Make the home page's AS name search work (closes #151)

The AS Name Search card on the home page said the search was coming soon.
It now asks the new GET /api/v1/search/as?q=<text> and lists the matches
as links to their AS pages. asinfo.Search ignores case, returns the first
matches up to a limit in AS number order, and counts all matches. An
empty q answers 400.

When the database has no record of an AS, its page and /api/v1/as/{asn}
take its handle and description from asinfo and still list its prefixes.
They answer 404 only for an AS with no record, no asinfo entry and no
prefix. AS 0 means no known origin: it always answers 404, and the search
never lists it.

Model: opus-5-5

pkg/asinfo/asinfo.go

@@ -2,10 +2,13 @@ package asinfo
 
 import (
 	"bytes"
+	"cmp"
 	"compress/gzip"
 	_ "embed"
 	"encoding/json"
 	"io"
+	"slices"
+	"strings"
 	"sync"
 )
 
@@ -23,6 +26,17 @@ type Info struct {
 type Registry struct {
 	mu    sync.RWMutex
 	byASN map[int]*Info
+	// searchEntries holds every entry in AS number order, for Search.
+	searchEntries []searchEntry
+}
+
+// searchEntry is an entry with its handle and description in lower case. They
+// are put in lower case once, when the data loads, so that Search only
+// compares.
+type searchEntry struct {
+	info             *Info
+	lowerHandle      string
+	lowerDescription string
 }
 
 var (
@@ -59,9 +73,21 @@ func initRegistry() {
 		panic("failed to unmarshal embedded AS data: " + err.Error())
 	}
 
+	slices.SortFunc(asInfos, func(a, b Info) int {
+		return cmp.Compare(a.ASN, b.ASN)
+	})
+
+	defaultRegistry.searchEntries = make([]searchEntry, 0, len(asInfos))
+
 	for i := range asInfos {
 		info := &asInfos[i]
 		defaultRegistry.byASN[info.ASN] = info
+		defaultRegistry.searchEntries = append(defaultRegistry.searchEntries,
+			searchEntry{
+				info:             info,
+				lowerHandle:      strings.ToLower(info.Handle),
+				lowerDescription: strings.ToLower(info.Description),
+			})
 	}
 }
 
@@ -129,36 +155,36 @@ func All() []Info {
 	return result
 }
 
-// Search searches for AS entries where the handle or description contains the query
-// This is a simple case-sensitive substring search
-func Search(query string) []Info {
+// Search finds the AS entries whose handle or description contains query,
+// ignoring case. It returns the first limit of them in AS number order, and the
+// number of entries that match. An empty query matches nothing.
+func Search(query string, limit int) ([]Info, int) {
 	once.Do(initRegistry)
 
+	if query == "" {
+		return nil, 0
+	}
+
+	query = strings.ToLower(query)
+
 	defaultRegistry.mu.RLock()
 	defer defaultRegistry.mu.RUnlock()
 
-	var results []Info
+	var (
+		results []Info
+		total   int
+	)
 
-	for _, info := range defaultRegistry.byASN {
-		if contains(info.Handle, query) || contains(info.Description, query) {
-			results = append(results, *info)
+	for _, entry := range defaultRegistry.searchEntries {
+		if strings.Contains(entry.lowerHandle, query) ||
+			strings.Contains(entry.lowerDescription, query) {
+			if total < limit {
+				results = append(results, *entry.info)
+			}
+
+			total++
 		}
 	}
 
-	return results
-}
-
-// contains is a simple substring search
-func contains(s, substr string) bool {
-	return len(substr) > 0 && len(s) >= len(substr) && containsImpl(s, substr)
-}
-
-func containsImpl(s, substr string) bool {
-	for i := 0; i <= len(s)-len(substr); i++ {
-		if s[i:i+len(substr)] == substr {
-			return true
-		}
-	}
-
-	return false
+	return results, total
 }