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⚡ Bolt: Zero-alloc optimization for proc/net decodeAddr #192

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⚡ Bolt: Zero-alloc optimization for proc/net decodeAddr #192

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3 changes: 3 additions & 0 deletions .jules/bolt.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
## 2025-02-01 - Zero-Alloc Patterns
**Learning:** Parsing IP addresses from strings/bytes (like in `/proc/net/tcp`) using `make([]byte, ...)` creates significant pressure on the GC in hot paths. Using stack-allocated arrays `[16]byte` and decoding directly into them eliminates these allocations entirely.
**Action:** Always prefer `[N]byte` over `make([]byte, N)` for small, fixed-size buffers in parsing loops, especially for IP addresses and ports.
23 changes: 13 additions & 10 deletions proc/net.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,6 @@ import (
"bytes"
"encoding/binary"
"encoding/hex"
"net"
"os"

"inet.af/netaddr"
Expand Down Expand Up @@ -93,24 +92,28 @@ func decodeAddr(src []byte) netaddr.IPPort {
if col == -1 || (col != 8 && col != 32) {
return netaddr.IPPort{}
}
ip := make([]byte, col/2)
if _, err := hex.Decode(ip, src[:col]); err != nil {

// Parsing to stack-allocated buffers to avoid heap allocations
var ip [16]byte
if _, err := hex.Decode(ip[:col/2], src[:col]); err != nil {
return netaddr.IPPort{}
}
port := make([]byte, 2)
if _, err := hex.Decode(port, src[col+1:]); err != nil {
var portBuf [2]byte
if _, err := hex.Decode(portBuf[:], src[col+1:]); err != nil {
return netaddr.IPPort{}
}

var v uint32
for i := 0; i < len(ip); i += 4 {
for i := 0; i < col/2; i += 4 {
v = binary.BigEndian.Uint32(ip[i : i+4])
binary.LittleEndian.PutUint32(ip[i:i+4], v)
}
Comment on lines 106 to 110

@gemini-code-assist gemini-code-assist Bot Feb 1, 2026

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medium

For clarity and potentially a minor performance improvement, you can perform the byte-swapping directly. This makes the 4-byte reversal explicit and removes the need for the temporary variable v.

Suggested change
var v uint32
for i := 0; i < len(ip); i += 4 {
for i := 0; i < col/2; i += 4 {
v = binary.BigEndian.Uint32(ip[i : i+4])
binary.LittleEndian.PutUint32(ip[i:i+4], v)
}
// The IP address in /proc/net/tcp* is in little-endian format for each 32-bit word.
// We need to swap the byte order of each word to get the standard big-endian representation.
for i := 0; i < col/2; i += 4 {
ip[i], ip[i+1], ip[i+2], ip[i+3] = ip[i+3], ip[i+2], ip[i+1], ip[i]
}


ipp, ok := netaddr.FromStdIP(net.IP(ip))
if !ok {
return netaddr.IPPort{}
var ipp netaddr.IP
if col == 8 {
ipp = netaddr.IPv4(ip[0], ip[1], ip[2], ip[3])
} else {
ipp = netaddr.IPFrom16(ip)
}
return netaddr.IPPortFrom(ipp, binary.BigEndian.Uint16(port))
return netaddr.IPPortFrom(ipp, binary.BigEndian.Uint16(portBuf[:]))
}
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