[8.10](backport #36518) packetbeat/protos/http: don't panic when host is empty

CHANGELOG.next.asciidoc

@@ -133,6 +133,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 
 *Packetbeat*
 
+- Fix panic in HTTP protocol parsing when host header has empty host part. {issue}36497[36497] {issue}36518[36518]
 
 *Winlogbeat*
 

packetbeat/protos/http/http.go

@@ -20,6 +20,7 @@ package http
 import (
 	"bytes"
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"net"
 	"net/url"
@@ -735,20 +736,29 @@ func parseCookieValue(raw string) string {
 }
 
 func extractHostHeader(header string) (host string, port int) {
-	if len(header) == 0 || net.ParseIP(header) != nil {
+	if header == "" || net.ParseIP(header) != nil {
 		return header, port
 	}
-	// Split :port trailer
-	if pos := strings.LastIndexByte(header, ':'); pos != -1 {
-		if num, err := strconv.Atoi(header[pos+1:]); err == nil && num > 0 && num < 65536 {
-			header, port = header[:pos], num
+	host, ps, err := net.SplitHostPort(header)
+	if err != nil {
+		var addrError *net.AddrError
+		if errors.As(err, &addrError) && addrError.Err == "missing port in address" {
+			return trimSquareBracket(header), port
 		}
 	}
-	// Remove square bracket boxing of IPv6 address.
-	if last := len(header) - 1; header[0] == '[' && header[last] == ']' && net.ParseIP(header[1:last]) != nil {
-		header = header[1:last]
+	pi, err := strconv.ParseInt(ps, 10, 16)
+	if err != nil || pi == 0 {
+		return header, port
+	}
+	return trimSquareBracket(host), int(pi)
+}
+
+func trimSquareBracket(s string) string {
+	s, ok := strings.CutPrefix(s, "[")
+	if !ok {
+		return s
 	}
-	return header, port
+	return strings.TrimSuffix(s, "]")
 }
 
 func (http *httpPlugin) hideHeaders(m *message) {

packetbeat/protos/http/http_test.go

@@ -1901,6 +1901,36 @@ func TestHttpParser_Extension(t *testing.T) {
 	}
 }
 
+func TestExtractHostHeader(t *testing.T) {
+	tests := []struct {
+		header   string
+		wantHost string
+		wantPort int
+	}{
+		{header: "", wantHost: "", wantPort: 0},
+		{header: "localhost:0", wantHost: "localhost:0", wantPort: 0},
+		{header: "127.0.0.1:0", wantHost: "127.0.0.1:0", wantPort: 0},
+		{header: "[::]:0", wantHost: "[::]:0", wantPort: 0},
+		{header: "localhost", wantHost: "localhost", wantPort: 0},
+		{header: "localhost:9001", wantHost: "localhost", wantPort: 9001},
+		{header: "localhost:9000000", wantHost: "localhost:9000000", wantPort: 0},
+		{header: "127.0.0.1:9001", wantHost: "127.0.0.1", wantPort: 9001},
+		{header: "127.0.0.1", wantHost: "127.0.0.1", wantPort: 0},
+		{header: "[::]", wantHost: "::", wantPort: 0},
+		{header: ":0", wantHost: ":0", wantPort: 0},
+		{header: ":9001", wantHost: "", wantPort: 9001},
+	}
+	for _, test := range tests {
+		host, port := extractHostHeader(test.header)
+		if host != test.wantHost {
+			t.Errorf("unexpected host for %q: got:%q want:%q", test.header, host, test.wantHost)
+		}
+		if port != test.wantPort {
+			t.Errorf("unexpected port for %q: got:%d want:%d", test.header, port, test.wantPort)
+		}
+	}
+}
+
 func benchmarkHTTPMessage(b *testing.B, data []byte) {
 	http := httpModForTests(nil)
 	parser := newParser(&http.parserConfig)