rust: restructure GitHub artifact downloading

Before, we initiated the HTTP requests all at once. On slow network
connections or machines this resulted in timeouts due to some requests
not being serviced in a timely manner.

This commit refactors the code so requests are issued when their
future is waited on and not before. This should result in more
reliable fetching of artifacts.

Author: indygreg

Cargo.lock

@@ -6,6 +6,7 @@ edition = "2018"
 
 [dependencies]
 anyhow = "1"
+bytes = "1.1"
 clap = "2"
 duct = "0"
 futures = "0"

Cargo.toml

@@ -6,7 +6,7 @@ use {
     anyhow::{anyhow, Result},
     clap::ArgMatches,
     futures::StreamExt,
-    octocrab::OctocrabBuilder,
+    octocrab::{Octocrab, OctocrabBuilder},
     once_cell::sync::Lazy,
     serde::Deserialize,
     std::{
@@ -70,6 +70,15 @@ struct Artifacts {
     total_count: u64,
 }
 
+async fn fetch_artifact(client: &Octocrab, artifact: Artifact) -> Result<bytes::Bytes> {
+    println!("downloading {}", artifact.name);
+    let res = client
+        .execute(client.request_builder(&artifact.archive_download_url, reqwest::Method::GET))
+        .await?;
+
+    Ok(res.bytes().await?)
+}
+
 pub async fn command_fetch_release_distributions(args: &ArgMatches<'_>) -> Result<()> {
     let dest_dir = PathBuf::from(args.value_of("dest").expect("dest directory should be set"));
     let org = args
@@ -134,14 +143,7 @@ pub async fn command_fetch_release_distributions(args: &ArgMatches<'_>) -> Resul
                 continue;
             }
 
-            println!("downloading {}", artifact.name);
-            let res = client
-                .execute(
-                    client.request_builder(artifact.archive_download_url, reqwest::Method::GET),
-                )
-                .await?;
-
-            fs.push(res.bytes());
+            fs.push(fetch_artifact(&client, artifact));
         }
     }