You can tune it with the --chunked-input-limit option (bytes).

Integration with proxies

If you plan to put uWSGI behind a proxy/router be sure it supports chunked input requests (or generally raw HTTP requests).

When using the uWSGI HTTP router just add --http-raw-body to support chunked input.

HAProxy works out of the box.

Nginx >= 1.4 supports chunked input.

Options

  • --chunked-input-limit: the limit (in bytes) of a chunk message (default 1MB)
  • --chunked-input-timeout: the default timeout (in seconds) for blocking chunked_read (default to the same --socket-timeout value, 4 seconds)

Notes

  • Calling chunked API functions after having consumed even a single byte of the request body is wrong (this includes --post-buffering).
  • Chunked API functions can be called independently by the presence of "Transfer-Encoding: chunked" header.