reqwless-linux#

A demonstration of a no_std reqwless http downloader for linux

Usage#

cargo run -- http://example.com

This prints the HTTP response body to stdout.

To enable baseline HTTPS support:

cargo run --features https -- https://example.com

Notes#

no_std + no_main binary using Linux libc syscalls
Uses reqwless with default-features = false
Default feature set is backend-posix-libc + dns-getaddrinfo
backend-rustix is available as an alternate transport backend
DNS mode is selected independently via dns-getaddrinfo or dns-ip-only
Alternate DNS mode dns-ip-only rejects hostnames and only accepts literal IP hosts
HTTPS is optional via --features https and requires an RNG backend
HTTPS currently uses TlsVerify::None (insecure baseline)
RNG backends: rng-dummy (fixed seed), rng-dev-urandom (reads /dev/urandom), rng-getrandom (syscall)
Uses fixed-size stack buffers for request/response and output chunks
Performs best-effort low-allocation operation (no String/Vec in app code)

Feature examples#

# Default build: posix-libc backend + getaddrinfo DNS mode
cargo run -- http://example.com

# HTTPS with dev-urandom RNG (recommended for production)
cargo run --no-default-features --features backend-posix-libc,dns-getaddrinfo,https,rng-dev-urandom -- https://example.com

# HTTPS with getrandom syscall RNG
cargo run --no-default-features --features backend-posix-libc,dns-getaddrinfo,https,rng-getrandom -- https://example.com

# HTTPS with dummy RNG (testing only, insecure)
cargo run --no-default-features --features backend-posix-libc,dns-getaddrinfo,https,rng-dummy -- https://example.com

# Minimal DNS mode (literal IP hosts only)
cargo run --no-default-features --features backend-posix-libc,dns-ip-only -- http://93.184.216.34

# Rustix backend with getaddrinfo DNS mode
cargo run --no-default-features --features backend-rustix,dns-getaddrinfo -- http://example.com

# Rustix backend with IP-only DNS mode
cargo run --no-default-features --features backend-rustix,dns-ip-only -- http://93.184.216.34

Validation#

Use the composite xtask validation flow for reproducible checks.

cargo run -p xtask -- validate

The xtask validate subcommand group is self-documented in CLI help and can be explored as needed.

Benchmarking#

To benchmark RNG backends with hyperfine:

# Install hyperfine first
cargo install hyperfine

# Run benchmarks
cargo run -p xtask -- benchmark

This builds three binaries with different RNG backends and compares their performance:

rng-dummy: ~0.3 ns (constant, no actual randomness)
rng-dev-urandom: ~1.2 μs (file I/O)
rng-getrandom: ~0.24 μs (syscall, 5x faster)

Manual benchmark:

cargo run --release --bin bench-rng --no-default-features --features rng-getrandom -- 10000

Binary size comparison#

Release builds are tuned for binary size in Cargo.toml:

panic = "abort"
strip = true
opt-level = "s"
lto = true
codegen-units = 1

Nightly aggressive builds use additional optimizations:

RUSTFLAGS="-Zlocation-detail=none -Zfmt-debug=none -Zunstable-options -Cpanic=immediate-abort"
-Z build-std=std,panic_abort
-Z build-std-features=

HTTP builds#

Backend	DNS	Release	Nightly	Savings
posix-libc	getaddrinfo	43,440 B	41,288 B	-2,152 B (-5.0%)
posix-libc	dns-ip-only	43,952 B	41,864 B	-2,088 B (-4.8%)
rustix	getaddrinfo	43,512 B	41,104 B	-2,408 B (-5.5%)
rustix	dns-ip-only	43,784 B	41,792 B	-1,992 B (-4.5%)

HTTPS builds#

Backend	DNS	RNG	Release	Nightly	Savings
posix-libc	getaddrinfo	dummy	296,824 B	296,112 B	-712 B (-0.2%)
posix-libc	getaddrinfo	dev-urandom	297,192 B	296,584 B	-608 B (-0.2%)
posix-libc	getaddrinfo	getrandom	297,072 B	296,464 B	-608 B (-0.2%)
posix-libc	dns-ip-only	dummy	297,304 B	296,832 B	-472 B (-0.2%)
posix-libc	dns-ip-only	dev-urandom	297,688 B	297,224 B	-464 B (-0.2%)
posix-libc	dns-ip-only	getrandom	297,552 B	297,168 B	-384 B (-0.1%)
rustix	getaddrinfo	dummy	296,592 B	295,768 B	-824 B (-0.3%)
rustix	getaddrinfo	dev-urandom	297,000 B	296,312 B	-688 B (-0.2%)
rustix	getaddrinfo	getrandom	296,824 B	296,120 B	-704 B (-0.2%)
rustix	dns-ip-only	dummy	297,344 B	296,600 B	-744 B (-0.3%)
rustix	dns-ip-only	dev-urandom	297,800 B	297,048 B	-752 B (-0.3%)
rustix	dns-ip-only	getrandom	297,592 B	296,920 B	-672 B (-0.2%)

Building for size#

For standard release builds:

cargo build --release --no-default-features --features <features>

For nightly aggressive size optimizations:

cargo run -p xtask -- nightly-size -- --no-default-features --features <features>

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