moonvar

// The fixed widths, either way round, reading nothing it was not given.
let buf = Buffer()
@fixed.write_u32(buf, 0x12345678)
@fixed.write_u16(buf, 0x1234, order=Little)
let wire = buf.to_bytes()
assert_eq(wire, b"\x12\x34\x56\x78\x34\x12")
assert_eq(@fixed.read_u32(wire[:]), Some(305419896))
assert_eq(@fixed.read_u32(wire[:], at=10), None) // the view is shorter

// A number the format gives no width to: the fewest octets that hold it.
assert_eq(@fixed.encode(1337UL), b"\x05\x39")
assert_eq(@fixed.decode(b"\x05\x39"[:]), Some(1337))

// One number, in each protocol's own spelling.
assert_eq(@quic.encode(1337UL), b"\x45\x39")
assert_eq(@prefix.encode(1337, prefix=5), b"\x1f\x9a\x0a")
assert_eq(@leb128.encode(1337UL), b"\xb9\x0a")
assert_eq(@lenenc.encode(1337UL), b"\xfc\x39\x05")

// Signed values have two spellings, and they are not the same octets: protobuf folds the
// sign onto an unsigned value, DWARF and WebAssembly keep it in the last group.
assert_eq(@leb128.encode(@leb128.zigzag(-2L)), b"\x03")
assert_eq(@leb128.encode_signed(-2L), b"\x7e")

#Packages

#The same number, five ways

#Reading is half of it

• Nothing read past the end. Every fixed reader checks the width it needs and answers None when the view is short. The variable-length readers raise a Refused that names the fault: Truncated, or past the ceiling the encoding allows.
• A width without writing it. Every package has size(): how many octets a value takes, without producing them. A length field has to be measured before the payload it describes is written.
• Signed values stay short. leb128.zigzag folds a negative onto an unsigned value, so -1 costs one octet rather than ten. leb128.encode_signed is the other spelling: the sign in the last group, which is what DWARF and WebAssembly write.
• A value with no width agreed. fixed.encode writes the fewest octets that hold a number and fixed.decode reads a run as one — the pair for a length the format does not put a width in front of.

#Install

moon add moonbitstack/moonvar

import {
  "moonbitstack/moonvar/quic",
}

#Examples

moon run src/examples/tour
moon run src/examples/frame

#Licence