node:dns

node:dns and node:dns/promises share one guest implementation and the jco:node/dns@0.1.0 capability. Jco adds that import and its dns.wit dependency when bundled source uses either specifier. The default provider throws ERR_JCO_DNS_ADAPTER_REQUIRED; applications opt into Node name resolution with:

jco transpile component.wasm \
  --map 'jco:node/dns@0.1.0=@bytecodealliance/jco-std/wasi/0.2.x/node/24.x.x/dns/host/node'

The WIT interface represents each DNS operation as a named, typed function; it does not tunnel requests through a serialized dispatcher. The Node provider calls the real asynchronous node:dns/promises operations directly. When an application supplies a DNS host map, Jco automatically enables JSPI for every function in jco:node/dns@0.1.0. The Preview 2 WIT calls therefore remain synchronous from the guest’s perspective without blocking Node’s event loop or creating a worker for each query. Because any component export may transitively call DNS, mapped components expose promise-returning exports that JavaScript hosts must await. Callback APIs retain callback delivery in the guest, and the promises subpath shares server and default-result-order state with the main module.

Resolver.cancel() throws ERR_JCO_UNSUPPORTED_NODE_API. The synchronous WIT boundary does not expose an outstanding c-ares request that a later guest call could cancel. The provider boundary otherwise remains Node-independent, leaving room for a future browser implementation.