Is there a way to limit the response size with Mechanize to save memory?

Mechanize is a Python library for stateful programmatic web browsing. It is used to interact with websites as if you were using a web browser, including form submission, link clicking, and cookie handling. However, unlike a web browser, Mechanize does not download images or JavaScript by default, which already saves some bandwidth and memory.

To limit the response size with Mechanize and save memory, you can't directly set a limit within the Mechanize API. However, you can achieve this goal by using a custom response class that limits the size of the data read or by overriding the HTTP handler to abort the fetch when a certain size limit is exceeded.

Here's a basic example of how you could implement a size limit on responses with Mechanize in Python:

import mechanize
from io import BytesIO

class LimitedSizeResponse(mechanize.response_seek_wrapper):
    def __init__(self, response, max_size):
        super(LimitedSizeResponse, self).__init__(response)
        self.max_size = max_size
        self.current_size = 0

    def read(self, size=-1):
        if self.current_size >= self.max_size:
            raise mechanize.BrowserStateError("Response body exceeds the maximum size limit.")
        if size < 0 or size > (self.max_size - self.current_size):
            size = self.max_size - self.current_size
        data = self.wrapped.read(size)
        self.current_size += len(data)
        return data

class LimitedSizeBrowser(mechanize.Browser):
    def __init__(self, max_size, *args, **kwargs):
        self.max_size = max_size
        super(LimitedSizeBrowser, self).__init__(*args, **kwargs)

    def open(self, *args, **kwargs):
        response = super(LimitedSizeBrowser, self).open(*args, **kwargs)
        if self.max_size:
            response = LimitedSizeResponse(response, self.max_size)
        return response

# Usage example
MAX_RESPONSE_SIZE = 1024 * 1024  # 1 MB limit

browser = LimitedSizeBrowser(MAX_RESPONSE_SIZE)
try:
    response = browser.open("http://example.com")
    content = response.read()
except mechanize.BrowserStateError as e:
    print(e)

# Do something with the content, if not too large

In this example, LimitedSizeResponse is a subclass of mechanize.response_seek_wrapper, which wraps the original response object. It overrides the read method to keep track of the cumulative size of data read and to raise an error if the specified size limit is exceeded.

The LimitedSizeBrowser class is a subclass of mechanize.Browser which adds the ability to specify a maximum response size. It overrides the open method to wrap the response with the LimitedSizeResponse.

Keep in mind that this approach will raise an error if the response exceeds the size limit, which you would need to handle in your code. This example does not continue to read the data in chunks to process partial content, but it could be modified to do so if only a portion of the response is needed.

Remember, this method will only limit the size of the response body; the headers will still be read in full. If a large amount of data is being transferred in headers, this method will not limit that. However, headers are generally small compared to the body of a response, so this should not be a significant issue for memory usage.