api: enforce vla is last and fixed string type

Enforce that variable length fields are the last element of API messages.

Add a 'fixed' version of string type, since dealing with
multiple variable length strings turned out too painful
for the C language bindings.

The string type is now:
{
  string name[64]; // NUL terminated C-string. Essentially decays to u8 name[64]
  string name[];   // Variable length string with embedded len field (vl_api_string_t)
};

The latter notation could be made available to other types as well.
e.g.
{
  vl_api_address_t addresses[];
}
instead of

{
  u32 n_addr;
  vl_api_address_t addresses[n_addr];
};

Type: fix
Change-Id: I18fa17ef47227633752ab50453e8d20a652a9f9b
Signed-off-by: Ole Troan <ot@cisco.com>
(cherry picked from commit e5ff5a36dd126ee57dca4e0b03da2f7704e0a4f5)
Signed-off-by: Ole Troan <ot@cisco.com>

2 files changed, 70 insertions, 16 deletions

diff --git a/src/vpp-api/python/vpp_papi/tests/test_vpp_serializer.py b/src/vpp-api/python/vpp_papi/tests/test_vpp_serializer.py
index bddaa9e00c2..6ca8e6c4ff3 100755
--- a/src/vpp-api/python/vpp_papi/tests/test_vpp_serializer.py
+++ b/src/vpp-api/python/vpp_papi/tests/test_vpp_serializer.py
@@ -11,11 +11,47 @@ from ipaddress import *
 
 
 class TestLimits(unittest.TestCase):
+    def test_string(self):
+        fixed_string = VPPType('fixed_string',
+                               [['string', 'name', 16]])
+
+        b = fixed_string.pack({'name': 'foobar'})
+        self.assertEqual(len(b), 16)
+
+        # Ensure string is nul terminated
+        self.assertEqual(b.decode('ascii')[6], '\x00')
+
+        nt, size = fixed_string.unpack(b)
+        self.assertEqual(size, 16)
+        self.assertEqual(nt.name, 'foobar')
+
+        # Empty string
+        b = fixed_string.pack({'name': ''})
+        self.assertEqual(len(b), 16)
+        nt, size = fixed_string.unpack(b)
+        self.assertEqual(size, 16)
+        self.assertEqual(nt.name, '')
+
+        # String too long
+        with self.assertRaises(VPPSerializerValueError):
+            b = fixed_string.pack({'name': 'foobarfoobar1234'})
+
+        variable_string = VPPType('variable_string',
+                                  [['string', 'name', 0]])
+        b = variable_string.pack({'name': 'foobar'})
+        self.assertEqual(len(b), 4 + len('foobar'))
+
+        nt, size = variable_string.unpack(b)
+        self.assertEqual(size, 4 + len('foobar'))
+        self.assertEqual(nt.name, 'foobar')
+        self.assertEqual(len(nt.name), len('foobar'))
+
+
     def test_limit(self):
         limited_type = VPPType('limited_type_t',
-                               [['string', 'name', {'limit': 16}]])
+                               [['string', 'name', 0, {'limit': 16}]])
         unlimited_type = VPPType('limited_type_t',
-                                 [['string', 'name']])
+                                 [['string', 'name', 0]])
 
         b = limited_type.pack({'name': 'foobar'})
         self.assertEqual(len(b), 10)
diff --git a/src/vpp-api/python/vpp_papi/vpp_serializer.py b/src/vpp-api/python/vpp_papi/vpp_serializer.py
index 9ce0287592f..ec6a06bb3d5 100644
--- a/src/vpp-api/python/vpp_papi/vpp_serializer.py
+++ b/src/vpp-api/python/vpp_papi/vpp_serializer.py
@@ -105,27 +105,42 @@ class BaseTypes(object):
 
 
 class String(object):
-    def __init__(self, options):
-        self.name = 'string'
+    def __init__(self, name, num, options):
+        self.name = name
+        self.num = num
         self.size = 1
         self.length_field_packer = BaseTypes('u32')
-        self.limit = options['limit'] if 'limit' in options else None
+        self.limit = options['limit'] if 'limit' in options else num
+        self.fixed = True if num else False
+        if self.fixed and not self.limit:
+            raise VPPSerializerValueError(
+                "Invalid argument length for: {}, {} maximum {}".
+                format(list, len(list), self.limit))
 
     def pack(self, list, kwargs=None):
         if not list:
+            if self.fixed:
+                return b"\x00" * self.limit
             return self.length_field_packer.pack(0) + b""
-        if self.limit and len(list) > self.limit:
+        if self.limit and len(list) > self.limit - 1:
             raise VPPSerializerValueError(
                 "Invalid argument length for: {}, {} maximum {}".
-                format(list, len(list), self.limit))
-
-        return self.length_field_packer.pack(len(list)) + list.encode('utf8')
+                format(list, len(list), self.limit - 1))
+        if self.fixed:
+            return list.encode('ascii').ljust(self.limit, b'\x00')
+        return self.length_field_packer.pack(len(list)) + list.encode('ascii')
 
     def unpack(self, data, offset=0, result=None, ntc=False):
+        if self.fixed:
+            p = BaseTypes('u8', self.num)
+            s = p.unpack(data, offset)
+            s2 = s[0].split(b'\0', 1)[0]
+            return (s2.decode('ascii'), self.num)
+
         length, length_field_size = self.length_field_packer.unpack(data,
                                                                     offset)
         if length == 0:
-            return b'', 0
+            return '', 0
         p = BaseTypes('u8', length)
         x, size = p.unpack(data, offset + length_field_size)
         x2 = x.split(b'\0', 1)[0]
@@ -181,10 +196,6 @@ class FixedList_u8(object):
                 'Invalid array length for "{}" got {}'
                 ' expected {}'
                 .format(self.name, len(data[offset:]), self.num))
-        if self.field_type == 'string':
-            s = self.packer.unpack(data, offset)
-            s2 = s[0].split(b'\0', 1)[0]
-            return (s2.decode('utf-8'), self.num)
         return self.packer.unpack(data, offset)
 
 
@@ -473,12 +484,19 @@ class VPPType(object):
             if fieldlen == 3:  # list
                 list_elements = f[2]
                 if list_elements == 0:
-                    p = VLAList_legacy(f_name, f_type)
+                    if f_type == 'string':
+                        p = String(f_name, 0, self.options)
+                    else:
+                        p = VLAList_legacy(f_name, f_type)
                     self.packers.append(p)
-                elif f_type == 'u8' or f_type == 'string':
+                elif f_type == 'u8':
                     p = FixedList_u8(f_name, f_type, list_elements)
                     self.packers.append(p)
                     size += p.size
+                elif f_type == 'string':
+                    p = String(f_name, list_elements, self.options)
+                    self.packers.append(p)
+                    size += p.size
                 else:
                     p = FixedList(f_name, f_type, list_elements)
                     self.packers.append(p)