Module handler

async_snmp

Module handler 

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Handler types and traits for SNMP MIB operations.

This module provides the interface for implementing SNMP agent handlers:

§Overview

Handlers are registered with an Agent using a prefix OID. When the agent receives a request, it dispatches to the handler with the longest matching prefix. Each handler implements the MibHandler trait to respond to GET, GETNEXT, and optionally SET operations.

§Basic Handler Example

A minimal handler that provides two scalar values:

use async_snmp::handler::{MibHandler, RequestContext, GetResult, GetNextResult, BoxFuture};
use async_snmp::{Oid, Value, VarBind, oid};

struct MyHandler;

impl MibHandler for MyHandler {
    fn get<'a>(&'a self, _ctx: &'a RequestContext, oid: &'a Oid) -> BoxFuture<'a, GetResult> {
        Box::pin(async move {
            if oid == &oid!(1, 3, 6, 1, 4, 1, 99999, 1, 0) {
                return GetResult::Value(Value::Integer(42));
            }
            GetResult::NoSuchObject
        })
    }

    fn get_next<'a>(&'a self, _ctx: &'a RequestContext, oid: &'a Oid) -> BoxFuture<'a, GetNextResult> {
        Box::pin(async move {
            let my_oid = oid!(1, 3, 6, 1, 4, 1, 99999, 1, 0);
            if oid < &my_oid {
                return GetNextResult::Value(VarBind::new(my_oid, Value::Integer(42)));
            }
            GetNextResult::EndOfMibView
        })
    }
}

§SET Operations and Two-Phase Commit

SET operations follow a two-phase commit protocol as defined in RFC 3416:

  1. Test Phase: MibHandler::test_set is called for ALL varbinds before any commits. If any test fails, no changes are made and the appropriate error is returned.

  2. Commit Phase: MibHandler::commit_set is called for each varbind in order. If a commit fails, MibHandler::undo_set is called for all previously committed varbinds in reverse order.

By default, handlers are read-only (returning SetResult::NotWritable). See MibHandler documentation for implementation details.

§Using OidTable for GETNEXT

For handlers with static or slowly-changing data, OidTable simplifies GETNEXT implementation by maintaining OIDs in sorted order:

use async_snmp::handler::{MibHandler, RequestContext, GetResult, GetNextResult, OidTable, BoxFuture};
use async_snmp::{Oid, Value, VarBind, oid};

struct StaticHandler {
    table: OidTable<Value>,
}

impl StaticHandler {
    fn new() -> Self {
        let mut table = OidTable::new();
        table.insert(oid!(1, 3, 6, 1, 4, 1, 99999, 1, 0), Value::Integer(100));
        table.insert(oid!(1, 3, 6, 1, 4, 1, 99999, 2, 0), Value::OctetString("test".into()));
        Self { table }
    }
}

impl MibHandler for StaticHandler {
    fn get<'a>(&'a self, _ctx: &'a RequestContext, oid: &'a Oid) -> BoxFuture<'a, GetResult> {
        Box::pin(async move {
            self.table.get(oid)
                .cloned()
                .map(GetResult::Value)
                .unwrap_or(GetResult::NoSuchObject)
        })
    }

    fn get_next<'a>(&'a self, _ctx: &'a RequestContext, oid: &'a Oid) -> BoxFuture<'a, GetNextResult> {
        Box::pin(async move {
            self.table.get_next(oid)
                .map(|(o, v)| GetNextResult::Value(VarBind::new(o.clone(), v.clone())))
                .unwrap_or(GetNextResult::EndOfMibView)
        })
    }
}

Re-exports§

pub use crate::agent::vacm::SecurityModel;

Structs§

OidTable
Helper for implementing GETNEXT with lexicographic OID ordering.
RequestContext
Request context passed to MIB handlers.
Response
Response to return from a handler.

Enums§

GetNextResult
Result of a GETNEXT operation (RFC 3416).
GetResult
Result of a GET operation on a specific OID (RFC 3416).
SetResult
Result of a SET operation phase (RFC 3416).

Traits§

MibHandler
Handler for SNMP MIB operations.

Type Aliases§

BoxFuture
Type alias for boxed async return type (dyn-compatible).