Add special support for long string records

Author: Araneidae

softioc/builder.py

@@ -182,6 +182,34 @@ def WaveformOut(name, *value, **fields):
     return PythonDevice.waveform_out(name, **fields)
 
 
+def _long_string(value, fields):
+    if 'initial_value' in fields:
+        assert not value, 'Can\'t specify initial value twice!'
+        value = (fields.pop('initial_value'),)
+
+    if value:
+        # If a value is specified it should be the *only* non keyword
+        # argument.
+        value, = value
+        fields['initial_value'] = value
+        length = len(value)
+    else:
+        # No value specified, so require length and datatype to be specified.
+        length = fields.pop('length')
+
+    fields['NELM'] = length
+    fields['FTVL'] = 'UCHAR'
+
+
+def longStringIn(name, *value, **fields):
+    _long_string(value, fields)
+    return _in_record('long_stringin', name, **fields)
+
+def longStringOut(name, *value, **fields):
+    _long_string(value, fields)
+    return PythonDevice.long_stringout(name, **fields)
+
+
 
 # ----------------------------------------------------------------------------
 #  Support routines for builder
@@ -227,6 +255,7 @@ def UnsetDevice():
     'stringIn', 'stringOut',
     'mbbIn',    'mbbOut',
     'Waveform', 'WaveformOut',
+    'longStringIn', 'longStringOut',
     'Action',
     # Other builder support functions
     'LoadDatabase',

softioc/device.dbd

@@ -10,5 +10,7 @@ device(waveform,  INST_IO, devPython_waveform,  "Python")
 device(mbbi,      INST_IO, devPython_mbbi,      "Python")
 device(mbbo,      INST_IO, devPython_mbbo,      "Python")
 
-# Waveforms as "out" devices need special treatment.
+# A variety of specialised versions of waveform need special treatment.
 device(waveform,  INST_IO, devPython_waveform_out, "PythonWfOut")
+device(waveform,  INST_IO, devPython_long_stringin, "PythonLongStringIn")
+device(waveform,  INST_IO, devPython_long_stringout, "PythonLongStringOut")

softioc/device.py

@@ -247,12 +247,11 @@ class EpicsString:
     _dbf_type_ = fields.DBF_STRING
 
     def _value_to_epics(self, value):
-        if isinstance(value, str):
-            value = value.encode()
         # It's a little odd: we can't simply construct a value from the byte
-        # string, but we can update the array in an existing value
+        # string, but we can update the array in an existing value.
+        # Value being written must be a string.
         result = self._ctype_()
-        result.value = value
+        result.value = value.encode()
         return result
 
     def _epics_to_value(self, epics):
@@ -345,17 +344,6 @@ def _compare_values(self, value, other):
         return numpy.all(value == other)
 
     def _value_to_epics(self, value):
-        '''Handles strings and bytearrays as values for Waveforms. Returns the
-        string converted to a numpy array.'''
-        if isinstance(value, str):
-            value = value.encode(errors = 'replace')
-        if isinstance(value, bytes):
-            # Convert a string into an array of characters.  This will produce
-            # the correct behaviour when treating a character array as a string.
-            # Note that the trailing null is needed to work around problems with
-            # some clients. Note this also exists in builder.py's _waveform().
-            value = numpy.frombuffer(value + b'\0', dtype = numpy.uint8)
-
         # Ensure we always convert incoming value into numpy array, regardless
         # of whether the record has been initialised or not
         value = numpy.require(value, dtype = self.dtype)
@@ -390,5 +378,39 @@ class waveform_out(WaveformBase, ProcessDeviceSupportOut):
     _device_name_ = 'devPython_waveform_out'
 
 
+# Convert string into numpy array of char
+def encode_string(value, length = None):
+    value = value.encode(errors = 'replace')
+    # Convert a string into an array of characters.  This will produce
+    # the correct behaviour when treating a character array as a string.
+    # Note that the trailing null is needed to work around problems with
+    # some clients.
+    value = numpy.frombuffer(value + b'\0', dtype = numpy.uint8)
+
+    # Truncate value to fit
+    if length:
+        value = value[:length]
+    return value
+
+
+class LongStringBase(WaveformBase):
+    dtype = numpy.dtype('uint8')
+
+    def _value_to_epics(self, value):
+        return encode_string(value, getattr(self, '_nelm', None))
+
+    def _epics_to_value(self, value):
+        return value.decode(errors = 'replace')
+
+
+class long_stringin(LongStringBase, ProcessDeviceSupportIn):
+    _record_type_ = 'waveform'
+    _device_name_ = 'devPython_long_stringin'
+
+class long_stringout(LongStringBase, ProcessDeviceSupportOut):
+    _record_type_ = 'waveform'
+    _device_name_ = 'devPython_long_stringout'
+
+
 # Ensure the .dbd file is loaded.
 dbLoadDatabase('device.dbd', os.path.dirname(__file__), None)

softioc/pythonSoftIoc.py

@@ -92,6 +92,12 @@ def __init_class__(cls):
         cls.waveform_out = cls.makeRecord(
             epicsdbbuilder.records.waveform, device.waveform_out,
             'PythonWfOut')
+        cls.long_stringin = cls.makeRecord(
+            epicsdbbuilder.records.waveform, device.long_stringin,
+            'PythonLongStringIn')
+        cls.long_stringout = cls.makeRecord(
+            epicsdbbuilder.records.waveform, device.long_stringout,
+            'PythonLongStringOut')
 
     class makeRecord:
         def __init__(self, builder, record, dtyp = 'Python'):

tests/expected_records.db

@@ -53,7 +53,7 @@ record(longout, "TS-DI-TEST-01:LONGOUT")
 record(waveform, "TS-DI-TEST-01:LONGSTRING")
 {
     field(DISP, "1")
-    field(DTYP, "Python")
+    field(DTYP, "PythonLongStringIn")
     field(FTVL, "UCHAR")
     field(INP,  "@TS-DI-TEST-01:LONGSTRING")
     field(NELM, "256")

tests/sim_records.py

@@ -57,7 +57,7 @@ def update_sin_wf(value):
 t_waveform_out = WaveformOut('WAVEFORM_OUT', wf, on_update = on_update)
 t_waveform_in2 = Waveform('WAVEFORM2', length = 10)
 
-t_longstring_in = Waveform('LONGSTRING', length = 256, datatype = numpy.uint8)
+t_longstring_in = longStringIn('LONGSTRING', length = 256)
 
 
 def Update():