From 65905b84ebde74f8561f4de965d343696b131e0e Mon Sep 17 00:00:00 2001
From: Martin Hutchinson <mhutchinson@gmail.com>
Date: Wed, 18 Mar 2026 13:27:44 +0000
Subject: [PATCH] [SumDB] Make MapFn even faster

Reduced amount of memory allocated and avoid expensive operations unless needed.

Before:
```
go test -bench=BenchmarkMapFn -benchmem

goos: linux
goarch: amd64
pkg: github.com/transparency-dev/incubator/vindex/cmd/sumdbindex
cpu: Intel(R) Xeon(R) CPU @ 2.20GHz
BenchmarkMapFn-24    	  354208	      3442 ns/op	    1041 B/op	      12 allocs/op
PASS
ok  	github.com/transparency-dev/incubator/vindex/cmd/sumdbindex	1.309s
```

After:
```
go test -bench=BenchmarkMapFn -benchmem

goos: linux
goarch: amd64
pkg: github.com/transparency-dev/incubator/vindex/cmd/sumdbindex
cpu: Intel(R) Xeon(R) CPU @ 2.20GHz
BenchmarkMapFn-24    	  698796	      1738 ns/op	     130 B/op	       4 allocs/op
PASS
ok  	github.com/transparency-dev/incubator/vindex/cmd/sumdbindex	1.302s
```
---
 vindex/cmd/sumdbindex/main.go      | 29 +++++++++++++++++------------
 vindex/cmd/sumdbindex/main_test.go | 10 ++++++++++
 2 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/vindex/cmd/sumdbindex/main.go b/vindex/cmd/sumdbindex/main.go
index 4b6162e..603c528 100644
--- a/vindex/cmd/sumdbindex/main.go
+++ b/vindex/cmd/sumdbindex/main.go
@@ -18,6 +18,7 @@
 package main
 
 import (
+	"bytes"
 	"context"
 	"crypto/sha256"
 	"errors"
@@ -30,7 +31,6 @@ import (
 	"os/signal"
 	"path"
 
-	"strings"
 	"syscall"
 	"time"
 
@@ -219,21 +219,26 @@ func getKeyFile(path string) (string, error) {
 }
 
 func mapFn(data []byte) [][32]byte {
-	lines := strings.Split(string(data), "\n")
-	if len(lines) < 2 {
-		panic(fmt.Errorf("expected 2 lines but got %d", len(lines)))
+	modEnd := bytes.IndexByte(data, ' ')
+	if modEnd == -1 {
+		panic("invalid line 0: no space")
 	}
 
-	line0Parts := strings.Fields(lines[0])
-	if len(line0Parts) < 2 {
-		panic(fmt.Errorf("expected at least 2 parts in line 0 but got %d", len(line0Parts)))
+	verStart := modEnd + 1
+	verLen := bytes.IndexByte(data[verStart:], ' ')
+	if verLen == -1 {
+		panic("invalid line 0: no second space")
 	}
-	line0Module, line0Version := line0Parts[0], line0Parts[1]
+	verBytes := data[verStart : verStart+verLen]
 
-	if module.IsPseudoVersion(line0Version) {
-		// Drop any emphemeral builds
-		return nil
+	// Fast path: pseudo-versions always contain a dash.
+	if bytes.IndexByte(verBytes, '-') != -1 {
+		// Only allocate a string and call IsPseudoVersion if a dash is present.
+		if module.IsPseudoVersion(string(verBytes)) {
+			// Drop any ephemeral builds
+			return nil
+		}
 	}
 
-	return [][32]byte{sha256.Sum256([]byte(line0Module))}
+	return [][32]byte{sha256.Sum256(data[:modEnd])}
 }
diff --git a/vindex/cmd/sumdbindex/main_test.go b/vindex/cmd/sumdbindex/main_test.go
index c4a2997..5ebedb9 100644
--- a/vindex/cmd/sumdbindex/main_test.go
+++ b/vindex/cmd/sumdbindex/main_test.go
@@ -14,6 +14,9 @@ var pseudoVersionLeaf = []byte(`github.com/transparency-dev/tessera v0.0.0-20240
 github.com/transparency-dev/tessera v0.0.0-20240222160914-411202e8d356/go.mod h1:T/Ym+5H1e28Qv6iMzT3w=
 `)
 
+var releaseCandidateLeaf = []byte(`github.1485827954.workers.dev/aws/amazon-vpc-cni-k8s v1.7.0-rc1 h1:f1nwnVa7t5Ftd+BPef/V/Y8XxT1Sdiif0cdIo/8R9i0=
+github.1485827954.workers.dev/aws/amazon-vpc-cni-k8s v1.7.0-rc1/go.mod h1:CuxOEw4CmUSK44owsXWkZ6Njh0G/gfboQoLl9hn1Voo=`)
+
 func TestMapFn(t *testing.T) {
 	for _, tc := range []struct {
 		name string
@@ -30,6 +33,11 @@ func TestMapFn(t *testing.T) {
 			leaf: pseudoVersionLeaf,
 			want: nil,
 		},
+		{
+			name: "release_candidate",
+			leaf: releaseCandidateLeaf,
+			want: [][32]byte{sha256.Sum256([]byte("github.1485827954.workers.dev/aws/amazon-vpc-cni-k8s"))},
+		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			got := mapFn(tc.leaf)
@@ -48,5 +56,7 @@ func TestMapFn(t *testing.T) {
 func BenchmarkMapFn(b *testing.B) {
 	for b.Loop() {
 		mapFn(exampleLeaf)
+		mapFn(pseudoVersionLeaf)
+		mapFn(releaseCandidateLeaf)
 	}
 }