dpy_cache/README.md

# dpy_cache

Persist images/files to Discord by uploading them to a storage channel, and get back
durable references — a message jump URL plus per-file CDN URLs keyed by their original
filename. Discord attachments live on the CDN permanently; this lib wraps "stash it, hand
me a URL" and also returns a re-resolvable reference so the ~24h URL-signature expiry never
bites you.

## Install

```
dpy_cache @ git+ssh://git@git.rethinkstudios.io/rethink-public/dpy_cache.git@v0.1.1
```

## Usage

The headline is dead-simple single-file caching:

```python
from dpy_cache import DPYCache

cache = DPYCache(bot.get_channel(STORAGE_CHANNEL_ID))

url = (await cache.cache_one("img.png", image_bytes)).url    # raw bytes -> url
url = (await cache.cache_url("img.png", "https://...")).url  # remote url -> url
```

Several files at once (batches automatically over 10 per message):

```python
result = await cache.cache({
    "avatar.png": avatar_bytes,
    "banner.png": "/tmp/banner.png",
})
result.files["avatar.png"].url      # cdn url now
result.message_url                  # jump link to the stored message

# later, if the url may have expired:
fresh = await cache.resolve(result.files["avatar.png"])
```

Reverse lookup a stored message back into refs:

```python
refs = await cache.lookup(result.message_url)   # jump url, message id, or discord.Message
refs["avatar.png"].url
```

`lookup()` accepts a message id as an `int` or as a digit-only `str` (the snowflake shape
JSON/DBs store), e.g. `cache.lookup("123456789012345678")`.

## What you inject

A resolved Discord channel object (`discord.abc.Messageable` that supports `.send` and
`.fetch_message` — a TextChannel or Thread). The lib holds **no client** and reads **no
global config**; it calls those two methods on the channel directly. The bot must already
have access to the channel — an inaccessible or bad channel raises Discord's own error on
first use.

### `FileContent` inputs

`cache_one` / `cache` accept, per file: `bytes`, a filesystem path (`str` or
`os.PathLike`), or a `discord.File`. In a **list** input, raw `bytes` have no filename and
raise `ValueError` — pass a dict `{name: bytes}` or a `discord.File` to name bytes. A
**list** input whose sources resolve to the same name (two paths with the same basename,
two `discord.File`s with the same `.filename`, ...) raises `DPYCacheError` before any
upload — a dict input can't collide since dict keys are already unique.

A `discord.File` source is safe to reuse across multiple names/batches: `cache()` always
builds a genuinely fresh `discord.File` per send (re-opening a path-backed source, or
seeking + copying a caller-supplied stream) rather than reusing the object you passed in.
An opaque stream that can't be safely re-read (already closed, not seekable) raises
`DPYCacheError` instead of silently sending stale or empty data.

## Why `resolve()` exists

Since late 2023, Discord attachment CDN URLs are signed and the signature expires (~24h).
The attachment itself is permanent; only the URL goes stale (a raw stored URL 403s after
expiry). `FileRef` carries the message/channel/attachment ids, and `resolve(ref)` re-fetches
the message and returns a freshly-signed URL. Use the URL immediately and you can ignore
`resolve()`; persist a reference and you call `resolve()` when you read it back.

## API & contract

The module docstring (`help(dpy_cache)` / IDE hover) is the source of truth for the full
API. In short:

- `cache(files, *, content=None) -> CacheResult`
- `cache_one(name, data, *, content=None) -> FileRef`
- `cache_url(name, url, *, content=None) -> FileRef`
- `resolve(ref) -> str`
- `lookup(message) -> dict[str, FileRef]`

**Fail-loud.** Nothing is swallowed. Lib-specific invariants raise `DPYCacheError`
(attachment-count mismatch after a send, a duplicate filename in a list input to `cache()`,
`cache_url` non-200, a `lookup` jump-URL pointing at a different channel than the injected
one, a `discord.File` source that can't be safely rebuilt for a repeat send). Unnamed
`bytes` in a list raise `ValueError`. Raw Discord errors (`Forbidden` / `HTTPException` /
`NotFound`) propagate **unwrapped** so you can still branch on Discord's own types.

## Versioning

Tagged `vX.Y.Z`; pin a tag in your install line. Targets `discord.py>=2.0` (not
`discord.py-self`).

### v0.1.1

- `cache()` now rejects a duplicate filename in a **list** input with `DPYCacheError`
  before any upload, instead of silently uploading both files and losing the first
  `FileRef` at merge time.
- `_to_file` now builds a genuinely fresh `discord.File` per send for `discord.File`
  sources (previously returned the same object, which could swap filename/URL when one
  `File` was reused under two names, or re-send 0 bytes / raise `ValueError` on a spent
  stream).
- `lookup()` now accepts a digit-only message-id string in addition to `int`.
- Dropped the redundant `discord.Forbidden` member from an `except` tuple (it already
  subclasses `discord.HTTPException`); no behavior change.