module ietf-restconf-server {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-restconf-server";
  prefix rcs;

  import ietf-yang-types {
    prefix yang;
    reference
      "RFC 6991: Common YANG Data Types";
  }

  import ietf-inet-types {
    prefix inet;
    reference
      "RFC 6991: Common YANG Data Types";
  }

  import ietf-x509-cert-to-name {
    prefix x509c2n;
    reference
      "RFC 7407: A YANG Data Model for SNMP Configuration";
  }

  import ietf-tcp-client {
    prefix tcpc;
    reference
      "RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
  }

  import ietf-tcp-server {
    prefix tcps;
    reference
      "RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
  }

  import ietf-tls-server {
    prefix tlss;
    reference
      "RFC FFFF: YANG Groupings for TLS Clients and TLS Servers";
  }

  import ietf-http-server {
    prefix https;
    reference
      "RFC GGGG: YANG Groupings for HTTP Clients and HTTP Servers";
  }

  organization
    "IETF NETCONF (Network Configuration) Working Group";

  contact
    "WG Web:   https://datatracker.ietf.org/wg/netconf
     WG List:  NETCONF WG list <mailto:netconf@ietf.org>
     Author:   Kent Watsen <mailto:kent+ietf@watsen.net>";

  description
    "This module contains a collection of YANG definitions
     for configuring RESTCONF servers.

     Copyright (c) 2024 IETF Trust and the persons identified
     as authors of the code. All rights reserved.

     Redistribution and use in source and binary forms, with
     or without modification, is permitted pursuant to, and
     subject to the license terms contained in, the Revised
     BSD License set forth in Section 4.c of the IETF Trust's
     Legal Provisions Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC IIII
     (https://www.rfc-editor.org/info/rfcIIII); see the RFC
     itself for full legal notices.

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
     'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
     'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
     are to be interpreted as described in BCP 14 (RFC 2119)
     (RFC 8174) when, and only when, they appear in all
     capitals, as shown here.";

  revision 2024-02-08 {
    description
      "Initial version";
    reference
      "RFC IIII: RESTCONF Client and Server Models";
  }

  // Features

  feature http-listen {
    description
      "The 'http-listen' feature indicates that the RESTCONF server
       supports opening a port to listen for incoming RESTCONF over
       TCP client connections, whereby the TLS connections are
       terminated by an external system.";
    reference
      "RFC 8040: RESTCONF Protocol";
  }

  feature https-listen {
    description
      "The 'https-listen' feature indicates that the RESTCONF server
       supports opening a port to listen for incoming RESTCONF over
       TLS client connections, whereby the TLS connections are
       terminated by the server itself.";
    reference
      "RFC 8040: RESTCONF Protocol";
  }

  feature https-call-home {
    description
      "The 'https-call-home' feature indicates that the RESTCONF
       server supports initiating connections to RESTCONF clients.";
    reference
      "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
  }

  feature central-restconf-server-supported {
   description
      "The 'central-restconf-server-supported' feature indicates
       that the server supports the top-level 'restconf-server'
       node.

       This feature is needed as some servers may want to use
       features defined in this module, which requires this
       module to be implemented, without having to support
       the top-level 'restconf-server' node.";
  }

  // Groupings

  grouping restconf-server-grouping {
    description
      "A reusable grouping for configuring a RESTCONF server
       without any consideration for how underlying transport
       sessions are established.

       Note that this grouping uses a fairly typical descendant
       node name such that a stack of 'uses' statements will
       have name conflicts.  It is intended that the consuming
       data model will resolve the issue by wrapping the 'uses'
       statement in a container called, e.g.,
       'restconf-server-parameters'.  This model purposely does
       not do this itself so as to provide maximum flexibility
       to consuming models.";

    container client-identity-mappings {
      description
        "Specifies mappings through which RESTCONF client X.509
         certificates are used to determine a RESTCONF username.
         If no matching and valid cert-to-name list entry can be
         found, then the RESTCONF server MUST close the connection,
         and MUST NOT accept RESTCONF messages over it.";
      reference
        "RFC 7407: A YANG Data Model for SNMP Configuration.";
      uses x509c2n:cert-to-name {
        refine "cert-to-name/fingerprint" {
          mandatory false;
          description
            "A 'fingerprint' value does not need to be specified
             when the 'cert-to-name' mapping is independent of
             fingerprint matching.  A 'cert-to-name' having no
             fingerprint value will match any client certificate
             and therefore should only be present at the end of
             the user-ordered 'cert-to-name' list.";
        }
      }
    }
  }

  grouping restconf-server-listen-stack-grouping {
    description
      "A reusable grouping for configuring a RESTCONF server
       'listen' protocol stack for listening on a single port.";
    choice transport {
      mandatory true;
      description
        "Selects between available transports.";
      case http {
        if-feature "http-listen";
        container http {
          description
            "Configures RESTCONF server stack assuming that
             TLS-termination is handled externally.

             How a RESTCONF-server identifies RESTCONF-clients
             authenticating using a TLS-level client-certificate
             with external TLS termination is out of scope of
             this document.";
          container external-endpoint {
            presence
              "Identifies that an external endpoint has been
               configured.  This statement is present so the
               mandatory descendant nodes do not imply that
               this node must be configured.";
            description
              "Identifies contact information for the external
               system that terminates connections before passing
               them through to this server (e.g., a network address
               translator or a load balancer).  These values have
               no effect on the local operation of this server,
               but may be used by the application when needing to
               inform other systems how to contact this server.";
            leaf address {
              type inet:host;
              mandatory true;
              description
                "The IP address or hostname of the external
                 system that terminates incoming RESTCONF
                 client connections before forwarding them
                 to this server.";
            }
            leaf port {
              type inet:port-number;
              default "443";
              description
                "The port number that the external system listens
                 on for incoming RESTCONF client connections that
                 are forwarded to this server.  The default HTTPS
                 port (443) is used, as expected for a RESTCONF
                 connection.";
            }
          }
          container tcp-server-parameters {
            description
              "TCP-level server parameters to listen for
               RESTCONF over HTTP connections.";
            uses tcps:tcp-server-grouping {
              refine "local-port" {
                default "80";
                description
                  "The RESTCONF server will listen on the IANA-
                   assigned well-known port value for 'http'
                   (80) if no value is specified.";
              }
            }
          }
          container http-server-parameters {
            description
              "HTTP-level server parameters to listen
               for RESTCONF over HTTP connections.";
            uses https:http-server-grouping;
          }
          container restconf-server-parameters {
            description
              "RESTCONF-level server parameters to listen
               for RESTCONF over HTTP connections.";
            uses rcs:restconf-server-grouping;
          }
        }
      }
      case https {
        if-feature "https-listen";
        container https {
          description
            "Configures RESTCONF server stack assuming that
             TLS-termination is handled internally (i.e.,
             not by a TLS-terminator in front of the RESTCONF
             server).";
          container tcp-server-parameters {
            description
              "TCP-level server parameters to listen for
               RESTCONF over HTTPS connections.";
            uses tcps:tcp-server-grouping {
              refine "local-port" {
                default "443";
                description
                  "The RESTCONF server will listen on the IANA-
                   assigned well-known port value for 'https'
                   (443) if no value is specified.";
              }
            }
          }
          container tls-server-parameters {
            description
              "TLS-level server parameters to listen
               for RESTCONF over HTTPS connections.";
            uses tlss:tls-server-grouping;
          }
          container http-server-parameters {
            description
              "HTTP-level server parameters to listen
               for RESTCONF over HTTPS connections.";
            uses https:http-server-grouping;
          }
          container restconf-server-parameters {
            description
              "RESTCONF-level server parameters to listen
               for RESTCONF over HTTPS connections.";
            uses rcs:restconf-server-grouping;
          }
        }
      }
    }
  }

  grouping restconf-server-callhome-stack-grouping {
    description
      "A reusable grouping for configuring a RESTCONF server
       'call-home' protocol stack, for a single outbound
       connection.";
    choice transport {
      mandatory true;
      description
        "Selects between available transports.";
      case https {
        if-feature "https-call-home";
        container https {
          description
            "Configures RESTCONF server stack assuming that
             TLS-termination is handled internally.";
          container tcp-client-parameters {
            description
              "TCP-level client parameters to initiate a
               RESTCONF over HTTPS Call Home connection.";
            uses tcpc:tcp-client-grouping {
              refine "remote-port" {
                default "4336";
                description
                  "The RESTCONF server will attempt to
                   connect to the IANA-assigned well-known
                   port for 'restconf-ch-tls' (4336) if no
                   value is specified.";
              }
            }
          }
          container tls-server-parameters {
            description
              "TLS-level server parameters to initiate a
               RESTCONF over HTTPS Call Home connection.";
            uses tlss:tls-server-grouping;
          }
          container http-server-parameters {
            description
              "HTTP-level server parameters to initiate a
               RESTCONF over HTTPS Call Home connection.";
            uses https:http-server-grouping;
          }
          container restconf-server-parameters {
            description
              "RESTCONF-level server parameters to initiate
               a RESTCONF over HTTPS Call Home connection.";
            uses rcs:restconf-server-grouping;
          }
        }
      }
    }
  }

  grouping restconf-server-app-grouping {
    description
      "A reusable grouping for configuring a RESTCONF server
       application that supports both 'listen' and 'call-home'
       protocol stacks for a multiplicity of connections.";
    container listen {
      if-feature "http-listen or https-listen";
      presence
        "Identifies that the server has been configured to
         listen for incoming client connections.  This statement
         is present so the mandatory descendant nodes do not
         imply that this node must be configured.";
      description
        "Configures the RESTCONF server to listen for RESTCONF
         client connections.";
      container endpoints {
        description
          "Container for a list of endpoints.";
        list endpoint {
          key "name";
          min-elements 1;
          description
            "List of endpoints to listen for RESTCONF connections.";
          leaf name {
            type string;
            description
              "An arbitrary name for the RESTCONF listen endpoint.";
          }
          uses restconf-server-listen-stack-grouping;
        }
      }
    }
    container call-home {
      if-feature "https-call-home";
      presence
        "Identifies that the server has been configured to initiate
         call home connections.  This statement is present so the
         mandatory descendant nodes do not imply that this node
         must be configured.";
      description
        "Configures the RESTCONF server to initiate the underlying
         transport connection to RESTCONF clients.";
      list restconf-client {
        key "name";
        min-elements 1;
        description
          "List of RESTCONF clients the RESTCONF server is to
           maintain simultaneous call-home connections with.";
        leaf name {
          type string;
          description
            "An arbitrary name for the remote RESTCONF client.";
        }
        container endpoints {
          description
            "Container for the list of endpoints.";
          list endpoint {
            key "name";
            min-elements 1;
            ordered-by user;
            description
              "User-ordered list of endpoints for this RESTCONF
               client.  Defining more than one enables high-
               availability.";
            leaf name {
              type string;
              description
                "An arbitrary name for this endpoint.";
            }
            uses restconf-server-callhome-stack-grouping;
          }
        }
        container connection-type {
          description
            "Indicates the RESTCONF server's preference for how the
             RESTCONF connection is maintained.";
          choice connection-type {
            mandatory true;
            description
              "Selects between available connection types.";
            case persistent-connection {
              container persistent {
                presence
                  "Indicates that a persistent connection is to be
                   maintained.";
                description
                  "Maintain a persistent connection to the RESTCONF
                   client. If the connection goes down, immediately
                   start trying to reconnect to the RESTCONF client,
                   using the reconnection strategy.

                   This connection type minimizes any RESTCONF
                   client to RESTCONF server data-transfer delay,
                   albeit at the expense of holding resources
                   longer.";
              }
            }
            case periodic-connection {
              container periodic {
                presence
                  "Indicates that a periodic connection is to be
                   maintained.";
                description
                  "Periodically connect to the RESTCONF client.

                   This connection type decreases resource
                   utilization, albeit with increased delay in
                   RESTCONF client to RESTCONF server interactions.

                   The RESTCONF client SHOULD gracefully close
                   the underlying TLS connection upon completing
                   planned activities.  If the underlying TLS
                   connection is not closed gracefully, the
                   RESTCONF server MUST immediately attempt
                   to reestablish the connection.

                   Connections are established at the same start
                   time regardless how long the previous connection
                   stayed open.

                   In the case that the previous connection is
                   still active (i.e., the RESTCONF client has not
                   closed it yet), establishing a new connection
                   is NOT RECOMMENDED.";

                leaf period {
                  type uint16;
                  units "minutes";
                  default "60";
                  description
                    "Duration of time between periodic connections.";
                }
                leaf anchor-time {
                  type yang:date-and-time {
                    // constrained to minute-level granularity
                    pattern '[0-9]{4}-(1[0-2]|0[1-9])-(0[1-9]|[1-2]'
                          + '[0-9]|3[0-1])T(0[0-9]|1[0-9]|2[0-3]):['
                          + '0-5][0-9]:00(Z|[\+\-]((1[0-3]|0[0-9]):'
                          + '([0-5][0-9])|14:00))?';
                  }
                  description
                    "Designates a timestamp before or after which a
                     series of periodic connections are determined.
                     The periodic connections occur at a whole
                     multiple interval from the anchor time.

                     If an 'anchor-time' is not provided, then the
                     server may implicitly set it to the time when
                     this configuraton is applied (e.g., on boot).

                     For example, for an anchor time is 15 minutes
                     past midnight and a period interval of 24 hours,
                     then a periodic connection will occur 15 minutes
                     past midnight everyday.";
                }
                leaf idle-timeout {
                  type uint16;
                  units "seconds";
                  default "180"; // three minutes
                  description
                    "Specifies the maximum number of seconds that
                     the underlying TCP session may remain idle.
                     A TCP session will be dropped if it is idle
                     for an interval longer than this number of
                     seconds.  If set to zero, then the server
                     will never drop a session because it is idle.";
                }
              }
            }
          }
        }
        container reconnect-strategy {
          description
            "The reconnection strategy directs how a RESTCONF server
             reconnects to a RESTCONF client after discovering its
             connection to the client has dropped, even if due to a
             reboot.  The RESTCONF server starts with the specified
             endpoint and tries to connect to it max-attempts times
             before trying the next endpoint in the list (round
             robin).";
          leaf start-with {
            type enumeration {
              enum first-listed {
                description
                  "Indicates that reconnections should start with
                   the first endpoint listed.";
              }
              enum last-connected {
                description
                  "Indicates that reconnections should start with
                   the endpoint last connected to.  If no previous
                   connection has ever been established, then the
                   first endpoint configured is used.   RESTCONF
                   servers SHOULD be able to remember the last
                   endpoint connected to across reboots.";
              }
              enum random-selection {
                description
                  "Indicates that reconnections should start with
                   a random endpoint.";
              }
            }
            default "first-listed";
            description
              "Specifies which of the RESTCONF client's endpoints
               the RESTCONF server should start with when trying
               to connect to the RESTCONF client.";
          }
          leaf max-wait {
            type uint16 {
              range "1..max";
            }
            units "seconds";
            default "5";
            description
              "Specifies the amount of time in seconds after which,
               if the connection is not established, an endpoint
               connection attempt is considered unsuccessful.";
          }
          leaf max-attempts {
            type uint8 {
              range "1..max";
            }
            default "3";
            description
              "Specifies the number times the RESTCONF server tries
               to connect to a specific endpoint before moving on to
               the next endpoint in the list (round robin).";
          }
        }
      } // restconf-client
    } // call-home
  } // restconf-server-app-grouping

  // Protocol accessible node for servers that implement this module.
  container restconf-server {
    if-feature central-restconf-server-supported;
    uses restconf-server-app-grouping;
    description
      "Top-level container for RESTCONF server configuration.";
  }
}