Profiled disaster recovery array (#8)

- Avoids duplicate read regression issue
- Implements isolated and testable logic

Author: BrianMichell

src/mdio/segy/_disaster_recovery_wrapper.py

@@ -0,0 +1,71 @@
+"""Consumer-side utility to get both raw and transformed header data with single filesystem read."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    import numpy as np
+    from segy.file import SegyFile
+    from segy.transforms import Transform, ByteSwapTransform, IbmFloatTransform
+    from numpy.typing import NDArray
+
+def _reverse_single_transform(data: NDArray, transform: Transform, endianness: Endianness) -> NDArray:
+    """Reverse a single transform operation."""
+    from segy.schema import Endianness
+    from segy.transforms import ByteSwapTransform
+    from segy.transforms import IbmFloatTransform
+
+    if isinstance(transform, ByteSwapTransform):
+        # Reverse the endianness conversion
+        if endianness == Endianness.LITTLE:
+            return data
+
+        reverse_transform = ByteSwapTransform(Endianness.BIG)
+        return reverse_transform.apply(data)
+
+    elif isinstance(transform, IbmFloatTransform):  # TODO: This seems incorrect...
+        # Reverse IBM float conversion
+        reverse_direction = "to_ibm" if transform.direction == "to_ieee" else "to_ieee"
+        reverse_transform = IbmFloatTransform(reverse_direction, transform.keys)
+        return reverse_transform.apply(data)
+
+    else:
+        # For unknown transforms, return data unchanged
+        return data
+
+def get_header_raw_and_transformed(
+    segy_file: SegyFile,
+    indices: int | list[int] | NDArray | slice,
+    do_reverse_transforms: bool = True
+) -> tuple[NDArray | None, NDArray, NDArray]:
+    """Get both raw and transformed header data.
+
+    Args:
+        segy_file: The SegyFile instance
+        indices: Which headers to retrieve
+        do_reverse_transforms: Whether to apply the reverse transform to get raw data
+
+    Returns:
+        Tuple of (raw_headers, transformed_headers, traces)
+    """
+    traces = segy_file.trace[indices]
+    transformed_headers = traces.header
+
+    # Reverse transforms to get raw data
+    if do_reverse_transforms:
+        raw_headers = _reverse_transforms(transformed_headers, segy_file.header.transform_pipeline, segy_file.spec.endianness)
+    else:
+        raw_headers = None
+
+    return raw_headers, transformed_headers, traces
+
+def _reverse_transforms(transformed_data: NDArray, transform_pipeline, endianness: Endianness) -> NDArray:
+    """Reverse the transform pipeline to get raw data."""
+    raw_data = transformed_data.copy() if hasattr(transformed_data, 'copy') else transformed_data
+
+    # Apply transforms in reverse order
+    for transform in reversed(transform_pipeline.transforms):
+        raw_data = _reverse_single_transform(raw_data, transform, endianness)
+
+    return raw_data

src/mdio/segy/_workers.py

@@ -13,6 +13,7 @@
 
 from mdio.api.io import to_mdio
 from mdio.builder.schemas.dtype import ScalarType
+from mdio.segy._disaster_recovery_wrapper import get_header_raw_and_transformed
 
 if TYPE_CHECKING:
     from segy.arrays import HeaderArray
@@ -81,7 +82,6 @@ def header_scan_worker(
 
     return cast("HeaderArray", trace_header)
 
-
 def trace_worker(  # noqa: PLR0913
     segy_kw: SegyFileArguments,
     output_path: UPath,
@@ -120,26 +120,30 @@ def trace_worker(  # noqa: PLR0913
     zarr_config.set({"threading.max_workers": 1})
 
     live_trace_indexes = local_grid_map[not_null].tolist()
-    traces = segy_file.trace[live_trace_indexes]
 
     header_key = "headers"
     raw_header_key = "raw_headers"
 
+    # Used to disable the reverse transforms if we aren't going to write the raw headers
+    do_reverse_transforms = False
+
     # Get subset of the dataset that has not yet been saved
     # The headers might not be present in the dataset
     worker_variables = [data_variable_name]
     if header_key in dataset.data_vars:  # Keeping the `if` here to allow for more worker configurations
         worker_variables.append(header_key)
     if raw_header_key in dataset.data_vars:
+
+        do_reverse_transforms = True
         worker_variables.append(raw_header_key)
 
+    raw_headers, transformed_headers, traces = get_header_raw_and_transformed(segy_file, live_trace_indexes, do_reverse_transforms=do_reverse_transforms)
     ds_to_write = dataset[worker_variables]
 
     if header_key in worker_variables:
         # Create temporary array for headers with the correct shape
-        # TODO(BrianMichell): Implement this better so that we can enable fill values without changing the code. #noqa: TD003
         tmp_headers = np.zeros_like(dataset[header_key])
-        tmp_headers[not_null] = traces.header
+        tmp_headers[not_null] = transformed_headers
         # Create a new Variable object to avoid copying the temporary array
         # The ideal solution is to use `ds_to_write[header_key][:] = tmp_headers`
         # but Xarray appears to be copying memory instead of doing direct assignment.
@@ -150,41 +154,19 @@ def trace_worker(  # noqa: PLR0913
             attrs=ds_to_write[header_key].attrs,
             encoding=ds_to_write[header_key].encoding,  # Not strictly necessary, but safer than not doing it.
         )
+    del transformed_headers  # Manage memory
     if raw_header_key in worker_variables:
         tmp_raw_headers = np.zeros_like(dataset[raw_header_key])
-
-        # Get the indices where we need to place results
-        live_mask = not_null
-        live_positions = np.where(live_mask.ravel())[0]
-
-        if len(live_positions) > 0:
-            # Calculate byte ranges for headers
-            header_size = 240
-            trace_offset = segy_file.spec.trace.offset
-            trace_itemsize = segy_file.spec.trace.itemsize
-
-            starts = []
-            ends = []
-            for global_trace_idx in live_trace_indexes:
-                header_start = trace_offset + global_trace_idx * trace_itemsize
-                header_end = header_start + header_size
-                starts.append(header_start)
-                ends.append(header_end)
-
-            # Capture raw bytes
-            raw_header_bytes = merge_cat_file(segy_file.fs, segy_file.url, starts, ends)
-
-            # Convert and place results
-            raw_headers_array = np.frombuffer(bytes(raw_header_bytes), dtype="|V240")
-            tmp_raw_headers.ravel()[live_positions] = raw_headers_array
+        tmp_raw_headers[not_null] = raw_headers.view("|V240")
 
         ds_to_write[raw_header_key] = Variable(
             ds_to_write[raw_header_key].dims,
             tmp_raw_headers,
             attrs=ds_to_write[raw_header_key].attrs,
-            encoding=ds_to_write[raw_header_key].encoding,
-        )
+            encoding=ds_to_write[raw_header_key].encoding,  # Not strictly necessary, but safer than not doing it.
+
 
+    del raw_headers  # Manage memory
     data_variable = ds_to_write[data_variable_name]
     fill_value = _get_fill_value(ScalarType(data_variable.dtype.name))
     tmp_samples = np.full_like(data_variable, fill_value=fill_value)

src/mdio/segy/blocked_io.py

@@ -280,4 +280,4 @@ def to_segy(
 
         non_consecutive_axes -= 1
 
-    return block_io_records
+    return block_io_records