Added basic support to read indexes (#100)

examples/read_metadata.rs

@@ -1,7 +1,8 @@
+use parquet2::bloom_filter;
 use parquet2::error::Result;
+use parquet2::indexes;
 
 // ANCHOR: deserialize
-use parquet2::bloom_filter;
 use parquet2::encoding::Encoding;
 use parquet2::metadata::ColumnDescriptor;
 use parquet2::page::{split_buffer, DataPage};
@@ -60,6 +61,23 @@ fn main() -> Result<()> {
     let column_metadata = metadata.row_groups[row_group].column(column);
     // ANCHOR_END: column_metadata
 
+    // ANCHOR: column_index
+    // read the column index
+    let index = indexes::read_column(&mut reader, column_metadata.column_chunk())?;
+    if let Some(index) = index {
+        // these are the minimum and maximum within each page, which can be used
+        // to skip pages.
+        println!("{index:?}");
+    }
+
+    // read the offset index containing page locations
+    let maybe_pages = indexes::read_page_locations(&mut reader, column_metadata.column_chunk())?;
+    if let Some(pages) = maybe_pages {
+        // there are page locations in the file
+        println!("{pages:?}");
+    }
+    // ANCHOR_END: column_index
+
     // ANCHOR: statistics
     if let Some(maybe_stats) = column_metadata.statistics() {
         let stats = maybe_stats?;

guide/src/README.md

@@ -113,11 +113,22 @@ which can be downcasted via its `Statistics::physical_type()`:
 
 ## Bloom filters
 
-The metadata of columns can contain bloom filter bitsets that
-can be used to pushdown filter operations.
+The column metadata may contain bloom filter bitsets that can be used to pushdown
+filter operations to row groups.
 
 This crate offers the necessary functionality to check whether an item is not in a column chunk:
 
 ```rust,no_run,noplayground
 {{#include ../../examples/read_metadata.rs:bloom_filter}}
 ```
+
+## Column and page indexes
+
+The column metadata may contain column and page indexes that can be used to push down filters
+when reading (IO) pages.
+
+This crate offers the necessary functionality to check whether an item is not in a column chunk:
+
+```rust,no_run,noplayground
+{{#include ../../examples/read_metadata.rs:column_metadata}}
+```

src/error.rs

@@ -70,6 +70,12 @@ impl From<std::io::Error> for ParquetError {
     }
 }
 
+impl From<std::num::TryFromIntError> for ParquetError {
+    fn from(e: std::num::TryFromIntError) -> ParquetError {
+        ParquetError::OutOfSpec(format!("Number must be zero or positive: {}", e))
+    }
+}
+
 /// A specialized `Result` for Parquet errors.
 pub type Result<T> = std::result::Result<T, ParquetError>;
 

src/indexes/mod.rs

@@ -0,0 +1,60 @@
+use std::convert::TryInto;
+use std::io::{Cursor, Read, Seek, SeekFrom};
+
+use parquet_format_async_temp::{
+    thrift::protocol::TCompactInputProtocol, ColumnChunk, ColumnIndex, OffsetIndex, PageLocation,
+};
+
+use crate::error::ParquetError;
+
+/// Read the [`ColumnIndex`] from the [`ColumnChunk`], if available.
+pub fn read_column<R: Read + Seek>(
+    reader: &mut R,
+    chunk: &ColumnChunk,
+) -> Result<Option<ColumnIndex>, ParquetError> {
+    let (offset, length): (u64, usize) = if let Some(offset) = chunk.column_index_offset {
+        let length = chunk.column_index_length.ok_or_else(|| {
+            ParquetError::OutOfSpec(
+                "The column length must exist if column offset exists".to_string(),
+            )
+        })?;
+        (offset.try_into()?, length.try_into()?)
+    } else {
+        return Ok(None);
+    };
+
+    reader.seek(SeekFrom::Start(offset))?;
+    let mut data = vec![0; length];
+    reader.read_exact(&mut data)?;
+
+    let mut d = Cursor::new(&data);
+    let mut prot = TCompactInputProtocol::new(&mut d);
+    Ok(Some(ColumnIndex::read_from_in_protocol(&mut prot)?))
+}
+
+/// Read [`PageLocation`]s from the [`ColumnChunk`], if available.
+pub fn read_page_locations<R: Read + Seek>(
+    reader: &mut R,
+    chunk: &ColumnChunk,
+) -> Result<Option<Vec<PageLocation>>, ParquetError> {
+    let (offset, length): (u64, usize) = if let Some(offset) = chunk.offset_index_offset {
+        let length = chunk.offset_index_length.ok_or_else(|| {
+            ParquetError::OutOfSpec(
+                "The column length must exist if column offset exists".to_string(),
+            )
+        })?;
+        (offset.try_into()?, length.try_into()?)
+    } else {
+        return Ok(None);
+    };
+
+    reader.seek(SeekFrom::Start(offset))?;
+    let mut data = vec![0; length];
+    reader.read_exact(&mut data)?;
+
+    let mut d = Cursor::new(&data);
+    let mut prot = TCompactInputProtocol::new(&mut d);
+    let offset = OffsetIndex::read_from_in_protocol(&mut prot)?;
+
+    Ok(Some(offset.page_locations))
+}

src/lib.rs

@@ -7,6 +7,7 @@ pub mod error;
 pub mod bloom_filter;
 pub mod compression;
 pub mod encoding;
+pub mod indexes;
 pub mod metadata;
 pub mod page;
 mod parquet_bridge;

src/metadata/column_chunk_metadata.rs

@@ -41,6 +41,11 @@ impl ColumnChunkMetaData {
         self.column_chunk.file_offset
     }
 
+    /// Returns this column's [`ColumnChunk`]
+    pub fn column_chunk(&self) -> &ColumnChunk {
+        &self.column_chunk
+    }
+
     // The column's metadata
     fn column_metadata(&self) -> &ColumnMetaData {
         self.column_chunk.meta_data.as_ref().unwrap()