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PROTOCOL.md, DECISIONS.md, README.md, AGENTS.md for plugins, processes, and JSON-RPC

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AGENTS.md
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caller. No configuration that nobody asked for.
3. **Readable.** A new reader must understand a file without the others.
Each module starts with a doc comment that says what it owns.
4. **Efficient** on the paths that run per message.
4. **Efficient** on the paths that run per call.
5. **Raw and minimal.** Sausage has no permissions, sandboxing beyond WASI,
limits, or authentication. Do not add them to the core. Add nothing to
the host that an actor (or the agent, by changing itself) could do.
the host that a plugin (or the agent, by changing itself) could do.
## Layout
- `cli/`: the host (`sausage` binary and library).
- `lib.rs`: `Host`, which starts and stops a world.
- `broker.rs`: routing, mailboxes, the version store, broker requests.
- `supervisor.rs`: runs one WASM actor (restarts, swaps, rollbacks).
- `runtime.rs`: Wasmtime instances and what they get (mounts, network).
- `candidate.rs`: tests a new version. `cargo_actor.rs`: builds Rust.
- `world.rs`: the on-disk layout. `console.rs`: the terminal.
- `sdk/`: `sausage-actor`, the SDK for Rust actors. Never published: the
`cargo` actor points `sausage-actor = "0.1"` at its local copy.
- `agent/`: the agent actor. `sausage init` embeds and builds it.
- `examples/`: small actors. They are not workspace members.
- `PROTOCOL.md`: the contract between the host and the actors. Change it in
- `cli/`: the host (`sausage` binary and library): the core, the native
`cargo` plugin, the WASI test runner, and the console.
- `vfs/`: `sausage-vfs`, the virtual filesystem for WASI guests. It knows
nothing about Sausage.
- `interface/`: `sausage-interface`: OpenRPC documents, the compatibility
check, and the generator of client code.
- `sdk/`: `sausage-plugin`, the SDK for Rust plugins, and `sdk/macros/`, its
macros. Never published: `cargo` points `sausage-plugin = "0.1"` at its
local copy.
- `agent/`: the agent plugin. `sausage init` embeds and builds it.
- `examples/`: small plugins. They are not workspace members.
- `PROTOCOL.md`: the contract between the core and the plugins. Change it in
the same commit as the behavior. `DECISIONS.md` says why; when the two
disagree, `PROTOCOL.md` and the code win.
@@ -36,7 +36,7 @@ Keep it that way.
```sh
nix flake check -L # all tests below; CI runs this on every push
nix develop -c cargo test -p sausage -p sausage-actor -p agent
nix develop -c cargo test --workspace
nix develop -c cargo build --release -p agent --target wasm32-wasip2
nix develop -c cargo clippy --workspace
```
DECISIONS.md
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# Decisions
Why Sausage is the way it is. `PROTOCOL.md` and the code own the details;
when this file disagrees with them, they win.
Why Sausage is the way it is. `PROTOCOL.md` and the code own the details.
When this file disagrees with them, they win.
## The shape
- **Actors are WASI commands, not components with interfaces.** stdin,
stdout, files, HTTP, and sockets are enough, and every language can do
them.
- **Messages are JSON lines through a broker, fire and forget.** Like
Erlang: no acknowledgments, no request/response. A reply is a message with
`reply_to`. Sausage is not a reliable message bus.
- **The broker accepts only `.wasm` files.** It knows no source language.
`cargo` is one compiler actor; others can add more languages.
- **The world folder is the source of truth.** Everything about an actor is
in `actor/<id>/`. Copy a folder into another world, and it runs there.
- **The agent is a normal WASM actor.** It can read and upgrade its own
source, and change how it does inference.
- **JSON-RPC, not component interfaces.** Every language can read and write
lines of JSON, and models know JSON-RPC from LSP and MCP. A call has a
result, like an LLM tool call.
- **A process per call.** WASI has no threads, so processes give
parallelism. A new version applies at the next call, and old processes
retire after a grace period.
- **Attached by default.** A process does not outlive its caller by
accident. A long-running process must ask for `detach`.
- **Services in one file.** Only the core starts and restarts them, so
upgrades and singletons need no logic in plugins.
- **Files to inspect, calls to act.** This keeps the core API small, and the
agent's file tools are enough to explore the world.
- **The core accepts only `.wasm` files.** It knows no source language.
`cargo` is one way to get a `.wasm` file.
- **The world folder is the source of truth.** Copy a plugin folder into
another world, and it works there.
- **The agent is a normal plugin.** It can read and upgrade its own source,
and change how it does inference.
## Interfaces
- **Generated imports and interface checks, without version numbers.** A
model that translates a description by hand makes errors. A generator does
not. The check catches the most common error in a world that changes
itself: a change to one plugin breaks another one.
- **A small schema subset.** With Draft 7 and a fixed subset, our own check
can decide every case. It never has to guess.
- **Docs are part of the interface.** Other agents work from them, so the
SDK requires a doc comment on each method, type, and field.
- **The check covers calls, not state.** Old and new versions share
`/state`. A plugin keeps its state format compatible, or migrates it in
`rpc.retired`.
## Minimal on purpose
The harness does only what it needs to keep going. Everything else can be an
actor, or a change that the agent makes to itself.
The core does only what a plugin cannot do for itself. Everything else can be
a plugin, or a change that the agent makes to itself.
- **The host is not self-modifiable; actors are.** So the host keeps only
what an actor cannot do for itself: routing, running instances, versions,
tests before an install, and the rollback of a version that crash-loops.
Without that rollback, a broken self-upgrade would end the agent.
- **No permissions, no limits, no hiding.** Any actor can message, upgrade,
or stop any actor, read every folder, and use the network. People who want rules
can build them.
- **No re-delivery and no state snapshots.** A crash loses the message, and
all versions of an actor share `data/` and `public/`. A rollback restores
code, not data.
- **No permissions, no limits, no hiding.** Any process can call, upgrade,
or stop any plugin, read and write every file, and use the network. The
checks protect against mistakes, not against plugins. Locks are advisory.
- **Locks are in the core.** A plugin cannot see that another process died,
so it cannot release that process's lock. The core can.
- **Our own VFS, in its own crate.** It works on Linux and macOS, it makes
`/proc` live, and plugin-served files need it later. Mounts now, overlays
later.
- **TCP endpoints for now.** They need no host code. VFS pipes can replace
them later behind the same SDK API.
- **Simple scheduling for now.** An epoch tick every 10 milliseconds keeps
the core responsive and makes kills reliable.
- **The agent is dumb.** It has a short prompt, a few tools, an append-only
history that it sends in full, and no compaction. When the context is too
large, it stops sending the oldest turns, so it never gets stuck.
## Small choices
- **Plain POSIX files.** An earlier version staged every write until close.
That broke `tempfile`, git, and SQLite, which expect normal files. Atomic
publishing is the usual temporary file + `rename`.
- **Test first, then switch.** A new version is tested where it lies. Only
a version that passes goes to `versions/`, and the old one runs until
then. `versions/` keeps every version that was installed, so a rollback
can always go back. A file that fails stays where it was put.
- **Tests are JSON transcripts** next to the source. They run on a copy of
the actor's state, without network, so a test cannot send real requests.
- **`broker` and `cargo` never answer a reply,** so no two actors answer
each other forever. The agent starts a turn only for text that is not a
reply, for the same reason.
- **The SDK is not published.** `cargo` points `sausage-actor = "0.1"` at its
own copy, which it also shows in `/actor/cargo/public/sdk/`.
- **Plain POSIX files.** Programs like `tempfile`, git, and SQLite expect
normal files. Atomic writes use a temporary file and `rename`.
- **Tests run under WASI.** `cargo test` on the host cannot find failures
that occur only in WASI, for example a missing WASI function or a panic at
start. The test runner uses the same Wasmtime and the same mounts as the
core.
- **The SDK is not published.** `cargo` points `sausage-plugin = "0.1"` at
its own copy, which it also shows in `/plugins/cargo/sdk/`.
PROTOCOL.md
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# The Sausage protocol
This is the contract between the host and the actors. An actor in any
language that follows it works in Sausage. The host publishes this file at
`/actor/broker/public/PROTOCOL.md`, so every actor can read it.
This is the contract between the core and the plugins. A plugin in any
language that follows it works in a Sausage world. The core shows this file
at `/proc/core/PROTOCOL.md`. `DECISIONS.md` in the repository says why the
contract is the way it is.
## Actors
Rust plugins use the SDK `sausage-plugin`. Its source is at
`/plugins/cargo/sdk/`, and its crate docs explain each item.
An actor is a WASI 0.2 command (`wasm32-wasip2`): a program with `main`. The
host runs one instance per actor. An instance can run forever.
## 1. Terms
The instance gets:
- **stdin:** one message per line, from the broker
- **stdout:** one message per line, to the broker
- **stderr:** free text, appended to `/actor/<id>/stderr.log`
- **environment:** `SAUSAGE_ACTOR` (its ID), `SAUSAGE_VERSION` (its version),
and `SAUSAGE_CANDIDATE=1` during a test run
- **the network:** outgoing HTTP and HTTPS through `wasi:http` (the host does
TLS), and TCP, UDP, and DNS through `wasi:sockets`, including listening on
a port of the host
- **the filesystem** described below
## Messages
A line on **stdin**:
```json
{"id": "m-17", "from": "console", "reply_to": "agent/a5", "body": {"type": "text", "text": "hi"}}
```
A line on **stdout**:
```json
{"to": "console", "id": "a6", "reply_to": "m-17", "body": {"type": "text", "text": "hello"}}
```
- `body` is required. By convention it is an object with a `"type"`.
Text for people is `{"type": "text", "text": "..."}`.
- `to` is the recipient. Without `to`, the broker publishes the message to
every subscriber of the sender.
- `id` is an optional string. If the actor sets it, the message ID is `"<sender>/<id>"`.
Otherwise, the broker assigns `m-<n>`. The broker always sets `from`.
- `reply_to` marks a reply: its value is the ID of the message it answers.
There is no request/response. A reply is a new message.
- **Never answer a reply,** or two actors can answer each other forever.
`broker` and `cargo` ignore messages that have a `reply_to`.
- Messages are fire and forget: delivery is at most once. Each actor has a
mailbox of 1,000 messages, which keeps messages while the actor restarts
or is upgraded. If the broker cannot deliver a message, the sender gets
`{"type": "undeliverable", "reason": "...", "to": "..."}` from `broker`.
- An actor must keep reading stdin. If the broker must stop or upgrade an
actor while a message waits for it to read stdin, it kills the actor.
Before the broker stops an instance, it sends
`{"id": "broker/shutdown", "from": "broker", "body": {"type": "shutdown"}}`
and then closes stdin. The broker still routes what the actor writes until
it exits. After 5 seconds, it kills the instance.
## Filesystem
The world folder is the foundation of every instance's filesystem:
| Path | Access | Contents |
| --- | --- | --- |
| `/` | read-write by every actor | the whole world folder |
| `/self` | read-write | alias for the actor's own folder (`public/`, `data/`, `source/`, etc.) |
| `/data` | read-write | alias for the actor's state folder |
| `/public` | read-write | alias for the actor's published files |
| `/actor` | read-write by every actor | the `actor/` folder of the world |
Every actor can read and write every file in the world, including other actors'
`/actor/<id>/data/` and `/actor/<id>/public/`. Nothing there is private.
Creating a folder in the world makes it visible to running actors immediately:
`/config`, `/docs`, `/www`, and `/skills` need no new mounts or host restart.
New worlds include an empty `/config` for global configuration by convention;
existing worlds can simply create it. Keep secrets out of global configuration.
Candidate instances see the same writable world root. Their `/self` alias
points to the scratch actor folder; `/public` and `/data` still point to its
corresponding children, and network access remains off;
absolute world paths are not isolated from the live world.
`/actor/<id>/` holds everything about an actor: `actor.wasm`, `actor.json`
(installed version, running, subscriptions, tapped, watches), `source/`, `public/`, `data/`,
`stderr.log`, and `versions/<n>/`. `ls /actor` lists all actors.
Files are plain POSIX files: a write is visible at once. To publish a file
so that readers never see half of it, write a temporary file and `rename` it
(the Rust SDK has `write_atomic`).
Send large or binary data as a path under `/actor/<id>/public/`, not inside a
message.
### Actor-served files: `/actor/<id>/fs/`
Files under `/actor/<id>/fs/` are not on disk: the actor `<id>` serves them.
Every actor can read and write them. The host turns each file operation into a
message from `fs` to `<id>` and waits up to 10 seconds for the reply. `path`
is relative to `fs/` and starts with `/` (the folder itself is `/`).
To make this virtual directory discoverable, an actor that serves it declares
`Actor-served files` and `fs_read` in its leading `//!` documentation in
`source/src/main.rs`. The host uses that declaration when listing
`/actor/<id>/`; it does not probe every actor (which could stall on actors that
do not handle filesystem messages). This is discovery metadata only: opening
and reading the path still requires a valid `fs_read` reply.
| Request | Reply |
| Term | Meaning |
| --- | --- |
| `{"type": "fs_read", "path"}` | `{"type": "fs_file", "text"}` (or `"base64"` instead of `"text"`), or `{"type": "fs_dir", "entries": [{"name", "type": "file" \| "dir"}]}` |
| `{"type": "fs_write", "path", "text"}` (or `"base64"` for non-UTF-8 data) | `{"type": "fs_done"}` |
| `{"type": "fs_mkdir", "path"}`, `{"type": "fs_remove", "path"}` | `{"type": "fs_done"}` |
| `{"type": "fs_rename", "path", "to"}` | `{"type": "fs_done"}` |
| world | The folder that a `sausage` host runs. It is `/` for every process. |
| core | The host. It runs processes, routes calls, serves the virtual files, and keeps the journal. |
| plugin | A folder `/plugins/<name>/` with a `plugin.wasm`. A plugin does not run by itself. |
| process | One run of a plugin version. Its ID is `<plugin>-<uuidv7>`, for example `notes-0197f3a2-7c1e-7d2b-9a41-5f0c2e8b1d34`. |
| call | A JSON-RPC request. `notes.add` calls the method `add` of the plugin `notes`. |
| interface | A set of methods. A plugin has one main interface. It can also declare endpoint interfaces. |
| endpoint | An interface that a running process serves on a TCP port. An endpoint file tells others where it is. |
| service | A call in `/config/boot.json`. The core starts it at boot and again after an upgrade of its plugin. |
| import | An interface of another plugin that a plugin uses. |
| provider, consumer | The plugin that has an interface, and a plugin that imports it. |
| journal | The central log of the world. |
Any request can be answered with `{"type": "fs_error", "errno": "no-entry"}`.
`errno` is a `wasi:filesystem` error code: `no-entry`, `exist`,
`not-directory`, `is-directory`, `not-empty`, `access`, `not-permitted`,
`invalid`, `unsupported`, `busy`, or `io` (also for anything else).
## 2. The world folder
- Opening a file sends `fs_read` once. Reads come from that copy.
- After a change, closing (or syncing) the file sends the whole file in one
`fs_write`.
- No reply within 10 seconds, or an actor that does not exist, makes the
operation fail (`io`, or `no-entry`). An actor that opens its own `fs/`
waits for itself and fails after the timeout.
- `fs` is reserved: no actor can have that ID. It also sends `fs_changed`
to watchers (see Watches).
```text
<world>/
plugins/<name>/
plugin.wasm the current version
plugin.prev.wasm the version before, for `core.revert`
source/ the source. `cargo.build` builds it from here.
imports/<plugin>.json descriptions of the imported plugins
state/<plugin>/ persistent state of a plugin, by convention
state/core/journal.sqlite the journal
config/ global configuration
boot.json the services
agent.json API, base URL, model, and token of the agent
```
## The broker
- Every process can read and write all of it. There are no permissions.
- Plugin names use `a-z`, `0-9`, `-`, and `_`. The name `core` is reserved.
- The world folder must not contain `proc`, `run`, or `self`. These names are
mount points (section 4). The host does not start a world that has them.
Requests to `broker`. The answer is a message whose `reply_to` is the ID of
the request: the request's `type` in past tense (`spawned`, `upgraded`,
`rolled_back`, `stopped`, `started`, `removed`, `subscribed`, `unsubscribed`,
`tapping`, `untapped`, `watching`, `unwatched`, `exiting`), or `{"type": "error", "reason": "..."}`.
## 3. Calls and processes
| `type` | Fields | Effect |
### 3.1 The wire protocol
- A plugin is a `wasi:cli/command` component for `wasm32-wasip2`.
- stdin and stdout carry JSON-RPC 2.0, one message per line.
- A line is a message only if it is a JSON object with `"jsonrpc": "2.0"`.
The core discards every other line on stdout. For the first discarded line
of a process, it writes one warning to the journal.
- Each line on stderr goes to the journal. Log to stderr.
- `params` is always an object. Batches are not supported.
- Write each message in one write, and write a newline before it. Then a
`print!` without a newline cannot damage a message.
### 3.2 Method names
- A method name has the form `<target>.<method>`. The core splits it at the
first `.`.
- `notes.add` starts a new process of `notes` and sends it the request `add`.
`notes.rpc.discover` sends it `rpc.discover`.
- `core.<method>` is a method of the core (section 9).
- Method names that start with `rpc.` are reserved: `rpc.discover`,
`rpc.retired`, and `rpc.endpoint`.
### 3.3 What a call does
1. The core gives the call a UUIDv7 and starts the process `<plugin>-<uuid>`
with the current version of the plugin.
2. The core writes the request to the stdin of the process. The request ID is
the process ID, and the method has no plugin prefix.
3. The process writes the response to stdout. The core sends the response to
the caller, with the caller's request ID.
4. If the process ends before it answers, the caller gets the error -32002.
Its `data` has the exit status and the last journal lines of the process.
Before the core decides this, it reads the stdout of the process to the
end.
- A process can write calls to stdout at any time, to the core and to
plugins. The responses come on stdin. A process can have many calls in
flight.
- The core keys each pending request by the process and the exact JSON ID.
The core drops a response with an unknown or late ID.
- A notification to `plugin.method` (without an ID) starts an attached
process. That process gets the notification without an ID, and nobody gets
a result.
### 3.4 Detached calls
`core.call {"method": "www.start", "params": {...}, "detach": true}` makes the
call and returns its result to the caller. The new process has no parent, so
it does not end with its caller.
Sent as a notification (without an ID), the same `core.call` starts the
process and forgets it.
### 3.5 Notifications to the caller
A process can tell its caller about progress. It sends the notification
`core.notify {"name": "text", "params": {...}}`. The core gives it to the
caller as `core.notify {"call": <ID of the caller's request>, "name": "text",
"params": {...}}`. After the call has ended, the core drops such
notifications.
So a process never needs to know who called it.
### 3.6 Lifetime
A process lives until `main` returns. A process that uses the SDK lives
while one of these runs:
- a handler of a call,
- a background task,
- an endpoint that listens.
A process has three states:
1. **running**
2. **stopping**: the core has closed stdin. EOF on stdin means "stop now".
- New calls of the process fail at once, and its pending calls fail.
- A stop hook can still write files and send notifications. It cannot
make calls, because no response can arrive.
- After 5 seconds, the core kills the process.
3. **ended**: the core releases the locks of the process (section 6) and
removes its folder in `/proc`.
Rules:
- `core.stop {pid}` starts the stopping state. `core.kill {pid}` kills the
process at once.
- When a process ends, the core stops each of its attached children. All
children stop in parallel, so a whole tree takes 5 seconds at most.
- A detached process has no parent. Only `core.stop`, `core.kill`, an
upgrade (section 3.7), and the end of the host stop it.
- At host shutdown, the core stops every process in parallel.
Note: on Unix, children outlive their parent. Here, an attached child ends
with its parent. Only `detach` makes a process independent.
### 3.7 Upgrades
A process is an instance of one plugin version. When a new version becomes
active (section 10.3):
1. New calls get the new version at once.
2. Each process of an older version gets a grace period to finish its work.
The default is 60 seconds. A plugin can declare its own value in
`rpc.discover` (`x-sausage-grace`). Then the core stops the process.
3. When the old process of a service has ended, the core starts the service
again with the new version.
4. When the last process of an older version has ended, the core starts a
process of the new version and calls `rpc.retired {"previous":
"<sha256 of the older file>"}`. A plugin can use this hook to migrate its
state, or to write a marker that its other new processes wait for. The
result goes to the journal.
During the grace period, an old process can call a method that a new
provider no longer has.
### 3.8 Environment and network
- `SAUSAGE_PID`: the process ID.
- `SAUSAGE_PLUGIN`: the plugin name.
- `SAUSAGE_PARENT`: the parent: `console`, `core`, or a process ID.
Every process gets the network: outgoing HTTP and HTTPS through `wasi:http`,
and TCP, UDP, and DNS through `wasi:sockets`.
A process that computes for a long time does not block other processes. The
core interrupts it every 10 milliseconds.
### 3.9 Errors
The standard JSON-RPC codes apply. The core adds these codes:
| Code | Meaning |
| --- | --- |
| -32001 | There is no such plugin. |
| -32002 | The process ended without an answer. `data` has the exit status and the last journal lines. |
| -32003 | The activation was rejected. `data` has the reasons. |
## 4. The filesystem
Each process gets one preopen, `/`. The core resolves each path through a
mount table:
| Path | What it is | Access |
| --- | --- | --- |
| `spawn` | `actor`, `wasm`, `source`?, `built_by`? | test, then start a new actor |
| `upgrade` | `actor`, `wasm`, `source`?, `built_by`? | test, then swap the version: a running actor is stopped (normal shutdown) and starts the new version; a stopped actor gets the new version and stays stopped, with its mailbox untouched, until `start`. The answer has `running` |
| `rollback` | `actor`, `version` | go back to an older version; like `upgrade`, a stopped actor stays stopped. The answer has `running` |
| `stop`, `start` | `actor` | stop or start an actor |
| `remove` | `actor` | stop the actor (normal shutdown), then delete its whole folder `/actor/<id>/` (all versions, `data/`, `public/`, logs); answer `{"type": "removed", "actor"}`. Messages to it are then undeliverable, and the ID can be spawned again. An unknown actor or a native one (`broker`, `console`, `cargo`, `fs`) is an `error` |
| `subscribe`, `unsubscribe` | `actor` | receive (or not) what `actor` publishes |
| `tap`, `untap` | | receive (or not) a copy of every message the broker routes |
| `watch`, `unwatch` | `path` | receive (or not) `fs_changed` for every change of `path` or anything under it; answer `{"type": "watching" \| "unwatched", "path"}` with the path as an absolute world path |
| `exit` | | answer `exiting`, stop every actor, and end the `sausage` process with exit code 75 (a wrapper like `nix run .#loop` starts it again, updated) |
| `/` | the world folder | read-write |
| `/proc` | generated by the core | read-only |
| `/self` | the folder `/proc/<own pid>/`, in memory | read-write |
| `/run` | in memory, shared, empty at each host start | read-write |
**Headless.** `sausage run --headless [dir]` (or `sausage --headless`, or `SAUSAGE_HEADLESS=1`) turns the console input off: the host does not read stdin, so end of input (`/dev/null`) does not stop the world. `nix run .#loop -- --headless <world>` passes it through the loop. It runs until SIGTERM or SIGINT (stops every actor, exit code 0) or a broker `exit` request (exit code 75, as above). Without the flag, EOF on stdin or `/quit` ends the host.
A listing of `/` shows `proc`, `run`, and `self`. A rename across two of
these areas fails.
Paths are absolute world paths, or the sender's `/self/...`, `/public/...` or
`/data/...` aliases. Native senders (such as the console) can also supply
absolute host paths; apart from `/actor` and these aliases,
these retain their host meaning.
**Taps.** After `tap`, the sender gets a copy of every message that the
broker routes (direct messages, replies, and publishes, between any actors,
including its own), for debugging, logging, or a live view of the world:
```json
{"type": "tapped", "message": {"id": "m-17", "from": "console", "to": "agent", "reply_to": null, "body": {...}}, "ts": 1792132579067}
```text
/proc/
core/
PROTOCOL.md this file
graph.json plugins, imports, and the result of each check
graph.dot the same graph for Graphviz
locks.json held locks and waiting processes
plugins/<name>/
discover.json the rpc.discover document of the current plugin.wasm
client.rs the Rust code that import!("<name>") generates
<pid>/
info.json plugin, version, method, params, parent, detached, start time, state
log the journal lines of this process
<files> the files that the process writes to /self
```
- `to` is `null` for a publish: one copy per publish, not per subscriber.
- `ts` is the time of routing, in milliseconds since the Unix epoch.
- Copies come from `broker`. They are not routed themselves, so they are
never tapped, and each message is tapped once per tapper.
- A copy that does not fit into the tapper's mailbox is dropped; routing
never waits for a tapper, and nobody gets `undeliverable` for a copy.
- Never answer a copy: the answer would be tapped again, forever.
- Like subscriptions, a tap is saved in `actor.json` (`"tapped": true`) and
survives restarts and upgrades. `untap` ends it.
Rules:
**Watches.** The host watches the whole world folder with the OS file
watcher: every change inside it counts, whoever makes it (actors, a 9P mount,
a shell or `git` on the host). Actor-served files (`/actor/<id>/fs/`) are not
on disk and do not count. After `watch {path}`, the sender gets for each
change of `path` or a path under it (`/actor/a` covers `/actor/a/x`, not
`/actor/ab`):
- A process writes its own folder only through `/self`. Writes through
`/proc` always fail.
- In a process folder, the names `info.json`, `log`, and `fs` belong to the
core. A write to `/self/info.json` fails.
- A read of a generated file returns a snapshot that ends. For example,
`/proc/<pid>/log` returns the lines up to the time of the open.
- The folder of a process goes away when the process ends. Its files are in
memory. Large or persistent data belongs in `/state`.
- Do not send a `/self` path to another process. There it means a different
folder, like `localhost` on another machine.
Principle: **inspect through files, act through calls.**
## 5. Endpoints
An endpoint is a JSON-RPC interface that a running process serves over TCP,
for example the control interface of a web server.
- The process binds a free port on 127.0.0.1. When the listener is ready, it
writes an endpoint file in one atomic step (write a temporary file, then
rename it). The file has one line: the address, the owner process, and the
interface. Example: `tcp:127.0.0.1:41234 www-0197… control`.
- Usually the file is in `/self`. A service that others must find uses a
fixed path in `/run`, for example `/run/secrets`.
- A client reads the file and connects. Its first request is
`rpc.endpoint`, which returns `{"owner", "plugin", "interface"}`. If they
do not match the file, the client disconnects. So a stale file or a reused
port cannot connect a client to the wrong process.
- JSON-RPC runs on the connection, one message per line, in both directions.
Notifications of a handler (`core.notify`) go over the connection.
- A plugin declares its endpoint interfaces in `rpc.discover`
(`x-sausage-endpoints`).
## 6. Locks
- `core.lock {"path": "/state/notes/notes.json"}` returns `{"held": true}`
when the caller holds the lock.
- Each acquisition gets its own place in a FIFO queue. The same process
cannot take one lock twice: its second acquisition waits behind its first.
- With `"wait": false`, the call returns at once with `{"held": true}` or
`{"held": false}`.
- `core.unlock {path}` (a notification) releases the lock.
- When a process ends, the core releases all of its locks, also after a
crash or a kill. It waits until the last file operation of the process has
returned. So a write of a killed process cannot land after the next
process got the lock.
- Locks are advisory. The core does not block writes to the file: the path
is only a name.
- SQLite has no file locks in WASI. Hold the lock while the database is open.
## 7. The journal
- An SQLite file at `/state/core/journal.sqlite`. Only the core writes it.
- Each entry has a UUIDv7 (it sorts by time), the process ID, the plugin, the
stream (`stderr` or `core`), and the line.
- The core writes its own events too: start (with method and params), exit
status, stop, kill, upgrades, and the warning about discarded stdout.
- `core.log {plugin?, pid?, since?, until?, grep?, limit?}` queries the
journal. `/proc/<pid>/log` shows the lines of one running process.
## 8. Boot and services
At start, the core starts each service in `/config/boot.json`, in order:
```json
{"type": "fs_changed", "path": "/actor/notes/public/list.md", "op": "write"}
[
{"method": "secrets.serve", "params": {}},
{"method": "www.start", "params": {"port": 8080}}
]
```
- `op` is `write`, `create`, `remove`, or `rename` (then `to` is the new
path; a watcher of either path gets it).
- Changes of one path within about 100 ms become one event (a `write` after
a `create` stays a `create`).
- The host's temporary files (names starting with `.sausage-tmp-`) are
skipped; renaming one onto a file is a `write` of that file.
- Events come from `fs`. Like tap copies, they are not routed, a full
mailbox drops them, and they never block the writer. Never answer them.
- If the OS drops events, every watcher gets one
`{"type": "fs_changed", "path": "/", "op": "rescan"}`: anything may
have changed.
- A watch is saved in `actor.json` (`"watches": [...]`) and survives
restarts and upgrades. `unwatch` with the same path ends it.
- A service is a detached call with the parent `core`. The core waits for
its result before it starts the next one. The result shows that the
service is ready.
- If a service fails, the core writes the error to the journal and continues.
- After an upgrade of the plugin of a service, the core starts the service
again with the new version (section 3.7).
- The core does not restart other detached processes.
- A singleton is a service with a fixed endpoint in `/run`. Only the core
starts it, so two instances cannot start at the same time.
**Versions.** A new version (from `spawn`, `upgrade`, or a changed
`actor.wasm` on disk) is tested first, while the old version keeps running.
Only when its tests pass does the broker copy it to `versions/<n>/`
(`actor.wasm`, `source/`, `meta.json`) and switch to it. So `versions/` holds
exactly the versions that were installed, and instances always run from
there. If the tests fail, nothing changes, and the sender gets an `error`
with the reason. All versions share the actor's `data/` and `public/`: a
new version must read the data of the old one.
## 9. The core API
**Tests.** The broker runs the candidate on a copy of the actor's `data/`
and `public/`, without network. The tests are JSON files in
`<source>/tests/*.json`, one scenario per file:
| Method | Params | Result |
| --- | --- | --- |
| `core.call` | `method`, `params`, `detach`? | the result of the method |
| `core.notify` | `name`, `params` | none (a notification) |
| `core.stop` | `pid` | `{}` when the process has ended |
| `core.kill` | `pid` | `{}` |
| `core.lock` | `path`, `wait`? | `{"held": bool}` |
| `core.unlock` | `path` | none (a notification) |
| `core.activate` | `plugin` and `wasm`, or `plugins: [{plugin, wasm}]`. `force`? | the new `rpc.discover` documents |
| `core.revert` | `plugin`, `force`? | like `core.activate` |
| `core.log` | filters (section 7) | journal entries |
| `core.exit` | none | `{}`. Then the host stops with exit code 75. |
```json
{
"description": "add, then list",
"steps": [
{"send": {"type": "add", "text": "milk"}, "expect": {"type": "added"}},
{"send": {"type": "list"}, "expect": [{"type": "notes"}]}
]
}
```
Everything else is a file.
Each step sends `send` (from `from`, default `test`), then reads the next
line that the candidate writes for each `expect` entry, in order, within 10
seconds. An entry matches when it is a subset of the message body. With
`to`, the message must also go to that recipient. Each file runs in a fresh
instance. A version without test files passes.
## 10. Interfaces
**Swap.** The broker holds the mailbox, stops the old instance, makes the
top-level `actor.wasm` and `source/` a copy of the new version, and starts
it. A stopped actor is not started: it keeps its mailbox and runs the new
version at the next `start`. A rollback does the same with the older version.
### 10.1 `rpc.discover`
**Crashes.** The broker restarts a crashed actor after 0.5 s, then doubles
the delay up to 30 s. A new version that crashes 3 times within 30 seconds
after an upgrade goes back to the previous version. The actor that asked for
the upgrade gets `{"type": "rolled_back", "from", "to", "reason", "last_exit"}`.
Each plugin answers `rpc.discover` with an OpenRPC 1.2 document. The schemas
are JSON Schema Draft 7, as OpenRPC requires. Shared schemas are in
`components.schemas`, and `$ref`s point to `#/components/schemas/<Name>`.
Params are by name. The document can have these extension fields:
**The folder is the truth.** At start, the broker boots every
`actor/<id>/actor.wasm`. Afterwards, the file watcher reports a new or
changed `actor/<id>/actor.wasm` (or a new folder `actor/<id>/`) once it is
quiet for about 100 ms: a new file becomes a new actor, a changed one an
upgrade, tested first with the tests in `actor/<id>/source/`. A file equal
to the installed version changes nothing. If its tests fail, the file stays
where it is, the reason goes to `stderr.log`, and the next change of the
file tries again. When the OS drops events, the broker checks every actor
folder again, as at start.
- `x-sausage-params` for each method: a `$ref` to the schema of the params
object.
- `x-sausage-endpoints`: the endpoint interfaces by name, each with its
`methods`.
- `x-sausage-imports`: for each provider, the part of its document that the
plugin uses.
- `x-sausage-grace`: the grace period in seconds.
## The `cargo` actor
The schema of params describes what the provider can read. The schema of a
result describes what the provider writes. Descriptions are part of the
interface: other agents read them to use it.
```json
{"type": "build", "source": "/actor/agent/public/drafts/notes"}
```
The core starts a process only to call `rpc.discover`. Do not do expensive
work at start.
The build request may include `"skip_tests": true` to skip Rust unit tests.
By default, `cargo` first runs `cargo test` for the host target (not WASI),
so pure-logic unit tests in a `wasm32-wasip2` actor crate can run without a
WASI test runner. If tests fail or cannot compile, the build fails before the
WASI build. The reply carries `tests: {"passed": <count>, "failed": <count>,
"output": "<cargo test stdout and stderr>"}`; counts sum Cargo's test-result
summaries, and a test command/compilation failure without a summary counts as
one failure. With `skip_tests: true`, counts are zero and output says tests
were skipped.
### 10.2 Compatibility
The reply is `{"type": "built", "wasm": "/actor/cargo/public/builds/<n>/<name>.wasm", "built_by": "cargo", "tests": {...}, ...}`
or `{"type": "build_failed", "errors": "...", "tests": {...}}`. Pass
`wasm`, `source`, and `built_by` on to `spawn` or `upgrade`.
A provider can add methods, optional params, and result fields. For each
imported method:
Build scripts can compile C for `wasm32-wasip2`: the host sets
`CC_wasm32_wasip2` and `AR_wasm32_wasip2` to a WASI clang with wasi-libc, so
the `cc` crate (for example `rusqlite` with `bundled`) works. Its headers are
WASI 0.1: C code that needs sockets does not build.
1. The provider has the method.
2. Each params value that the consumer can send is valid for the provider.
3. Each result that the provider can return is valid for the consumer.
A Rust actor depends on the SDK with `sausage-actor = "0.1"`. `cargo` points
that dependency at the SDK of the host, which it publishes at
`/actor/cargo/public/sdk/`.
- The same rules apply to endpoint interfaces.
- There are no version numbers. This check replaces them.
- The check covers a fixed subset of JSON Schema: objects with `properties`
and `required`, the primitive types, arrays, optional and nullable values,
string enums, integer ranges, and `$ref`. A construct outside the subset
fails the check.
- The check covers calls, not state. Old and new processes share the files in
`/state`, and `core.revert` restores only code. A plugin must keep its
state format compatible, or migrate it in `rpc.retired`.
### 10.3 Activation
`core.activate {"plugin": "notes", "wasm": "/state/cargo/builds/7/notes.wasm"}`:
1. The core copies the file. All further steps use this copy, even if the
file changes.
2. It starts the copy and calls `rpc.discover`.
3. It waits until it has the documents of all plugins (section 10.4).
4. It checks the imports of the new version against the current providers.
5. It checks each current consumer of the plugin against the new version.
6. If all checks pass, `plugin.wasm` becomes `plugin.prev.wasm`, and the copy
becomes `plugin.wasm`. Then the upgrade starts (section 3.7).
If a check fails, nothing changes, and the error -32003 lists each problem,
with a counterexample where possible.
- The core runs one activation at a time.
- `plugins: [...]` activates several plugins together. The checks then use
the new set.
- `force: true` skips steps 4 and 5.
- `core.revert {plugin}` activates `plugin.prev.wasm` in the same way, and
the current version becomes `plugin.prev.wasm`.
- A person can also copy a file to `plugin.wasm` by hand. That skips the
checks.
### 10.4 The graph
- The core keeps the `rpc.discover` documents of all plugins, by file hash.
At start, it gets them in the background.
- A file watcher on `/plugins/*/plugin.wasm` updates them, for example after
a copy by hand. `/proc/core/graph.json` then shows each broken import, and
the journal records it.
- An import of a plugin that does not exist is "missing".
## 11. Building and tests
The core has one native plugin: `cargo`. `cargo.build {"plugin": "notes"}`
builds `/plugins/notes/source/`:
1. It copies the source once. The tests and the build both use this copy.
2. It runs the tests under WASI.
3. It builds the release `.wasm` for `wasm32-wasip2`.
4. It returns `{"wasm": "/state/cargo/builds/<n>/notes.wasm", "tests":
{"passed", "failed", "output"}, "warnings"}`. If a step fails, it returns
an error with the compiler or test output.
- A call to `cargo.build` gets a process ID, a folder in `/proc`, and journal
entries, like other calls.
- The dependency `sausage-plugin = "0.1"` points to the SDK copy at
`/plugins/cargo/sdk/`.
- Build scripts can compile C: `CC_wasm32_wasip2` and `AR_wasm32_wasip2`
point to a WASI clang.
- The build does not activate the result. Call `core.activate` next.
Tests:
- Each test runs in its own instance, so a panic ends only its own test.
- The normal Rust test setup works: `#[test]`, `tests/*.rs`, name filters,
and `--ignored`. `#[should_panic]` cannot work, because WASI cannot catch
a panic.
- Each test gets an empty temporary world as `/`, the package folder at its
path, and its own `/proc`, `/self`, and `/run`.
- The test runner answers `core.lock`, `core.unlock`, `core.notify`, and
`core.log`. A call to a plugin fails: a test has no other plugins.
README.md
+43 -42
View File
@@ -2,11 +2,11 @@
You can see how the sausage is made.
Sausage is a world of small programs ("actors") that you grow by talking to
it. Each actor is a WASI program with stdin and stdout. Actors send each other
JSON messages, one per line, through a broker. The agent is an actor too: it
writes new actors in Rust, builds them, tests them, starts them, and can
change its own code.
Sausage is a world of small WASI programs ("plugins") that you grow by
talking to it. A plugin is a `.wasm` file with JSON-RPC methods. Each call
to a plugin starts a new process. The agent is a plugin too: it writes new
plugins in Rust, builds them, tests them, activates them, and can change its
own code.
## Start
@@ -29,8 +29,8 @@ nix run git+https://gitea.surma.technology/surma/sausage -- run # starts the
`init` asks for the API shape (`openai-responses` or `anthropic-messages`),
the base URL, the model, and the token. It reads `SAUSAGE_API`,
`SAUSAGE_BASE_URL`, `SAUSAGE_MODEL`, and `SAUSAGE_API_TOKEN` first. The
values go to `world/actor/agent/data/config.json`. Both commands take another
folder as an argument, for example `... -- run my-world`.
values go to `world/config/agent.json`. Both commands take another folder as
an argument, for example `... -- run my-world`.
To keep a world on the newest version, run it in a loop:
@@ -39,60 +39,61 @@ nix run git+https://gitea.surma.technology/surma/sausage#loop # ./
nix run git+https://gitea.surma.technology/surma/sausage#loop -- my-world # an existing world
```
The loop runs `nix run --refresh git+https://gitea.surma.technology/surma/sausage -- run my-world`.
When the host crashes or an actor sends `@broker {"type":"exit"}`, the loop
fetches the newest commit and starts it again. `/quit` ends the loop. Set
`SAUSAGE_FLAKE` to run another flake URL instead, for example your fork.
When the host crashes or a plugin calls `core.exit`, the loop fetches the
newest commit and starts it again. `quit` ends the loop. Set `SAUSAGE_FLAKE`
to run another flake URL instead, for example your fork.
From a clone (`git clone https://gitea.surma.technology/surma/sausage`), the
same commands are `nix run`, `nix run -- init`, `nix run -- run` and
same commands are `nix run`, `nix run -- init`, `nix run -- run`, and
`nix run .#loop`.
### Headless
`--headless` (or `SAUSAGE_HEADLESS=1`) turns the console input off: the host
never reads stdin, so end of input does not stop the world. It runs until
SIGTERM/SIGINT (clean stop, exit code 0) or a broker `exit` request (exit
code 75, so the loop starts the newest version). Create the world first
(`init`), then pass the flag through the loop:
`--headless` (or `SAUSAGE_HEADLESS=1`) turns the console input off. The host
runs until SIGTERM or SIGINT (exit code 0) or until a plugin calls
`core.exit` (exit code 75, so the loop starts the newest version):
```sh
nix run git+https://gitea.surma.technology/surma/sausage#loop -- --headless my-world
```
In the console:
## The console
```text
write an actor "notes" that stores notes, and start it → text to the agent
@notes {"type":"add","text":"milk"} → a JSON message to an actor
@agent hello → text to an actor
/quit
```
| Input | Effect |
| --- | --- |
| text | a message to the agent (`agent.chat`) |
| `<plugin>.<method> {json}` | a call. The console prints the result. |
| `ls [path]`, `cat <path>` | the filesystem as a process sees it, with `/proc` and `/run` |
| `methods <plugin>` | the methods of a plugin, with params and docs |
| `ps` | the running processes |
| `log [plugin or pid] [-n N]` | the journal |
| `activate <plugin> <wasm>`, `revert <plugin>` | activate a new version, or go back |
| `stop <pid>`, `kill <pid>` | stop a process |
| `help`, `quit` | |
## The world folder
The folder is the source of truth. Every actor lives in `world/actor/<id>/`:
```text
actor.wasm the current version
actor.json installed version, running, subscriptions
source/ the source of the current version
public/ files that the actor publishes
data/ actor state; owner-writable, world-readable via /actor/<id>/data/ (not private)
stderr.log what the actor and the broker write about it
versions/<n>/ every installed version: actor.wasm, source/, meta.json
plugins/<name>/plugin.wasm the current version of a plugin
plugins/<name>/source/ its source
state/<plugin>/ the state of a plugin, by convention
state/core/journal.sqlite the journal: stderr of all processes, and core events
config/boot.json the services that start with the world
config/agent.json the configuration of the agent
```
To add or replace an actor by hand, put an `actor.wasm` (and its `source/`,
with the tests in `source/tests/`) into its folder; the host watches the
world folder and picks the file up once it stops changing. The broker tests
the file before it uses it.
If the tests fail, the old version keeps running, and `stderr.log` says why.
Each process also sees `/proc` (the processes and the state of the core),
`/self` (its own folder in `/proc`), and `/run` (shared files in memory).
To replace a plugin by hand, copy a `.wasm` file to its `plugin.wasm`. That
skips the interface checks. `revert <plugin>` goes back to the version
before the last activation.
## More
- [PROTOCOL.md](PROTOCOL.md): messages, the filesystem, the broker, `cargo`.
Read this to write an actor in any language.
- [`sdk/`](sdk/): `sausage-actor`, the SDK for Rust actors.
- [`examples/notes`](examples/notes): a small actor with a test.
- [PROTOCOL.md](PROTOCOL.md): calls, processes, the filesystem, locks,
interfaces, and `cargo`. Read this to write a plugin in any language.
- [DECISIONS.md](DECISIONS.md): why Sausage is the way it is.
- [`sdk/`](sdk/): `sausage-plugin`, the SDK for Rust plugins.
- [`examples/`](examples/): small plugins.
- [AGENTS.md](AGENTS.md): how to work on Sausage itself.