Feature Flags

aioduct uses feature flags to control runtime, TLS, and serialization dependencies. The default feature set is empty — you must enable at least one runtime.

Available Features

Feature	Dependencies	Stability	Description
`tokio`	tokio	Stable	Tokio async runtime
`smol`	smol, async-io, futures-io	Stable	Smol async runtime
`compio`	compio-runtime, async-io	Experimental	Compio runtime (io_uring / IOCP)
`wasm`	wasm-bindgen, web-sys, js-sys	Experimental	Compatible browser/worker Fetch runtime
`wasi-p2`	wasi	Experimental	WASI Preview 2 guest HTTP client
`wasmtime`	wasmtime, wasmtime-wasi, wasmtime-wasi-http	Experimental	Wasmtime host-side WASI HTTP adapter
`rustls`	rustls, webpki-roots, rustls-pemfile	Stable	TLS backend via rustls; requires exactly one rustls provider
`rustls-ring`	rustls ring provider	Stable	Ring crypto provider for rustls
`rustls-aws-lc-rs`	rustls AWS-LC provider	Stable	AWS-LC crypto provider for rustls
`rustls-native-roots`	rustls-native-certs	Stable	Use OS certificate store with either rustls provider
`json`	serde, serde_json, serde_urlencoded	Stable	JSON request/response helpers
`charset`	encoding_rs, mime	Stable	Charset decoding for response text
`gzip`	flate2	Stable	Gzip response decompression
`deflate`	flate2	Stable	Deflate response decompression
`brotli`	brotli	Stable	Brotli response decompression
`zstd`	zstd	Stable	Zstd response decompression
`blocking`	selected native runtime	Stable	Synchronous wrapper for Tokio, smol, or compio clients
`hickory-dns`	hickory-resolver, tokio	Stable	DNS resolution via hickory
`doh`	hickory-resolver (https)	Stable	DNS-over-HTTPS (implies `hickory-dns`)
`dot`	hickory-resolver (tls)	Stable	DNS-over-TLS (implies `hickory-dns`)
`tower`	tower-service, tower-layer	Stable	Tower Service/Layer integration
`tracing`	tracing	Stable	Tracing spans for HTTP requests
`otel`	opentelemetry, opentelemetry-http	Stable	OpenTelemetry middleware
`precise-timing`	none	Stable	Use `std::time::Instant` instead of the default coarse clock for sub-millisecond observer and timeout measurements
`http3`	h3, quinn	Experimental	HTTP/3 transport; currently requires Tokio, `rustls`, and one rustls provider

Use rustls for the HTTPS backend and choose exactly one rustls crypto provider: rustls-ring or rustls-aws-lc-rs. The backend and provider flags are separate so future TLS backends, such as a reserved native-tls/OpenSSL backend, can compose with higher-level HTTP features without changing the rustls provider model. rustls-native-roots is provider-neutral: it enables the rustls backend and composes with either provider.

Compile Error Without Runtime

If no runtime feature is selected, aioduct emits a compile error:

error: aioduct: enable at least one runtime feature: tokio, smol, compio, wasm, or wasi-p2

Common Feature Combinations

# HTTP only, tokio runtime
aioduct = { version = "0.2.5", features = ["tokio"] }

# HTTPS + JSON, tokio runtime
aioduct = { version = "0.2.5", features = ["tokio", "rustls", "rustls-ring", "json"] }

# HTTPS with AWS-LC, tokio runtime
aioduct = { version = "0.2.5", features = ["tokio", "rustls", "rustls-aws-lc-rs"] }

# HTTPS with AWS-LC and OS native roots
aioduct = { version = "0.2.5", features = ["tokio", "rustls-native-roots", "rustls-aws-lc-rs"] }

# HTTP only, smol runtime
aioduct = { version = "0.2.5", features = ["smol"] }

# HTTPS, smol runtime
aioduct = { version = "0.2.5", features = ["smol", "rustls", "rustls-ring"] }

# HTTP only, compio runtime (experimental)
aioduct = { version = "0.2.5", features = ["compio"] }

# HTTPS + JSON + compression, tokio runtime
aioduct = { version = "0.2.5", features = ["tokio", "rustls", "rustls-ring", "json", "gzip", "brotli", "zstd", "deflate"] }

# Blocking client (select one native runtime; Tokio shown)
aioduct = { version = "0.2.5", features = ["tokio", "rustls", "rustls-ring", "blocking"] }

# With tracing and OpenTelemetry
aioduct = { version = "0.2.5", features = ["tokio", "rustls", "rustls-ring", "tracing", "otel"] }

# With tower integration
aioduct = { version = "0.2.5", features = ["tokio", "rustls", "rustls-ring", "tower"] }

# Hickory DNS resolver
aioduct = { version = "0.2.5", features = ["tokio", "rustls", "rustls-ring", "hickory-dns"] }

# DNS-over-HTTPS
aioduct = { version = "0.2.5", features = ["tokio", "rustls", "rustls-ring", "doh"] }

# DNS-over-TLS
aioduct = { version = "0.2.5", features = ["tokio", "rustls", "rustls-ring", "dot"] }

# HTTP/3 with ring
aioduct = { version = "0.2.5", features = ["tokio", "http3", "rustls", "rustls-ring"] }

# HTTP/3 with AWS-LC
aioduct = { version = "0.2.5", features = ["tokio", "http3", "rustls", "rustls-aws-lc-rs"] }

Wasmtime Host Adapter

Wasmtime host integration is first-party under aioduct::wasmtime. Enable the wasmtime feature together with the host runtime and TLS provider:

# Wasmtime host adapter with tokio + rustls/ring
aioduct = { version = "0.2.5", features = ["wasmtime", "tokio", "rustls", "rustls-ring"] }

# Wasmtime host adapter with smol + rustls/ring
aioduct = { version = "0.2.5", features = ["wasmtime", "smol", "rustls", "rustls-ring"] }

# Wasmtime host adapter with compio + rustls/ring
aioduct = { version = "0.2.5", features = ["wasmtime", "compio", "rustls", "rustls-ring"] }

aioduct::wasmtime accepts native RuntimePoll transports such as TokioClient and SmolClient. It also provides CompioHostTransport, which owns a local-runtime worker bridge for CompioClient builders. It does not enable browser wasm, because browser Fetch has no Wasmtime host hook. See examples/wasmtime-host for runnable host examples for each native forwarding transport.

Core Dependencies (Always Included)

These are pulled in regardless of feature flags:

hyper 1.x — HTTP/1.1 and HTTP/2 protocol engine
http — Standard HTTP types (Method, StatusCode, HeaderMap, etc.)
http-body-util — Body combinators for hyper
bytes — Zero-copy byte buffers
pin-project-lite — Safe pin projections
thiserror — Error derive macros
base64 — Base64 encoding for basic auth
percent-encoding — URL percent-encoding for query params and forms

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