Module sys/dns

DNS resolution operations.

Provides async DNS resolution wrapping getaddrinfo/getnameinfo, plus accessors for iterating the linked list of addrinfo results.

All async operations return IoFuture which resolves to:

• 0: success
• a DNS_ERR_* code below: the runtime classifies the resolver's EAI_* answer into one stable negative code per kind, the same on every platform (EAI_* values differ per platform, and Linux's are negative and collide with errno). The codes sit above every errno, so they never read as one (plans/ASYNC_IO_API_AUDIT.md A4).

Stability

unstable — a raw wrapper over getaddrinfo/getnameinfo whose results are a linked list walked through accessor functions and whose errors are DNS_ERR_* codes, not IoError. std/net/dns's lookup_host is the typed face and is what callers want.

It is also where a real open question lives rather than just a rough edge: a plaintext connect uses the FIRST address this returns and does not fall back to the next on failure, so a host whose IPv6 route is dead fails instead of reaching its IPv4 address. There is no happy-eyeballs, and the resolver's order decides. Fixing that will change what the typed layer asks of this one.