put all the dex swapping & resigning shenanigans in a function

apk_frauder/src/lib.rs

@@ -1,4 +1,10 @@
 use androscalpel_serializer::Serializable;
+use std::env;
+use std::fs;
+use std::fs::File;
+use std::io::{Read, Seek};
+use std::path::Path;
+use std::process::Command;
 
 pub mod apk_signing_block;
 pub mod compression;
@@ -132,3 +138,87 @@ impl FileInfo {
         }
     }
 }
+
+/// Replace the dex files a an apk an resigned the apk.
+///
+/// # Warning
+///
+/// For now, only jks keystore are allowed.
+///
+/// The `zipalign` and `apksigner` args allow to use a specific version of the
+/// tools instead of the one in the PATH (if it even exist)
+pub fn replace_dex(
+    apk: impl AsRef<Path>,
+    dst: impl AsRef<Path>,
+    dexfiles: &mut [impl Read + Seek],
+    keystore: impl AsRef<Path>, // TODO enum for handling p11 and generating a random cert
+    // `keytool -genkey -v -keystore KEYSTORE.jks -keyalg RSA -keysize
+    // 2048 -validity 10000 -alias ALIAS`
+    zipalign: Option<impl AsRef<Path>>,
+    apksigner: Option<impl AsRef<Path>>,
+) {
+    let zipalign = if let Some(path) = &zipalign {
+        path.as_ref().as_os_str()
+    } else {
+        "zipalign".as_ref()
+    };
+    let apksigner = if let Some(path) = &apksigner {
+        path.as_ref().as_os_str()
+    } else {
+        "apksigner".as_ref()
+    };
+    let tmp_dir = env::temp_dir().join(format!("apk_frauder_{:x}", rand::random::<u128>()));
+    let unaligned_path = tmp_dir.join("stripped.apk");
+    let aligned_path = tmp_dir.join("aligned.apk");
+    fs::create_dir_all(&tmp_dir).expect("Failed to create temporary directory");
+
+    let file = File::open(apk).expect("failed to open file");
+    let mut apk = ZipFileReader::new(file);
+    let file = File::create(&unaligned_path).expect("failed to create file");
+    let mut apk_out = ZipFileWriter::new(file, apk.zip64_end_of_central_directory.clone());
+
+    let mut file_info_ref = (*apk
+        .get_classes_file_info()
+        .first()
+        .expect("No dex file found in apk"))
+    .clone();
+
+    apk.unlink_signature_files();
+    apk.unlink_bytecode_files();
+    for f in apk.files.clone() {
+        apk_out.insert_file_from_zip(f, &mut apk);
+    }
+    for (i, mut dex) in dexfiles.iter_mut().enumerate() {
+        if i == 0 {
+            file_info_ref.set_name("classes.dex");
+        } else {
+            file_info_ref.set_name(&format!("classes{}.dex", i + 1));
+        }
+        apk_out.insert_file(
+            &mut dex,
+            file_info_ref.header.clone(),
+            Some(file_info_ref.local_header.clone()),
+        );
+    }
+    apk_out.write_central_directory();
+    // TODO: we can probably do that ourself an spare ourself the trouble of finding zipalign
+    Command::new(zipalign)
+        .arg("-v")
+        .arg("-p")
+        .arg("4")
+        .arg(unaligned_path.as_os_str())
+        .arg(aligned_path.as_os_str())
+        .status()
+        .unwrap();
+
+    Command::new(apksigner)
+        .arg("sign")
+        .arg("--ks")
+        .arg(keystore.as_ref().as_os_str())
+        .arg("--out")
+        .arg(dst.as_ref().as_os_str())
+        .arg(aligned_path.as_os_str())
+        .status()
+        .unwrap();
+    fs::remove_dir_all(tmp_dir).expect("Failled to remove tmp dir");
+}