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producers.py

# -*- Mode: Python -*-

RCS_ID = '$Id: producers.py,v 1.1 2004/03/25 06:29:57 ngps Exp $'

"""
A collection of producers.
Each producer implements a particular feature:  They can be combined
in various ways to get interesting and useful behaviors.

For example, you can feed dynamically-produced output into the compressing
producer, then wrap this with the 'chunked' transfer-encoding producer.
"""

import string
from asynchat import find_prefix_at_end

class simple_producer:
    "producer for a string"
    def __init__ (self, data, buffer_size=1024):
        self.data = data
        self.buffer_size = buffer_size

    def more (self):
        if len (self.data) > self.buffer_size:
            result = self.data[:self.buffer_size]
            self.data = self.data[self.buffer_size:]
            return result
        else:
            result = self.data
            self.data = ''
            return result

class scanning_producer:
    "like simple_producer, but more efficient for large strings"
    def __init__ (self, data, buffer_size=1024):
        self.data = data
        self.buffer_size = buffer_size
        self.pos = 0

    def more (self):
        if self.pos < len(self.data):
            lp = self.pos
            rp = min (
                    len(self.data),
                    self.pos + self.buffer_size
                    )
            result = self.data[lp:rp]
            self.pos = self.pos + len(result)
            return result
        else:
            return ''

class lines_producer:
    "producer for a list of lines"

    def __init__ (self, lines):
        self.lines = lines

    def more (self):
        if self.lines:
            chunk = self.lines[:50]
            self.lines = self.lines[50:]
            return string.join (chunk, '\r\n') + '\r\n'
        else:
            return ''

class buffer_list_producer:
    "producer for a list of strings"

    # i.e., data == string.join (buffers, '')

    def __init__ (self, buffers):

        self.index = 0
        self.buffers = buffers

    def more (self):
        if self.index >= len(self.buffers):
            return ''
        else:
            data = self.buffers[self.index]
            self.index = self.index + 1
            return data

class file_producer:
    "producer wrapper for file[-like] objects"

    # match http_channel's outgoing buffer size
    out_buffer_size = 1<<16

    def __init__ (self, file):
        self.done = 0
        self.file = file

    def more (self):
        if self.done:
            return ''
        else:
            data = self.file.read (self.out_buffer_size)
            if not data:
                self.file.close()
                del self.file
                self.done = 1
                return ''
            else:
                return data

# A simple output producer.  This one does not [yet] have
# the safety feature builtin to the monitor channel:  runaway
# output will not be caught.

# don't try to print from within any of the methods
# of this object.

class output_producer:
    "Acts like an output file; suitable for capturing sys.stdout"
    def __init__ (self):
        self.data = ''

    def write (self, data):
        lines = string.splitfields (data, '\n')
        data = string.join (lines, '\r\n')
        self.data = self.data + data

    def writeline (self, line):
        self.data = self.data + line + '\r\n'

    def writelines (self, lines):
        self.data = self.data + string.joinfields (
                lines,
                '\r\n'
                ) + '\r\n'

    def flush (self):
        pass

    def softspace (self, *args):
        pass

    def more (self):
        if self.data:
            result = self.data[:512]
            self.data = self.data[512:]
            return result
        else:
            return ''

class composite_producer:
    "combine a fifo of producers into one"
    def __init__ (self, producers):
        self.producers = producers

    def more (self):
        while len(self.producers):
            p = self.producers[0]
            d = p.more()
            if d:
                return d
            else:
                self.producers.pop(0)
        else:
            return ''


00165 class globbing_producer:
    """
    'glob' the output from a producer into a particular buffer size.
    helps reduce the number of calls to send().  [this appears to
    gain about 30% performance on requests to a single channel]
    """

    def __init__ (self, producer, buffer_size=1<<16):
        self.producer = producer
        self.buffer = ''
        self.buffer_size = buffer_size

    def more (self):
        while len(self.buffer) < self.buffer_size:
            data = self.producer.more()
            if data:
                self.buffer = self.buffer + data
            else:
                break
        r = self.buffer
        self.buffer = ''
        return r


00189 class hooked_producer:
    """
    A producer that will call <function> when it empties,.
    with an argument of the number of bytes produced.  Useful
    for logging/instrumentation purposes.
    """

    def __init__ (self, producer, function):
        self.producer = producer
        self.function = function
        self.bytes = 0

    def more (self):
        if self.producer:
            result = self.producer.more()
            if not result:
                self.producer = None
                self.function (self.bytes)
            else:
                self.bytes = self.bytes + len(result)
            return result
        else:
            return ''

# HTTP 1.1 emphasizes that an advertised Content-Length header MUST be
# correct.  In the face of Strange Files, it is conceivable that
# reading a 'file' may produce an amount of data not matching that
# reported by os.stat() [text/binary mode issues, perhaps the file is
# being appended to, etc..]  This makes the chunked encoding a True
# Blessing, and it really ought to be used even with normal files.
# How beautifully it blends with the concept of the producer.

00221 class chunked_producer:
    """A producer that implements the 'chunked' transfer coding for HTTP/1.1.
    Here is a sample usage:
            request['Transfer-Encoding'] = 'chunked'
            request.push (
                    producers.chunked_producer (your_producer)
                    )
            request.done()
    """

    def __init__ (self, producer, footers=None):
        self.producer = producer
        self.footers = footers

    def more (self):
        if self.producer:
            data = self.producer.more()
            if data:
                return '%x\r\n%s\r\n' % (len(data), data)
            else:
                self.producer = None
                if self.footers:
                    return string.join (
                            ['0'] + self.footers,
                            '\r\n'
                            ) + '\r\n\r\n'
                else:
                    return '0\r\n\r\n'
        else:
            return ''

# Unfortunately this isn't very useful right now (Aug 97), because
# apparently the browsers don't do on-the-fly decompression.  Which
# is sad, because this could _really_ speed things up, especially for
# low-bandwidth clients (i.e., most everyone).

try:
    import zlib
except ImportError:
    zlib = None

00262 class compressed_producer:
    """
    Compress another producer on-the-fly, using ZLIB
    [Unfortunately, none of the current browsers seem to support this]
    """

    # Note: It's not very efficient to have the server repeatedly
    # compressing your outgoing files: compress them ahead of time, or
    # use a compress-once-and-store scheme.  However, if you have low
    # bandwidth and low traffic, this may make more sense than
    # maintaining your source files compressed.
    #
    # Can also be used for compressing dynamically-produced output.

    def __init__ (self, producer, level=5):
        self.producer = producer
        self.compressor = zlib.compressobj (level)

    def more (self):
        if self.producer:
            cdata = ''
            # feed until we get some output
            while not cdata:
                data = self.producer.more()
                if not data:
                    self.producer = None
                    return self.compressor.flush()
                else:
                    cdata = self.compressor.compress (data)
            return cdata
        else:
            return ''

class escaping_producer:

    "A producer that escapes a sequence of characters"
    " Common usage: escaping the CRLF.CRLF sequence in SMTP, NNTP, etc..."

    def __init__ (self, producer, esc_from='\r\n.', esc_to='\r\n..'):
        self.producer = producer
        self.esc_from = esc_from
        self.esc_to = esc_to
        self.buffer = ''
        self.find_prefix_at_end = find_prefix_at_end

    def more (self):
        esc_from = self.esc_from
        esc_to   = self.esc_to

        buffer = self.buffer + self.producer.more()

        if buffer:
            buffer = string.replace (buffer, esc_from, esc_to)
            i = self.find_prefix_at_end (buffer, esc_from)
            if i:
                # we found a prefix
                self.buffer = buffer[-i:]
                return buffer[:-i]
            else:
                # no prefix, return it all
                self.buffer = ''
                return buffer
        else:
            return buffer

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