cli: determine archive type based on filename instead of path (#224602)

Refs #219632

Seems like PRSS sometimes(?) doesn't return the full archive name in
the response. I don't reproduce this, but others consistently do. This
PR removes the dependency on the URL path and instead checks for the
gzip magic number in the first two bytes of the archive to figure out
what to do.

cli/src/update_service.rs

@@ -3,7 +3,7 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-use std::{ffi::OsStr, fmt, path::Path};
+use std::{fmt, path::Path};
 
 use serde::{Deserialize, Serialize};
 
@@ -11,10 +11,11 @@ use crate::{
 	constants::VSCODE_CLI_UPDATE_ENDPOINT,
 	debug, log, options, spanf,
 	util::{
-		errors::{AnyError, CodeError, WrappedError},
+		errors::{wrap, AnyError, CodeError, WrappedError},
 		http::{BoxedHttp, SimpleResponse},
 		io::ReportCopyProgress,
-		tar, zipper,
+		tar::{self, has_gzip_header},
+		zipper,
 	},
 };
 
@@ -178,10 +179,10 @@ pub fn unzip_downloaded_release<T>(
 where
 	T: ReportCopyProgress,
 {
-	if compressed_file.extension() == Some(OsStr::new("zip")) {
-		zipper::unzip_file(compressed_file, target_dir, reporter)
-	} else {
-		tar::decompress_tarball(compressed_file, target_dir, reporter)
+	match has_gzip_header(compressed_file) {
+		Ok((f, true)) => tar::decompress_tarball(f, target_dir, reporter),
+		Ok((f, false)) => zipper::unzip_file(f, target_dir, reporter),
+		Err(e) => Err(wrap(e, "error checking for gzip header")),
 	}
 }