Add IpcSchemaEncoder, deprecate ipc schema functions, Fix IPC not r…

…especting not preserving dict ID (#6444)

* arrow-ipc: Add test for non preserving dict ID behavior with same ID

* arrow-ipc: Always set dict ID in IPC from dictionary tracker

This decouples dictionary IDs that end up in IPC from the schema further
because the dictionary tracker always first gathers the dict ID for each
field whether it is pre-defined and preserved or not.

Then when actually writing the IPC bytes the dictionary ID is always
taken from the dictionary tracker as opposed to falling back to the
`Field` of the `Schema`.

* arrow-ipc: Read dictionary IDs from dictionary tracker in correct order

When dictionary IDs are not preserved, then they are assigned depth
first, however, when reading them from the dictionary tracker to write
the IPC bytes, they were previously read from the dictionary tracker in
the order that the schema is traversed (first come first serve), which
caused an incorrect order of dictionaries serialized in IPC.

* Refine IpcSchemaEncoder API and docs

* reduce repeated code

* Fix lints

---------

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

arrow-flight/src/lib.rs

@@ -137,7 +137,9 @@ pub struct IpcMessage(pub Bytes);
 
 fn flight_schema_as_encoded_data(arrow_schema: &Schema, options: &IpcWriteOptions) -> EncodedData {
     let data_gen = writer::IpcDataGenerator::default();
-    data_gen.schema_to_bytes(arrow_schema, options)
+    let mut dict_tracker =
+        writer::DictionaryTracker::new_with_preserve_dict_id(false, options.preserve_dict_id());
+    data_gen.schema_to_bytes_with_dictionary_tracker(arrow_schema, &mut dict_tracker, options)
 }
 
 fn flight_schema_as_flatbuffer(schema: &Schema, options: &IpcWriteOptions) -> IpcMessage {

arrow-ipc/src/convert.rs

@@ -27,18 +27,110 @@ use std::collections::HashMap;
 use std::fmt::{Debug, Formatter};
 use std::sync::Arc;
 
+use crate::writer::DictionaryTracker;
 use crate::{size_prefixed_root_as_message, KeyValue, Message, CONTINUATION_MARKER};
 use DataType::*;
 
-/// Serialize a schema in IPC format
-pub fn schema_to_fb(schema: &Schema) -> FlatBufferBuilder {
-    let mut fbb = FlatBufferBuilder::new();
+/// Low level Arrow [Schema] to IPC bytes converter
+///
+/// See also [`fb_to_schema`] for the reverse operation
+///
+/// # Example
+/// ```
+/// # use arrow_ipc::convert::{fb_to_schema, IpcSchemaEncoder};
+/// # use arrow_ipc::root_as_schema;
+/// # use arrow_ipc::writer::DictionaryTracker;
+/// # use arrow_schema::{DataType, Field, Schema};
+/// // given an arrow schema to serialize
+/// let schema = Schema::new(vec![
+///    Field::new("a", DataType::Int32, false),
+/// ]);
+///
+/// // Use a dictionary tracker to track dictionary id if needed
+///  let mut dictionary_tracker = DictionaryTracker::new(true);
+/// // create a FlatBuffersBuilder that contains the encoded bytes
+///  let fb = IpcSchemaEncoder::new()
+///    .with_dictionary_tracker(&mut dictionary_tracker)
+///    .schema_to_fb(&schema);
+///
+/// // the bytes are in `fb.finished_data()`
+/// let ipc_bytes = fb.finished_data();
+///
+///  // convert the IPC bytes back to an Arrow schema
+///  let ipc_schema = root_as_schema(ipc_bytes).unwrap();
+///  let schema2 = fb_to_schema(ipc_schema);
+/// assert_eq!(schema, schema2);
+/// ```
+#[derive(Debug)]
+pub struct IpcSchemaEncoder<'a> {
+    dictionary_tracker: Option<&'a mut DictionaryTracker>,
+}
+
+impl<'a> Default for IpcSchemaEncoder<'a> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
 
-    let root = schema_to_fb_offset(&mut fbb, schema);
+impl<'a> IpcSchemaEncoder<'a> {
+    /// Create a new schema encoder
+    pub fn new() -> IpcSchemaEncoder<'a> {
+        IpcSchemaEncoder {
+            dictionary_tracker: None,
+        }
+    }
+
+    /// Specify a dictionary tracker to use
+    pub fn with_dictionary_tracker(
+        mut self,
+        dictionary_tracker: &'a mut DictionaryTracker,
+    ) -> Self {
+        self.dictionary_tracker = Some(dictionary_tracker);
+        self
+    }
 
-    fbb.finish(root, None);
+    /// Serialize a schema in IPC format, returning a completed [`FlatBufferBuilder`]
+    ///
+    /// Note: Call [`FlatBufferBuilder::finished_data`] to get the serialized bytes
+    pub fn schema_to_fb<'b>(&mut self, schema: &Schema) -> FlatBufferBuilder<'b> {
+        let mut fbb = FlatBufferBuilder::new();
+
+        let root = self.schema_to_fb_offset(&mut fbb, schema);
+
+        fbb.finish(root, None);
+
+        fbb
+    }
 
-    fbb
+    /// Serialize a schema to an in progress [`FlatBufferBuilder`], returning the in progress offset.
+    pub fn schema_to_fb_offset<'b>(
+        &mut self,
+        fbb: &mut FlatBufferBuilder<'b>,
+        schema: &Schema,
+    ) -> WIPOffset<crate::Schema<'b>> {
+        let fields = schema
+            .fields()
+            .iter()
+            .map(|field| build_field(fbb, &mut self.dictionary_tracker, field))
+            .collect::<Vec<_>>();
+        let fb_field_list = fbb.create_vector(&fields);
+
+        let fb_metadata_list =
+            (!schema.metadata().is_empty()).then(|| metadata_to_fb(fbb, schema.metadata()));
+
+        let mut builder = crate::SchemaBuilder::new(fbb);
+        builder.add_fields(fb_field_list);
+        if let Some(fb_metadata_list) = fb_metadata_list {
+            builder.add_custom_metadata(fb_metadata_list);
+        }
+        builder.finish()
+    }
+}
+
+/// Serialize a schema in IPC format
+#[deprecated(since = "54.0.0", note = "Use `IpcSchemaConverter`.")]
+pub fn schema_to_fb(schema: &Schema) -> FlatBufferBuilder<'_> {
+    IpcSchemaEncoder::new().schema_to_fb(schema)
 }
 
 pub fn metadata_to_fb<'a>(
@@ -60,26 +152,12 @@ pub fn metadata_to_fb<'a>(
     fbb.create_vector(&custom_metadata)
 }
 
+#[deprecated(since = "54.0.0", note = "Use `IpcSchemaConverter`.")]
 pub fn schema_to_fb_offset<'a>(
     fbb: &mut FlatBufferBuilder<'a>,
     schema: &Schema,
 ) -> WIPOffset<crate::Schema<'a>> {
-    let fields = schema
-        .fields()
-        .iter()
-        .map(|field| build_field(fbb, field))
-        .collect::<Vec<_>>();
-    let fb_field_list = fbb.create_vector(&fields);
-
-    let fb_metadata_list =
-        (!schema.metadata().is_empty()).then(|| metadata_to_fb(fbb, schema.metadata()));
-
-    let mut builder = crate::SchemaBuilder::new(fbb);
-    builder.add_fields(fb_field_list);
-    if let Some(fb_metadata_list) = fb_metadata_list {
-        builder.add_custom_metadata(fb_metadata_list);
-    }
-    builder.finish()
+    IpcSchemaEncoder::new().schema_to_fb_offset(fbb, schema)
 }
 
 /// Convert an IPC Field to Arrow Field
@@ -114,7 +192,7 @@ impl<'a> From<crate::Field<'a>> for Field {
     }
 }
 
-/// Deserialize a Schema table from flat buffer format to Schema data type
+/// Deserialize an ipc [crate::Schema`] from flat buffers to an arrow [Schema].
 pub fn fb_to_schema(fb: crate::Schema) -> Schema {
     let mut fields: Vec<Field> = vec![];
     let c_fields = fb.fields().unwrap();
@@ -424,6 +502,7 @@ pub(crate) struct FBFieldType<'b> {
 /// Create an IPC Field from an Arrow Field
 pub(crate) fn build_field<'a>(
     fbb: &mut FlatBufferBuilder<'a>,
+    dictionary_tracker: &mut Option<&mut DictionaryTracker>,
     field: &Field,
 ) -> WIPOffset<crate::Field<'a>> {
     // Optional custom metadata.
@@ -433,19 +512,29 @@ pub(crate) fn build_field<'a>(
     };
 
     let fb_field_name = fbb.create_string(field.name().as_str());
-    let field_type = get_fb_field_type(field.data_type(), fbb);
+    let field_type = get_fb_field_type(field.data_type(), dictionary_tracker, fbb);
 
     let fb_dictionary = if let Dictionary(index_type, _) = field.data_type() {
-        Some(get_fb_dictionary(
-            index_type,
-            field
-                .dict_id()
-                .expect("All Dictionary types have `dict_id`"),
-            field
-                .dict_is_ordered()
-                .expect("All Dictionary types have `dict_is_ordered`"),
-            fbb,
-        ))
+        match dictionary_tracker {
+            Some(tracker) => Some(get_fb_dictionary(
+                index_type,
+                tracker.set_dict_id(field),
+                field
+                    .dict_is_ordered()
+                    .expect("All Dictionary types have `dict_is_ordered`"),
+                fbb,
+            )),
+            None => Some(get_fb_dictionary(
+                index_type,
+                field
+                    .dict_id()
+                    .expect("Dictionary type must have a dictionary id"),
+                field
+                    .dict_is_ordered()
+                    .expect("All Dictionary types have `dict_is_ordered`"),
+                fbb,
+            )),
+        }
     } else {
         None
     };
@@ -473,6 +562,7 @@ pub(crate) fn build_field<'a>(
 /// Get the IPC type of a data type
 pub(crate) fn get_fb_field_type<'a>(
     data_type: &DataType,
+    dictionary_tracker: &mut Option<&mut DictionaryTracker>,
     fbb: &mut FlatBufferBuilder<'a>,
 ) -> FBFieldType<'a> {
     // some IPC implementations expect an empty list for child data, instead of a null value.
@@ -673,7 +763,7 @@ pub(crate) fn get_fb_field_type<'a>(
             }
         }
         List(ref list_type) => {
-            let child = build_field(fbb, list_type);
+            let child = build_field(fbb, dictionary_tracker, list_type);
             FBFieldType {
                 type_type: crate::Type::List,
                 type_: crate::ListBuilder::new(fbb).finish().as_union_value(),
@@ -682,15 +772,15 @@ pub(crate) fn get_fb_field_type<'a>(
         }
         ListView(_) | LargeListView(_) => unimplemented!("ListView/LargeListView not implemented"),
         LargeList(ref list_type) => {
-            let child = build_field(fbb, list_type);
+            let child = build_field(fbb, dictionary_tracker, list_type);
             FBFieldType {
                 type_type: crate::Type::LargeList,
                 type_: crate::LargeListBuilder::new(fbb).finish().as_union_value(),
                 children: Some(fbb.create_vector(&[child])),
             }
         }
         FixedSizeList(ref list_type, len) => {
-            let child = build_field(fbb, list_type);
+            let child = build_field(fbb, dictionary_tracker, list_type);
             let mut builder = crate::FixedSizeListBuilder::new(fbb);
             builder.add_listSize(*len);
             FBFieldType {
@@ -703,7 +793,7 @@ pub(crate) fn get_fb_field_type<'a>(
             // struct's fields are children
             let mut children = vec![];
             for field in fields {
-                children.push(build_field(fbb, field));
+                children.push(build_field(fbb, dictionary_tracker, field));
             }
             FBFieldType {
                 type_type: crate::Type::Struct_,
@@ -712,8 +802,8 @@ pub(crate) fn get_fb_field_type<'a>(
             }
         }
         RunEndEncoded(run_ends, values) => {
-            let run_ends_field = build_field(fbb, run_ends);
-            let values_field = build_field(fbb, values);
+            let run_ends_field = build_field(fbb, dictionary_tracker, run_ends);
+            let values_field = build_field(fbb, dictionary_tracker, values);
             let children = [run_ends_field, values_field];
             FBFieldType {
                 type_type: crate::Type::RunEndEncoded,
@@ -724,7 +814,7 @@ pub(crate) fn get_fb_field_type<'a>(
             }
         }
         Map(map_field, keys_sorted) => {
-            let child = build_field(fbb, map_field);
+            let child = build_field(fbb, dictionary_tracker, map_field);
             let mut field_type = crate::MapBuilder::new(fbb);
             field_type.add_keysSorted(*keys_sorted);
             FBFieldType {
@@ -737,7 +827,7 @@ pub(crate) fn get_fb_field_type<'a>(
             // In this library, the dictionary "type" is a logical construct. Here we
             // pass through to the value type, as we've already captured the index
             // type in the DictionaryEncoding metadata in the parent field
-            get_fb_field_type(value_type, fbb)
+            get_fb_field_type(value_type, dictionary_tracker, fbb)
         }
         Decimal128(precision, scale) => {
             let mut builder = crate::DecimalBuilder::new(fbb);
@@ -764,7 +854,7 @@ pub(crate) fn get_fb_field_type<'a>(
         Union(fields, mode) => {
             let mut children = vec![];
             for (_, field) in fields.iter() {
-                children.push(build_field(fbb, field));
+                children.push(build_field(fbb, dictionary_tracker, field));
             }
 
             let union_mode = match mode {
@@ -1067,7 +1157,10 @@ mod tests {
             md,
         );
 
-        let fb = schema_to_fb(&schema);
+        let mut dictionary_tracker = DictionaryTracker::new(true);
+        let fb = IpcSchemaEncoder::new()
+            .with_dictionary_tracker(&mut dictionary_tracker)
+            .schema_to_fb(&schema);
 
         // read back fields
         let ipc = crate::root_as_schema(fb.finished_data()).unwrap();
@@ -1098,9 +1191,14 @@ mod tests {
 
         // generate same message with Rust
         let data_gen = crate::writer::IpcDataGenerator::default();
+        let mut dictionary_tracker = DictionaryTracker::new(true);
         let arrow_schema = Schema::new(vec![Field::new("field1", DataType::UInt32, false)]);
         let bytes = data_gen
-            .schema_to_bytes(&arrow_schema, &crate::writer::IpcWriteOptions::default())
+            .schema_to_bytes_with_dictionary_tracker(
+                &arrow_schema,
+                &mut dictionary_tracker,
+                &crate::writer::IpcWriteOptions::default(),
+            )
             .ipc_message;
 
         let ipc2 = crate::root_as_message(&bytes).unwrap();

arrow-ipc/src/reader.rs

@@ -2283,4 +2283,59 @@ mod tests {
         let err = reader.next().unwrap().unwrap_err();
         assert!(matches!(err, ArrowError::InvalidArgumentError(_)));
     }
+
+    #[test]
+    fn test_same_dict_id_without_preserve() {
+        let batch = RecordBatch::try_new(
+            Arc::new(Schema::new(
+                ["a", "b"]
+                    .iter()
+                    .map(|name| {
+                        Field::new_dict(
+                            name.to_string(),
+                            DataType::Dictionary(
+                                Box::new(DataType::Int32),
+                                Box::new(DataType::Utf8),
+                            ),
+                            true,
+                            0,
+                            false,
+                        )
+                    })
+                    .collect::<Vec<Field>>(),
+            )),
+            vec![
+                Arc::new(
+                    vec![Some("c"), Some("d")]
+                        .into_iter()
+                        .collect::<DictionaryArray<Int32Type>>(),
+                ) as ArrayRef,
+                Arc::new(
+                    vec![Some("e"), Some("f")]
+                        .into_iter()
+                        .collect::<DictionaryArray<Int32Type>>(),
+                ) as ArrayRef,
+            ],
+        )
+        .expect("Failed to create RecordBatch");
+
+        // serialize the record batch as an IPC stream
+        let mut buf = vec![];
+        {
+            let mut writer = crate::writer::StreamWriter::try_new_with_options(
+                &mut buf,
+                batch.schema().as_ref(),
+                crate::writer::IpcWriteOptions::default().with_preserve_dict_id(false),
+            )
+            .expect("Failed to create StreamWriter");
+            writer.write(&batch).expect("Failed to write RecordBatch");
+            writer.finish().expect("Failed to finish StreamWriter");
+        }
+
+        StreamReader::try_new(std::io::Cursor::new(buf), None)
+            .expect("Failed to create StreamReader")
+            .for_each(|decoded_batch| {
+                assert_eq!(decoded_batch.expect("Failed to read RecordBatch"), batch);
+            });
+    }
 }