util/examples: Add async variant view example

noodles-util/Cargo.toml

@@ -51,7 +51,7 @@ futures = { workspace = true, optional = true, features = ["std"] }
 tokio = { workspace = true, optional = true, features = ["fs", "io-util"] }
 
 [dev-dependencies]
-tokio = { workspace = true, features = ["macros", "rt-multi-thread"] }
+tokio = { workspace = true, features = ["io-std", "macros", "rt-multi-thread"] }
 
 [package.metadata.docs.rs]
 all-features = true
@@ -83,3 +83,7 @@ required-features = ["variant"]
 [[example]]
 name = "util_variant_view"
 required-features = ["variant"]
+
+[[example]]
+name = "util_variant_view_async"
+required-features = ["async", "variant"]

noodles-util/examples/util_variant_view_async.rs

@@ -0,0 +1,40 @@
+//! Prints a variant file in the VCF format.
+//!
+//! The result matches the output of `bcftools view <src>`.
+
+use std::env;
+
+use futures::TryStreamExt;
+use noodles_util::variant;
+use noodles_vcf as vcf;
+use tokio::io::{self, AsyncWriteExt};
+
+#[tokio::main]
+async fn main() -> io::Result<()> {
+    let src = env::args().nth(1).expect("missing src");
+
+    let builder = variant::r#async::io::reader::Builder::default();
+
+    let mut reader = if src == "-" {
+        builder.build_from_reader(io::stdin()).await?
+    } else {
+        builder.build_from_path(src).await?
+    };
+
+    let header = reader.read_header().await?;
+
+    let mut writer = vcf::r#async::io::Writer::new(io::stdout());
+    writer.write_header(&header).await?;
+
+    let mut records = reader.records();
+
+    while let Some(record) = records.try_next().await? {
+        writer
+            .write_variant_record(&header, record.as_ref())
+            .await?;
+    }
+
+    writer.get_mut().shutdown().await?;
+
+    Ok(())
+}