From d0527a8cf4fb85e6a5bb0b427b3325fb615df3d0 Mon Sep 17 00:00:00 2001
From: Ben Lenarts <ben@lenarts.nl>
Date: Sun, 5 Apr 2026 08:06:28 +0200
Subject: [PATCH] feat(email): add attachment extraction support
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Save inbound email attachments to the media directory with configurable
MIME type filtering (glob patterns like "image/*"), per-attachment size
limits, and max attachment count. Filenames are sanitized to prevent
path traversal. Controlled by allowed_attachment_types — empty (default)
means disabled, non-empty enables extraction for matching types.
---
 nanobot/channels/email.py            |  81 ++++++++++
 tests/channels/test_email_channel.py | 222 +++++++++++++++++++++++++++
 2 files changed, 303 insertions(+)

diff --git a/nanobot/channels/email.py b/nanobot/channels/email.py
index bee2ceccd..15edff490 100644
--- a/nanobot/channels/email.py
+++ b/nanobot/channels/email.py
@@ -1,6 +1,7 @@
 """Email channel implementation using IMAP polling + SMTP replies."""
 
 import asyncio
+from fnmatch import fnmatch
 import html
 import imaplib
 import re
@@ -14,13 +15,17 @@ from email.parser import BytesParser
 from email.utils import parseaddr
 from typing import Any
 
+from pathlib import Path
+
 from loguru import logger
 from pydantic import Field
 
 from nanobot.bus.events import OutboundMessage
 from nanobot.bus.queue import MessageBus
 from nanobot.channels.base import BaseChannel
+from nanobot.config.paths import get_media_dir
 from nanobot.config.schema import Base
+from nanobot.utils.helpers import safe_filename
 
 
 class EmailConfig(Base):
@@ -55,6 +60,11 @@ class EmailConfig(Base):
     verify_dkim: bool = True   # Require Authentication-Results with dkim=pass
     verify_spf: bool = True    # Require Authentication-Results with spf=pass
 
+    # Attachment handling — set allowed types to enable (e.g. ["application/pdf", "image/*"], or ["*"] for all)
+    allowed_attachment_types: list[str] = Field(default_factory=list)
+    max_attachment_size: int = 2_000_000  # 2MB per attachment
+    max_attachments_per_email: int = 5
+
 
 class EmailChannel(BaseChannel):
     """
@@ -153,6 +163,7 @@ class EmailChannel(BaseChannel):
                         sender_id=sender,
                         chat_id=sender,
                         content=item["content"],
+                        media=item.get("media") or None,
                         metadata=item.get("metadata", {}),
                     )
             except Exception as e:
@@ -404,6 +415,20 @@ class EmailChannel(BaseChannel):
                     f"{body}"
                 )
 
+                # --- Attachment extraction ---
+                attachment_paths: list[str] = []
+                if self.config.allowed_attachment_types:
+                    saved = self._extract_attachments(
+                        parsed,
+                        uid or "noid",
+                        allowed_types=self.config.allowed_attachment_types,
+                        max_size=self.config.max_attachment_size,
+                        max_count=self.config.max_attachments_per_email,
+                    )
+                    for p in saved:
+                        attachment_paths.append(str(p))
+                        content += f"\n[attachment: {p.name} — saved to {p}]"
+
                 metadata = {
                     "message_id": message_id,
                     "subject": subject,
@@ -418,6 +443,7 @@ class EmailChannel(BaseChannel):
                         "message_id": message_id,
                         "content": content,
                         "metadata": metadata,
+                        "media": attachment_paths,
                     }
                 )
 
@@ -537,6 +563,61 @@ class EmailChannel(BaseChannel):
                 dkim_pass = True
         return spf_pass, dkim_pass
 
+    @classmethod
+    def _extract_attachments(
+        cls,
+        msg: Any,
+        uid: str,
+        *,
+        allowed_types: list[str],
+        max_size: int,
+        max_count: int,
+    ) -> list[Path]:
+        """Extract and save email attachments to the media directory.
+
+        Returns list of saved file paths.
+        """
+        if not msg.is_multipart():
+            return []
+
+        saved: list[Path] = []
+        media_dir = get_media_dir("email")
+
+        for part in msg.walk():
+            if len(saved) >= max_count:
+                break
+            if part.get_content_disposition() != "attachment":
+                continue
+
+            content_type = part.get_content_type()
+            if not any(fnmatch(content_type, pat) for pat in allowed_types):
+                logger.debug("Email attachment skipped (type {}): not in allowed list", content_type)
+                continue
+
+            payload = part.get_payload(decode=True)
+            if payload is None:
+                continue
+            if len(payload) > max_size:
+                logger.warning(
+                    "Email attachment skipped: size {} exceeds limit {}",
+                    len(payload),
+                    max_size,
+                )
+                continue
+
+            raw_name = part.get_filename() or "attachment"
+            sanitized = safe_filename(raw_name) or "attachment"
+            dest = media_dir / f"{uid}_{sanitized}"
+
+            try:
+                dest.write_bytes(payload)
+                saved.append(dest)
+                logger.info("Email attachment saved: {}", dest)
+            except Exception as exc:
+                logger.warning("Failed to save email attachment {}: {}", dest, exc)
+
+        return saved
+
     @staticmethod
     def _html_to_text(raw_html: str) -> str:
         text = re.sub(r"<\s*br\s*/?>", "\n", raw_html, flags=re.IGNORECASE)
diff --git a/tests/channels/test_email_channel.py b/tests/channels/test_email_channel.py
index 2d0e33ce3..6d6d2f74f 100644
--- a/tests/channels/test_email_channel.py
+++ b/tests/channels/test_email_channel.py
@@ -1,5 +1,6 @@
 from email.message import EmailMessage
 from datetime import date
+from pathlib import Path
 import imaplib
 
 import pytest
@@ -650,3 +651,224 @@ def test_check_authentication_results_method() -> None:
     spf, dkim = EmailChannel._check_authentication_results(parsed)
     assert spf is False
     assert dkim is True
+
+
+# ---------------------------------------------------------------------------
+# Attachment extraction tests
+# ---------------------------------------------------------------------------
+
+
+def _make_raw_email_with_attachment(
+    from_addr: str = "alice@example.com",
+    subject: str = "With attachment",
+    body: str = "See attached.",
+    attachment_name: str = "doc.pdf",
+    attachment_content: bytes = b"%PDF-1.4 fake pdf content",
+    attachment_mime: str = "application/pdf",
+    auth_results: str | None = None,
+) -> bytes:
+    msg = EmailMessage()
+    msg["From"] = from_addr
+    msg["To"] = "bot@example.com"
+    msg["Subject"] = subject
+    msg["Message-ID"] = "<m1@example.com>"
+    if auth_results:
+        msg["Authentication-Results"] = auth_results
+    msg.set_content(body)
+    maintype, subtype = attachment_mime.split("/", 1)
+    msg.add_attachment(
+        attachment_content,
+        maintype=maintype,
+        subtype=subtype,
+        filename=attachment_name,
+    )
+    return msg.as_bytes()
+
+
+def test_extract_attachments_saves_pdf(tmp_path, monkeypatch) -> None:
+    """PDF attachment is saved to media dir and path returned in media list."""
+    monkeypatch.setattr("nanobot.channels.email.get_media_dir", lambda ch: tmp_path)
+
+    raw = _make_raw_email_with_attachment()
+    fake = _make_fake_imap(raw)
+    monkeypatch.setattr("nanobot.channels.email.imaplib.IMAP4_SSL", lambda _h, _p: fake)
+
+    cfg = _make_config(allowed_attachment_types=["application/pdf"], verify_dkim=False, verify_spf=False)
+    channel = EmailChannel(cfg, MessageBus())
+    items = channel._fetch_new_messages()
+
+    assert len(items) == 1
+    assert len(items[0]["media"]) == 1
+    saved_path = Path(items[0]["media"][0])
+    assert saved_path.exists()
+    assert saved_path.read_bytes() == b"%PDF-1.4 fake pdf content"
+    assert "500_doc.pdf" in saved_path.name
+    assert "[attachment:" in items[0]["content"]
+
+
+def test_extract_attachments_disabled_by_default(monkeypatch) -> None:
+    """With no allowed_attachment_types (default), no attachments are extracted."""
+    raw = _make_raw_email_with_attachment()
+    fake = _make_fake_imap(raw)
+    monkeypatch.setattr("nanobot.channels.email.imaplib.IMAP4_SSL", lambda _h, _p: fake)
+
+    cfg = _make_config(verify_dkim=False, verify_spf=False)
+    assert cfg.allowed_attachment_types == []
+    channel = EmailChannel(cfg, MessageBus())
+    items = channel._fetch_new_messages()
+
+    assert len(items) == 1
+    assert items[0]["media"] == []
+    assert "[attachment:" not in items[0]["content"]
+
+
+def test_extract_attachments_mime_type_filter(tmp_path, monkeypatch) -> None:
+    """Non-allowed MIME types are skipped."""
+    monkeypatch.setattr("nanobot.channels.email.get_media_dir", lambda ch: tmp_path)
+
+    raw = _make_raw_email_with_attachment(
+        attachment_name="image.png",
+        attachment_content=b"\x89PNG fake",
+        attachment_mime="image/png",
+    )
+    fake = _make_fake_imap(raw)
+    monkeypatch.setattr("nanobot.channels.email.imaplib.IMAP4_SSL", lambda _h, _p: fake)
+
+    cfg = _make_config(
+        allowed_attachment_types=["application/pdf"],
+        verify_dkim=False,
+        verify_spf=False,
+    )
+    channel = EmailChannel(cfg, MessageBus())
+    items = channel._fetch_new_messages()
+
+    assert len(items) == 1
+    assert items[0]["media"] == []
+
+
+def test_extract_attachments_empty_allowed_types_rejects_all(tmp_path, monkeypatch) -> None:
+    """Empty allowed_attachment_types means no types are accepted."""
+    monkeypatch.setattr("nanobot.channels.email.get_media_dir", lambda ch: tmp_path)
+
+    raw = _make_raw_email_with_attachment(
+        attachment_name="image.png",
+        attachment_content=b"\x89PNG fake",
+        attachment_mime="image/png",
+    )
+    fake = _make_fake_imap(raw)
+    monkeypatch.setattr("nanobot.channels.email.imaplib.IMAP4_SSL", lambda _h, _p: fake)
+
+    cfg = _make_config(
+        allowed_attachment_types=[],
+        verify_dkim=False,
+        verify_spf=False,
+    )
+    channel = EmailChannel(cfg, MessageBus())
+    items = channel._fetch_new_messages()
+
+    assert len(items) == 1
+    assert items[0]["media"] == []
+
+
+def test_extract_attachments_wildcard_pattern(tmp_path, monkeypatch) -> None:
+    """Glob patterns like 'image/*' match attachment MIME types."""
+    monkeypatch.setattr("nanobot.channels.email.get_media_dir", lambda ch: tmp_path)
+
+    raw = _make_raw_email_with_attachment(
+        attachment_name="photo.jpg",
+        attachment_content=b"\xff\xd8\xff fake jpeg",
+        attachment_mime="image/jpeg",
+    )
+    fake = _make_fake_imap(raw)
+    monkeypatch.setattr("nanobot.channels.email.imaplib.IMAP4_SSL", lambda _h, _p: fake)
+
+    cfg = _make_config(
+        allowed_attachment_types=["image/*"],
+        verify_dkim=False,
+        verify_spf=False,
+    )
+    channel = EmailChannel(cfg, MessageBus())
+    items = channel._fetch_new_messages()
+
+    assert len(items) == 1
+    assert len(items[0]["media"]) == 1
+
+
+def test_extract_attachments_size_limit(tmp_path, monkeypatch) -> None:
+    """Attachments exceeding max_attachment_size are skipped."""
+    monkeypatch.setattr("nanobot.channels.email.get_media_dir", lambda ch: tmp_path)
+
+    raw = _make_raw_email_with_attachment(
+        attachment_content=b"x" * 1000,
+    )
+    fake = _make_fake_imap(raw)
+    monkeypatch.setattr("nanobot.channels.email.imaplib.IMAP4_SSL", lambda _h, _p: fake)
+
+    cfg = _make_config(
+        allowed_attachment_types=["*"],
+        max_attachment_size=500,
+        verify_dkim=False,
+        verify_spf=False,
+    )
+    channel = EmailChannel(cfg, MessageBus())
+    items = channel._fetch_new_messages()
+
+    assert len(items) == 1
+    assert items[0]["media"] == []
+
+
+def test_extract_attachments_max_count(tmp_path, monkeypatch) -> None:
+    """Only max_attachments_per_email are saved."""
+    monkeypatch.setattr("nanobot.channels.email.get_media_dir", lambda ch: tmp_path)
+
+    # Build email with 3 attachments
+    msg = EmailMessage()
+    msg["From"] = "alice@example.com"
+    msg["To"] = "bot@example.com"
+    msg["Subject"] = "Many attachments"
+    msg["Message-ID"] = "<m1@example.com>"
+    msg.set_content("See attached.")
+    for i in range(3):
+        msg.add_attachment(
+            f"content {i}".encode(),
+            maintype="application",
+            subtype="pdf",
+            filename=f"doc{i}.pdf",
+        )
+    raw = msg.as_bytes()
+
+    fake = _make_fake_imap(raw)
+    monkeypatch.setattr("nanobot.channels.email.imaplib.IMAP4_SSL", lambda _h, _p: fake)
+
+    cfg = _make_config(
+        allowed_attachment_types=["*"],
+        max_attachments_per_email=2,
+        verify_dkim=False,
+        verify_spf=False,
+    )
+    channel = EmailChannel(cfg, MessageBus())
+    items = channel._fetch_new_messages()
+
+    assert len(items) == 1
+    assert len(items[0]["media"]) == 2
+
+
+def test_extract_attachments_sanitizes_filename(tmp_path, monkeypatch) -> None:
+    """Path traversal in filenames is neutralized."""
+    monkeypatch.setattr("nanobot.channels.email.get_media_dir", lambda ch: tmp_path)
+
+    raw = _make_raw_email_with_attachment(
+        attachment_name="../../../etc/passwd",
+    )
+    fake = _make_fake_imap(raw)
+    monkeypatch.setattr("nanobot.channels.email.imaplib.IMAP4_SSL", lambda _h, _p: fake)
+
+    cfg = _make_config(allowed_attachment_types=["*"], verify_dkim=False, verify_spf=False)
+    channel = EmailChannel(cfg, MessageBus())
+    items = channel._fetch_new_messages()
+
+    assert len(items) == 1
+    assert len(items[0]["media"]) == 1
+    saved_path = Path(items[0]["media"][0])
+    # File must be inside the media dir, not escaped via path traversal
+    assert saved_path.parent == tmp_path