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 reports that a prior `ExecStdin` write to the child's
91    /// stdin failed (e.g. the child closed its read end). Non-terminal:
92    /// the session continues and may still produce stdout/stderr and
93    /// an exit code.
94    ExecStdinError,
95
96    /// Guest sends stdout data.
97    ExecStdout,
98
99    /// Guest sends stderr data.
100    ExecStderr,
101
102    /// Guest reports command exit.
103    ExecExited,
104
105    /// Guest reports command failed to spawn (binary not found,
106    /// permission denied, etc.). Distinct from `ExecExited` —
107    /// `ExecFailed` means the user code never ran. Terminal.
108    ExecFailed,
109
110    /// Host requests PTY resize.
111    ExecResize,
112
113    /// Host sends signal to process.
114    ExecSignal,
115
116    /// Host requests a filesystem operation.
117    FsRequest,
118
119    /// Guest sends a terminal filesystem response.
120    FsResponse,
121
122    /// Streaming file data chunk (bidirectional).
123    FsData,
124}
125
126//--------------------------------------------------------------------------------------------------
127// Methods
128//--------------------------------------------------------------------------------------------------
129
130impl Message {
131    /// Creates a new message with the current protocol version and raw payload bytes.
132    pub fn new(t: MessageType, id: u32, p: Vec<u8>) -> Self {
133        let flags = t.flags();
134        Self {
135            v: PROTOCOL_VERSION,
136            t,
137            id,
138            flags,
139            p,
140        }
141    }
142
143    /// Creates a new message by serializing the given payload to CBOR.
144    pub fn with_payload<T: Serialize>(
145        t: MessageType,
146        id: u32,
147        payload: &T,
148    ) -> ProtocolResult<Self> {
149        let mut p = Vec::new();
150        ciborium::into_writer(payload, &mut p)?;
151        let flags = t.flags();
152        Ok(Self {
153            v: PROTOCOL_VERSION,
154            t,
155            id,
156            flags,
157            p,
158        })
159    }
160
161    /// Deserializes the payload bytes into the given type.
162    pub fn payload<T: DeserializeOwned>(&self) -> ProtocolResult<T> {
163        Ok(ciborium::from_reader(&self.p[..])?)
164    }
165}
166
167impl MessageType {
168    /// Computes the frame flags byte for this message type.
169    pub fn flags(&self) -> u8 {
170        match self {
171            Self::ExecExited | Self::ExecFailed | Self::FsResponse => FLAG_TERMINAL,
172            Self::ExecRequest | Self::FsRequest => FLAG_SESSION_START,
173            Self::Shutdown => FLAG_SHUTDOWN,
174            _ => 0,
175        }
176    }
177
178    /// Returns the wire string representation.
179    pub fn as_str(&self) -> &'static str {
180        match self {
181            Self::Ready => "core.ready",
182            Self::Shutdown => "core.shutdown",
183            Self::ExecRequest => "core.exec.request",
184            Self::ExecStarted => "core.exec.started",
185            Self::ExecStdin => "core.exec.stdin",
186            Self::ExecStdinError => "core.exec.stdin.error",
187            Self::ExecStdout => "core.exec.stdout",
188            Self::ExecStderr => "core.exec.stderr",
189            Self::ExecExited => "core.exec.exited",
190            Self::ExecFailed => "core.exec.failed",
191            Self::ExecResize => "core.exec.resize",
192            Self::ExecSignal => "core.exec.signal",
193            Self::FsRequest => "core.fs.request",
194            Self::FsResponse => "core.fs.response",
195            Self::FsData => "core.fs.data",
196        }
197    }
198
199    /// Parses a wire string into a message type.
200    pub fn from_wire_str(s: &str) -> Option<Self> {
201        match s {
202            "core.ready" => Some(Self::Ready),
203            "core.shutdown" => Some(Self::Shutdown),
204            "core.exec.request" => Some(Self::ExecRequest),
205            "core.exec.started" => Some(Self::ExecStarted),
206            "core.exec.stdin" => Some(Self::ExecStdin),
207            "core.exec.stdin.error" => Some(Self::ExecStdinError),
208            "core.exec.stdout" => Some(Self::ExecStdout),
209            "core.exec.stderr" => Some(Self::ExecStderr),
210            "core.exec.exited" => Some(Self::ExecExited),
211            "core.exec.failed" => Some(Self::ExecFailed),
212            "core.exec.resize" => Some(Self::ExecResize),
213            "core.exec.signal" => Some(Self::ExecSignal),
214            "core.fs.request" => Some(Self::FsRequest),
215            "core.fs.response" => Some(Self::FsResponse),
216            "core.fs.data" => Some(Self::FsData),
217            _ => None,
218        }
219    }
220}
221
222//--------------------------------------------------------------------------------------------------
223// Trait Implementations
224//--------------------------------------------------------------------------------------------------
225
226impl Serialize for MessageType {
227    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
228    where
229        S: serde::Serializer,
230    {
231        serializer.serialize_str(self.as_str())
232    }
233}
234
235impl<'de> Deserialize<'de> for MessageType {
236    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
237    where
238        D: serde::Deserializer<'de>,
239    {
240        let s = String::deserialize(deserializer)?;
241        Self::from_wire_str(&s)
242            .ok_or_else(|| serde::de::Error::custom(format!("unknown message type: {s}")))
243    }
244}
245
246//--------------------------------------------------------------------------------------------------
247// Tests
248//--------------------------------------------------------------------------------------------------
249
250#[cfg(test)]
251mod tests {
252    use super::*;
253
254    #[test]
255    fn test_message_type_roundtrip() {
256        let types = [
257            (MessageType::Ready, "core.ready"),
258            (MessageType::Shutdown, "core.shutdown"),
259            (MessageType::ExecRequest, "core.exec.request"),
260            (MessageType::ExecStarted, "core.exec.started"),
261            (MessageType::ExecStdin, "core.exec.stdin"),
262            (MessageType::ExecStdinError, "core.exec.stdin.error"),
263            (MessageType::ExecStdout, "core.exec.stdout"),
264            (MessageType::ExecStderr, "core.exec.stderr"),
265            (MessageType::ExecExited, "core.exec.exited"),
266            (MessageType::ExecFailed, "core.exec.failed"),
267            (MessageType::ExecResize, "core.exec.resize"),
268            (MessageType::ExecSignal, "core.exec.signal"),
269            (MessageType::FsRequest, "core.fs.request"),
270            (MessageType::FsResponse, "core.fs.response"),
271            (MessageType::FsData, "core.fs.data"),
272        ];
273
274        for (mt, expected_str) in &types {
275            assert_eq!(mt.as_str(), *expected_str);
276            assert_eq!(MessageType::from_wire_str(expected_str).unwrap(), *mt);
277        }
278    }
279
280    #[test]
281    fn test_message_type_serde_roundtrip() {
282        let types = [
283            MessageType::Ready,
284            MessageType::Shutdown,
285            MessageType::ExecRequest,
286            MessageType::ExecStarted,
287            MessageType::ExecStdin,
288            MessageType::ExecStdinError,
289            MessageType::ExecStdout,
290            MessageType::ExecStderr,
291            MessageType::ExecExited,
292            MessageType::ExecFailed,
293            MessageType::ExecResize,
294            MessageType::ExecSignal,
295            MessageType::FsRequest,
296            MessageType::FsResponse,
297            MessageType::FsData,
298        ];
299
300        for mt in &types {
301            let mut buf = Vec::new();
302            ciborium::into_writer(mt, &mut buf).unwrap();
303            let decoded: MessageType = ciborium::from_reader(&buf[..]).unwrap();
304            assert_eq!(&decoded, mt);
305        }
306    }
307
308    #[test]
309    fn test_unknown_message_type() {
310        assert!(MessageType::from_wire_str("core.unknown").is_none());
311    }
312
313    #[test]
314    fn test_message_with_payload_roundtrip() {
315        use crate::exec::ExecExited;
316
317        let msg =
318            Message::with_payload(MessageType::ExecExited, 7, &ExecExited { code: 42 }).unwrap();
319
320        assert_eq!(msg.t, MessageType::ExecExited);
321        assert_eq!(msg.id, 7);
322        assert_eq!(msg.flags, FLAG_TERMINAL);
323
324        let payload: ExecExited = msg.payload().unwrap();
325        assert_eq!(payload.code, 42);
326    }
327
328    #[test]
329    fn test_message_type_flags() {
330        assert_eq!(MessageType::ExecExited.flags(), FLAG_TERMINAL);
331        assert_eq!(MessageType::ExecFailed.flags(), FLAG_TERMINAL);
332        assert_eq!(MessageType::FsResponse.flags(), FLAG_TERMINAL);
333        assert_eq!(MessageType::ExecRequest.flags(), FLAG_SESSION_START);
334        assert_eq!(MessageType::FsRequest.flags(), FLAG_SESSION_START);
335        assert_eq!(MessageType::Ready.flags(), 0);
336        assert_eq!(MessageType::Shutdown.flags(), FLAG_SHUTDOWN);
337        assert_eq!(MessageType::ExecStarted.flags(), 0);
338        assert_eq!(MessageType::ExecStdin.flags(), 0);
339        assert_eq!(MessageType::ExecStdout.flags(), 0);
340        assert_eq!(MessageType::ExecStderr.flags(), 0);
341        assert_eq!(MessageType::ExecResize.flags(), 0);
342        assert_eq!(MessageType::ExecSignal.flags(), 0);
343        assert_eq!(MessageType::FsData.flags(), 0);
344    }
345
346    #[test]
347    fn test_message_new_computes_flags() {
348        let msg = Message::new(MessageType::ExecRequest, 1, Vec::new());
349        assert_eq!(msg.flags, FLAG_SESSION_START);
350
351        let msg = Message::new(MessageType::ExecStdout, 1, Vec::new());
352        assert_eq!(msg.flags, 0);
353    }
354}
microsandbox_protocol/message.rs

microsandbox_protocol/
message.rs
