download: check for failure status codes

Check for HTTP status codes for immediate failures in download_and_hash,
for now only 403 Forbidden and 404 Not found.

src/download.rs

@@ -2,6 +2,8 @@ use std::error::Error;
 use std::io::Write;
 use std::io;
 
+use reqwest::StatusCode;
+
 use sha2::{Sha256, Digest};
 
 pub struct DownloadResult<W: std::io::Write> {
@@ -19,6 +21,17 @@ where
         .send()
         .await?;
 
+    // Return immediately on download failure on the client side.
+    let status = res.status();
+    if status.is_client_error() {
+        match status {
+            StatusCode::FORBIDDEN | StatusCode::NOT_FOUND => {
+                return Err(format!("cannnot fetch remotely with status code {:?}", status).into());
+            }
+            _ => (),
+        }
+    }
+
     let mut hasher = Sha256::new();
 
     let mut bytes_read = 0usize;