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quic: Avoid bytes for VariableLengthInteger

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Allocation of bytes objects due to parsing and usage of pack and the
invocation of to_uint() showed significantly in profiles (3.3% sample
matches). Switch to a more procedural approach to avoid the allocation
overhead.

From zeek/spicy-quic/pull/13
This commit is contained in:
Arne Welzel 2023-10-12 11:15:09 +02:00
parent e33528ec5b
commit 994d66185c
1 changed files with 5 additions and 9 deletions
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14
src/analyzer/protocol/quic/QUIC.spicy
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@ -140,17 +140,13 @@ type VariableLengthInteger = unit {
#
# https://datatracker.ietf.org/doc/rfc9000/
# Section 16 and Appendix A
#
first_byte: bytes &size=1 {
local uint8_val = uint8($$.to_uint(spicy::ByteOrder::Big));
self.bytes_to_parse = 2**((0xC0 & uint8_val) >> 6);
# Re-pack without most significant two bits for later use.
self.first_byte = pack(0x3f & uint8_val, spicy::ByteOrder::Big);
: uint8 {
self.bytes_to_parse = 2**((0xC0 & $$) >> 6);
self.result = $$ & 0x3F;
}
remaining_bytes: bytes &size=self.bytes_to_parse - 1;
on %done {
self.result = (self.first_byte + self.remaining_bytes).to_uint(spicy::ByteOrder::Big);
: uint8[self.bytes_to_parse - 1] if (self.bytes_to_parse > 1) foreach {
self.result = (self.result << 8) | $$;
}
};