feat(process): add a method to retrieve the number of concurrent channels

This change is justified since this environment variable is read in more
than one place.

Author: FranciscoTGouveia

src/cli/rustup_mode.rs

@@ -3,7 +3,6 @@ use std::{
     env::consts::EXE_SUFFIX,
     fmt,
     io::{self, Write},
-    num::NonZeroU64,
     path::{Path, PathBuf},
     process::ExitStatus,
     str::FromStr,
@@ -800,11 +799,9 @@ async fn check_updates(cfg: &Cfg<'_>, opts: CheckOpts) -> Result<utils::ExitCode
     let use_colors = matches!(t.color_choice(), ColorChoice::Auto | ColorChoice::Always);
     let mut update_available = false;
     let channels = cfg.list_channels()?;
-    let num_channels = match cfg.process.var("RUSTUP_CONCURRENT_DOWNLOADS") {
-        Ok(s) => NonZeroU64::from_str(&s).context(
-            "invalid value in RUSTUP_CONCURRENT_DOWNLOADS -- must be a natural number greater than zero"
-        )?.get() as usize,
-        Err(_) => channels.len(),
+    let num_channels = match cfg.process.concurrent_downloads() {
+        Some(n) => n,
+        None => channels.len(),
     };
 
     // Ensure that `.buffered()` is never called with 0 as this will cause a hang.

src/dist/manifestation.rs

@@ -4,9 +4,7 @@
 #[cfg(test)]
 mod tests;
 
-use std::num::NonZeroU64;
 use std::path::Path;
-use std::str::FromStr;
 
 use anyhow::{Context, Result, anyhow, bail};
 use futures_util::stream::StreamExt;
@@ -156,11 +154,9 @@ impl Manifestation {
         let mut things_to_install: Vec<(Component, CompressionKind, File)> = Vec::new();
         let mut things_downloaded: Vec<String> = Vec::new();
         let components = update.components_urls_and_hashes(new_manifest)?;
-        let num_channels = match download_cfg.process.var("RUSTUP_CONCURRENT_DOWNLOADS") {
-            Ok(s) => NonZeroU64::from_str(&s).context(
-                "invalid value in RUSTUP_CONCURRENT_DOWNLOADS -- must be a natural number greater than zero"
-            )?.get() as usize,
-            Err(_) => components.len(),
+        let num_channels = match download_cfg.process.concurrent_downloads() {
+            Some(n) => n,
+            None => components.len(),
         };
 
         const DEFAULT_MAX_RETRIES: usize = 3;

src/process.rs

@@ -2,6 +2,7 @@ use std::ffi::OsString;
 use std::fmt::Debug;
 use std::io;
 use std::io::IsTerminal;
+use std::num::NonZeroU64;
 use std::path::PathBuf;
 use std::str::FromStr;
 #[cfg(feature = "test")]
@@ -167,6 +168,15 @@ impl Process {
             _ => ProgressDrawTarget::hidden(),
         }
     }
+
+    pub fn concurrent_downloads(&self) -> Option<usize> {
+        match self.var("RUSTUP_CONCURRENT_DOWNLOADS") {
+            Ok(s) => Some(NonZeroU64::from_str(&s).context(
+                "invalid value in RUSTUP_CONCURRENT_DOWNLOADS -- must be a natural number greater than zero"
+            ).ok()?.get() as usize),
+            Err(_) => None,
+        }
+    }
 }
 
 impl home::env::Env for Process {