docs: add example for custom file format with COPY TO

ci/scripts/rust_example.sh

@@ -29,5 +29,6 @@ do
   # Skip tests that rely on external storage and flight
   if [ ! -d $filename ]; then
      cargo run --example $example_name
+     cargo clean -p datafusion-examples
   fi
 done

datafusion-examples/examples/custom_file_format.rs

@@ -0,0 +1,224 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::{any::Any, sync::Arc};
+
+use arrow::array::{RecordBatch, StringArray, UInt8Array};
+use arrow_schema::{DataType, Field, Schema, SchemaRef};
+use datafusion::{
+    datasource::{
+        file_format::{
+            csv::CsvFormatFactory, file_compression_type::FileCompressionType,
+            FileFormat, FileFormatFactory,
+        },
+        physical_plan::{FileScanConfig, FileSinkConfig},
+        MemTable,
+    },
+    error::Result,
+    execution::{context::SessionState, runtime_env::RuntimeEnv},
+    physical_plan::ExecutionPlan,
+    prelude::{SessionConfig, SessionContext},
+};
+use datafusion_common::{GetExt, Statistics};
+use datafusion_physical_expr::{PhysicalExpr, PhysicalSortRequirement};
+use object_store::{ObjectMeta, ObjectStore};
+use tempfile::tempdir;
+
+/// Example of a custom file format that reads and writes TSV files.
+///
+/// TSVFileFormatFactory is responsible for creating instances of TSVFileFormat.
+/// The former, once registered with the SessionState, will then be used
+/// to facilitate SQL operations on TSV files, such as `COPY TO` shown here.
+
+#[derive(Debug)]
+/// Custom file format that reads and writes TSV files
+///
+/// This file format is a wrapper around the CSV file format
+/// for demonstration purposes.
+struct TSVFileFormat {
+    csv_file_format: Arc<dyn FileFormat>,
+}
+
+impl TSVFileFormat {
+    pub fn new(csv_file_format: Arc<dyn FileFormat>) -> Self {
+        Self { csv_file_format }
+    }
+}
+
+#[async_trait::async_trait]
+impl FileFormat for TSVFileFormat {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn get_ext(&self) -> String {
+        "tsv".to_string()
+    }
+
+    fn get_ext_with_compression(
+        &self,
+        c: &FileCompressionType,
+    ) -> datafusion::error::Result<String> {
+        if c == &FileCompressionType::UNCOMPRESSED {
+            Ok("tsv".to_string())
+        } else {
+            todo!("Compression not supported")
+        }
+    }
+
+    async fn infer_schema(
+        &self,
+        state: &SessionState,
+        store: &Arc<dyn ObjectStore>,
+        objects: &[ObjectMeta],
+    ) -> Result<SchemaRef> {
+        self.csv_file_format
+            .infer_schema(state, store, objects)
+            .await
+    }
+
+    async fn infer_stats(
+        &self,
+        state: &SessionState,
+        store: &Arc<dyn ObjectStore>,
+        table_schema: SchemaRef,
+        object: &ObjectMeta,
+    ) -> Result<Statistics> {
+        self.csv_file_format
+            .infer_stats(state, store, table_schema, object)
+            .await
+    }
+
+    async fn create_physical_plan(
+        &self,
+        state: &SessionState,
+        conf: FileScanConfig,
+        filters: Option<&Arc<dyn PhysicalExpr>>,
+    ) -> Result<Arc<dyn ExecutionPlan>> {
+        self.csv_file_format
+            .create_physical_plan(state, conf, filters)
+            .await
+    }
+
+    async fn create_writer_physical_plan(
+        &self,
+        input: Arc<dyn ExecutionPlan>,
+        state: &SessionState,
+        conf: FileSinkConfig,
+        order_requirements: Option<Vec<PhysicalSortRequirement>>,
+    ) -> Result<Arc<dyn ExecutionPlan>> {
+        self.csv_file_format
+            .create_writer_physical_plan(input, state, conf, order_requirements)
+            .await
+    }
+}
+
+#[derive(Default)]
+/// Factory for creating TSV file formats
+///
+/// This factory is a wrapper around the CSV file format factory
+/// for demonstration purposes.
+pub struct TSVFileFactory {
+    csv_file_factory: CsvFormatFactory,
+}
+
+impl TSVFileFactory {
+    pub fn new() -> Self {
+        Self {
+            csv_file_factory: CsvFormatFactory::new(),
+        }
+    }
+}
+
+impl FileFormatFactory for TSVFileFactory {
+    fn create(
+        &self,
+        state: &SessionState,
+        format_options: &std::collections::HashMap<String, String>,
+    ) -> Result<std::sync::Arc<dyn FileFormat>> {
+        let mut new_options = format_options.clone();
+        new_options.insert("format.delimiter".to_string(), "\t".to_string());
+
+        let csv_file_format = self.csv_file_factory.create(state, &new_options)?;
+        let tsv_file_format = Arc::new(TSVFileFormat::new(csv_file_format));
+
+        Ok(tsv_file_format)
+    }
+
+    fn default(&self) -> std::sync::Arc<dyn FileFormat> {
+        todo!()
+    }
+}
+
+impl GetExt for TSVFileFactory {
+    fn get_ext(&self) -> String {
+        "tsv".to_string()
+    }
+}
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    // Create a new context with the default configuration
+    let config = SessionConfig::new();
+    let runtime = RuntimeEnv::default();
+    let mut state = SessionState::new_with_config_rt(config, Arc::new(runtime));
+
+    // Register the custom file format
+    let file_format = Arc::new(TSVFileFactory::new());
+    state.register_file_format(file_format, true).unwrap();
+
+    // Create a new context with the custom file format
+    let ctx = SessionContext::new_with_state(state);
+
+    let mem_table = create_mem_table();
+    ctx.register_table("mem_table", mem_table).unwrap();
+
+    let temp_dir = tempdir().unwrap();
+    let table_save_path = temp_dir.path().join("mem_table.tsv");
+
+    let d = ctx
+        .sql(&format!(
+            "COPY mem_table TO '{}' STORED AS TSV;",
+            table_save_path.display(),
+        ))
+        .await?;
+
+    let results = d.collect().await?;
+    println!("Number of inserted rows: {:?}", results[0]);
+
+    Ok(())
+}
+
+// create a simple mem table
+fn create_mem_table() -> Arc<MemTable> {
+    let fields = vec![
+        Field::new("id", DataType::UInt8, false),
+        Field::new("data", DataType::Utf8, false),
+    ];
+    let schema = Arc::new(Schema::new(fields));
+
+    let partitions = RecordBatch::try_new(
+        schema.clone(),
+        vec![
+            Arc::new(UInt8Array::from(vec![1, 2])),
+            Arc::new(StringArray::from(vec!["foo", "bar"])),
+        ],
+    )
+    .unwrap();
+
+    Arc::new(MemTable::try_new(schema, vec![vec![partitions]]).unwrap())
+}