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Fix EpicsCATransport to pass length with initial_value for string records #262

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Merged
merged 1 commit into from
Nov 10, 2025
Merged

Fix EpicsCATransport to pass length with initial_value for string records #262

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3 changes: 3 additions & 0 deletions src/fastcs/datatypes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -128,6 +128,9 @@ def initial_value(self) -> bool:
class String(DataType[str]):
"""`DataType` mapping to builtin ``str``."""

length: int | None = None
"""Maximum length of string to display in transports"""

@property
def dtype(self) -> type[str]:
return str
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8 changes: 5 additions & 3 deletions src/fastcs/transport/epics/ca/util.py
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Expand Up @@ -32,7 +32,7 @@


EPICS_ALLOWED_DATATYPES = (Bool, DataType, Enum, Float, Int, String, Waveform)
EPICS_WAVEFORM_LENGTH = 256
DEFAULT_STRING_WAVEFORM_LENGTH = 256

DATATYPE_FIELD_TO_RECORD_FIELD = {
"prec": "PREC",
Expand Down Expand Up @@ -79,6 +79,8 @@ def record_metadata_from_datatype(
arguments.pop("DRVH", None)

match datatype:
case String():
arguments["length"] = datatype.length or DEFAULT_STRING_WAVEFORM_LENGTH
case Waveform():
if len(datatype.shape) != 1:
raise TypeError(
Expand Down Expand Up @@ -138,8 +140,8 @@ def cast_to_epics_type(datatype: DataType[T], value: T) -> Any:
return datatype.index_of(datatype.validate(value))
else: # enum backed by string record
return datatype.validate(value).name
case String():
return value[: EPICS_WAVEFORM_LENGTH - 1]
case String() as string:
return value[: string.length]
case datatype if issubclass(type(datatype), EPICS_ALLOWED_DATATYPES):
return value
case _:
Expand Down