rust/datafusion/examples/flight_client.rs

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use std::convert::TryFrom;
use std::sync::Arc;

use arrow::datatypes::Schema;
use arrow::util::pretty;

use arrow_flight::flight_descriptor;
use arrow_flight::flight_service_client::FlightServiceClient;
use arrow_flight::utils::flight_data_to_arrow_batch;
use arrow_flight::{FlightDescriptor, Ticket};

/// This example shows how to wrap DataFusion with `FlightService` to support looking up schema information for
/// Parquet files and executing SQL queries against them on a remote server.
/// This example is run along-side the example `flight_server`.
#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let testdata = arrow::util::test_util::parquet_test_data();

    // Create Flight client
    let mut client = FlightServiceClient::connect("http://localhost:50051").await?;

    // Call get_schema to get the schema of a Parquet file
    let request = tonic::Request::new(FlightDescriptor {
        r#type: flight_descriptor::DescriptorType::Path as i32,
        cmd: vec![],
        path: vec![format!("{}/alltypes_plain.parquet", testdata)],
    });

    let schema_result = client.get_schema(request).await?.into_inner();
    let schema = Schema::try_from(&schema_result)?;
    println!("Schema: {:?}", schema);

    // Call do_get to execute a SQL query and receive results
    let request = tonic::Request::new(Ticket {
        ticket: "SELECT id FROM alltypes_plain".into(),
    });

    let mut stream = client.do_get(request).await?.into_inner();

    // the schema should be the first message returned, else client should error
    let flight_data = stream.message().await?.unwrap();
    // convert FlightData to a stream
    let schema = Arc::new(Schema::try_from(&flight_data)?);
    println!("Schema: {:?}", schema);

    // all the remaining stream messages should be dictionary and record batches
    let mut results = vec![];
    let dictionaries_by_field = vec![None; schema.fields().len()];
    while let Some(flight_data) = stream.message().await? {
        let record_batch = flight_data_to_arrow_batch(
            &flight_data,
            schema.clone(),
            &dictionaries_by_field,
        )?;
        results.push(record_batch);
    }

    // print the results
    pretty::print_batches(&results)?;

    Ok(())
}