coreshift_core/

dex.rs

// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

//! Minimal ZIP + DEX parser for reading TRANSACTION_* static int field values
//! from `framework.jar` without any subprocess or external tool.
//!
//! Only handles STORED (uncompressed) DEX entries. Android framework JARs
//! store DEX uncompressed so ART can mmap directly from the ZIP.

// ── Byte readers ──────────────────────────────────────────────────────────────

fn u16le(b: &[u8], off: usize) -> Option<u16> {
    let s = b.get(off..off + 2)?;
    Some(u16::from_le_bytes([s[0], s[1]]))
}

fn u32le(b: &[u8], off: usize) -> Option<u32> {
    let s = b.get(off..off + 4)?;
    Some(u32::from_le_bytes([s[0], s[1], s[2], s[3]]))
}

fn uleb128(b: &[u8], off: &mut usize) -> Option<u32> {
    let mut result = 0u32;
    let mut shift = 0u32;
    loop {
        let byte = *b.get(*off)?;
        *off += 1;
        result |= ((byte & 0x7f) as u32) << shift;
        if byte & 0x80 == 0 {
            return Some(result);
        }
        shift += 7;
        if shift >= 35 {
            return None;
        }
    }
}

// ── ZIP ───────────────────────────────────────────────────────────────────────

const ZIP_EOCD_SIG: [u8; 4] = [0x50, 0x4b, 0x05, 0x06];
const ZIP_CD_SIG: [u8; 4] = [0x50, 0x4b, 0x01, 0x02];
const ZIP_LOCAL_SIG: [u8; 4] = [0x50, 0x4b, 0x03, 0x04];
const ZIP_STORED: u16 = 0;

struct ZipEntry {
    local_off: usize,
    comp_size: usize,
}

fn zip_find_dex_entries(data: &[u8]) -> Vec<ZipEntry> {
    // Scan backwards for EOCD (ignore ZIP comment — Android JARs have none).
    let scan_start = data.len().saturating_sub(65558);
    let eocd_pos = match data[scan_start..]
        .windows(4)
        .rposition(|w| w == ZIP_EOCD_SIG)
    {
        Some(p) => scan_start + p,
        None => return Vec::new(),
    };

    let cd_size = match u32le(data, eocd_pos + 12) {
        Some(v) => v as usize,
        None => return Vec::new(),
    };
    let cd_off = match u32le(data, eocd_pos + 16) {
        Some(v) => v as usize,
        None => return Vec::new(),
    };

    let mut pos = cd_off;
    let cd_end = cd_off.saturating_add(cd_size);
    let mut entries = Vec::new();

    while pos + 46 <= cd_end && pos + 46 <= data.len() {
        if data.get(pos..pos + 4) != Some(&ZIP_CD_SIG) {
            break;
        }

        let compression = match u16le(data, pos + 10) {
            Some(v) => v,
            None => break,
        };
        let comp_size = match u32le(data, pos + 20) {
            Some(v) => v as usize,
            None => break,
        };
        let local_off = match u32le(data, pos + 42) {
            Some(v) => v as usize,
            None => break,
        };
        let fname_len = match u16le(data, pos + 28) {
            Some(v) => v as usize,
            None => break,
        };
        let extra_len = match u16le(data, pos + 30) {
            Some(v) => v as usize,
            None => break,
        };
        let comment_len = match u16le(data, pos + 32) {
            Some(v) => v as usize,
            None => break,
        };

        let fname_end = pos + 46 + fname_len;
        if fname_end > data.len() {
            break;
        }
        let fname = &data[pos + 46..fname_end];

        // Collect classes*.dex entries that are STORED.
        let is_dex = fname.starts_with(b"classes") && fname.ends_with(b".dex");
        if is_dex && compression == ZIP_STORED {
            entries.push(ZipEntry {
                local_off,
                comp_size,
            });
        }

        pos = match pos.checked_add(46 + fname_len + extra_len + comment_len) {
            Some(v) => v,
            None => break,
        };
    }

    // Sort by comp_size descending: the largest DEX is most likely to
    // contain IActivityManager.
    entries.sort_by_key(|e| std::cmp::Reverse(e.comp_size));
    entries
}

fn zip_entry_data<'a>(data: &'a [u8], entry: &ZipEntry) -> Option<&'a [u8]> {
    let lh = entry.local_off;
    if data.get(lh..lh + 4) != Some(&ZIP_LOCAL_SIG) {
        return None;
    }
    let fname_len = u16le(data, lh + 26)? as usize;
    let extra_len = u16le(data, lh + 28)? as usize;
    let data_start = lh + 30 + fname_len + extra_len;
    data.get(data_start..data_start + entry.comp_size)
}

// ── DEX ───────────────────────────────────────────────────────────────────────

const DEX_MAGIC: &[u8] = b"dex\n";

fn dex_string(dex: &[u8], string_ids_off: usize, idx: usize) -> Option<&[u8]> {
    let str_data_off = u32le(dex, string_ids_off + idx * 4)? as usize;
    // Skip ULEB128 UTF-16 length
    let mut off = str_data_off;
    loop {
        let b = *dex.get(off)?;
        off += 1;
        if b & 0x80 == 0 {
            break;
        }
    }
    // Null-terminated MUTF-8 bytes
    let start = off;
    while *dex.get(off)? != 0 {
        off += 1;
    }
    dex.get(start..off)
}

fn skip_encoded_value(dex: &[u8], off: &mut usize) -> Option<()> {
    let vbyte = *dex.get(*off)?;
    *off += 1;
    let vtype = vbyte & 0x1f;
    let varg = (vbyte >> 5) as usize;
    match vtype {
        // value_arg+1 bytes follow
        0x00 | 0x02 | 0x03 | 0x04 | 0x06 | 0x10 | 0x11 | 0x15 | 0x16 | 0x17 | 0x18 | 0x19
        | 0x1a | 0x1b => {
            *off = off.checked_add(varg + 1)?;
        }
        0x1c => {
            // VALUE_ARRAY
            let size = uleb128(dex, off)?;
            for _ in 0..size {
                skip_encoded_value(dex, off)?;
            }
        }
        0x1d => {
            // VALUE_ANNOTATION
            uleb128(dex, off)?; // type_idx
            let size = uleb128(dex, off)?;
            for _ in 0..size {
                uleb128(dex, off)?; // name_idx
                skip_encoded_value(dex, off)?;
            }
        }
        0x1e | 0x1f => {} // VALUE_NULL / VALUE_BOOLEAN — no extra bytes
        _ => return None,
    }
    Some(())
}

fn read_int_encoded_value(dex: &[u8], off: &mut usize) -> Option<u32> {
    let vbyte = *dex.get(*off)?;
    *off += 1;
    let vtype = vbyte & 0x1f;
    let varg = (vbyte >> 5) as usize;
    // VALUE_INT = 0x04, value_arg+1 bytes, little-endian
    if vtype != 0x04 {
        return None;
    }
    let size = varg + 1;
    if size > 4 {
        return None;
    }
    let mut val = 0u32;
    for i in 0..size {
        val |= (*dex.get(*off + i)? as u32) << (i * 8);
    }
    *off += size;
    Some(val)
}

fn find_in_dex(dex: &[u8], class_desc: &[u8], field_name: &[u8]) -> Option<u32> {
    if !dex.starts_with(DEX_MAGIC) || dex.len() < 112 {
        return None;
    }

    let string_ids_size = u32le(dex, 56)? as usize;
    let string_ids_off = u32le(dex, 60)? as usize;
    let type_ids_size = u32le(dex, 64)? as usize;
    let type_ids_off = u32le(dex, 68)? as usize;
    let field_ids_size = u32le(dex, 80)? as usize;
    let field_ids_off = u32le(dex, 84)? as usize;
    let class_defs_size = u32le(dex, 96)? as usize;
    let class_defs_off = u32le(dex, 100)? as usize;

    // Find string index for class descriptor
    let mut class_str_idx: Option<usize> = None;
    for i in 0..string_ids_size {
        if dex_string(dex, string_ids_off, i) == Some(class_desc) {
            class_str_idx = Some(i);
            break;
        }
    }
    let class_str_idx = class_str_idx?;

    // Find type index
    let mut class_type_idx: Option<usize> = None;
    for i in 0..type_ids_size {
        if u32le(dex, type_ids_off + i * 4)? as usize == class_str_idx {
            class_type_idx = Some(i);
            break;
        }
    }
    let class_type_idx = class_type_idx?;

    // Find string index for field name
    let mut field_str_idx: Option<u32> = None;
    for i in 0..string_ids_size {
        if dex_string(dex, string_ids_off, i) == Some(field_name) {
            field_str_idx = Some(i as u32);
            break;
        }
    }
    let field_str_idx = field_str_idx?;

    // Find global field_idx in field_ids
    let mut target_field_idx: Option<u32> = None;
    for i in 0..field_ids_size {
        let foff = field_ids_off + i * 8;
        let fclass = u16le(dex, foff)? as usize;
        let fname = u32le(dex, foff + 4)?;
        if fclass == class_type_idx && fname == field_str_idx {
            target_field_idx = Some(i as u32);
            break;
        }
    }
    let target_field_idx = target_field_idx?;

    // Find class def
    let mut class_data_off = None;
    let mut static_vals_off = None;
    for i in 0..class_defs_size {
        let coff = class_defs_off + i * 32;
        if u32le(dex, coff)? as usize == class_type_idx {
            class_data_off = Some(u32le(dex, coff + 24)? as usize);
            static_vals_off = Some(u32le(dex, coff + 28)? as usize);
            break;
        }
    }
    let class_data_off = class_data_off?;
    let static_vals_off = static_vals_off?;
    if class_data_off == 0 || static_vals_off == 0 {
        return None;
    }

    // Walk class_data_item static fields to find position of target_field_idx
    let mut off = class_data_off;
    let static_fields_size = uleb128(dex, &mut off)?;
    let _instance_fields = uleb128(dex, &mut off)?;
    let _direct_methods = uleb128(dex, &mut off)?;
    let _virtual_methods = uleb128(dex, &mut off)?;

    let mut field_pos: Option<usize> = None;
    let mut cur_field_idx = 0u32;
    for i in 0..static_fields_size as usize {
        let diff = uleb128(dex, &mut off)?;
        let _access_flags = uleb128(dex, &mut off)?;
        cur_field_idx += diff;
        if cur_field_idx == target_field_idx {
            field_pos = Some(i);
            break;
        }
    }
    let field_pos = field_pos?;

    // Read encoded_array at static_vals_off, skip to field_pos, read int
    let mut sv = static_vals_off;
    let sv_size = uleb128(dex, &mut sv)? as usize;
    if field_pos >= sv_size {
        return None;
    }

    for i in 0..=field_pos {
        if i == field_pos {
            return read_int_encoded_value(dex, &mut sv);
        }
        skip_encoded_value(dex, &mut sv)?;
    }
    None
}

/// Return the declared parameter types of a DEX method's proto.
///
/// Looks up `class_desc.method_name` in the method_ids table and returns the
/// type descriptor list from the referenced proto's type_list. Returns `None`
/// when any section is unreadable, the class is absent, or the method does
/// not exist (so callers can distinguish "method present" from "not found").
///
/// Needed DEX sections: string_ids (56/60), type_ids (64/68), proto_ids
/// (72/76), method_ids (88/92).
fn method_param_types<'a>(
    dex: &'a [u8],
    class_desc: &[u8],
    method_name: &[u8],
) -> Option<Vec<&'a [u8]>> {
    if !dex.starts_with(DEX_MAGIC) || dex.len() < 112 {
        return None;
    }

    let string_ids_size = u32le(dex, 56)? as usize;
    let string_ids_off = u32le(dex, 60)? as usize;
    let type_ids_size = u32le(dex, 64)? as usize;
    let type_ids_off = u32le(dex, 68)? as usize;
    let proto_ids_size = u32le(dex, 72)? as usize;
    let proto_ids_off = u32le(dex, 76)? as usize;
    let method_ids_size = u32le(dex, 88)? as usize;
    let method_ids_off = u32le(dex, 92)? as usize;

    // String idx for the class descriptor
    let mut class_str_idx: Option<usize> = None;
    for i in 0..string_ids_size {
        if dex_string(dex, string_ids_off, i) == Some(class_desc) {
            class_str_idx = Some(i);
            break;
        }
    }
    let class_str_idx = class_str_idx?;

    // Type idx for the class descriptor
    let mut class_type_idx: Option<usize> = None;
    for i in 0..type_ids_size {
        if u32le(dex, type_ids_off + i * 4)? as usize == class_str_idx {
            class_type_idx = Some(i);
            break;
        }
    }
    let class_type_idx = class_type_idx?;

    // String idx for the method name
    let mut method_str_idx: Option<u32> = None;
    for i in 0..string_ids_size {
        if dex_string(dex, string_ids_off, i) == Some(method_name) {
            method_str_idx = Some(i as u32);
            break;
        }
    }
    let method_str_idx = method_str_idx?;

    // Method idx → proto_idx, matching class and name
    let mut proto_idx: Option<usize> = None;
    for i in 0..method_ids_size {
        let moff = method_ids_off + i * 8;
        let fclass = u16le(dex, moff)? as usize;
        let fproto = u16le(dex, moff + 2)? as usize;
        let fname = u32le(dex, moff + 4)?;
        if fclass == class_type_idx && fname == method_str_idx {
            proto_idx = Some(fproto);
            break;
        }
    }
    let proto_idx = proto_idx?;
    if proto_idx >= proto_ids_size {
        return None;
    }

    // proto_id_item: shorty_idx, return_type_idx, parameters_off
    let poff = proto_ids_off + proto_idx * 12;
    let params_off = u32le(dex, poff + 8)? as usize;
    if params_off == 0 {
        return Some(Vec::new());
    }

    // type_list: size u32, then u16 type indices
    let param_count = u32le(dex, params_off)? as usize;
    let mut params = Vec::with_capacity(param_count);
    for i in 0..param_count {
        let tidx = u16le(dex, params_off + 4 + i * 2)? as usize;
        let desc_str_idx = u32le(dex, type_ids_off + tidx * 4)? as usize;
        let desc = dex_string(dex, string_ids_off, desc_str_idx)?;
        params.push(desc);
    }
    Some(params)
}

// ── Public API ────────────────────────────────────────────────────────────────

/// Search `framework.jar` for the value of a static int field.
///
/// `class_desc` uses DEX descriptor syntax, e.g.
/// `"Landroid/app/IActivityManager$Stub;"`.
///
/// Returns `None` if the JAR is unreadable, the class/field is absent, or
/// the entry is compressed (DEFLATE — not expected for framework DEX).
pub fn find_transaction_code(jar_path: &str, class_desc: &str, field_name: &str) -> Option<u32> {
    let data = std::fs::read(jar_path).ok()?;
    let entries = zip_find_dex_entries(&data);
    for entry in &entries {
        if let Some(dex) = zip_entry_data(&data, entry) {
            if let Some(code) = find_in_dex(dex, class_desc.as_bytes(), field_name.as_bytes()) {
                return Some(code);
            }
        }
    }
    None
}

/// Resolve all four tx codes needed for binder observer mode.
///
/// Returns `(observer_code, query_code, api_mode, fg_code)` where:
/// - `observer_code` = `TRANSACTION_registerProcessObserver`
/// - `query_code`    = `TRANSACTION_getFocusedRootTaskInfo` (or StackInfo on API 29)
/// - `api_mode`      = 1 (RootTaskInfo) or 2 (StackInfo)
/// - `fg_code`       = `TRANSACTION_onForegroundActivitiesChanged`
pub fn resolve_tx_codes_from_dex() -> Option<(u32, u32, u8, u32)> {
    const JAR: &str = "/system/framework/framework.jar";
    const AM_STUB: &str = "Landroid/app/IActivityManager$Stub;";
    const OBS_STUB: &str = "Landroid/app/IProcessObserver$Stub;";

    let observer_code = find_transaction_code(JAR, AM_STUB, "TRANSACTION_registerProcessObserver")?;
    let fg_code =
        find_transaction_code(JAR, OBS_STUB, "TRANSACTION_onForegroundActivitiesChanged")?;

    if let Some(query_code) =
        find_transaction_code(JAR, AM_STUB, "TRANSACTION_getFocusedRootTaskInfo")
    {
        return Some((observer_code, query_code, 1, fg_code));
    }
    // API 29 fallback
    let query_code = find_transaction_code(JAR, AM_STUB, "TRANSACTION_getFocusedStackInfo")?;
    Some((observer_code, query_code, 2, fg_code))
}

/// Resolve `IPowerManager.isInteractive()` transaction code from DEX.
pub fn resolve_is_interactive_tx() -> Option<u32> {
    const JAR: &str = "/system/framework/framework.jar";
    find_transaction_code(
        JAR,
        "Landroid/os/IPowerManager$Stub;",
        "TRANSACTION_isInteractive",
    )
}

/// Resolve the `IForegroundProcessObserver` registration tx codes from DEX.
///
/// Returns `(register_code, on_change_code)` where:
/// - `register_code` = `TRANSACTION_registerForegroundProcessObserver`
/// - `on_change_code` = `TRANSACTION_onForegroundProcessChanged`
pub fn resolve_fgproc_codes() -> Option<(u32, u32)> {
    const JAR: &str = "/system/framework/framework.jar";
    const AM_STUB: &str = "Landroid/app/IActivityManager$Stub;";
    const FGPROC_STUB: &str = "Landroid/app/IForegroundProcessObserver$Stub;";

    let register_code = find_transaction_code(
        JAR,
        AM_STUB,
        "TRANSACTION_registerForegroundProcessObserver",
    )?;
    let on_change_code =
        find_transaction_code(JAR, FGPROC_STUB, "TRANSACTION_onForegroundProcessChanged")?;
    Some((register_code, on_change_code))
}

/// Resolve the fallback `IProcessObserver` foreground observer tx codes used
/// by ROMs that removed `IForegroundProcessObserver`.
///
/// Custom ROMs drop the stock `IForegroundProcessObserver` (no
/// `registerForegroundProcessObserver` / `onForegroundProcessChanged`) but
/// repurpose `IProcessObserver.onForegroundActivitiesChanged` to deliver the
/// foreground **pid** (`(I,I,Z)V` — pid, uid, fg) instead of the stock
/// package string (`(String,I,Z)V`). For those ROMs the daemon can register
/// via the classic `registerProcessObserver` and read the pid straight out of
/// the callback parcel.
///
/// Returns `None` when the stock [`resolve_fgproc_codes`] path succeeds
/// (callers must prefer it), when `onForegroundActivitiesChanged` does not
/// lead with an `int` parameter, or when either tx code cannot be resolved.
pub fn resolve_fgproc_codes_fallback() -> Option<(u32, u32)> {
    const JAR: &str = "/system/framework/framework.jar";
    const AM_STUB: &str = "Landroid/app/IActivityManager$Stub;";
    const OBS_STUB: &str = "Landroid/app/IProcessObserver$Stub;";
    const OBS_IFACE: &str = "Landroid/app/IProcessObserver;";

    // Stock IForegroundProcessObserver present → stock path is fine.
    if resolve_fgproc_codes().is_some() {
        return None;
    }

    let data = std::fs::read(JAR).ok()?;
    let entries = zip_find_dex_entries(&data);

    // onForegroundActivitiesChanged must declare an int first param (pid);
    // stock String-first (pkg) form cannot serve this daemon.
    let mut pid_first = false;
    for entry in &entries {
        if let Some(dex) = zip_entry_data(&data, entry) {
            if let Some(params) =
                method_param_types(dex, OBS_IFACE.as_bytes(), b"onForegroundActivitiesChanged")
            {
                pid_first = params.first().map(|t| *t == b"I").unwrap_or(false);
                break;
            }
        }
    }
    if !pid_first {
        return None;
    }

    let register_code = find_transaction_code(JAR, AM_STUB, "TRANSACTION_registerProcessObserver")?;
    let on_change_code =
        find_transaction_code(JAR, OBS_STUB, "TRANSACTION_onForegroundActivitiesChanged")?;
    Some((register_code, on_change_code))
}

/// Resolve the `IWindowManager` task-FPS callback tx codes from DEX.
///
/// Returns `(register_code, unregister_code, on_fps_code)` where:
/// - `register_code`   = `TRANSACTION_registerTaskFpsCallback`
/// - `unregister_code` = `TRANSACTION_unregisterTaskFpsCallback`
/// - `on_fps_code`     = `TRANSACTION_onFpsReported` on `ITaskFpsCallback`
pub fn resolve_fps_codes() -> Option<(u32, u32, u32)> {
    const JAR: &str = "/system/framework/framework.jar";
    const IWM_STUB: &str = "Landroid/view/IWindowManager$Stub;";
    const FPS_STUB: &str = "Landroid/window/ITaskFpsCallback$Stub;";

    let register_code =
        find_transaction_code(JAR, IWM_STUB, "TRANSACTION_registerTaskFpsCallback")?;
    let unregister_code =
        find_transaction_code(JAR, IWM_STUB, "TRANSACTION_unregisterTaskFpsCallback")?;
    let on_fps_code = find_transaction_code(JAR, FPS_STUB, "TRANSACTION_onFpsReported")?;
    Some((register_code, unregister_code, on_fps_code))
}

/// Resolve the `IActivityTaskManager` task-stack listener tx codes from DEX.
///
/// Returns `(register_code, unregister_code)`:
/// - `register_code`   = `TRANSACTION_registerTaskStackListener`
/// - `unregister_code` = `TRANSACTION_unregisterTaskStackListener`
///
/// This target's ROM exposes the legacy `ITaskStackListener` /
/// `registerTaskStackListener` pair on `IActivityTaskManager`; the newer
/// `ITaskChangeListener` / `registerTaskChangeListener` interface is absent
/// and must not be relied on.
pub fn resolve_task_stack_codes() -> Option<(u32, u32)> {
    const JAR: &str = "/system/framework/framework.jar";
    const ATM_STUB: &str = "Landroid/app/IActivityTaskManager$Stub;";

    let register_code =
        find_transaction_code(JAR, ATM_STUB, "TRANSACTION_registerTaskStackListener")?;
    let unregister_code =
        find_transaction_code(JAR, ATM_STUB, "TRANSACTION_unregisterTaskStackListener")?;
    Some((register_code, unregister_code))
}

#[cfg(test)]
mod tests {
    use super::*;

    fn u32put(b: &mut [u8], off: usize, v: u32) {
        b[off..off + 4].copy_from_slice(&v.to_le_bytes());
    }

    // Build a minimal DEX header + string/type/proto/method id tables for a
    // single class with a single method whose proto has the given param type
    // descriptors. Only the sections method_param_types() reads are populated.
    fn build_dex(class_desc: &[u8], method_name: &[u8], params: &[&[u8]]) -> Vec<u8> {
        let mut out = vec![0u8; 112];
        out[0..4].copy_from_slice(DEX_MAGIC);
        out[4..8].copy_from_slice(b"035\0");

        let mut strings: Vec<Vec<u8>> = vec![class_desc.to_vec(), method_name.to_vec()];
        for p in params {
            if !strings.iter().any(|s| s == p) {
                strings.push(p.to_vec());
            }
        }
        let n_string = strings.len();
        let mut types: Vec<Vec<u8>> = vec![class_desc.to_vec()];
        for p in params {
            if !types.iter().any(|t| t == p) {
                types.push(p.to_vec());
            }
        }
        let n_type = types.len();

        let off_string_ids = 112;
        let off_type_ids = off_string_ids + n_string * 4;
        let off_proto_ids = off_type_ids + n_type * 4;
        let off_method_ids = off_proto_ids + 12; // one proto

        // Reserve id table space.
        out.resize(off_method_ids + 8, 0); // one method

        // string_data items (in file order, referenced by string_ids)
        let mut string_offs = Vec::with_capacity(n_string);
        for s in &strings {
            string_offs.push(out.len());
            let n = s.len() as u8;
            out.push(n); // short ULEB128 length (ASCII only)
            out.extend_from_slice(s);
            out.push(0);
        }

        // type_list for the single proto's parameters.
        let params_off = out.len();
        out.extend_from_slice(&(params.len() as u32).to_le_bytes());
        for p in params {
            let ti = types.iter().position(|t| t == p).unwrap();
            out.extend_from_slice(&(ti as u16).to_le_bytes());
        }

        // Header: counts + offsets (offsets 56..=100).
        u32put(&mut out, 56, n_string as u32);
        u32put(&mut out, 60, off_string_ids as u32);
        u32put(&mut out, 64, n_type as u32);
        u32put(&mut out, 68, off_type_ids as u32);
        u32put(&mut out, 72, 1); // proto count
        u32put(&mut out, 76, off_proto_ids as u32);
        u32put(&mut out, 80, 0); // field_ids count
        u32put(&mut out, 84, 0);
        u32put(&mut out, 88, 1); // method count
        u32put(&mut out, 92, off_method_ids as u32);
        u32put(&mut out, 96, 0); // class_defs count
        u32put(&mut out, 100, 0);

        // string_ids
        for (i, &so) in string_offs.iter().enumerate() {
            u32put(&mut out, off_string_ids + i * 4, so as u32);
        }
        // type_ids → descriptor string index
        for (i, t) in types.iter().enumerate() {
            let si = strings.iter().position(|s| s == t).unwrap();
            u32put(&mut out, off_type_ids + i * 4, si as u32);
        }
        // proto_ids: shorty, return, params_off
        u32put(&mut out, off_proto_ids, 0);
        u32put(&mut out, off_proto_ids + 4, 0);
        u32put(&mut out, off_proto_ids + 8, params_off as u32);
        // method_ids: class_idx, proto_idx, name_idx
        let m = off_method_ids;
        out[m..m + 2].copy_from_slice(&0u16.to_le_bytes());
        out[m + 2..m + 4].copy_from_slice(&0u16.to_le_bytes());
        u32put(&mut out, m + 4, 1);

        out
    }

    #[test]
    fn parses_int_first_proto() {
        let dex = build_dex(
            b"Landroid/app/IProcessObserver;",
            b"onForegroundActivitiesChanged",
            &[b"I", b"I", b"Z"],
        );
        let params = method_param_types(
            &dex,
            b"Landroid/app/IProcessObserver;",
            b"onForegroundActivitiesChanged",
        )
        .expect("method present");
        assert_eq!(params, [&b"I"[..], &b"I"[..], &b"Z"[..]]);
    }

    #[test]
    fn rejects_string_first_proto() {
        // Stock signature onForegroundActivitiesChanged(String, int, boolean)
        let dex = build_dex(
            b"Landroid/app/IProcessObserver;",
            b"onForegroundActivitiesChanged",
            &[b"Ljava/lang/String;", b"I", b"Z"],
        );
        let params = method_param_types(
            &dex,
            b"Landroid/app/IProcessObserver;",
            b"onForegroundActivitiesChanged",
        )
        .expect("method present");
        assert_eq!(params.first().map(|t| *t == b"I"), Some(false));
    }

    #[test]
    fn absent_method_returns_none() {
        let dex = build_dex(
            b"Landroid/app/IProcessObserver;",
            b"onForegroundActivitiesChanged",
            &[b"I"],
        );
        assert!(
            method_param_types(&dex, b"Landroid/app/IProcessObserver;", b"onProcessDied").is_none()
        );
    }
}