droidsaw 1.0.0

//! Layout-aware bulk emit for `decompile --all --out <dir>`.
//!
//! Output tree:
//! ```text
//! <dir>/
//! ├── meta.json                     ← provenance + canonical counts + per-format breakdown
//! ├── dex/
//! │   ├── classes/sources/com/foo/Bar.java
//! │   ├── classes2/sources/...
//! │   └── ...
//! ├── hbc/
//! │   ├── f00000_global.js
//! │   └── f00001_<name>.js
//! └── strings/
//!     ├── dex.txt
//!     └── hbc.txt
//! ```
//!
//! Design notes:
//! - Per-DEX subdirs (named after the APK entry) preserve provenance back
//!   to source bytes and prevent silent multi-dex class-descriptor
//!   collisions from clobbering output.
//! - HBC functions emit per-file so diffs between APK versions stay
//!   function-scoped: a per-bundle file would churn whole-file on every
//!   byte change anywhere in the bundle.
//! - meta.json is written LAST: its presence == clean run; absence ==
//!   partial output. SHA-256 fields make the tree reproducibly verifiable.
//! - Canonical counts (classes_emitted / methods_emitted / functions_emitted)
//!   live once per layer. Per-format file counts under `formats.<n>.files`
//!   describe the *representation* of the same set, NEVER summed into
//!   totals. See `tests/bulk_emit_hybrid.rs` for the schema contract.

use std::fs;
use std::path::{Path, PathBuf};
use std::time::{SystemTime, UNIX_EPOCH};

use anyhow::{anyhow, bail, Context};
use serde_json::{json, Value};
use sha2::{Digest, Sha256};

use crate::context::CrossLayerContext;

/// Padded width for HBC function-id filename prefixes. 6 digits handles up
/// to 999,999 functions; React-Native bundles top out well under that.
const HBC_ID_WIDTH: usize = 6;

/// Bulk-decompile every loaded layer to a structured directory tree.
/// Writes meta.json (the canonical summary) and returns the same JSON value
/// for the caller to emit on stdout.
///
/// `overwrite`: when false, errors if `dir` is a non-empty existing directory.
/// When true, writes into the existing tree (files overwrite, residual files
/// from prior runs left intact — operator can `rm -rf <dir>` for clean slate).
pub fn bulk_emit_to_dir(
    ctx: &CrossLayerContext,
    dir: &Path,
    overwrite: bool,
    input_path: &Path,
    command_line: String,
) -> anyhow::Result<Value> {
    if ctx.hbc.is_none() && ctx.dex.is_empty() {
        bail!("no bytecode found in target");
    }

    let started_at = chrono::Utc::now();

    // Non-empty-dir guard: bail loud unless --overwrite was asked for,
    // so prior output is not silently clobbered.
    if dir.exists() {
        if !dir.is_dir() {
            bail!("--out target exists and is not a directory: {}", dir.display());
        }
        let non_empty = fs::read_dir(dir)
            .with_context(|| format!("reading --out dir: {}", dir.display()))?
            .next()
            .is_some();
        if non_empty && !overwrite {
            bail!(
                "--out dir {} is not empty; pass --overwrite or pick a fresh dir",
                dir.display()
            );
        }
    } else {
        fs::create_dir_all(dir)
            .with_context(|| format!("creating --out dir: {}", dir.display()))?;
    }

    let input_bytes = fs::read(input_path)
        .with_context(|| format!("reading input for sha256: {}", input_path.display()))?;
    let input_sha = hex_sha256(&input_bytes);
    let input_size = input_bytes.len();
    drop(input_bytes);

    // ── DEX layers ─────────────────────────────────────────────────────
    // Two-level rayon:
    //   Phase 1 — outer per-DEX loop (each DEX is fully independent).
    //   Phase 2 — inner per-class loop inside each DEX.
    //
    // Per-DEX: collect into a Vec keyed by index so meta.json
    // `layers.dex.files[]` ordering stays deterministic (dex1, dex2, ...)
    // regardless of thread completion order.
    //
    // Per-class (Phase 2): `decompile_class_with_census` is safe to call
    // concurrently — it takes only `&` refs, returns owned `String`, and
    // all interior diagnostics route through `thread_local! DIAG` (each
    // rayon worker gets its own instance). `count_class_methods` is a
    // pure read of a HashMap. `fs::create_dir_all` is idempotent on
    // POSIX and handles concurrent calls on the same path correctly.
    //
    // Accumulator reduction: each parallel work-item returns a
    // `ClassEmit` (0 or 1 classes, method count, byte count). The
    // post-collect serial fold sums them — simpler than fold+reduce
    // inside par_iter and matches Phase 1's pattern.
    use rayon::iter::{IndexedParallelIterator, IntoParallelIterator, IntoParallelRefIterator, ParallelIterator};

    /// Per-class emit stats accumulated across the parallel inner loop.
    struct ClassEmit {
        classes: u64,
        methods: u64,
        sources_bytes: u64,
    }

    let per_dex: Vec<anyhow::Result<Option<Value>>> = (0..ctx.dex.len())
        .into_par_iter()
        .map(|i| -> anyhow::Result<Option<Value>> {
            let dex = &ctx.dex[i];
            let Some(dex_data) = ctx.dex_bytes(i) else {
                return Ok(None);
            };
            let apk_entry = dex_entry_name(ctx, i);
            let subdir = sanitize_subdir(&apk_entry);
            let dex_root = dir.join("dex").join(&subdir);
            let sources_root = dex_root.join("sources");
            fs::create_dir_all(&sources_root)
                .with_context(|| format!("creating {}", sources_root.display()))?;

            let census = droidsaw_dex::r8_inversion::build_trampoline_census(dex);

            // Inner per-class parallel loop. Each work-item is independent:
            // different class_def, different output path, no shared mutable
            // state. Shadowed / invalid-descriptor / path-traversal-rejected
            // classes produce a zero-count ClassEmit; write errors propagate.
            let class_results: Vec<anyhow::Result<ClassEmit>> = dex
                .class_defs
                .par_iter()
                .enumerate()
                .map(|(class_defs_idx, class_def)| -> anyhow::Result<ClassEmit> {
                    if dex.class_def_is_shadowed(class_defs_idx) {
                        return Ok(ClassEmit { classes: 0, methods: 0, sources_bytes: 0 });
                    }
                    let Some(descriptor) = dex
                        .type_descriptors
                        .get(class_def.class_idx.0 as usize)
                        .cloned()
                    else {
                        return Ok(ClassEmit { classes: 0, methods: 0, sources_bytes: 0 });
                    };
                    // Reject adversarial descriptors that would escape
                    // `sources_root` via `..` / absolute / prefix components.
                    let Some(rel) = safe_class_file_rel_path(&descriptor) else {
                        return Ok(ClassEmit { classes: 0, methods: 0, sources_bytes: 0 });
                    };
                    let source = droidsaw_dex::classes::decompile_class_with_census(
                        dex, dex_data, class_def, &census,
                    );
                    let full = sources_root.join(&rel);
                    if let Some(parent) = full.parent() {
                        fs::create_dir_all(parent)
                            .with_context(|| format!("creating {}", parent.display()))?;
                    }
                    fs::write(&full, source.as_bytes())
                        .with_context(|| format!("writing {}", full.display()))?;

                    Ok(ClassEmit {
                        classes: 1,
                        methods: count_class_methods(dex, class_def),
                        sources_bytes: source.len() as u64,
                    })
                })
                .collect();

            // Fold class-level results; propagate any write error.
            let mut classes_emitted: u64 = 0;
            let mut methods_emitted: u64 = 0;
            let mut sources_files: u64 = 0;
            let mut sources_bytes: u64 = 0;
            for r in class_results {
                let emit = r?;
                classes_emitted = classes_emitted.saturating_add(emit.classes);
                methods_emitted = methods_emitted.saturating_add(emit.methods);
                // sources_files == classes_emitted (one .java file per emitted class)
                sources_files = sources_files.saturating_add(emit.classes);
                sources_bytes = sources_bytes.saturating_add(emit.sources_bytes);
            }

            let dex_sha = hex_sha256(dex_data);
            let dex_size = dex_data.len();

            Ok(Some(json!({
                "apk_entry": apk_entry,
                "subdir": subdir,
                "sha256": dex_sha,
                "size_bytes": dex_size,
                "classes_emitted": classes_emitted,
                "methods_emitted": methods_emitted,
                "formats": {
                    "sources": {"files": sources_files, "bytes": sources_bytes},
                },
            })))
        })
        .collect();

    let mut dex_files_meta: Vec<Value> = Vec::with_capacity(ctx.dex.len());
    let mut total_dex_classes: u64 = 0;
    let mut total_dex_methods: u64 = 0;
    for r in per_dex {
        let Some(v) = r? else {
            continue;
        };
        // Accumulate totals from the canonical per-DEX counts. Pull via
        // `.get()` rather than `&str` indexing to keep this code safe
        // against future schema renames; the field set is locally pinned
        // a few lines above so this is a tight contract.
        let classes = v
            .pointer("/classes_emitted")
            .and_then(Value::as_u64)
            .unwrap_or(0);
        let methods = v
            .pointer("/methods_emitted")
            .and_then(Value::as_u64)
            .unwrap_or(0);
        total_dex_classes = total_dex_classes.saturating_add(classes);
        total_dex_methods = total_dex_methods.saturating_add(methods);
        dex_files_meta.push(v);
    }

    // ── HBC layer ──────────────────────────────────────────────────────
    let hbc_meta = if let Some(hbc_owned) = ctx.hbc.as_ref() {
        let hbc_root = dir.join("hbc");
        fs::create_dir_all(&hbc_root)
            .with_context(|| format!("creating {}", hbc_root.display()))?;
        let hbc = hbc_owned.hbc();
        let function_count = hbc.function_count;
        let bundle_bytes = hbc_owned.bytes();
        let hbc_sha = hex_sha256(bundle_bytes);
        let hbc_size = bundle_bytes.len();

        // Phase 3 — per-function parallel HBC emit.
        //
        // Each fid is fully independent: different output path, no shared
        // mutable state. `decompile_hbc_function` takes only `&ctx`; both
        // `CrossLayerContext` and `HbcFile<'_>` are `Sync` (no interior
        // mutability in either type).
        //
        // HermesFindingDrainGuard concern: FINDINGS is a thread_local channel.
        // Installing ONE guard at the outer loop boundary (Phase 2 shape)
        // only drains the calling thread's channel; rayon workers accumulate
        // findings in their own per-thread channels that persist across work
        // items on the same worker thread (rayon reuses threads across the
        // par_iter scope). Fix: install a per-closure guard inside each
        // work item. `install_discard()` calls `discard_findings()` at
        // install AND Drop fires discard at exit — both ends covered.
        // Per-closure overhead is ~50 µs (one TLS clear), negligible vs
        // the decompile work itself.

        /// Per-function emit stats for the parallel reduction.
        struct HbcEmit {
            functions: u64,
            js_bytes: u64,
        }

        let fn_results: Vec<anyhow::Result<HbcEmit>> = (0..function_count)
            .into_par_iter()
            .map(|fid| -> anyhow::Result<HbcEmit> {
                // Per-worker drain guard — defends against rayon worker reuse
                // leaking findings between work items on the same thread.
                let _drain_guard =
                    crate::context::HermesFindingDrainGuard::install_discard();
                let Some((raw_name, source)) =
                    super::decompile::decompile_hbc_function(ctx, fid, true)
                else {
                    return Ok(HbcEmit { functions: 0, js_bytes: 0 });
                };
                let fname = hbc_function_filename(fid, &raw_name, "js");
                let full = hbc_root.join(&fname);
                fs::write(&full, source.as_bytes())
                    .with_context(|| format!("writing {}", full.display()))?;
                Ok(HbcEmit {
                    functions: 1,
                    js_bytes: source.len() as u64,
                })
            })
            .collect();

        let mut functions_emitted: u64 = 0;
        let mut js_files: u64 = 0;
        let mut js_bytes: u64 = 0;
        for r in fn_results {
            let emit = r?;
            functions_emitted = functions_emitted.saturating_add(emit.functions);
            // js_files is 1:1 with functions (one .js per emitted function).
            js_files = js_files.saturating_add(emit.functions);
            js_bytes = js_bytes.saturating_add(emit.js_bytes);
        }

        Some(json!({
            "sha256": hbc_sha,
            "size_bytes": hbc_size,
            "bundle_version": hbc.opcode_version(),
            "functions_emitted": functions_emitted,
            "formats": {
                "js": {"files": js_files, "bytes": js_bytes},
            },
        }))
    } else {
        None
    };

    // ── strings (per layer) ────────────────────────────────────────────
    let strings_meta = write_strings_dump(ctx, dir)?;

    let completed_at = chrono::Utc::now();
    let wall_seconds = (completed_at - started_at).num_milliseconds() as f64 / 1000.0;

    let mut layers = serde_json::Map::new();
    if !ctx.dex.is_empty() {
        layers.insert(
            "dex".to_string(),
            json!({
                "files": dex_files_meta,
                "totals": {
                    "classes_emitted": total_dex_classes,
                    "methods_emitted": total_dex_methods,
                },
            }),
        );
    }
    if let Some(h) = hbc_meta {
        layers.insert("hbc".to_string(), h);
    }

    // ── APK identity (manifest + signing) for cross-version reproducibility ─
    // Reverser comparing droidsaw runs across APK versions needs more than
    // input.sha256 — package + versionCode + signer cert are what answer
    // "is this the same app from the same vendor at version N?". All cheap
    // to compute from already-parsed Apk; included when APK input only.
    let apk_meta = ctx.apk.as_ref().map(|apk| {
        let manifest = apk.decode_manifest();
        let manifest_json = manifest.map(|m| {
            json!({
                "package": m.package,
                "version_code": m.version_code,
                "version_name": m.version_name,
                "min_sdk": m.min_sdk,
                "target_sdk": m.target_sdk,
                "target_sdk_int": m.target_sdk_int,
            })
        });
        let signing_json = apk.signing_info().ok().map(|s| {
            // v1_cert.not_before is the earliest UTC moment the signing
            // cert was valid — the closest in-APK proxy for "when was
            // this built / released?". APK zip entry timestamps are
            // zeroed at build time so they carry no signal; the cert
            // validity window is the only intrinsic date.
            json!({
                "v1_present": s.v1_cert.is_some(),
                "v2_present": s.v2_present,
                "v3_present": s.v3_present,
                "v4_present": s.v4_present,
                "source_stamp_present": s.source_stamp_present,
                "signers_count": s.signers.len(),
                "v1_cert_sha256_fingerprint": s.v1_cert.as_ref().map(|c| c.sha256_fingerprint.clone()),
                "v1_cert_subject": s.v1_cert.as_ref().map(|c| c.subject.clone()),
                "v1_cert_not_before": s.v1_cert.as_ref().map(|c| c.not_before.clone()),
                "v1_cert_not_after": s.v1_cert.as_ref().map(|c| c.not_after.clone()),
            })
        });
        json!({
            "manifest": manifest_json,
            "signing": signing_json,
        })
    });

    let meta = json!({
        "schema_version": 2,
        "input": {
            "path": input_path.to_string_lossy(),
            "sha256": input_sha,
            "size_bytes": input_size,
        },
        "apk": apk_meta,
        "droidsaw": {
            "version": env!("CARGO_PKG_VERSION"),
            "rev": option_env!("DROIDSAW_GIT_REV").unwrap_or("unknown"),
            "build_profile": if cfg!(debug_assertions) { "debug" } else { "release" },
        },
        "command": command_line,
        "started_at": started_at.to_rfc3339(),
        "completed_at": completed_at.to_rfc3339(),
        "wall_seconds": wall_seconds,
        "layers": layers,
        "strings": strings_meta,
    });

    // Write meta.json LAST so its presence == clean run. Operator checks
    // for meta.json as the gauge.
    let meta_path = dir.join("meta.json");
    let serialized = serde_json::to_string_pretty(&meta)?;
    fs::write(&meta_path, &serialized)
        .with_context(|| format!("writing {}", meta_path.display()))?;

    Ok(meta)
}

/// SHA-256 hex digest of a byte slice.
fn hex_sha256(bytes: &[u8]) -> String {
    let mut h = Sha256::new();
    h.update(bytes);
    let digest = h.finalize();
    let mut s = String::with_capacity(64);
    for byte in digest {
        let _ = std::fmt::Write::write_fmt(&mut s, format_args!("{byte:02x}"));
    }
    s
}

/// Name of the i-th DEX in the loaded context. For APK input, this is the
/// in-zip filename (e.g., `classes.dex`, `assets/longtail/classes.dex`).
/// For raw-DEX input, returns `classes.dex` as a stable fallback so the
/// subdir is non-empty and consistent across runs.
fn dex_entry_name(ctx: &CrossLayerContext, i: usize) -> String {
    if let Some(apk) = ctx.apk.as_ref() {
        if let Some(entry) = apk.dex.get(i) {
            return entry.name.clone();
        }
    }
    if i == 0 {
        return "classes.dex".to_string();
    }
    format!("classes{}.dex", i.saturating_add(1))
}

/// Convert an APK entry name into a filesystem-safe subdir name.
/// `classes.dex` → `classes`. `assets/longtail/classes.dex` →
/// `assets_longtail_classes`. `<split>:classes.dex` →
/// `<split>_classes` (droidsaw-apk qualifies multi-split DEX names
/// with `<apk-prefix>:` for disambiguation; `:` breaks fs portability
/// on some targets so we normalize it).
///
/// Drops the `.dex` suffix; replaces every character outside
/// `[A-Za-z0-9_-]` (including `.`) with `_` to prevent any traversal
/// component from surviving. Names that sanitize to empty, dot-only,
/// or underscore-only get replaced with `unnamed_dex` so we never
/// produce a subdir whose name resolves to a parent / cwd traversal
/// component on join.
fn sanitize_subdir(entry: &str) -> String {
    let no_ext = entry.strip_suffix(".dex").unwrap_or(entry);
    let sanitized: String = no_ext
        .chars()
        .map(|c| if c.is_ascii_alphanumeric() || c == '_' || c == '-' { c } else { '_' })
        .collect();
    if sanitized.is_empty() || sanitized.chars().all(|c| c == '_') {
        return "unnamed_dex".to_string();
    }
    sanitized
}

/// Approximate method count for a class_def by walking class_data (direct +
/// virtual methods). Canonical denominator for `methods_emitted`. Counts
/// methods INCLUDING abstract/native (which have no body) — matches the
/// "emitted as a method declaration" notion since the decompiler emits a
/// signature even when there's no body.
fn count_class_methods(
    dex: &droidsaw_dex::DexFile,
    class_def: &droidsaw_dex::ids::ClassDefItem,
) -> u64 {
    dex.class_datas
        .get(&class_def.class_data_off)
        .map(|cd| {
            cd.direct_methods
                .len()
                .saturating_add(cd.virtual_methods.len()) as u64
        })
        .unwrap_or(0)
}

/// Translate a JVM descriptor into a relative .java file path, validating
/// that every resulting path component is `Component::Normal` (no `..`,
/// no `/`, no absolute root, no `.` traversal). Returns `None` for
/// descriptors that would escape the caller's output directory if joined
/// — attacker-controlled DEX descriptors can otherwise embed `../` to
/// write files outside the intended tree.
fn safe_class_file_rel_path(descriptor: &str) -> Option<PathBuf> {
    let inner = descriptor
        .strip_prefix('L')
        .and_then(|s| s.strip_suffix(';'))
        .unwrap_or(descriptor);
    let raw = PathBuf::from(inner);
    let mut out = PathBuf::new();
    for comp in raw.components() {
        match comp {
            std::path::Component::Normal(seg) => out.push(seg),
            // ParentDir, CurDir, RootDir, Prefix all rejected as
            // traversal vectors regardless of source.
            _ => return None,
        }
    }
    if out.as_os_str().is_empty() {
        return None;
    }
    out.set_extension("java");
    Some(out)
}

/// Construct a per-function filename: `f<padded-id>_<sanitized-name>.<ext>`.
/// Function name characters outside `[A-Za-z0-9_-]` get replaced with `_`
/// so the filename is portable across filesystems. Original name preserved
/// in meta.json (when meta.json carries per-function metadata; this commit
/// keeps only aggregate counts).
fn hbc_function_filename(fid: u32, raw_name: &str, ext: &str) -> String {
    // Build the sanitized name and cap by char count (not byte index) so
    // a future relaxation of the char allowlist can't introduce a
    // panic-on-non-ASCII-boundary slice. Current sanitizer maps every
    // input char to one ASCII char, but the take(80) shape is safe under
    // any relaxation.
    let safe: String = raw_name
        .chars()
        .map(|c| if c.is_ascii_alphanumeric() || c == '_' || c == '-' { c } else { '_' })
        .take(80)
        .collect();
    format!("f{fid:0width$}_{safe}.{ext}", width = HBC_ID_WIDTH)
}

/// Dump per-layer string tables. Returns a JSON object with per-layer
/// `{lines, bytes, sha256}` entries (or `null` if a layer is absent).
fn write_strings_dump(ctx: &CrossLayerContext, dir: &Path) -> anyhow::Result<Value> {
    let strings_root = dir.join("strings");
    fs::create_dir_all(&strings_root)?;

    let mut out = serde_json::Map::new();
    for (layer, present) in [
        ("dex", !ctx.dex.is_empty()),
        ("hbc", ctx.hbc.is_some()),
    ] {
        if !present {
            out.insert(layer.to_string(), Value::Null);
            continue;
        }
        let v = super::strings::strings(ctx, None, None, None, Some(layer))?;
        let path = strings_root.join(format!("{layer}.txt"));
        let entries = v
            .get("strings")
            .and_then(Value::as_array)
            .ok_or_else(|| anyhow!("strings command did not return a `strings` array"))?;
        let mut buf = String::new();
        let mut lines: u64 = 0;
        for entry in entries {
            if let Some(s) = entry.get("value").and_then(Value::as_str) {
                buf.push_str(s);
                buf.push('\n');
                lines = lines.saturating_add(1);
            }
        }
        let bytes = buf.len() as u64;
        fs::write(&path, &buf)?;
        let sha = hex_sha256(buf.as_bytes());
        out.insert(
            layer.to_string(),
            json!({"lines": lines, "bytes": bytes, "sha256": sha}),
        );
    }
    // Native strings: extracted via the existing strings command with
    // `layer_filter=Some("native")` IF the APK has native libs. Same
    // shape; absent → null.
    let native_present = ctx
        .apk
        .as_ref()
        .map(|a| !a.native_libs.is_empty())
        .unwrap_or(false);
    if native_present {
        let v = super::strings::strings(ctx, None, None, None, Some("native"))?;
        let path = strings_root.join("native.txt");
        let entries = v
            .get("strings")
            .and_then(Value::as_array)
            .ok_or_else(|| anyhow!("strings command did not return a `strings` array"))?;
        let mut buf = String::new();
        let mut lines: u64 = 0;
        for entry in entries {
            if let Some(s) = entry.get("value").and_then(Value::as_str) {
                buf.push_str(s);
                buf.push('\n');
                lines = lines.saturating_add(1);
            }
        }
        let bytes = buf.len() as u64;
        fs::write(&path, &buf)?;
        let sha = hex_sha256(buf.as_bytes());
        out.insert(
            "native".to_string(),
            json!({"lines": lines, "bytes": bytes, "sha256": sha}),
        );
    } else {
        out.insert("native".to_string(), Value::Null);
    }
    Ok(Value::Object(out))
}

#[allow(dead_code, reason = "exported for the SystemTime epoch alias if future commits need raw epoch fallback when chrono is unavailable")]
fn unix_epoch_seconds() -> u64 {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|d| d.as_secs())
        .unwrap_or(0)
}

#[cfg(test)]
#[allow(clippy::unwrap_used, clippy::expect_used, reason = "test module")]
mod path_safety_tests {
    use super::*;

    #[test]
    fn safe_class_file_rel_path_accepts_normal_descriptor() {
        let p = safe_class_file_rel_path("Lcom/example/Foo;").unwrap();
        assert_eq!(p, PathBuf::from("com/example/Foo.java"));
    }

    #[test]
    fn safe_class_file_rel_path_accepts_inner_class_dollar() {
        let p = safe_class_file_rel_path("Lcom/example/Foo$Bar;").unwrap();
        assert_eq!(p, PathBuf::from("com/example/Foo$Bar.java"));
    }

    #[test]
    fn safe_class_file_rel_path_rejects_parent_dir_traversal() {
        // Adversarial DEX with crafted descriptor: `..` component would
        // join above `sources_root` and write outside the operator's tree.
        assert!(safe_class_file_rel_path("L../etc/passwd;").is_none());
        assert!(safe_class_file_rel_path("L../../etc/passwd;").is_none());
        assert!(safe_class_file_rel_path("Lcom/../../etc/passwd;").is_none());
    }

    #[test]
    fn safe_class_file_rel_path_rejects_root_absolute() {
        assert!(safe_class_file_rel_path("L/etc/passwd;").is_none());
    }

    #[test]
    fn safe_class_file_rel_path_rejects_empty() {
        assert!(safe_class_file_rel_path("L;").is_none());
        assert!(safe_class_file_rel_path("").is_none());
    }

    #[test]
    fn sanitize_subdir_rejects_dot_traversal() {
        // Even with `.` allowed elsewhere, the subdir name must never be
        // a traversal component. APK entry literally named `..dex` would
        // strip the `.dex` suffix to `.` and historically pass through.
        assert_ne!(sanitize_subdir("..dex"), "..");
        assert_ne!(sanitize_subdir("..dex"), ".");
        assert_ne!(sanitize_subdir(".dex"), "");
        assert_eq!(sanitize_subdir(".dex"), "unnamed_dex");
        // Plain dots in any position become `_`.
        assert_eq!(sanitize_subdir("foo.bar.dex"), "foo_bar");
    }

    #[test]
    fn sanitize_subdir_replaces_colon_and_slash() {
        // droidsaw-apk multi-split DEX entry: `<split>:classes.dex`.
        assert_eq!(sanitize_subdir("my-split:classes.dex"), "my-split_classes");
        // Nested entries: `assets/longtail/classes.dex`.
        assert_eq!(sanitize_subdir("assets/longtail/classes.dex"), "assets_longtail_classes");
    }

    #[test]
    fn hbc_function_filename_caps_at_80_chars_after_sanitize() {
        let raw = "a".repeat(200);
        let f = hbc_function_filename(42, &raw, "js");
        // f<6>_<80 chars>.js → 1 + 6 + 1 + 80 + 3 = 91
        assert_eq!(f.len(), 91, "filename should cap at f<6>_<80 chars>.<ext>; got {f}");
        assert!(f.starts_with("f000042_"));
        assert!(f.ends_with(".js"));
    }

    #[test]
    fn hbc_function_filename_sanitizes_non_ascii_and_path_chars() {
        // Function name with `/`, `..`, non-ASCII, NUL: every non-
        // [A-Za-z0-9_-] char maps to `_`. Alphanumeric runs (`etc`,
        // `passwd`) survive verbatim. Demonstrates: no path separators
        // escape, no traversal components reach the filesystem layer.
        let f = hbc_function_filename(7, "../etc/passwd\0🤖", "js");
        assert_eq!(f, "f000007____etc_passwd__.js");
        assert!(!f.contains('/'));
        assert!(!f.contains(".."));
    }
}