[C++][Python][Parquet] bloom_filter_offset not present in ColumnChunkMetaData.to_dict() output despite bloom filter being written

[haziqishere]

Describe the bug, including details regarding any error messages, version, and platform.

Describe the bug

When writing a Parquet file with bloom_filter_options via pyarrow.parquet.write_table, the bloom filter is correctly written to disk (verified via file size delta matching SBBF sizing formula), but the bloom filter offset and length are not reflected in ColumnChunkMetaData.to_dict(). The keys bloom_filter_offset and bloom_filter_length are absent from the returned dict, making it impossible to programmatically verify bloom filter presence via the Python metadata API.

pyarrow version: 24.0.0

---

I've propose a fix for this issue in #49926

To Reproduce Error

import os
import pyarrow as pa
import pyarrow.parquet as pq

table = pa.table({
    "event_id": [f"id_{i:06d}" for i in range(10_000)],
    "value":    [f"data_{i}"   for i in range(10_000)],
})

# Write without bloom filter
pq.write_table(table, "/tmp/no_bloom.parquet")

# Write with bloom filter
pq.write_table(
    table,
    "/tmp/with_bloom.parquet",
    bloom_filter_options={"event_id": {"fpp": 0.05, "ndv": 10_000}},
)

# File size confirms bloom filter is written
size_no   = os.path.getsize("/tmp/no_bloom.parquet")
size_with = os.path.getsize("/tmp/with_bloom.parquet")
print(f"Without bloom: {size_no:,} bytes")
print(f"With bloom:    {size_with:,} bytes")
print(f"Difference:    {size_with - size_no:,} bytes")  # ~16KB confirming bloom written

# But metadata does not reflect it
pf = pq.ParquetFile("/tmp/with_bloom.parquet")
col = pf.metadata.row_group(0).column(0)  # event_id column
print(col.to_dict())
# Expected: dict contains 'bloom_filter_offset' and 'bloom_filter_length'
# Actual:   neither key is present

Expected output

Without bloom: 135,278 bytes
With bloom:    151,687 bytes
Difference:    +16,409 bytes

{
  'path_in_schema': 'event_id',
  ...
  'bloom_filter_offset': <some_int>,
  'bloom_filter_length': <some_int>,   # if exposed
  ...
}

Actual output

Without bloom: 135,278 bytes
With bloom:    151,687 bytes
Difference:    +16,409 bytes

{
  'file_offset': 0,
  'file_path': '',
  'physical_type': 'BYTE_ARRAY',
  'num_values': 10000,
  'path_in_schema': 'event_id',
  'is_stats_set': True,
  'statistics': {...},
  'compression': 'SNAPPY',
  'encodings': ('PLAIN', 'RLE', 'RLE_DICTIONARY'),
  'has_dictionary_page': True,
  'dictionary_page_offset': 4,
  'data_page_offset': 49,
  'total_compressed_size': 96,
  'total_uncompressed_size': 93
  # bloom_filter_offset is absent
}

---

Additional context

The bloom_filter_offset field exists in the underlying Parquet Thrift ColumnMetaData spec and is populated when a bloom filter is written. The file size delta between the two files matches the expected SBBF sizing for ndv=10_000, fpp=0.05 confirming the bloom filter data is physically present in the file.

The ColumnChunkMetaData C++ class exposes bloom_filter_offset() — it would be useful to have this surfaced in the Python to_dict() output so users can programmatically verify bloom filter presence without resorting to file size comparison.

Tested variants of bloom_filter_options and their observed file size deltas confirming bloom filters are written in all cases:

bool_true   → ndv=1,048,576 (default) → +1,048,603 bytes
empty_dict  → ndv=1,048,576 (default) → +1,048,603 bytes  
fpp_only    → ndv=1,048,576 (default) → +1,048,603 bytes
ndv_only    → ndv=10,000              → +16,409 bytes
fpp_and_ndv → ndv=10,000              → +16,409 bytes
tight_fpp   → fpp=0.001, ndv=10,000  → +32,793 bytes
both_cols   → 2 columns, default ndv  → +2,097,207 bytes (~2×)

Related: #49376 (added bloom_filter_options to write_table in 24.0.0)

Component(s)

C++