microsandbox_protocol/
message.rs

1//! Message envelope and type definitions for the agent protocol.
2
3use serde::{Deserialize, Serialize, de::DeserializeOwned};
4
5use crate::error::ProtocolResult;
6
7//--------------------------------------------------------------------------------------------------
8// Constants
9//--------------------------------------------------------------------------------------------------
10
11/// Current protocol version.
12pub const PROTOCOL_VERSION: u8 = 1;
13
14/// Frame flag: this is the last message for the given correlation ID.
15///
16/// Set on terminal message types such as `ExecExited` and `FsResponse`.
17pub const FLAG_TERMINAL: u8 = 0b0000_0001;
18
19/// Frame flag: this is the first message of a new session.
20///
21/// Set on session-initiating message types such as `ExecRequest` and `FsRequest`.
22pub const FLAG_SESSION_START: u8 = 0b0000_0010;
23
24/// Frame flag: this message requests sandbox shutdown.
25///
26/// Set on `Shutdown` messages. The sandbox-process relay uses this to trigger
27/// drain escalation (SIGTERM → SIGKILL) if the guest doesn't exit voluntarily.
28pub const FLAG_SHUTDOWN: u8 = 0b0000_0100;
29
30/// Size of the frame header fields that sit between the length prefix and the
31/// CBOR payload: `[id: u32 BE][flags: u8]` = 5 bytes.
32pub const FRAME_HEADER_SIZE: usize = 5;
33
34//--------------------------------------------------------------------------------------------------
35// Types
36//--------------------------------------------------------------------------------------------------
37
38/// The message envelope sent over the wire.
39///
40/// Each message contains a version, type, correlation ID, flags, and a CBOR payload.
41///
42/// Wire format: `[len: u32 BE][id: u32 BE][flags: u8][CBOR(v, t, p)]`
43///
44/// The `id` and `flags` fields live in the binary frame header (outside CBOR)
45/// so that relay intermediaries can route frames without CBOR parsing.
46#[derive(Debug, Clone, Serialize, Deserialize)]
47pub struct Message {
48    /// Protocol version.
49    pub v: u8,
50
51    /// Message type.
52    pub t: MessageType,
53
54    /// Correlation ID used to associate requests with responses and
55    /// to identify exec sessions.
56    ///
57    /// Serialized in the binary frame header, not in CBOR.
58    #[serde(skip)]
59    pub id: u32,
60
61    /// Frame flags computed from the message type.
62    ///
63    /// Serialized in the binary frame header, not in CBOR.
64    #[serde(skip)]
65    pub flags: u8,
66
67    /// The CBOR-encoded payload bytes.
68    #[serde(with = "serde_bytes")]
69    pub p: Vec<u8>,
70}
71
72/// Identifies the type of a protocol message.
73#[derive(Debug, Clone, PartialEq, Eq, Hash)]
74pub enum MessageType {
75    /// Guest agent is ready.
76    Ready,
77
78    /// Host requests shutdown.
79    Shutdown,
80
81    /// Host requests command execution.
82    ExecRequest,
83
84    /// Guest confirms command started.
85    ExecStarted,
86
87    /// Host sends stdin data.
88    ExecStdin,
89
90    /// Guest sends stdout data.
91    ExecStdout,
92
93    /// Guest sends stderr data.
94    ExecStderr,
95
96    /// Guest reports command exit.
97    ExecExited,
98
99    /// Guest reports command failed to spawn (binary not found,
100    /// permission denied, etc.). Distinct from `ExecExited` —
101    /// `ExecFailed` means the user code never ran. Terminal.
102    ExecFailed,
103
104    /// Host requests PTY resize.
105    ExecResize,
106
107    /// Host sends signal to process.
108    ExecSignal,
109
110    /// Host requests a filesystem operation.
111    FsRequest,
112
113    /// Guest sends a terminal filesystem response.
114    FsResponse,
115
116    /// Streaming file data chunk (bidirectional).
117    FsData,
118}
119
120//--------------------------------------------------------------------------------------------------
121// Methods
122//--------------------------------------------------------------------------------------------------
123
124impl Message {
125    /// Creates a new message with the current protocol version and raw payload bytes.
126    pub fn new(t: MessageType, id: u32, p: Vec<u8>) -> Self {
127        let flags = t.flags();
128        Self {
129            v: PROTOCOL_VERSION,
130            t,
131            id,
132            flags,
133            p,
134        }
135    }
136
137    /// Creates a new message by serializing the given payload to CBOR.
138    pub fn with_payload<T: Serialize>(
139        t: MessageType,
140        id: u32,
141        payload: &T,
142    ) -> ProtocolResult<Self> {
143        let mut p = Vec::new();
144        ciborium::into_writer(payload, &mut p)?;
145        let flags = t.flags();
146        Ok(Self {
147            v: PROTOCOL_VERSION,
148            t,
149            id,
150            flags,
151            p,
152        })
153    }
154
155    /// Deserializes the payload bytes into the given type.
156    pub fn payload<T: DeserializeOwned>(&self) -> ProtocolResult<T> {
157        Ok(ciborium::from_reader(&self.p[..])?)
158    }
159}
160
161impl MessageType {
162    /// Computes the frame flags byte for this message type.
163    pub fn flags(&self) -> u8 {
164        match self {
165            Self::ExecExited | Self::ExecFailed | Self::FsResponse => FLAG_TERMINAL,
166            Self::ExecRequest | Self::FsRequest => FLAG_SESSION_START,
167            Self::Shutdown => FLAG_SHUTDOWN,
168            _ => 0,
169        }
170    }
171
172    /// Returns the wire string representation.
173    pub fn as_str(&self) -> &'static str {
174        match self {
175            Self::Ready => "core.ready",
176            Self::Shutdown => "core.shutdown",
177            Self::ExecRequest => "core.exec.request",
178            Self::ExecStarted => "core.exec.started",
179            Self::ExecStdin => "core.exec.stdin",
180            Self::ExecStdout => "core.exec.stdout",
181            Self::ExecStderr => "core.exec.stderr",
182            Self::ExecExited => "core.exec.exited",
183            Self::ExecFailed => "core.exec.failed",
184            Self::ExecResize => "core.exec.resize",
185            Self::ExecSignal => "core.exec.signal",
186            Self::FsRequest => "core.fs.request",
187            Self::FsResponse => "core.fs.response",
188            Self::FsData => "core.fs.data",
189        }
190    }
191
192    /// Parses a wire string into a message type.
193    pub fn from_wire_str(s: &str) -> Option<Self> {
194        match s {
195            "core.ready" => Some(Self::Ready),
196            "core.shutdown" => Some(Self::Shutdown),
197            "core.exec.request" => Some(Self::ExecRequest),
198            "core.exec.started" => Some(Self::ExecStarted),
199            "core.exec.stdin" => Some(Self::ExecStdin),
200            "core.exec.stdout" => Some(Self::ExecStdout),
201            "core.exec.stderr" => Some(Self::ExecStderr),
202            "core.exec.exited" => Some(Self::ExecExited),
203            "core.exec.failed" => Some(Self::ExecFailed),
204            "core.exec.resize" => Some(Self::ExecResize),
205            "core.exec.signal" => Some(Self::ExecSignal),
206            "core.fs.request" => Some(Self::FsRequest),
207            "core.fs.response" => Some(Self::FsResponse),
208            "core.fs.data" => Some(Self::FsData),
209            _ => None,
210        }
211    }
212}
213
214//--------------------------------------------------------------------------------------------------
215// Trait Implementations
216//--------------------------------------------------------------------------------------------------
217
218impl Serialize for MessageType {
219    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
220    where
221        S: serde::Serializer,
222    {
223        serializer.serialize_str(self.as_str())
224    }
225}
226
227impl<'de> Deserialize<'de> for MessageType {
228    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
229    where
230        D: serde::Deserializer<'de>,
231    {
232        let s = String::deserialize(deserializer)?;
233        Self::from_wire_str(&s)
234            .ok_or_else(|| serde::de::Error::custom(format!("unknown message type: {s}")))
235    }
236}
237
238//--------------------------------------------------------------------------------------------------
239// Tests
240//--------------------------------------------------------------------------------------------------
241
242#[cfg(test)]
243mod tests {
244    use super::*;
245
246    #[test]
247    fn test_message_type_roundtrip() {
248        let types = [
249            (MessageType::Ready, "core.ready"),
250            (MessageType::Shutdown, "core.shutdown"),
251            (MessageType::ExecRequest, "core.exec.request"),
252            (MessageType::ExecStarted, "core.exec.started"),
253            (MessageType::ExecStdin, "core.exec.stdin"),
254            (MessageType::ExecStdout, "core.exec.stdout"),
255            (MessageType::ExecStderr, "core.exec.stderr"),
256            (MessageType::ExecExited, "core.exec.exited"),
257            (MessageType::ExecFailed, "core.exec.failed"),
258            (MessageType::ExecResize, "core.exec.resize"),
259            (MessageType::ExecSignal, "core.exec.signal"),
260            (MessageType::FsRequest, "core.fs.request"),
261            (MessageType::FsResponse, "core.fs.response"),
262            (MessageType::FsData, "core.fs.data"),
263        ];
264
265        for (mt, expected_str) in &types {
266            assert_eq!(mt.as_str(), *expected_str);
267            assert_eq!(MessageType::from_wire_str(expected_str).unwrap(), *mt);
268        }
269    }
270
271    #[test]
272    fn test_message_type_serde_roundtrip() {
273        let types = [
274            MessageType::Ready,
275            MessageType::Shutdown,
276            MessageType::ExecRequest,
277            MessageType::ExecStarted,
278            MessageType::ExecStdin,
279            MessageType::ExecStdout,
280            MessageType::ExecStderr,
281            MessageType::ExecExited,
282            MessageType::ExecFailed,
283            MessageType::ExecResize,
284            MessageType::ExecSignal,
285            MessageType::FsRequest,
286            MessageType::FsResponse,
287            MessageType::FsData,
288        ];
289
290        for mt in &types {
291            let mut buf = Vec::new();
292            ciborium::into_writer(mt, &mut buf).unwrap();
293            let decoded: MessageType = ciborium::from_reader(&buf[..]).unwrap();
294            assert_eq!(&decoded, mt);
295        }
296    }
297
298    #[test]
299    fn test_unknown_message_type() {
300        assert!(MessageType::from_wire_str("core.unknown").is_none());
301    }
302
303    #[test]
304    fn test_message_with_payload_roundtrip() {
305        use crate::exec::ExecExited;
306
307        let msg =
308            Message::with_payload(MessageType::ExecExited, 7, &ExecExited { code: 42 }).unwrap();
309
310        assert_eq!(msg.t, MessageType::ExecExited);
311        assert_eq!(msg.id, 7);
312        assert_eq!(msg.flags, FLAG_TERMINAL);
313
314        let payload: ExecExited = msg.payload().unwrap();
315        assert_eq!(payload.code, 42);
316    }
317
318    #[test]
319    fn test_message_type_flags() {
320        assert_eq!(MessageType::ExecExited.flags(), FLAG_TERMINAL);
321        assert_eq!(MessageType::ExecFailed.flags(), FLAG_TERMINAL);
322        assert_eq!(MessageType::FsResponse.flags(), FLAG_TERMINAL);
323        assert_eq!(MessageType::ExecRequest.flags(), FLAG_SESSION_START);
324        assert_eq!(MessageType::FsRequest.flags(), FLAG_SESSION_START);
325        assert_eq!(MessageType::Ready.flags(), 0);
326        assert_eq!(MessageType::Shutdown.flags(), FLAG_SHUTDOWN);
327        assert_eq!(MessageType::ExecStarted.flags(), 0);
328        assert_eq!(MessageType::ExecStdin.flags(), 0);
329        assert_eq!(MessageType::ExecStdout.flags(), 0);
330        assert_eq!(MessageType::ExecStderr.flags(), 0);
331        assert_eq!(MessageType::ExecResize.flags(), 0);
332        assert_eq!(MessageType::ExecSignal.flags(), 0);
333        assert_eq!(MessageType::FsData.flags(), 0);
334    }
335
336    #[test]
337    fn test_message_new_computes_flags() {
338        let msg = Message::new(MessageType::ExecRequest, 1, Vec::new());
339        assert_eq!(msg.flags, FLAG_SESSION_START);
340
341        let msg = Message::new(MessageType::ExecStdout, 1, Vec::new());
342        assert_eq!(msg.flags, 0);
343    }
344}
microsandbox_protocol/message.rs

microsandbox_protocol/
message.rs
