Why Mechanize for Proxy Work
Mechanize occupies a unique niche: it simulates browser behavior (cookies, history, form submission, redirect following) without actually running a browser. Through a proxy, Mechanize maintains stateful browsing sessions across multiple pages while routing all traffic through residential IPs.
This makes Mechanize ideal for multi-step proxy workflows: login to a site through a residential IP, navigate to a protected page, fill and submit a form, then extract the result. Each step uses the same proxy and session, mimicking a real user browsing through that IP.
Mechanize-Specific Proxy Features
agent.set_proxy(host, port, user, pass) configures the proxy globally for the Mechanize agent. All subsequent page loads, form submissions, and link follows route through this proxy. The proxy persists across the agent's cookie jar and browsing history.
Mechanize tracks history with agent.history and supports agent.back() for navigation. Through a proxy, this lets you build browsing patterns that mimic human navigation, reducing detection on anti-bot systems.
Form interaction through proxies is Mechanize's strongest feature. Use page.form_with() to find forms, fill fields with form.field_with(name: 'query').value = 'search', and submit with agent.submit(form). The submission routes through your proxy with all cookies and referer headers intact.
Common Pitfalls with Mechanize
Mechanize does not execute JavaScript. Dynamic forms that require JS validation will not work. For JS-heavy sites, use Watir or Capybara with a browser driver and proxy instead.
Mechanize follows redirects automatically but does not cap the redirect count aggressively. Infinite redirect loops through a proxy will hang until the connection times out. Set agent.redirect_ok = false for manual redirect control on untrusted targets.
SSL certificate verification through proxies can fail with older Ruby versions. Update your CA bundle or set agent.verify_mode = OpenSSL::SSL::VERIFY_PEER explicitly with a current cert store.
Advanced Configuration
Use agent.pre_connect_hooks << lambda { |agent, request| } to modify requests before they go through the proxy. Add custom headers, log request details, or implement conditional proxy routing.
Combine Mechanize with Nokogiri for advanced HTML parsing. Mechanize uses Nokogiri internally, so page.search('css-selector') works directly on proxied page responses.
Performance Tuning for Mechanize
Mechanize stores full page history including HTML bodies. For long scraping sessions through proxies, call agent.max_history = 10 to limit memory usage. Without this limit, history grows unbounded.
Set agent.read_timeout = 30 and agent.open_timeout = 10 to bound proxy connection times. The open_timeout covers the initial proxy handshake, while read_timeout covers content download.