Three open issues — #8242, #6587, #11345 — all trace to the same root
cause: the image / audio / document download paths in
`DiscordAdapter._handle_message` used plain, unauthenticated HTTP to
fetch `att.url`. That broke in three independent ways:
#8242 cdn.discordapp.com attachment URLs increasingly require the
bot session to download; unauthenticated httpx sees 403
Forbidden, image/voice analysis fail silently.
#6587 Some user environments (VPNs, corporate DNS, tunnels) resolve
cdn.discordapp.com to private-looking IPs. Our is_safe_url()
guard correctly blocks them as SSRF risks, but the user
environment is legitimate — image analysis and voice STT die.
#11345 The document download path skipped is_safe_url() entirely —
raw aiohttp.ClientSession.get(att.url) with no SSRF check,
inconsistent with the image/audio branches.
Unified fix: use `discord.Attachment.read()` as the primary download
path on all three branches. `att.read()` routes through discord.py's
own authenticated HTTPClient, so:
- Discord CDN auth is handled (#8242 resolved).
- Our is_safe_url() gate isn't consulted for the attachment path at
all — the bot session handles networking internally (#6587 resolved).
- All three branches now share the same code path, eliminating the
document-path SSRF gap (#11345 resolved).
Falls back to the existing cache_*_from_url helpers (image/audio) or an
SSRF-gated aiohttp fetch (documents) when `att.read()` is unavailable
or fails — preserves defense-in-depth for any future payload-schema
drift that could slip a non-CDN URL into att.url.
New helpers on DiscordAdapter:
- _read_attachment_bytes(att) — safe att.read() wrapper
- _cache_discord_image(att, ext) — primary + URL fallback
- _cache_discord_audio(att, ext) — primary + URL fallback
- _cache_discord_document(att, ext) — primary + SSRF-gated aiohttp fallback
Tests:
- tests/gateway/test_discord_attachment_download.py — 12 new cases
covering all three helpers: primary path, fallback on missing
.read(), fallback on validator rejection, SSRF guard on document
fallback, aiohttp fallback happy-path, and an E2E case via
_handle_message confirming cache_image_from_url is never invoked
when att.read() succeeds.
- All 11 existing document-handling tests continue to pass via the
aiohttp fallback path (their SimpleNamespace attachments have no
.read(), which triggers the fallback — now SSRF-gated).
Closes#8242, closes#6587, closes#11345.
