[bug] Prevent assets.copy() truncating file when fetch_asset fails

implants/lib/eldritch/src/assets/copy_impl.rs

@@ -20,6 +20,9 @@ fn copy_local(src: String, dst: String) -> Result<()> {
 }
 
 fn copy_remote(rx: Receiver<FetchAssetResponse>, dst_path: String) -> Result<()> {
+    // Wait for our first chunk
+    let resp = rx.recv()?;
+
     // Truncate file
     let mut dst = OpenOptions::new()
         .create(true)
@@ -40,6 +43,10 @@ fn copy_remote(rx: Receiver<FetchAssetResponse>, dst_path: String) -> Result<()>
         .open(&dst_path)
         .context(format!("failed to open file for writing: {}", &dst_path))?;
 
+    // Write our first chunk
+    dst.write_all(&resp.chunk)
+        .context(format!("failed to write file chunk: {}", &dst_path))?;
+
     // Listen for downloaded chunks and write them
     for resp in rx {
         dst.write_all(&resp.chunk)

implants/lib/eldritch/src/crypto/hash_file_impl.rs

@@ -1,13 +1,10 @@
-use std::fs::File;
-use std::io::Read;
-
 use sha1::{Digest, Sha1};
 use sha2::{Sha256, Sha512};
 
 use anyhow::{anyhow, Result};
 
 pub fn hash_file(file: String, algo: String) -> Result<String> {
-    let mut file_data = std::fs::read(file)?;
+    let file_data = std::fs::read(file)?;
     match algo.to_lowercase().as_str() {
         "md5" => Ok(format!("{:02x}", md5::compute(file_data))),
         "sha1" => {