feat: add Node SSR Nginx upstream switching

internal/hostnginx/nodessr.go

@@ -0,0 +1,134 @@
+package hostnginx
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"strconv"
+	"strings"
+)
+
+const (
+	nodeSsrManagedBegin = "# yms-update managed nodeSsr upstream begin"
+	nodeSsrManagedEnd   = "# yms-update managed nodeSsr upstream end"
+	nodeSsrPort18910    = 18910
+	nodeSsrPort28910    = 28910
+)
+
+// ActiveNodeSsrPort 从 Node SSR 受控 upstream 区块读取唯一活动槽位端口。
+func ActiveNodeSsrPort(content []byte) (int, error) {
+	block, err := parseNodeSsrBlock(content)
+	if err != nil {
+		return 0, err
+	}
+	active := 0
+	for _, server := range block.servers {
+		if !server.commented {
+			if active != 0 {
+				return 0, errors.New("managed Nginx upstream contains more than one active Node SSR server")
+			}
+			active = server.port
+		}
+	}
+	if active == 0 {
+		return 0, errors.New("managed Nginx upstream does not contain an active Node SSR server")
+	}
+	return active, nil
+}
+
+// RenderNodeSsrPort 只切换 Node SSR 受控 upstream 区块中的活动服务器行。
+func RenderNodeSsrPort(content []byte, activePort int) ([]byte, error) {
+	if activePort != nodeSsrPort18910 && activePort != nodeSsrPort28910 {
+		return nil, fmt.Errorf("host Nginx Node SSR port must be 18910 or 28910: %d", activePort)
+	}
+	block, err := parseNodeSsrBlock(content)
+	if err != nil {
+		return nil, err
+	}
+	for _, server := range block.servers {
+		indentLength := len(block.lines[server.line]) - len(strings.TrimLeft(block.lines[server.line], " \t"))
+		indent := block.lines[server.line][:indentLength]
+		serverText := strings.TrimPrefix(strings.TrimSpace(block.lines[server.line]), "# ")
+		if server.port == activePort {
+			block.lines[server.line] = indent + serverText
+		} else {
+			block.lines[server.line] = indent + "# " + serverText
+		}
+	}
+	rendered := []byte(strings.Join(block.lines, "\n"))
+	if _, err := ActiveNodeSsrPort(rendered); err != nil {
+		return nil, fmt.Errorf("validate rendered host Nginx Node SSR upstream: %w", err)
+	}
+	return rendered, nil
+}
+
+type nodeSsrBlock struct {
+	lines   []string
+	servers []nodeSsrServer
+}
+
+type nodeSsrServer struct {
+	line      int
+	port      int
+	commented bool
+}
+
+func parseNodeSsrBlock(content []byte) (nodeSsrBlock, error) {
+	if len(content) == 0 {
+		return nodeSsrBlock{}, errors.New("host Nginx configuration is empty")
+	}
+	lines := strings.Split(string(content), "\n")
+	begin, end := -1, -1
+	for index, line := range lines {
+		switch strings.TrimSpace(line) {
+		case nodeSsrManagedBegin:
+			if begin != -1 {
+				return nodeSsrBlock{}, errors.New("host Nginx configuration contains duplicate Node SSR upstream begin markers")
+			}
+			begin = index
+		case nodeSsrManagedEnd:
+			if end != -1 {
+				return nodeSsrBlock{}, errors.New("host Nginx configuration contains duplicate Node SSR upstream end markers")
+			}
+			end = index
+		}
+	}
+	if begin == -1 || end <= begin {
+		return nodeSsrBlock{}, errors.New("host Nginx configuration requires one ordered Node SSR upstream marker pair")
+	}
+	servers := make([]nodeSsrServer, 0, 2)
+	seen := make(map[int]struct{}, 2)
+	for index := begin + 1; index < end; index++ {
+		trimmed := strings.TrimSpace(lines[index])
+		commented := strings.HasPrefix(trimmed, "# server ")
+		active := strings.HasPrefix(trimmed, "server ")
+		if !commented && !active {
+			if trimmed != "" {
+				return nodeSsrBlock{}, fmt.Errorf("managed Node SSR upstream contains an unexpected line: %q", trimmed)
+			}
+			continue
+		}
+		serverText := strings.TrimPrefix(trimmed, "# ")
+		fields := strings.Fields(serverText)
+		if len(fields) != 4 || fields[0] != "server" || fields[2] != "max_fails=1" || fields[3] != "fail_timeout=2s;" {
+			return nodeSsrBlock{}, fmt.Errorf("managed Node SSR upstream server line has an unsupported format: %q", trimmed)
+		}
+		_, portText, err := net.SplitHostPort(fields[1])
+		if err != nil {
+			return nodeSsrBlock{}, fmt.Errorf("parse managed Node SSR upstream address %q: %w", fields[1], err)
+		}
+		port, err := strconv.Atoi(portText)
+		if err != nil || (port != nodeSsrPort18910 && port != nodeSsrPort28910) {
+			return nodeSsrBlock{}, fmt.Errorf("managed Node SSR upstream contains unsupported port %q", portText)
+		}
+		if _, exists := seen[port]; exists {
+			return nodeSsrBlock{}, fmt.Errorf("managed Node SSR upstream contains duplicate port %d", port)
+		}
+		seen[port] = struct{}{}
+		servers = append(servers, nodeSsrServer{line: index, port: port, commented: commented})
+	}
+	if len(servers) != 2 {
+		return nodeSsrBlock{}, fmt.Errorf("managed Node SSR upstream must contain exactly two servers, got %d", len(servers))
+	}
+	return nodeSsrBlock{lines: lines, servers: servers}, nil
+}