feat(proxmox): add tail endpoint and enhance journalctl with multi-service support

Add new `/proxmox/tail` API endpoint for streaming file contents from Proxmox
nodes and LXC containers via WebSocket. Extend journalctl endpoint to support
filtering by multiple services simultaneously.

Changes:
- Add `GET /proxmox/tail` endpoint supporting node-level and LXC container file tailing
- Change `service` parameter from string to array in journalctl endpoints
- Add input validation (`checkValidInput`) to prevent command injection
- Refactor command formatting with proper shell quoting

Security: All command inputs are validated for dangerous characters before

internal/proxmox/command_common.go

@@ -0,0 +1,59 @@
+package proxmox
+
+import (
+	"fmt"
+	"strings"
+)
+
+// checkValidInput checks if the input contains invalid characters.
+//
+// The characters are: & | $ ; ' " ` $( ${ < >
+// These characters are used in the command line to escape the input or to expand variables.
+// We need to check if the input contains these characters and return an error if it does.
+// This is to prevent command injection.
+func checkValidInput(input string) error {
+	if strings.ContainsAny(input, "&|$;'\"`<>") {
+		return fmt.Errorf("input contains invalid characters: %q", input)
+	}
+	if strings.Contains(input, "$(") {
+		return fmt.Errorf("input contains $(: %q", input)
+	}
+	if strings.Contains(input, "${") {
+		return fmt.Errorf("input contains ${: %q", input)
+	}
+	return nil
+}
+
+func formatTail(files []string, limit int) (string, error) {
+	for _, file := range files {
+		if err := checkValidInput(file); err != nil {
+			return "", err
+		}
+	}
+	var command strings.Builder
+	command.WriteString("tail -f -q --retry ")
+	for _, file := range files {
+		fmt.Fprintf(&command, " %q ", file)
+	}
+	if limit > 0 {
+		fmt.Fprintf(&command, " -n %d", limit)
+	}
+	return command.String(), nil
+}
+
+func formatJournalctl(services []string, limit int) (string, error) {
+	for _, service := range services {
+		if err := checkValidInput(service); err != nil {
+			return "", err
+		}
+	}
+	var command strings.Builder
+	command.WriteString("journalctl -f")
+	for _, service := range services {
+		fmt.Fprintf(&command, " -u %q ", service)
+	}
+	if limit > 0 {
+		fmt.Fprintf(&command, " -n %d", limit)
+	}
+	return command.String(), nil
+}

internal/proxmox/lxc_command.go

@@ -39,15 +39,23 @@ func (n *Node) LXCCommand(ctx context.Context, vmid int, command string) (io.Rea
 
 // LXCJournalctl streams journalctl output for the given service.
 //
-// If service is not empty, it will be used to filter the output by service.
+// If services are not empty, it will be used to filter the output by service.
 // If limit is greater than 0, it will be used to limit the number of lines of output.
-func (n *Node) LXCJournalctl(ctx context.Context, vmid int, service string, limit int) (io.ReadCloser, error) {
-	command := "journalctl -f"
-	if service != "" {
-		command = fmt.Sprintf("journalctl -u %q -f", service)
-	}
-	if limit > 0 {
-		command = fmt.Sprintf("%s -n %d", command, limit)
+func (n *Node) LXCJournalctl(ctx context.Context, vmid int, services []string, limit int) (io.ReadCloser, error) {
+	command, err := formatJournalctl(services, limit)
+	if err != nil {
+		return nil, err
+	}
+	return n.LXCCommand(ctx, vmid, command)
+}
+
+// LXCTail streams tail output for the given file.
+//
+// If limit is greater than 0, it will be used to limit the number of lines of output.
+func (n *Node) LXCTail(ctx context.Context, vmid int, files []string, limit int) (io.ReadCloser, error) {
+	command, err := formatTail(files, limit)
+	if err != nil {
+		return nil, err
 	}
 	return n.LXCCommand(ctx, vmid, command)
 }

internal/proxmox/node.go

@@ -14,6 +14,7 @@ type NodeConfig struct {
 	VMID     *int     `json:"vmid"` // unset: auto discover; explicit 0: node-level route; >0: lxc/qemu resource route
 	VMName   string   `json:"vmname,omitempty"`
 	Services []string `json:"services,omitempty" aliases:"service"`
+	Files    []string `json:"files,omitempty" aliases:"file"`
 } // @name ProxmoxNodeConfig
 
 type Node struct {

internal/proxmox/node_command.go

@@ -120,13 +120,25 @@ func (n *Node) NodeCommand(ctx context.Context, command string) (io.ReadCloser,
 	return pr, nil
 }
 
-func (n *Node) NodeJournalctl(ctx context.Context, service string, limit int) (io.ReadCloser, error) {
-	command := "journalctl -f"
-	if service != "" {
-		command = fmt.Sprintf("journalctl -u %q -f", service)
-	}
-	if limit > 0 {
-		command = fmt.Sprintf("%s -n %d", command, limit)
+// NodeJournalctl streams journalctl output for the given service.
+//
+// If services are not empty, it will be used to filter the output by services.
+// If limit is greater than 0, it will be used to limit the number of lines of output.
+func (n *Node) NodeJournalctl(ctx context.Context, services []string, limit int) (io.ReadCloser, error) {
+	command, err := formatJournalctl(services, limit)
+	if err != nil {
+		return nil, err
+	}
+	return n.NodeCommand(ctx, command)
+}
+
+// NodeTail streams tail output for the given file.
+//
+// If limit is greater than 0, it will be used to limit the number of lines of output.
+func (n *Node) NodeTail(ctx context.Context, files []string, limit int) (io.ReadCloser, error) {
+	command, err := formatTail(files, limit)
+	if err != nil {
+		return nil, err
 	}
 	return n.NodeCommand(ctx, command)
 }