feat: add AsyncPlasmateCrawlerStrategy — lightweight alternative to Playwright

Closes unclecode#1256 (memory leak in Docker from Chrome)
Related to unclecode#1874 (token usage tracking)

Plasmate (https://github.com/plasmate-labs/plasmate) is an open-source
Rust browser engine that replaces Chrome/Playwright for static pages.
No browser process, ~64MB RAM vs ~300MB, 10-100x fewer tokens per page.

Changes:
- crawl4ai/async_plasmate_strategy.py: AsyncPlasmateCrawlerStrategy
  - Implements AsyncCrawlerStrategy ABC (drop-in replacement)
  - Supports output_format: text (default), markdown, som, links
  - Supports --selector, --header, --timeout flags
  - Optional fallback_to_playwright=True for JS-heavy SPAs
  - Subprocess runs in asyncio executor — safe for concurrent use
- crawl4ai/__init__.py: export AsyncPlasmateCrawlerStrategy
- tests/general/test_plasmate_strategy.py: 20 unit tests

Install: pip install plasmate

Usage:
  from crawl4ai import AsyncWebCrawler
  from crawl4ai.async_plasmate_strategy import AsyncPlasmateCrawlerStrategy

  strategy = AsyncPlasmateCrawlerStrategy(
      output_format="markdown",
      fallback_to_playwright=True,   # SPA safety net
  )
  async with AsyncWebCrawler(crawler_strategy=strategy) as crawler:
      result = await crawler.arun("https://docs.python.org/3/")

Author: dbhurley

crawl4ai/__init__.py

@@ -2,6 +2,7 @@
 import warnings
 
 from .async_webcrawler import AsyncWebCrawler, CacheMode
+from .async_plasmate_strategy import AsyncPlasmateCrawlerStrategy
 # MODIFIED: Add SeedingConfig and VirtualScrollConfig here
 from .async_configs import BrowserConfig, CrawlerRunConfig, HTTPCrawlerConfig, LLMConfig, ProxyConfig, GeolocationConfig, SeedingConfig, VirtualScrollConfig, LinkPreviewConfig, MatchMode
 

crawl4ai/async_plasmate_strategy.py

@@ -0,0 +1,237 @@
+"""
+AsyncPlasmateCrawlerStrategy — lightweight alternative to AsyncPlaywrightCrawlerStrategy.
+
+Uses Plasmate (https://github.com/plasmate-labs/plasmate) instead of Chrome/Playwright.
+Plasmate is an open-source Rust browser engine that outputs Structured Object Model (SOM)
+instead of raw HTML, using ~64MB RAM per session vs ~300MB and delivering
+10-100x fewer tokens per page — significantly reducing LLM costs.
+
+Install: pip install plasmate
+Docs:    https://plasmate.app
+"""
+
+from __future__ import annotations
+
+import asyncio
+import shutil
+import subprocess
+from typing import Dict, List, Optional
+
+from .async_crawler_strategy import AsyncCrawlerStrategy
+from .async_logger import AsyncLogger
+from .models import AsyncCrawlResponse
+
+_INSTALL_MSG = (
+    "plasmate is required for AsyncPlasmateCrawlerStrategy. "
+    "Install it with: pip install plasmate\n"
+    "Docs: https://plasmate.app"
+)
+
+_VALID_FORMATS = ("text", "markdown", "som", "links")
+
+
+def _find_plasmate() -> Optional[str]:
+    """Return the resolved path to the plasmate binary, or None."""
+    path = shutil.which("plasmate")
+    if path:
+        return path
+    try:
+        import plasmate as _p  # noqa: F401
+        return shutil.which("plasmate")
+    except ImportError:
+        return None
+
+
+class AsyncPlasmateCrawlerStrategy(AsyncCrawlerStrategy):
+    """Lightweight crawler strategy using Plasmate instead of Chrome/Playwright.
+
+    Plasmate fetches pages and returns them as Structured Object Model (SOM)
+    or plain text / markdown — no browser process, no GPU, no 300 MB Chrome.
+
+    This strategy is a drop-in replacement for ``AsyncPlaywrightCrawlerStrategy``
+    for static and server-rendered pages. For JavaScript-heavy SPAs that require
+    a real browser, set ``fallback_to_playwright=True``.
+
+    Attributes:
+        output_format: Page output format — ``"text"`` (default), ``"markdown"``,
+            ``"som"`` (full JSON), or ``"links"``.
+        timeout: Per-request timeout in seconds. Defaults to 30.
+        selector: Optional ARIA role or CSS id selector to scope extraction
+            (e.g. ``"main"`` or ``"#article"``).
+        extra_headers: Optional HTTP headers forwarded with each request.
+        fallback_to_playwright: If True, retry with Playwright when Plasmate
+            returns an empty response (handles SPAs automatically).
+        verbose: Whether to emit log messages. Defaults to True.
+
+    Example — drop-in replacement::
+
+        import asyncio
+        from crawl4ai import AsyncWebCrawler
+        from crawl4ai.async_plasmate_strategy import AsyncPlasmateCrawlerStrategy
+
+        async def main():
+            strategy = AsyncPlasmateCrawlerStrategy(
+                output_format="markdown",
+                timeout=30,
+                fallback_to_playwright=True,
+            )
+            async with AsyncWebCrawler(crawler_strategy=strategy) as crawler:
+                result = await crawler.arun("https://docs.python.org/3/")
+                print(result.markdown[:500])
+
+        asyncio.run(main())
+
+    Example — direct use::
+
+        strategy = AsyncPlasmateCrawlerStrategy(output_format="text")
+        async with strategy:
+            response = await strategy.crawl("https://example.com")
+            print(response.html)  # clean text output, no HTML boilerplate
+    """
+
+    def __init__(
+        self,
+        output_format: str = "text",
+        timeout: int = 30,
+        selector: Optional[str] = None,
+        extra_headers: Optional[Dict[str, str]] = None,
+        fallback_to_playwright: bool = False,
+        verbose: bool = True,
+        logger: Optional[AsyncLogger] = None,
+        **kwargs,
+    ):
+        if output_format not in _VALID_FORMATS:
+            raise ValueError(
+                f"output_format must be one of {_VALID_FORMATS}; got {output_format!r}"
+            )
+        self.output_format = output_format
+        self.timeout = timeout
+        self.selector = selector
+        self.extra_headers = extra_headers or {}
+        self.fallback_to_playwright = fallback_to_playwright
+        self.verbose = verbose
+        self.logger = logger or AsyncLogger(verbose=verbose)
+        self._plasmate_bin: Optional[str] = None
+
+    # ------------------------------------------------------------------
+    # Context manager
+    # ------------------------------------------------------------------
+
+    async def __aenter__(self) -> "AsyncPlasmateCrawlerStrategy":
+        self._plasmate_bin = _find_plasmate()
+        if self._plasmate_bin is None:
+            raise ImportError(_INSTALL_MSG)
+        if self.verbose:
+            self.logger.info(
+                f"AsyncPlasmateCrawlerStrategy ready (format={self.output_format}, "
+                f"timeout={self.timeout}s, fallback={self.fallback_to_playwright})",
+                tag="INIT",
+            )
+        return self
+
+    async def __aexit__(self, exc_type, exc_val, exc_tb) -> None:
+        # No persistent process to clean up — each fetch is a short-lived subprocess.
+        pass
+
+    # ------------------------------------------------------------------
+    # Internal helpers
+    # ------------------------------------------------------------------
+
+    def _build_cmd(self, url: str) -> List[str]:
+        """Build the plasmate CLI command for a URL."""
+        cmd = [
+            self._plasmate_bin,
+            "fetch",
+            url,
+            "--format", self.output_format,
+            "--timeout", str(self.timeout * 1000),  # plasmate uses ms
+        ]
+        if self.selector:
+            cmd += ["--selector", self.selector]
+        for key, value in self.extra_headers.items():
+            cmd += ["--header", f"{key}: {value}"]
+        return cmd
+
+    async def _fetch(self, url: str) -> tuple[str, int]:
+        """Run plasmate in a thread-pool executor; returns (content, status_code)."""
+        loop = asyncio.get_event_loop()
+
+        def _run() -> tuple[str, int]:
+            try:
+                result = subprocess.run(
+                    self._build_cmd(url),
+                    capture_output=True,
+                    text=True,
+                    timeout=self.timeout + 5,
+                )
+                if result.returncode != 0:
+                    if self.verbose:
+                        self.logger.warning(
+                            f"plasmate exited {result.returncode} for {url}: "
+                            f"{result.stderr[:200]}",
+                            tag="FETCH",
+                        )
+                    return "", 500
+                return result.stdout.strip(), 200
+            except subprocess.TimeoutExpired:
+                if self.verbose:
+                    self.logger.warning(f"Timeout fetching {url}", tag="FETCH")
+                return "", 504
+            except FileNotFoundError:
+                raise ImportError(_INSTALL_MSG)
+
+        return await loop.run_in_executor(None, _run)
+
+    async def _playwright_fallback(self, url: str) -> tuple[str, int]:
+        """Delegate to AsyncPlaywrightCrawlerStrategy and return its raw HTML."""
+        if self.verbose:
+            self.logger.info(
+                f"Plasmate returned empty — falling back to Playwright for {url}",
+                tag="FALLBACK",
+            )
+        from .async_crawler_strategy import AsyncPlaywrightCrawlerStrategy
+
+        strategy = AsyncPlaywrightCrawlerStrategy()
+        async with strategy:
+            response = await strategy.crawl(url)
+        return response.html, response.status_code
+
+    # ------------------------------------------------------------------
+    # Public API
+    # ------------------------------------------------------------------
+
+    async def crawl(self, url: str, **kwargs) -> AsyncCrawlResponse:
+        """Fetch *url* with Plasmate and return an :class:`AsyncCrawlResponse`.
+
+        The ``html`` field of the response contains the Plasmate output in the
+        requested format (text / markdown / SOM JSON / links) rather than raw HTML.
+        Downstream Crawl4AI extraction strategies receive this pre-processed content,
+        reducing token consumption before any LLM call.
+
+        Args:
+            url: The URL to fetch.
+            **kwargs: Ignored (accepted for interface compatibility).
+
+        Returns:
+            :class:`AsyncCrawlResponse` with ``html`` set to Plasmate output.
+        """
+        if self.verbose:
+            self.logger.info(f"Fetching: {url}", tag="FETCH")
+
+        content, status_code = await self._fetch(url)
+
+        if not content.strip() and self.fallback_to_playwright:
+            content, status_code = await self._playwright_fallback(url)
+
+        if self.verbose and content:
+            self.logger.success(
+                f"Got {len(content):,} chars from {url} "
+                f"(format={self.output_format})",
+                tag="FETCH",
+            )
+
+        return AsyncCrawlResponse(
+            html=content,
+            response_headers={},
+            status_code=status_code,
+        )