From 0e4d420f69030e5f94758b34283ffc80a211a41c Mon Sep 17 00:00:00 2001
From: Alex Konradi <akonradi@signal.org>
Date: Tue, 9 Jul 2024 13:07:36 -0400
Subject: [PATCH] Add libsignal-jni-testing crate with test-only functions for
 Java

This parallels the exiting libsignal-jni crate but exports functions from
libsignal-bridge-testing instead of libsignal-bridge. The crate is compiled as
a separate shared object that is included in the published libsignal package,
but which can be excluded at Android packaging time.
---
 Cargo.lock                                    | 32 ++++++++++++
 Cargo.toml                                    |  1 +
 acknowledgments/acknowledgments.html          |  4 +-
 acknowledgments/acknowledgments.md            |  2 +-
 acknowledgments/acknowledgments.plist         |  2 +-
 bin/update_versions.py                        |  5 +-
 java/android/build.gradle                     |  1 +
 java/build.gradle                             |  4 +-
 java/build_jni.sh                             |  5 +-
 .../org/signal/libsignal/internal/Native.java | 51 ++++++++++++-------
 .../libsignal/internal/NativeTesting.java     | 48 +++++++++++++++++
 .../libsignal/internal/NativeTestingTest.java | 18 +++++++
 rust/bridge/jni/bin/Native.java.in            | 51 ++++++++++++-------
 rust/bridge/jni/bin/NativeTesting.java.in     | 48 +++++++++++++++++
 rust/bridge/jni/bin/gen_java_decl.py          | 19 ++++---
 rust/bridge/jni/testing/Cargo.toml            | 25 +++++++++
 rust/bridge/jni/testing/cbindgen.toml         | 28 ++++++++++
 rust/bridge/jni/testing/src/lib.rs            |  9 ++++
 rust/bridge/shared/macros/src/ffi.rs          |  1 +
 rust/bridge/shared/macros/src/jni.rs          |  2 +
 rust/bridge/shared/src/message_backup.rs      |  2 -
 rust/bridge/shared/testing/Cargo.toml         | 34 +++++++++++++
 rust/bridge/shared/testing/build.rs           | 14 +++++
 rust/bridge/shared/testing/src/lib.rs         | 16 ++++++
 24 files changed, 371 insertions(+), 51 deletions(-)
 create mode 100644 java/shared/java/org/signal/libsignal/internal/NativeTesting.java
 create mode 100644 java/shared/test/java/org/signal/libsignal/internal/NativeTestingTest.java
 create mode 100644 rust/bridge/jni/bin/NativeTesting.java.in
 create mode 100644 rust/bridge/jni/testing/Cargo.toml
 create mode 100644 rust/bridge/jni/testing/cbindgen.toml
 create mode 100644 rust/bridge/jni/testing/src/lib.rs
 create mode 100644 rust/bridge/shared/testing/Cargo.toml
 create mode 100644 rust/bridge/shared/testing/build.rs
 create mode 100644 rust/bridge/shared/testing/src/lib.rs

diff --git a/Cargo.lock b/Cargo.lock
index e3931af71..45f2a3f1a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2007,6 +2007,25 @@ dependencies = [
  "syn-mid",
 ]
 
+[[package]]
+name = "libsignal-bridge-testing"
+version = "0.1.0"
+dependencies = [
+ "bytemuck",
+ "futures-util",
+ "jni 0.21.1",
+ "libsignal-bridge-macros",
+ "libsignal-bridge-types",
+ "libsignal-message-backup",
+ "linkme",
+ "neon",
+ "paste",
+ "scopeguard",
+ "signal-neon-futures",
+ "strum",
+ "thiserror",
+]
+
 [[package]]
 name = "libsignal-bridge-types"
 version = "0.1.0"
@@ -2108,6 +2127,19 @@ dependencies = [
  "signal-crypto",
 ]
 
+[[package]]
+name = "libsignal-jni-testing"
+version = "0.52.1"
+dependencies = [
+ "async-trait",
+ "cfg-if",
+ "jni 0.21.1",
+ "libsignal-bridge-testing",
+ "log",
+ "log-panics",
+ "rand",
+]
+
 [[package]]
 name = "libsignal-message-backup"
 version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
index 023dea88e..34870366a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,6 +16,7 @@ members = [
     "rust/zkgroup",
     "rust/bridge/ffi",
     "rust/bridge/jni",
+    "rust/bridge/jni/testing",
     "rust/bridge/node",
 ]
 default-members = [
diff --git a/acknowledgments/acknowledgments.html b/acknowledgments/acknowledgments.html
index f4f1208d2..2128840ec 100644
--- a/acknowledgments/acknowledgments.html
+++ b/acknowledgments/acknowledgments.html
@@ -47,7 +47,7 @@ <h1>Third Party Licenses</h1>
         <h2>Overview of licenses:</h2>
         <ul class="licenses-overview">
             <li><a href="#MIT">MIT License</a> (315)</li>
-            <li><a href="#AGPL-3.0">GNU Affero General Public License v3.0</a> (25)</li>
+            <li><a href="#AGPL-3.0">GNU Affero General Public License v3.0</a> (27)</li>
             <li><a href="#Apache-2.0">Apache License 2.0</a> (12)</li>
             <li><a href="#BSD-3-Clause">BSD 3-Clause &quot;New&quot; or &quot;Revised&quot; License</a> (8)</li>
             <li><a href="#ISC">ISC License</a> (6)</li>
@@ -736,11 +736,13 @@ <h4>Used by:</h4>
                     <li><a href="https://crates.io/crates/attest">attest 0.1.0</a></li>
                     <li><a href="https://crates.io/crates/libsignal-ffi">libsignal-ffi 0.52.1</a></li>
                     <li><a href="https://crates.io/crates/libsignal-jni">libsignal-jni 0.52.1</a></li>
+                    <li><a href="https://crates.io/crates/libsignal-jni-testing">libsignal-jni-testing 0.52.1</a></li>
                     <li><a href="https://crates.io/crates/libsignal-node">libsignal-node 0.52.1</a></li>
                     <li><a href="https://crates.io/crates/signal-neon-futures">signal-neon-futures 0.1.0</a></li>
                     <li><a href="https://crates.io/crates/signal-neon-futures-tests">signal-neon-futures-tests 0.1.0</a></li>
                     <li><a href="https://crates.io/crates/libsignal-bridge">libsignal-bridge 0.1.0</a></li>
                     <li><a href="https://crates.io/crates/libsignal-bridge-macros">libsignal-bridge-macros 0.1.0</a></li>
+                    <li><a href="https://crates.io/crates/libsignal-bridge-testing">libsignal-bridge-testing 0.1.0</a></li>
                     <li><a href="https://crates.io/crates/libsignal-bridge-types">libsignal-bridge-types 0.1.0</a></li>
                     <li><a href="https://crates.io/crates/libsignal-core">libsignal-core 0.1.0</a></li>
                     <li><a href="https://crates.io/crates/signal-crypto">signal-crypto 0.1.0</a></li>
diff --git a/acknowledgments/acknowledgments.md b/acknowledgments/acknowledgments.md
index 3aed74613..314431f6c 100644
--- a/acknowledgments/acknowledgments.md
+++ b/acknowledgments/acknowledgments.md
@@ -669,7 +669,7 @@ For more information on this, and how to apply and follow the GNU AGPL, see
 
 ```
 
-## attest 0.1.0, libsignal-ffi 0.52.1, libsignal-jni 0.52.1, libsignal-node 0.52.1, signal-neon-futures 0.1.0, signal-neon-futures-tests 0.1.0, libsignal-bridge 0.1.0, libsignal-bridge-macros 0.1.0, libsignal-bridge-types 0.1.0, libsignal-core 0.1.0, signal-crypto 0.1.0, device-transfer 0.1.0, signal-media 0.1.0, libsignal-message-backup 0.1.0, libsignal-message-backup-macros 0.1.0, libsignal-net 0.1.0, signal-pin 0.1.0, poksho 0.7.0, libsignal-protocol 0.1.0, libsignal-svr3 0.1.0, usernames 0.1.0, zkcredential 0.1.0, zkgroup 0.9.0
+## attest 0.1.0, libsignal-ffi 0.52.1, libsignal-jni 0.52.1, libsignal-jni-testing 0.52.1, libsignal-node 0.52.1, signal-neon-futures 0.1.0, signal-neon-futures-tests 0.1.0, libsignal-bridge 0.1.0, libsignal-bridge-macros 0.1.0, libsignal-bridge-testing 0.1.0, libsignal-bridge-types 0.1.0, libsignal-core 0.1.0, signal-crypto 0.1.0, device-transfer 0.1.0, signal-media 0.1.0, libsignal-message-backup 0.1.0, libsignal-message-backup-macros 0.1.0, libsignal-net 0.1.0, signal-pin 0.1.0, poksho 0.7.0, libsignal-protocol 0.1.0, libsignal-svr3 0.1.0, usernames 0.1.0, zkcredential 0.1.0, zkgroup 0.9.0
 
 ```
 GNU AFFERO GENERAL PUBLIC LICENSE
diff --git a/acknowledgments/acknowledgments.plist b/acknowledgments/acknowledgments.plist
index acc045c1c..0d4105bfe 100644
--- a/acknowledgments/acknowledgments.plist
+++ b/acknowledgments/acknowledgments.plist
@@ -924,7 +924,7 @@ You should also get your employer (if you work as a programmer) or school, if an
 			<key>License</key>
 			<string>GNU Affero General Public License v3.0</string>
 			<key>Title</key>
-			<string>attest 0.1.0, libsignal-ffi 0.52.1, libsignal-jni 0.52.1, libsignal-node 0.52.1, signal-neon-futures 0.1.0, signal-neon-futures-tests 0.1.0, libsignal-bridge 0.1.0, libsignal-bridge-macros 0.1.0, libsignal-bridge-types 0.1.0, libsignal-core 0.1.0, signal-crypto 0.1.0, device-transfer 0.1.0, signal-media 0.1.0, libsignal-message-backup 0.1.0, libsignal-message-backup-macros 0.1.0, libsignal-net 0.1.0, signal-pin 0.1.0, poksho 0.7.0, libsignal-protocol 0.1.0, libsignal-svr3 0.1.0, usernames 0.1.0, zkcredential 0.1.0, zkgroup 0.9.0</string>
+			<string>attest 0.1.0, libsignal-ffi 0.52.1, libsignal-jni 0.52.1, libsignal-jni-testing 0.52.1, libsignal-node 0.52.1, signal-neon-futures 0.1.0, signal-neon-futures-tests 0.1.0, libsignal-bridge 0.1.0, libsignal-bridge-macros 0.1.0, libsignal-bridge-testing 0.1.0, libsignal-bridge-types 0.1.0, libsignal-core 0.1.0, signal-crypto 0.1.0, device-transfer 0.1.0, signal-media 0.1.0, libsignal-message-backup 0.1.0, libsignal-message-backup-macros 0.1.0, libsignal-net 0.1.0, signal-pin 0.1.0, poksho 0.7.0, libsignal-protocol 0.1.0, libsignal-svr3 0.1.0, usernames 0.1.0, zkcredential 0.1.0, zkgroup 0.9.0</string>
 			<key>Type</key>
 			<string>PSGroupSpecifier</string>
 		</dict>
diff --git a/bin/update_versions.py b/bin/update_versions.py
index aea6e2ddf..66b99c9c3 100755
--- a/bin/update_versions.py
+++ b/bin/update_versions.py
@@ -36,8 +36,8 @@ def update_version(file, pattern, new_version):
 RUST_PATTERN = re.compile(r'^(pub const VERSION: &str = ")(.*)(")')
 
 
-def bridge_path(bridge):
-    return os.path.join('rust', 'bridge', bridge, 'Cargo.toml')
+def bridge_path(*bridge):
+    return os.path.join('rust', 'bridge', *bridge, 'Cargo.toml')
 
 
 VERSION_FILES = [
@@ -47,6 +47,7 @@ def bridge_path(bridge):
     (os.path.join('rust', 'core', 'src', 'version.rs'), RUST_PATTERN),
     (bridge_path('ffi'), CARGO_PATTERN),
     (bridge_path('jni'), CARGO_PATTERN),
+    (bridge_path('jni', 'testing'), CARGO_PATTERN),
     (bridge_path('node'), CARGO_PATTERN),
 ]
 
diff --git a/java/android/build.gradle b/java/android/build.gradle
index 767d4e9c1..edba9df79 100644
--- a/java/android/build.gradle
+++ b/java/android/build.gradle
@@ -52,6 +52,7 @@ android {
     packagingOptions {
         jniLibs {
             pickFirst 'lib/*/libsignal_jni.so'
+            pickFirst 'lib/*/libsignal_jni_testing.so'
         }
     }
 
diff --git a/java/build.gradle b/java/build.gradle
index 3b7427f84..c864821b5 100644
--- a/java/build.gradle
+++ b/java/build.gradle
@@ -35,7 +35,7 @@ subprojects {
     spotless {
         java {
             target('**/*.java')
-            targetExclude('**/Native.java')
+            targetExclude('**/Native.java', '**/NativeTesting.java')
             importOrder()
             removeUnusedImports()
 
@@ -76,7 +76,7 @@ clean.dependsOn([cargoClean, cleanJni])
 
 // PUBLISHING
 
-ext.setUpSigningKey = { signingExt -> 
+ext.setUpSigningKey = { signingExt ->
     def signingKeyId = findProperty("signingKeyId")
     def signingKey = findProperty("signingKey")
     def signingPassword = findProperty("signingPassword")
diff --git a/java/build_jni.sh b/java/build_jni.sh
index eb3bfe8b9..00b497be9 100755
--- a/java/build_jni.sh
+++ b/java/build_jni.sh
@@ -53,9 +53,10 @@ while [ "${1:-}" != "" ]; do
             # https://github.com/rust-lang/rfcs/issues/2771
             export CARGO_PROFILE_RELEASE_LTO=thin
             FEATURES+=("testing-fns")
-            echo_then_run cargo build -p libsignal-jni --release --features "${FEATURES[*]}"
+            echo_then_run cargo build -p libsignal-jni -p libsignal-jni-testing --release ${FEATURES:+--features "${FEATURES[*]}"}
             if [[ -z "${CARGO_BUILD_TARGET:-}" ]]; then
                 copy_built_library target/release signal_jni "${DESKTOP_LIB_DIR}/"
+                copy_built_library target/release signal_jni_testing "${DESKTOP_LIB_DIR}/"
             fi
             exit
             ;;
@@ -136,5 +137,5 @@ target_for_abi() {
 
 for abi in "${android_abis[@]}"; do
     rust_target=$(target_for_abi "$abi")
-    echo_then_run cargo build -p libsignal-jni --release ${FEATURES:+--features "${FEATURES[*]}"} -Z unstable-options --target "$rust_target" --out-dir "${ANDROID_LIB_DIR}/$abi"
+    echo_then_run cargo build -p libsignal-jni -p libsignal-jni-testing --release ${FEATURES:+--features "${FEATURES[*]}"} -Z unstable-options --target "$rust_target" --out-dir "${ANDROID_LIB_DIR}/$abi"
 done
diff --git a/java/shared/java/org/signal/libsignal/internal/Native.java b/java/shared/java/org/signal/libsignal/internal/Native.java
index 67f62aa41..64aecdb05 100644
--- a/java/shared/java/org/signal/libsignal/internal/Native.java
+++ b/java/shared/java/org/signal/libsignal/internal/Native.java
@@ -24,13 +24,23 @@
 import java.io.OutputStream;
 import java.nio.ByteBuffer;
 import java.nio.file.Files;
+import java.nio.file.Path;
 import java.util.concurrent.Future;
 import java.util.UUID;
 import java.util.Map;
 
 public final class Native {
-  private static void copyToTempFileAndLoad(InputStream in, String name) throws IOException {
-    File tempFile = Files.createTempFile(null, name).toFile();
+  private static Path tempDir;
+
+  private static void copyToTempDirAndLoad(InputStream in, String name) throws IOException {
+    // This isn't thread-safe but that's okay because it's only ever called from
+    // static initializers, which are themselves thread-safe.
+    if (tempDir == null) {
+      tempDir = Files.createTempDirectory("libsignal");
+      tempDir.toFile().deleteOnExit();
+    }
+
+    File tempFile = Files.createFile(tempDir.resolve(name)).toFile();
     tempFile.deleteOnExit();
 
     try (OutputStream out = new FileOutputStream(tempFile)) {
@@ -44,28 +54,35 @@ private static void copyToTempFileAndLoad(InputStream in, String name) throws IO
     System.load(tempFile.getAbsolutePath());
   }
 
-  /*
-  If libsignal_jni is embedded within this jar as a resource file, attempt
-  to copy it to a temporary file and then load it. This allows the jar to be
-  used even without a shared library existing on the filesystem.
-  */
-  private static void loadLibrary() {
-    try {
-      String libraryName = System.mapLibraryName("signal_jni");
-      try (InputStream in = Native.class.getResourceAsStream("/" + libraryName)) {
-        if (in != null) {
-          copyToTempFileAndLoad(in, libraryName);
-        } else {
-          System.loadLibrary("signal_jni");
-        }
+  /**
+   * If the library is embedded within this jar as a resource file, attempt to
+   * copy it to a temporary file and then load it. This allows the jar to be
+   * used even without a shared library existing on the filesystem.
+   *
+   * Package-private to allow the NativeTest class to load its shared library.
+   * This method should only be called from a static initializer.
+   */
+  static void loadLibrary(String name) throws IOException {
+    String libraryName = System.mapLibraryName(name);
+    try (InputStream in = Native.class.getResourceAsStream("/" + libraryName)) {
+      if (in != null) {
+        copyToTempDirAndLoad(in, libraryName);
+      } else {
+        System.loadLibrary(name);
       }
+    }
+  }
+
+  private static void loadNativeCode() {
+    try {
+      loadLibrary("signal_jni");
     } catch (Exception e) {
       throw new RuntimeException(e);
     }
   }
 
   static {
-    loadLibrary();
+    loadNativeCode();
     initializeLibrary();
   }
 
diff --git a/java/shared/java/org/signal/libsignal/internal/NativeTesting.java b/java/shared/java/org/signal/libsignal/internal/NativeTesting.java
new file mode 100644
index 000000000..ad6d64610
--- /dev/null
+++ b/java/shared/java/org/signal/libsignal/internal/NativeTesting.java
@@ -0,0 +1,48 @@
+//
+// Copyright (C) 2024 Signal Messenger, LLC.
+// SPDX-License-Identifier: AGPL-3.0-only
+//
+
+// WARNING: this file was automatically generated
+
+package org.signal.libsignal.internal;
+
+import org.signal.libsignal.protocol.message.CiphertextMessage;
+import org.signal.libsignal.protocol.state.IdentityKeyStore;
+import org.signal.libsignal.protocol.state.SessionStore;
+import org.signal.libsignal.protocol.state.PreKeyStore;
+import org.signal.libsignal.protocol.state.SignedPreKeyStore;
+import org.signal.libsignal.protocol.state.KyberPreKeyStore;
+import org.signal.libsignal.protocol.groups.state.SenderKeyStore;
+import org.signal.libsignal.protocol.logging.Log;
+import org.signal.libsignal.protocol.logging.SignalProtocolLogger;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.concurrent.Future;
+import java.util.UUID;
+import java.util.Map;
+
+public final class NativeTesting {
+  private static void loadNativeCode() {
+    try {
+      Native.loadLibrary("signal_jni_testing");
+    } catch (Exception e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  static {
+    loadNativeCode();
+  }
+
+  private NativeTesting() {}
+
+  public static native int test_only_fn_returns_123();
+}
diff --git a/java/shared/test/java/org/signal/libsignal/internal/NativeTestingTest.java b/java/shared/test/java/org/signal/libsignal/internal/NativeTestingTest.java
new file mode 100644
index 000000000..7f0764703
--- /dev/null
+++ b/java/shared/test/java/org/signal/libsignal/internal/NativeTestingTest.java
@@ -0,0 +1,18 @@
+//
+// Copyright 2024 Signal Messenger, LLC.
+// SPDX-License-Identifier: AGPL-3.0-only
+//
+
+package org.signal.libsignal.internal;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class NativeTestingTest {
+  @Test
+  public void canCallNativeTestingFns() throws Exception {
+    int result = NativeTesting.test_only_fn_returns_123();
+    assertEquals(123, result);
+  }
+}
diff --git a/rust/bridge/jni/bin/Native.java.in b/rust/bridge/jni/bin/Native.java.in
index fd5477a0f..b9a4ba678 100644
--- a/rust/bridge/jni/bin/Native.java.in
+++ b/rust/bridge/jni/bin/Native.java.in
@@ -24,13 +24,23 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.nio.ByteBuffer;
 import java.nio.file.Files;
+import java.nio.file.Path;
 import java.util.concurrent.Future;
 import java.util.UUID;
 import java.util.Map;
 
 public final class Native {
-  private static void copyToTempFileAndLoad(InputStream in, String name) throws IOException {
-    File tempFile = Files.createTempFile(null, name).toFile();
+  private static Path tempDir;
+
+  private static void copyToTempDirAndLoad(InputStream in, String name) throws IOException {
+    // This isn't thread-safe but that's okay because it's only ever called from
+    // static initializers, which are themselves thread-safe.
+    if (tempDir == null) {
+      tempDir = Files.createTempDirectory("libsignal");
+      tempDir.toFile().deleteOnExit();
+    }
+
+    File tempFile = Files.createFile(tempDir.resolve(name)).toFile();
     tempFile.deleteOnExit();
 
     try (OutputStream out = new FileOutputStream(tempFile)) {
@@ -44,28 +54,35 @@ public final class Native {
     System.load(tempFile.getAbsolutePath());
   }
 
-  /*
-  If libsignal_jni is embedded within this jar as a resource file, attempt
-  to copy it to a temporary file and then load it. This allows the jar to be
-  used even without a shared library existing on the filesystem.
-  */
-  private static void loadLibrary() {
-    try {
-      String libraryName = System.mapLibraryName("signal_jni");
-      try (InputStream in = Native.class.getResourceAsStream("/" + libraryName)) {
-        if (in != null) {
-          copyToTempFileAndLoad(in, libraryName);
-        } else {
-          System.loadLibrary("signal_jni");
-        }
+  /**
+   * If the library is embedded within this jar as a resource file, attempt to
+   * copy it to a temporary file and then load it. This allows the jar to be
+   * used even without a shared library existing on the filesystem.
+   *
+   * Package-private to allow the NativeTest class to load its shared library.
+   * This method should only be called from a static initializer.
+   */
+  static void loadLibrary(String name) throws IOException {
+    String libraryName = System.mapLibraryName(name);
+    try (InputStream in = Native.class.getResourceAsStream("/" + libraryName)) {
+      if (in != null) {
+        copyToTempDirAndLoad(in, libraryName);
+      } else {
+        System.loadLibrary(name);
       }
+    }
+  }
+
+  private static void loadNativeCode() {
+    try {
+      loadLibrary("signal_jni");
     } catch (Exception e) {
       throw new RuntimeException(e);
     }
   }
 
   static {
-    loadLibrary();
+    loadNativeCode();
     initializeLibrary();
   }
 
diff --git a/rust/bridge/jni/bin/NativeTesting.java.in b/rust/bridge/jni/bin/NativeTesting.java.in
new file mode 100644
index 000000000..c39461cc9
--- /dev/null
+++ b/rust/bridge/jni/bin/NativeTesting.java.in
@@ -0,0 +1,48 @@
+//
+// Copyright (C) 2024 Signal Messenger, LLC.
+// SPDX-License-Identifier: AGPL-3.0-only
+//
+
+// WARNING: this file was automatically generated
+
+package org.signal.libsignal.internal;
+
+import org.signal.libsignal.protocol.message.CiphertextMessage;
+import org.signal.libsignal.protocol.state.IdentityKeyStore;
+import org.signal.libsignal.protocol.state.SessionStore;
+import org.signal.libsignal.protocol.state.PreKeyStore;
+import org.signal.libsignal.protocol.state.SignedPreKeyStore;
+import org.signal.libsignal.protocol.state.KyberPreKeyStore;
+import org.signal.libsignal.protocol.groups.state.SenderKeyStore;
+import org.signal.libsignal.protocol.logging.Log;
+import org.signal.libsignal.protocol.logging.SignalProtocolLogger;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.concurrent.Future;
+import java.util.UUID;
+import java.util.Map;
+
+public final class NativeTesting {
+  private static void loadNativeCode() {
+    try {
+      Native.loadLibrary("signal_jni_testing");
+    } catch (Exception e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  static {
+    loadNativeCode();
+  }
+
+  private NativeTesting() {}
+
+  // INSERT DECLS HERE
+}
diff --git a/rust/bridge/jni/bin/gen_java_decl.py b/rust/bridge/jni/bin/gen_java_decl.py
index 7631601a1..51e59a890 100755
--- a/rust/bridge/jni/bin/gen_java_decl.py
+++ b/rust/bridge/jni/bin/gen_java_decl.py
@@ -128,12 +128,12 @@ def translate_to_java(typ):
 
 
 JAVA_DECL = re.compile(r"""
-    ([a-zA-Z0-9]+(?:<.+>)?)[ ]                 # (0) A possibly-generic return type
-    Java_org_signal_libsignal_internal_Native_ # The required JNI prefix
-    (([a-zA-Z0-9]+)                            # (1) The method name, with (2) a grouping prefix
-    (?:_1[a-zA-Z0-9_]*)?)                      # ...possibly followed by an underscore and then more name
-    \(JNIEnv[ ].?env,[ ]JClass[ ]class_        # and then the required JNI args,
-    (,[ ].*)?\);                               # then (3) actual args
+    ([a-zA-Z0-9]+(?:<.+>)?)[ ]                             # (0) A possibly-generic return type
+    Java_org_signal_libsignal_internal_Native(?:Testing)?_ # The required JNI prefix
+    (([a-zA-Z0-9]+)                                        # (1) The method name, with (2) a grouping prefix
+    (?:_1[a-zA-Z0-9_]*)?)                                  # ...possibly followed by an underscore and then more name
+    \(JNIEnv[ ].?env,[ ]JClass[ ]class_                    # and then the required JNI args,
+    (,[ ].*)?\);                                           # then (3) actual args
     """, re.VERBOSE)
 
 
@@ -217,6 +217,13 @@ def main():
         verify=args.verify,
     )
 
+    convert_to_java(
+        rust_crate_dir=os.path.join(our_abs_dir, '..', 'testing'),
+        java_in_path=os.path.join(our_abs_dir, 'NativeTesting.java.in'),
+        java_out_path=os.path.join(our_abs_dir, '..', '..', '..', '..', 'java', 'shared', 'java', 'org', 'signal', 'libsignal', 'internal', 'NativeTesting.java'),
+        verify=args.verify,
+    )
+
 
 if __name__ == "__main__":
     main()
diff --git a/rust/bridge/jni/testing/Cargo.toml b/rust/bridge/jni/testing/Cargo.toml
new file mode 100644
index 000000000..e38c3dfac
--- /dev/null
+++ b/rust/bridge/jni/testing/Cargo.toml
@@ -0,0 +1,25 @@
+#
+# Copyright (C) 2024 Signal Messenger, LLC.
+# SPDX-License-Identifier: AGPL-3.0-only
+#
+
+[package]
+name = "libsignal-jni-testing"
+version = "0.52.1"
+authors = ["Signal Messenger LLC"]
+edition = "2021"
+license = "AGPL-3.0-only"
+
+[lib]
+name = "signal_jni_testing"
+crate-type = ["cdylib"]
+
+[dependencies]
+libsignal-bridge-testing = { path = "../../shared/testing", features = ["jni"] }
+
+async-trait = "0.1.41"
+cfg-if = "1.0.0"
+jni = "0.21.0"
+log = { version = "0.4", features = ["release_max_level_info"] }
+log-panics = { version = "2.1.0", features = ["with-backtrace"] }
+rand = "0.8"
diff --git a/rust/bridge/jni/testing/cbindgen.toml b/rust/bridge/jni/testing/cbindgen.toml
new file mode 100644
index 000000000..479015b83
--- /dev/null
+++ b/rust/bridge/jni/testing/cbindgen.toml
@@ -0,0 +1,28 @@
+#
+# Copyright (C) 2024 Signal Messenger, LLC.
+# SPDX-License-Identifier: AGPL-3.0-only
+#
+
+language = "C"
+no_includes = true
+documentation = false
+
+[export]
+item_types = ["functions"]
+
+[export.rename]
+"JavaSyncInputStream" = "JavaInputStream"
+
+[fn]
+args = "horizontal"
+sort_by = "Name"
+rename_args = "camelCase"
+
+[parse]
+parse_deps = true
+include = []
+extra_bindings = ["libsignal-bridge", "libsignal-bridge-testing"]
+
+[parse.expand]
+crates = ["libsignal-jni-testing", "libsignal-bridge-testing"]
+features = ["libsignal-bridge-testing/jni"]
diff --git a/rust/bridge/jni/testing/src/lib.rs b/rust/bridge/jni/testing/src/lib.rs
new file mode 100644
index 000000000..04b295408
--- /dev/null
+++ b/rust/bridge/jni/testing/src/lib.rs
@@ -0,0 +1,9 @@
+//
+// Copyright 2024 Signal Messenger, LLC.
+// SPDX-License-Identifier: AGPL-3.0-only
+//
+
+// Import bridged functions. Without this, the compiler and/or linker are too
+// smart and don't include the symbols in the library.
+#[allow(unused_imports)]
+use libsignal_bridge_testing::*;
diff --git a/rust/bridge/shared/macros/src/ffi.rs b/rust/bridge/shared/macros/src/ffi.rs
index e61be1685..b1fad5249 100644
--- a/rust/bridge/shared/macros/src/ffi.rs
+++ b/rust/bridge/shared/macros/src/ffi.rs
@@ -90,6 +90,7 @@ fn bridge_fn_body(
     // "Support" async operations by requiring them to complete synchronously.
     let await_if_needed = sig.asyncness.map(|_| {
         quote! {
+            use ::futures_util::future::FutureExt as _;
             let __result = __result.now_or_never().unwrap();
         }
     });
diff --git a/rust/bridge/shared/macros/src/jni.rs b/rust/bridge/shared/macros/src/jni.rs
index 45d1f657f..d2b15a63d 100644
--- a/rust/bridge/shared/macros/src/jni.rs
+++ b/rust/bridge/shared/macros/src/jni.rs
@@ -94,6 +94,8 @@ fn bridge_fn_body(
 
     let await_if_needed = await_needed.then(|| {
         quote! {
+            #[allow(unused)]
+            use ::futures_util::future::FutureExt as _;
             let __result = __result.now_or_never().unwrap();
         }
     });
diff --git a/rust/bridge/shared/src/message_backup.rs b/rust/bridge/shared/src/message_backup.rs
index 2d82787f8..89f243502 100644
--- a/rust/bridge/shared/src/message_backup.rs
+++ b/rust/bridge/shared/src/message_backup.rs
@@ -3,8 +3,6 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 //
 
-#[cfg(any(feature = "jni", feature = "ffi"))]
-use futures_util::FutureExt as _;
 use libsignal_bridge_macros::*;
 use libsignal_bridge_types::message_backup::*;
 use libsignal_message_backup::backup::Purpose;
diff --git a/rust/bridge/shared/testing/Cargo.toml b/rust/bridge/shared/testing/Cargo.toml
new file mode 100644
index 000000000..5a56ef2b1
--- /dev/null
+++ b/rust/bridge/shared/testing/Cargo.toml
@@ -0,0 +1,34 @@
+#
+# Copyright (C) 2024 Signal Messenger, LLC.
+# SPDX-License-Identifier: AGPL-3.0-only
+#
+
+[package]
+name = "libsignal-bridge-testing"
+version = "0.1.0"
+authors = ["Signal Messenger LLC"]
+edition = "2021"
+license = "AGPL-3.0-only"
+
+[dependencies]
+libsignal-bridge-macros = { path = "../macros" }
+libsignal-bridge-types = { path = "../types" }
+libsignal-message-backup = { path = "../../../message-backup" }
+
+futures-util = "0.3.7"
+paste = "1.0"
+scopeguard = "1.0"
+thiserror = "1.0.50"
+
+bytemuck = { version = "1.13.0", optional = true }
+jni = { version = "0.21", package = "jni", optional = true }
+linkme = { version = "0.3.9", optional = true }
+neon = { version = "1.0.0", optional = true, default-features = false, features = ["napi-6"] }
+signal-neon-futures = { path = "../../node/futures", optional = true }
+strum = { version = "0.26", features = ["derive"] }
+
+[features]
+ffi = ["libsignal-bridge-types/ffi"]
+jni = ["dep:jni", "libsignal-bridge-types/jni"]
+node = ["libsignal-bridge-types/node"]
+signal-media = ["libsignal-bridge-types/signal-media"]
diff --git a/rust/bridge/shared/testing/build.rs b/rust/bridge/shared/testing/build.rs
new file mode 100644
index 000000000..2796d812c
--- /dev/null
+++ b/rust/bridge/shared/testing/build.rs
@@ -0,0 +1,14 @@
+//
+// Copyright 2024 Signal Messenger, LLC.
+// SPDX-License-Identifier: AGPL-3.0-only
+//
+
+fn main() {
+    // Set environment variables for bridge_fn to produce correctly-named symbols for FFI and JNI.
+    println!("cargo:rustc-env=LIBSIGNAL_BRIDGE_FN_PREFIX_FFI=signal_");
+    // This naming convention comes from JNI:
+    // https://docs.oracle.com/en/java/javase/20/docs/specs/jni/design.html#resolving-native-method-names
+    println!(
+        "cargo:rustc-env=LIBSIGNAL_BRIDGE_FN_PREFIX_JNI=Java_org_signal_libsignal_internal_NativeTesting_"
+    );
+}
diff --git a/rust/bridge/shared/testing/src/lib.rs b/rust/bridge/shared/testing/src/lib.rs
new file mode 100644
index 000000000..7c9ead858
--- /dev/null
+++ b/rust/bridge/shared/testing/src/lib.rs
@@ -0,0 +1,16 @@
+//
+// Copyright 2024 Signal Messenger, LLC.
+// SPDX-License-Identifier: AGPL-3.0-only
+//
+
+#[cfg(not(any(feature = "ffi", feature = "jni", feature = "node")))]
+compile_error!("Feature \"ffi\", \"jni\", or \"node\" must be enabled for this crate.");
+
+use libsignal_bridge_macros::bridge_fn;
+use libsignal_bridge_types::support::*;
+use libsignal_bridge_types::*;
+
+#[bridge_fn]
+pub fn test_only_fn_returns_123() -> u32 {
+    123
+}