Add following APIs and test cases: (sonic-net#44)

*     Add following APIs and test cases:
    - get Yang module's prefix
    - get the datanode's data type
    - get the data type of the node that leafref node points to

* Add new libyang python APIs:
- get_leafref_path()
- get_leafref_type_schema()

src/sonic-yang-mgmt/sonic_yang.py

@@ -540,3 +540,122 @@ def find_data_dependencies (self, data_xpath):
             self.fail(e)
 
         return ref_list
+
+    """
+    get_module_prefix:   get the prefix of a Yang module
+    input:    name of the Yang module
+    output:   prefix of the Yang module
+    """
+    def get_module_prefix(self, module_name):
+        prefix = ""
+        try:
+            module = self.get_module(module_name)
+        except Exception as e:
+            self.fail(e)
+            return prefix
+        else:
+            return module.prefix()
+
+    """
+    str_to_type:   map string to type of node
+    input:    string
+    output:   type
+    """
+    def str_to_type (self, type_str):
+           mapped_type = {
+                "LY_TYPE_DER":ly.LY_TYPE_DER,
+                "LY_TYPE_BINARY":ly.LY_TYPE_BINARY,
+                "LY_TYPE_BITS":ly.LY_TYPE_BITS,
+                "LY_TYPE_BOOL":ly.LY_TYPE_BOOL,
+                "LY_TYPE_DEC64":ly.LY_TYPE_DEC64,
+                "LY_TYPE_EMPTY":ly.LY_TYPE_EMPTY,
+                "LY_TYPE_ENUM":ly.LY_TYPE_ENUM,
+                "LY_TYPE_IDENT":ly.LY_TYPE_IDENT,
+                "LY_TYPE_INST":ly.LY_TYPE_INST,
+                "LY_TYPE_LEAFREF":ly.LY_TYPE_LEAFREF,
+                "LY_TYPE_STRING":ly.LY_TYPE_STRING,
+                "LY_TYPE_UNION":ly.LY_TYPE_UNION,
+                "LY_TYPE_INT8":ly.LY_TYPE_INT8,
+                "LY_TYPE_UINT8":ly.LY_TYPE_UINT8,
+                "LY_TYPE_INT16":ly.LY_TYPE_INT16,
+                "LY_TYPE_UINT16":ly.LY_TYPE_UINT16,
+                "LY_TYPE_INT32":ly.LY_TYPE_INT32,
+                "LY_TYPE_UINT32":ly.LY_TYPE_UINT32,
+                "LY_TYPE_INT64":ly.LY_TYPE_INT64,
+                "LY_TYPE_UINT64":ly.LY_TYPE_UINT64,
+                "LY_TYPE_UNKNOWN":ly.LY_TYPE_UNKNOWN
+           }
+
+           if type_str not in mapped_type:
+               return ly.LY_TYPE_UNKNOWN
+
+           return mapped_type[type_str]
+
+    def get_data_type (self, schema_xpath):
+        try:
+            schema_node = self.find_schema_node(schema_xpath)
+        except Exception as e:
+            print("get_data_type(): Failed to find schema node from xpath: {}".format(schema_xpath))
+            self.fail(e)
+            return None
+
+        if (schema_node is not None):
+           return schema_node.subtype().type().base()
+
+        return ly.LY_TYPE_UNKNOWN
+
+    """
+    get_leafref_type:   find the type of node that leafref references to
+    input:    data_xpath - xpath of a data node
+    output:   type of the node this leafref references to
+    """
+    def get_leafref_type (self, data_xpath):
+        data_node = self.find_data_node(data_xpath)
+        if (data_node is not None):
+            subtype = data_node.subtype()
+            if (subtype is not None):
+                if data_node.schema().subtype().type().base() != ly.LY_TYPE_LEAFREF:
+                    print("get_leafref_type() node type for data xpath: {} is not LEAFREF".format(data_xpath))
+                    return ly.LY_TYPE_UNKNOWN
+                else:
+                    return subtype.value_type()
+
+        return ly.LY_TYPE_UNKNOWN
+
+    """
+    get_leafref_path():   find the leafref path
+    input:    schema_xpath - xpath of a schema node
+    output:   path value of the leafref node
+    """
+    def get_leafref_path (self, schema_xpath):
+        schema_node = self.find_schema_node(schema_xpath)
+        if (schema_node is not None):
+            subtype = schema_node.subtype()
+            if (subtype is not None):
+                if subtype.type().base() != ly.LY_TYPE_LEAFREF:
+                    return None
+                else:
+                    return subtype.type().info().lref().path()
+
+        return None
+
+    """
+    get_leafref_type_schema:   find the type of node that leafref references to
+    input:    schema_xpath - xpath of a schema node
+    output:   type of the node this leafref references to
+    """
+    def get_leafref_type_schema (self, schema_xpath):
+        schema_node = self.find_schema_node(schema_xpath)
+        if (schema_node is not None):
+            subtype = schema_node.subtype()
+            if (subtype is not None):
+                if subtype.type().base() != ly.LY_TYPE_LEAFREF:
+                    return None
+                else:
+                    leafref_path = subtype.type().info().lref().path()
+                    target = subtype.type().info().lref().target()
+                    target_path = target.path()
+                    target_type = self.get_data_type(target_path)
+                    return target_type
+
+        return None

src/sonic-yang-mgmt/tests/libyang-python-tests/test_SonicYang.json

@@ -99,5 +99,43 @@
            "parent":"/sonic-vlan:sonic-vlan/VLAN_INTERFACE/VLAN_INTERFACE_LIST[vlanid='111'][ip-prefix='10.1.1.64/26']"},
 	  {"xpath":"/sonic-port:sonic-port/PORT/PORT_LIST[port_name='Ethernet9']/speed",
            "parent":"/sonic-port:sonic-port/PORT/PORT_LIST[port_name='Ethernet9']"}
-  ]
+  ],
+  "prefix":[
+    {"module_name":"sonic-head", "module_prefix":"sonic-head"},
+    {"module_name":"sonic-port", "module_prefix":"port"},
+    {"module_name":"sonic-acl",  "module_prefix":"acl"},
+    {"module_name":"sonic-interface", "module_prefix":"intf"},
+    {"module_name":"sonic-portchannel", "module_prefix":"lag"},
+    {"module_name":"sonic-vlan", "module_prefix":"vlan"}
+    ],
+  "data_type":[
+    {"xpath":"/sonic-port:sonic-port/sonic-port:PORT/sonic-port:PORT_LIST/sonic-port:port_name", "data_type":"LY_TYPE_STRING"},
+    {"xpath":"/sonic-vlan:sonic-vlan/sonic-vlan:VLAN_INTERFACE/sonic-vlan:VLAN_INTERFACE_LIST/sonic-vlan:vlanid", "data_type":"LY_TYPE_LEAFREF"}
+    ],
+  "leafref_type":[
+    {"xpath":"/sonic-vlan:sonic-vlan/VLAN_INTERFACE/VLAN_INTERFACE_LIST[vlanid='111'][ip-prefix='2000:f500:45:6709::/64']/vlanid", "data_type":"LY_TYPE_UINT16"},
+    {"xpath":"/sonic-interface:sonic-interface/INTERFACE/INTERFACE_LIST[interface='Ethernet8'][ip-prefix='2000:f500:40:a749::/126']/interface", "data_type":"LY_TYPE_STRING"},
+    {"xpath":"/sonic-vlan:sonic-vlan/VLAN_MEMBER/VLAN_MEMBER_LIST[vlanid='111'][port='Ethernet0']/port", "data_type":"LY_TYPE_STRING"},
+    {"xpath":"/sonic-vlan:sonic-vlan/VLAN_MEMBER/VLAN_MEMBER_LIST[vlanid='111'][port='Ethernet0']/vlanid", "data_type":"LY_TYPE_UINT16"}
+   ],
+  "leafref_type_schema":[
+    {"xpath":"/sonic-vlan:sonic-vlan/sonic-vlan:VLAN_INTERFACE/sonic-vlan:VLAN_INTERFACE_LIST/sonic-vlan:vlanid",
+     "data_type":"LY_TYPE_UINT16"},
+    {"xpath":"/sonic-interface:sonic-interface/sonic-interface:INTERFACE/sonic-interface:INTERFACE_LIST/sonic-interface:interface",
+     "data_type":"LY_TYPE_STRING"},
+    {"xpath":"/sonic-vlan:sonic-vlan/sonic-vlan:VLAN_MEMBER/sonic-vlan:VLAN_MEMBER_LIST/sonic-vlan:port",
+     "data_type":"LY_TYPE_STRING"},
+    {"xpath":"/sonic-vlan:sonic-vlan/sonic-vlan:VLAN_MEMBER/sonic-vlan:VLAN_MEMBER_LIST/sonic-vlan:vlanid",
+     "data_type":"LY_TYPE_UINT16"}
+   ],
+  "leafref_path":[
+    {"xpath":"/sonic-vlan:sonic-vlan/sonic-vlan:VLAN_INTERFACE/sonic-vlan:VLAN_INTERFACE_LIST/sonic-vlan:vlanid",
+     "leafref_path":"../../../VLAN/VLAN_LIST/vlanid"},
+    {"xpath":"/sonic-interface:sonic-interface/sonic-interface:INTERFACE/sonic-interface:INTERFACE_LIST/sonic-interface:interface",
+     "leafref_path":"/sonic-port:sonic-port/sonic-port:PORT/sonic-port:PORT_LIST/sonic-port:port_name"},
+    {"xpath":"/sonic-vlan:sonic-vlan/sonic-vlan:VLAN_MEMBER/sonic-vlan:VLAN_MEMBER_LIST/sonic-vlan:port",
+     "leafref_path":"/sonic-port:sonic-port/sonic-port:PORT/sonic-port:PORT_LIST/sonic-port:port_name"},
+    {"xpath":"/sonic-vlan:sonic-vlan/sonic-vlan:VLAN_MEMBER/sonic-vlan:VLAN_MEMBER_LIST/sonic-vlan:vlanid",
+     "leafref_path":"../../../VLAN/VLAN_LIST/vlanid"}
+   ]
 }

src/sonic-yang-mgmt/tests/libyang-python-tests/test_sonic_yang.py

@@ -214,6 +214,46 @@ def test_merge_data_tree(self, data, yang_s):
         yang_s.merge_data(data_merge_file, yang_dir)
         #yang_s.root.print_mem(ly.LYD_JSON, ly.LYP_FORMAT)
 
+    #test get module prefix
+    def test_get_module_prefix(self, yang_s, data):
+        for node in data['prefix']:
+            xpath = str(node['module_name'])
+            expected = node['module_prefix']
+            prefix = yang_s.get_module_prefix(xpath)
+            assert expected == prefix
+
+    #test get data type
+    def test_get_data_type(self, yang_s, data):
+        for node in data['data_type']:
+            xpath = str(node['xpath'])
+            expected = node['data_type']
+            expected_type = yang_s.str_to_type(expected)
+            data_type = yang_s.get_data_type(xpath)
+            assert expected_type == data_type
+
+    def test_get_leafref_type(self, yang_s, data):
+        for node in data['leafref_type']:
+            xpath = str(node['xpath'])
+            expected = node['data_type']
+            expected_type = yang_s.str_to_type(expected)
+            data_type = yang_s.get_leafref_type(xpath)
+            assert expected_type == data_type
+
+    def test_get_leafref_path(self, yang_s, data):
+        for node in data['leafref_path']:
+            xpath = str(node['xpath'])
+            expected_path = node['leafref_path']
+            path = yang_s.get_leafref_path(xpath)
+            assert expected_path == path
+
+    def test_get_leafref_type_schema(self, yang_s, data):
+        for node in data['leafref_type_schema']:
+            xpath = str(node['xpath'])
+            expected = node['data_type']
+            expected_type = yang_s.str_to_type(expected)
+            data_type = yang_s.get_leafref_type_schema(xpath)
+            assert expected_type == data_type
+
     def test_xlate_rev_xlate(self):
         # This Test is with Sonic YANG model, so create class from start
         # read the config