Upload backend/services/exchange_dns_resolver.py with huggingface_hub

backend/services/exchange_dns_resolver.py

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+#!/usr/bin/env python3
+"""DoH (DNS-over-HTTPS) resolver — non-US DNS providers for exchange API hosts."""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+import socket
+from typing import Dict, List, Optional
+
+import httpx
+
+logger = logging.getLogger(__name__)
+
+# Prefer EU/global resolvers (not US-centric filtering)
+DOH_PROVIDERS: List[Dict[str, str]] = [
+    {"name": "quad9", "url": "https://dns.quad9.net/dns-query"},
+    {"name": "cloudflare", "url": "https://cloudflare-dns.com/dns-query"},
+    {"name": "adguard", "url": "https://dns.adguard-dns.com/dns-query"},
+    {"name": "google", "url": "https://dns.google/resolve"},
+]
+
+
+class ExchangeDNSResolver:
+    """Resolve exchange hostnames via DoH, cache A records."""
+
+    def __init__(self) -> None:
+        self._cache: Dict[str, List[str]] = {}
+
+    async def resolve(self, hostname: str) -> Optional[str]:
+        if hostname in self._cache and self._cache[hostname]:
+            return self._cache[hostname][0]
+
+        for provider in DOH_PROVIDERS:
+            try:
+                async with httpx.AsyncClient(timeout=6.0) as client:
+                    resp = await client.get(
+                        provider["url"],
+                        params={"name": hostname, "type": "A"},
+                        headers={"accept": "application/dns-json"},
+                    )
+                    if resp.status_code != 200:
+                        continue
+                    data = resp.json()
+                    answers = data.get("Answer") or []
+                    ips = [a["data"] for a in answers if a.get("type") == 1 and a.get("data")]
+                    if ips:
+                        self._cache[hostname] = ips
+                        logger.info("DoH %s: %s -> %s", provider["name"], hostname, ips[0])
+                        return ips[0]
+            except Exception as exc:
+                logger.debug("DoH %s failed for %s: %s", provider["name"], hostname, exc)
+
+        try:
+            loop = asyncio.get_event_loop()
+            ip = await loop.run_in_executor(None, socket.gethostbyname, hostname)
+            if ip:
+                self._cache[hostname] = [ip]
+                return ip
+        except Exception:
+            pass
+
+        return None
+
+    async def fetch_via_doh(
+        self,
+        base_url: str,
+        path: str,
+        params: Optional[dict] = None,
+        timeout: float = 12.0,
+    ) -> Optional[httpx.Response]:
+        """HTTP GET to resolved IP with correct Host header (SNI)."""
+        hostname = base_url.split("://", 1)[-1].split("/")[0]
+        ip = await self.resolve(hostname)
+        if not ip:
+            return None
+
+        url = f"https://{ip}{path}"
+        headers = {"Host": hostname, "Accept": "application/json"}
+        try:
+            async with httpx.AsyncClient(
+                timeout=timeout,
+                verify=False,
+                headers=headers,
+            ) as client:
+                return await client.get(url, params=params)
+        except Exception as exc:
+            logger.debug("DoH fetch failed %s%s: %s", hostname, path, exc)
+            return None