# sift

LLM-oriented fetch and search for the Hermes fleet: fetch a resource and get it back cleaned,
compact, and with useful context attached — using local models (Dixie), SearXNG and Brave on
orion, and Honcho for retrieval.

Status: implemented through P5a: P1 clean fetch (`/v2/scrape`, `/v1/fetch`, CLI, auth), P2
digest, fleet context and recover, P3 search, P2.7 Prometheus metrics, P5a PDF documents. The design
is [`docs/PLAN.md`](docs/PLAN.md); each phase has its own doc (`docs/P1.md` … `docs/P5a.md`).

## API

All endpoints except `/healthz` take `Authorization: Bearer <key>` (per caller; see `sift keys`).
The server binds `127.0.0.1:8890` and is published on the tailnet by `tailscale serve` at
`https://orion.scylla-hammerhead.ts.net:8443`.

| Endpoint | What |
|---|---|
| `POST /v2/scrape` | Firecrawl-compatible fetch (`url`, `formats`) — what Hermes `web_extract` calls |
| `POST /v2/search` | Firecrawl-compatible search (`query`, `limit`) — what Hermes `web_search` calls |
| `POST /v1/fetch` | native fetch: `url`, `mode` (`clean`/`raw`/`digest`), `question`, `jq`, `context`, `recover`, and for PDFs `pages`, `grep` |
| `POST /v1/search` | native search: `query`, `question`, `k`, `rerank`, `digest` |
| `GET /metrics`, `/metrics.json` | Prometheus text or JSON; open on loopback, bearer elsewhere |
| `GET /healthz` | liveness |

Every outbound connection goes through the SSRF guard (`internal/guard`): private, tailnet and
configured `deny_prefixes` addresses, and the host's own WAN address (`[self_ip]`), are refused
with `blocked: …`.

## CLI

```
sift serve  [-listen addr] [-config /etc/sift/config.toml] [-keys /var/lib/sift/keys.toml] [-deny-prefix CIDR]...
sift fetch  <url> [--question q] [--mode clean|raw|digest] [--jq filter] [--pages a-b] [--grep re]
                  [--no-context] [--recover] [--json]
sift search "<query>" [--k n] [--json]
sift keys   add --caller name [--workspace ws] [--out file] | list | revoke --caller name
sift version
```

`sift fetch` and `sift search` are clients: they read `url` and `key_file` from `client.toml`
(`$SIFT_CLIENT`, else `$HERMES_HOME/sift/client.toml`, else `~/.config/sift/client.toml`); the key
file must be mode 0600. The agent-facing guide is [`skill/SKILL.md`](skill/SKILL.md).

## Configuration

`/etc/sift/config.toml` (`$SIFT_CONFIG`); every key is shown in
[`dist/sift.toml.example`](dist/sift.toml.example). Paid-search keys (`BRAVE_API_KEY`,
`TAVILY_API_KEY`) live on the box in `/var/lib/sift/secret.env` (`$SIFT_SECRET`), never in git or
the Nix store. On NixOS use `nixosModules.sift` (`services.sift`), which writes the config and
the hardened unit.

## Build

Makefile is the source of truth for flags (`CGO_ENABLED=0`, `-trimpath`, `-s -w -X main.version=`).

```
make build          # bin/sift
make test           # go test -race ./...
make lint           # go vet, and staticcheck if installed
make install        # PREFIX=/usr/local; example config in /etc/sift/
nix build           # packages.sift, same ldflags
nix flake check     # make test lint
```

The service does not assume Nix store paths. Non-Nix hosts: `make install` plus `dist/sift.service`.

## PDF documents

A resource whose content type (or magic bytes) look like a PDF is extracted instead of cleaned.
Extraction runs in a **child process** — the `sift pdftext` subcommand of this binary, built on the
`go-pdfkit/extract` v0.3.0 engine, chosen by the bake-off in [`docs/P5a.md`](docs/P5a.md) §3 — so a
malicious PDF can't take down the server: the child is isolated (empty environment, native syscalls
only), killed at a deadline, and its output capped.

Limits: a PDF may be **100 MB** and take up to **120 s** to download; extraction is capped at
**60 s** and **2,000 pages**, with child output bounded to 64 MiB. Extraction runs under a **pool**
of **2 slots**, **4 waiting**, a **20 s** wait cap — a caller that can't get a slot gets `503 busy`,
and a caller with a job already in flight gets `429`. A PDF already extracted is answered from the
**cache** for **24 h**, then revalidated with a conditional GET (a `304` reuses the stored text).

Answers (through `/v1/fetch` or `/v2/scrape`):

- whole text when it fits the output cap, each page prefixed with `--- page N ---`;
- otherwise a **map** — the outline (with page numbers) and the first pages;
- `--pages 41-60` for a range, `--grep 'pattern'` for matching lines with page context;
- `--question "…"` for a **digest** that, on a PDF, cites each fact as `(p. N)`.

A range returns at most 100 pages; grep shows at most 100 matches and takes a pattern of at most
200 bytes. `pages` and `grep` on anything but a PDF are a `400`. A question over a document too long
to digest (more than 200 chunks) is refused with
`422 document too long for question (N chunks); use grep or pages`.

Scanned PDFs have no text layer and return `no text layer (scanned PDF?)`; point them at an OCR
source rather than fixing them here.

Errors (all `422` unless noted — a PDF never yields a `500`):

| cause | Status | Message | Hint | Retry-After |
|---|---|---|---|---|
| no text layer (`ErrNoText`) | 422 | `no text layer (scanned PDF?)` | `ocr` | — |
| encrypted (`ErrEncrypted`) | 422 | `encrypted PDF (password required)` | — | — |
| unreadable (`ErrUnreadable`) | 422 | `unreadable PDF` | — | — |
| timeout (`ErrTimeout`) | 422 | `pdf extraction timed out` | — | — |
| too much text (`ErrTooMuchText`) | 422 | `pdf text over the output limit` | — | — |
| pool full (`ErrBusy`) | 503 | `pdf workers busy` | — | 10 |
| caller busy (`ErrCallerBusy`) | 429 | `busy` | — | — |
| anything else (e.g. a recovered panic) | 422 | `unreadable PDF` | — | — |

Metrics (scraped at `http://127.0.0.1:8890/metrics`): `sift_pdf_extract_total{outcome}`
(`ok`, `no_text`, `encrypted`, `unreadable`, `timeout`, `too_large`, `busy`, or `other`),
`sift_pdf_extract_seconds`, `sift_pdf_pages_total`, `sift_pdf_pool_wait_seconds`, and
`sift_pdf_cache_hits_total`.