def _create(self, message_h, **fields):
'''
Render the supplied message values to the bytearray.
'''
#
# ensure that the fields match the schema
if message_h not in self.gruel_protocol:
raise Exception("No message exists matching [%s]"%message_h)
message_stencil = self.gruel_protocol.get_message_stencil(
message_h=message_h)
set_sch = set(message_stencil.field_names())
set_got = set(fields.keys())
if set_sch != set_got:
raise Exception("Inconsistent fields/want:%s/got:%s"%(
str(set_sch), str(set_got)))
#
# render
offset = 0
for (field_h, field_dt) in message_stencil.items():
field_value = fields[field_h]
# struct docs: https://docs.python.org/3.1/library/struct.html
#log('** o%s press %s %s'%(offset, field_h, field_value))
if field_dt.name == 'u1':
bsize = 1
struct.pack_into(
'!B', # fmt. B is unsigned char
self.arr, # buffer
offset, # offset
field_value)
offset += bsize
elif field_dt.name == 'u2':
bsize = 2
struct.pack_into(
'!H', # fmt. H is unsigned short
self.arr, # buffer
offset, # offset
field_value)
offset += bsize
elif field_dt.name == 'vs':
s_len = len(field_value)
# first we do a two-byte length, network-endian
bsize = 2
struct.pack_into(
'!H', # fmt. H is unsigned short
self.arr, # buffer
offset, # offset
s_len)
offset += bsize
# Now we put that string into the array. Emphasis: these
# strings are not zero-terminated.
struct.pack_into(
'%ss'%s_len, # fmt.
self.arr, # buffer
offset, # offset
bytes(field_value, 'utf8'))
offset += s_len
else:
raise Exception("Datatype not recognised/handled: %s"%(
field_dt.name))
return self.arr
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