Fetch package metadata in parallel

crates/puffin-cli/Cargo.toml

@@ -18,3 +18,4 @@ async-std = { version = "1.12.0", features = [
     "tokio1",
     "unstable",
 ] }
+futures = "0.3.28"

crates/puffin-cli/src/commands/install.rs

@@ -2,7 +2,10 @@ use std::path::Path;
 use std::str::FromStr;
 
 use anyhow::Result;
+use futures::{StreamExt, TryFutureExt};
+
 use puffin_client::PypiClientBuilder;
+use puffin_requirements::Requirement;
 
 use crate::commands::ExitStatus;
 
@@ -16,14 +19,41 @@ pub(crate) async fn install(src: &Path) -> Result<ExitStatus> {
     // Instantiate a client.
     let client = PypiClientBuilder::default().build();
 
+    // Fetch metadata in parallel.
+    let (package_sink, package_stream) = futures::channel::mpsc::unbounded();
+
+    // Create a stream of futures that fetch metadata for each requirement.
+    let mut package_stream = package_stream
+        .map(|requirement: Requirement| {
+            client
+                .simple(requirement.clone().name)
+                .map_ok(move |metadata| (metadata, requirement))
+        })
+        .buffer_unordered(32)
+        .ready_chunks(32);
+
+    // Push all the requirements into the sink.
+    let mut in_flight = 0;
     for requirement in requirements.iter() {
-        let packument = client.simple(&requirement.name).await?;
+        package_sink.unbounded_send(requirement.clone())?;
+        in_flight += 1;
+    }
+
+    while let Some(chunk) = package_stream.next().await {
+        in_flight -= chunk.len();
+        for result in chunk {
+            let (metadata, requirement) = result?;
             #[allow(clippy::print_stdout)]
             {
-            println!("{packument:#?}");
+                println!("{metadata:#?}");
                 println!("{requirement:#?}");
             }
         }
 
+        if in_flight == 0 {
+            break;
+        }
+    }
+
     Ok(ExitStatus::Success)
 }

crates/puffin-requirements/src/lib.rs

@@ -4,7 +4,7 @@ use std::str::FromStr;
 
 use anyhow::Result;
 use memchr::{memchr2, memchr_iter};
-use pep508_rs::{Pep508Error, Requirement};
+pub use pep508_rs::{Pep508Error, Requirement};
 
 #[derive(Debug)]
 pub struct Requirements(Vec<Requirement>);