Add pycurl extension for proxy header support

IMPLEMENTATION_PRIORITY.md

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+# Implementation Priority List for python-proxy-headers Extensions
+
+Based on library analysis considering GitHub stars, activity level, technical feasibility, and user impact.
+
+---
+
+## Priority Rankings
+
+### 🔴 Priority 1: HIGH - Implement First
+
+#### 1. pycurl Extension
+**File:** `python_proxy_headers/pycurl_proxy.py`
+
+| Metric | Value |
+|--------|-------|
+| GitHub Stars | 1,146 |
+| Last Active | 2026-01-30 |
+| Feasibility | ✅ HIGH |
+| Impact | HIGH - Direct libcurl access |
+
+**Why High Priority:**
+- libcurl already supports `CURLOPT_PROXYHEADER` for sending custom headers
+- Can capture CONNECT response headers via `CURLOPT_HEADERFUNCTION`
+- Foundation for curl_cffi work
+
+**Implementation Plan:**
+```python
+# pycurl_proxy.py - Proposed API
+
+class ProxyCurl:
+    """PycURL wrapper with proxy header support."""
+
+    def __init__(self, proxy_headers=None):
+        self.proxy_headers = proxy_headers or {}
+        self._response_proxy_headers = {}
+
+    def get(self, url, proxy=None) -> ProxyResponse:
+        """Make GET request with proxy header support."""
+        pass
+
+    @property
+    def received_proxy_headers(self) -> dict:
+        """Headers received from proxy during CONNECT."""
+        return self._response_proxy_headers
+
+def request(method, url, proxy=None, proxy_headers=None) -> ProxyResponse:
+    """Convenience function for one-off requests."""
+    pass
+```
+
+**Technical Approach:**
+1. Use `pycurl.PROXYHEADER` option to send custom headers
+2. Use `HEADERFUNCTION` callback to capture CONNECT response headers
+3. Parse headers to separate proxy headers from origin headers
+4. Expose via clean API matching existing python-proxy-headers style
+
+---
+
+#### 2. curl_cffi Extension
+**File:** `python_proxy_headers/curl_cffi_proxy.py`
+
+| Metric | Value |
+|--------|-------|
+| GitHub Stars | 4,873 |
+| Last Active | 2026-01-30 |
+| Feasibility | ⚠️ MEDIUM-HIGH |
+| Impact | VERY HIGH - Popular anti-bot library |
+
+**Why High Priority:**
+- Very popular for bypassing bot detection
+- Uses libcurl which has proxy header capabilities
+- Active development means potential upstream contributions
+
+**Implementation Plan:**
+```python
+# curl_cffi_proxy.py - Proposed API
+
+from curl_cffi import Session
+
+class ProxySession(Session):
+    """curl_cffi Session with proxy header support."""
+
+    def __init__(self, proxy_headers=None, **kwargs):
+        super().__init__(**kwargs)
+        self._proxy_headers = proxy_headers or {}
+        self._last_proxy_response_headers = {}
+
+    def request(self, method, url, **kwargs) -> ProxyResponse:
+        """Make request capturing proxy headers."""
+        pass
+
+    @property
+    def proxy_response_headers(self) -> dict:
+        """Headers from last proxy CONNECT response."""
+        return self._last_proxy_response_headers
+
+# Convenience functions
+def get(url, proxy=None, proxy_headers=None, impersonate=None, **kwargs):
+    pass
+```
+
+**Technical Approach:**
+1. Investigate if curl_cffi exposes low-level curl options
+2. If yes: Use `CURLOPT_PROXYHEADER` directly
+3. If no: Create PR to curl_cffi to expose these options
+4. May need to work with curl_cffi maintainers
+
+**Upstream Contribution Opportunity:**
+- File issue requesting `proxy_headers` parameter
+- Contribute PR if welcomed
+
+---
+
+#### 3. cloudscraper Extension  
+**File:** `python_proxy_headers/cloudscraper_proxy.py`
+
+| Metric | Value |
+|--------|-------|
+| GitHub Stars | 6,060 |
+| Last Active | 2025-06-10 |
+| Feasibility | ✅ HIGH |
+| Impact | HIGH - Popular for Cloudflare bypass |
+
+**Why High Priority:**
+- Built on requests - can use our existing adapter
+- Popular for accessing protected sites
+- Easy integration
+
+**Implementation Plan:**
+```python
+# cloudscraper_proxy.py - Proposed API
+
+import cloudscraper
+from .requests_adapter import HTTPProxyHeaderAdapter
+
+class ProxyCloudScraper(cloudscraper.CloudScraper):
+    """CloudScraper with proxy header support."""
+
+    def __init__(self, proxy_headers=None, **kwargs):
+        super().__init__(**kwargs)
+        adapter = HTTPProxyHeaderAdapter(proxy_headers=proxy_headers)
+        self.mount('https://', adapter)
+        self.mount('http://', adapter)
+
+def create_scraper(proxy_headers=None, **kwargs):
+    """Create a CloudScraper with proxy header support."""
+    return ProxyCloudScraper(proxy_headers=proxy_headers, **kwargs)
+```
+
+**Technical Approach:**
+1. Subclass `cloudscraper.CloudScraper`
+2. Mount our `HTTPProxyHeaderAdapter` 
+3. Preserve all cloudscraper functionality
+4. Simple integration - likely <50 lines of code
+
+---
+
+### 🟡 Priority 2: MEDIUM - Implement Second
+
+#### 4. autoscraper Extension
+**File:** `python_proxy_headers/autoscraper_proxy.py`
+
+| Metric | Value |
+|--------|-------|
+| GitHub Stars | 7,082 |
+| Last Active | 2025-06-09 |
+| Feasibility | ✅ HIGH |
+| Impact | MEDIUM - Niche use case |
+
+**Implementation Plan:**
+```python
+# autoscraper_proxy.py
+
+from autoscraper import AutoScraper
+from .requests_adapter import ProxySession
+
+class ProxyAutoScraper(AutoScraper):
+    """AutoScraper with proxy header support."""
+
+    def __init__(self, proxy_headers=None):
+        super().__init__()
+        self._proxy_session = ProxySession(proxy_headers=proxy_headers)
+
+    def build(self, url, wanted_list, proxy_headers=None, **kwargs):
+        """Build scraper with proxy header support."""
+        # Use our ProxySession for requests
+        pass
+```
+
+---
+
+#### 5. treq Extension
+**File:** `python_proxy_headers/treq_proxy.py`
+
+| Metric | Value |
+|--------|-------|
+| GitHub Stars | 606 |
+| Last Active | 2026-01-03 |
+| Feasibility | ⚠️ MEDIUM |
+| Impact | MEDIUM - Twisted ecosystem |
+
+**Implementation Plan:**
+```python
+# treq_proxy.py
+
+from twisted.web.client import Agent, ProxyAgent
+from twisted.internet import reactor
+
+class ProxyHeaderAgent(ProxyAgent):
+    """Twisted Agent with proxy header support."""
+
+    def __init__(self, proxy_headers=None, **kwargs):
+        super().__init__(**kwargs)
+        self._proxy_headers = proxy_headers or {}
+
+    # Override connection methods to inject headers
+```
+
+**Technical Approach:**
+1. Subclass `ProxyAgent`
+2. Override `_connect` method to add custom headers
+3. Capture CONNECT response headers
+4. More complex due to Twisted's async nature
+
+---
+
+#### 6. crawlee-python Extension
+**File:** `python_proxy_headers/crawlee_proxy.py`
+
+| Metric | Value |
+|--------|-------|
+| GitHub Stars | 7,968 |
+| Last Active | 2026-01-30 |
+| Feasibility | ⚠️ MEDIUM |
+| Impact | MEDIUM - Only HTTP crawler portion |
+
+**Implementation Plan:**
+```python
+# crawlee_proxy.py
+
+from crawlee.crawlers import BeautifulSoupCrawler
+from .httpx_proxy import HTTPProxyTransport
+
+class ProxyBeautifulSoupCrawler(BeautifulSoupCrawler):
+    """Crawler with proxy header support for HTTP requests."""
+
+    def __init__(self, proxy_headers=None, **kwargs):
+        # Configure httpx client with our transport
+        pass
+```
+
+**Note:** Only applies to `BeautifulSoupCrawler`, not `PlaywrightCrawler`
+
+---
+
+#### 7. requestium Extension
+**File:** `python_proxy_headers/requestium_proxy.py`
+
+| Metric | Value |
+|--------|-------|
+| GitHub Stars | 1,838 |
+| Last Active | 2026-01-26 |
+| Feasibility | ⚠️ MEDIUM |
+| Impact | LOW - Requests portion only |
+
+**Implementation Plan:**
+```python
+# requestium_proxy.py
+
+from requestium import Session
+from .requests_adapter import HTTPProxyHeaderAdapter
+
+class ProxySession(Session):
+    """Requestium Session with proxy header support."""
+
+    def __init__(self, proxy_headers=None, **kwargs):
+        super().__init__(**kwargs)
+        adapter = HTTPProxyHeaderAdapter(proxy_headers=proxy_headers)
+        self.mount('https://', adapter)
+        self.mount('http://', adapter)
+```
+
+---
+
+#### 8. botasaurus Extension
+**File:** `python_proxy_headers/botasaurus_proxy.py`
+
+| Metric | Value |
+|--------|-------|
+| GitHub Stars | 3,808 |
+| Last Active | 2026-01-10 |
+| Feasibility | ⚠️ MEDIUM |
+| Impact | LOW - Request decorator only |
+
+**Implementation Plan:**
+- Investigate botasaurus's request module internals
+- May require monkey-patching or upstream PR
+
+---
+
+### 🟢 Priority 3: LOW - Browser-Based (Not Recommended)
+
+These libraries use browser automation where proxy handling is delegated to the browser engine. Custom proxy header support is **not feasible** without browser extensions or significant browser-level modifications.
+
+| Library | Stars | Reason for Low Priority |
+|---------|-------|------------------------|
+| crawl4ai | 59,235 | Browser-based (Playwright) |
+| Scrapegraph-ai | 22,434 | Browser-based (Playwright) |
+| playwright-python | 14,209 | Browser handles proxy |
+| SeleniumBase | 12,139 | Browser handles proxy |
+| Selenium | N/A | Browser handles proxy |
+| splash | 4,198 | Qt WebKit-based |
+
+**Recommendation:** Do not implement extensions for these libraries. Instead, document that proxy header support is not possible due to browser architecture limitations.
+
+---
+
+## Implementation Roadmap
+
+### Phase 1: Foundation (Weeks 1-2)
+1. ✅ pycurl extension
+2. ✅ cloudscraper extension (quick win)
+
+### Phase 2: High-Impact (Weeks 3-4)
+3. curl_cffi extension (may require upstream work)
+4. autoscraper extension
+
+### Phase 3: Ecosystem (Weeks 5-6)
+5. treq extension
+6. crawlee-python extension
+7. requestium extension
+
+### Phase 4: Optional
+8. botasaurus extension (if feasible)
+
+---
+
+## File Structure
+
+```
+python_proxy_headers/
+├── __init__.py
+├── urllib3_proxy_manager.py     # Existing
+├── requests_adapter.py          # Existing
+├── httpx_proxy.py               # Existing
+├── aiohttp_proxy.py             # Existing
+├── pycurl_proxy.py              # NEW - Priority 1
+├── curl_cffi_proxy.py           # NEW - Priority 1
+├── cloudscraper_proxy.py        # NEW - Priority 1
+├── autoscraper_proxy.py         # NEW - Priority 2
+├── treq_proxy.py                # NEW - Priority 2
+├── crawlee_proxy.py             # NEW - Priority 2
+├── requestium_proxy.py          # NEW - Priority 2
+└── botasaurus_proxy.py          # NEW - Priority 2
+```
+
+---
+
+## Documentation Updates
+
+For each new extension, add:
+1. RST doc file in `docs/`
+2. Entry in `docs/index.rst`
+3. Usage example in README.md
+4. Example code in proxy-examples repo
+
+---
+
+*Created: January 30, 2026*