Add API for custom library loading

Loading the native library can cause a crash on some older versions of
Android. This CL provides a way for embedders to implement custom library
loading logic that works around the issue.

BUG=550584
R=xunjieli@chromium.org

Committed: https://crrev.com/12d01cb35ec0ed7a259c19dd1390b5a486d61a9d
Cr-Commit-Position: refs/heads/master@{#371319}

Review URL: https://codereview.chromium.org/1619673004

Cr-Commit-Position: refs/heads/master@{#371571}

components/cronet/android/api/src/org/chromium/net/CronetEngine.java

@@ -41,6 +41,21 @@ public abstract class CronetEngine {
      * then {@link #build} is called to create the {@code CronetEngine}.
      */
     public static class Builder {
+        /**
+         * A class which provides a method for loading the cronet native library. Apps needing to
+         * implement custom library loading logic can inherit from this class and pass an instance
+         * to {@link CronetEngine.Builder#setLibraryLoader}. For example, this might be required
+         * to work around {@code UnsatisfiedLinkError}s caused by flaky installation on certain
+         * older devices.
+         */
+        public abstract static class LibraryLoader {
+            /**
+             * Loads the native library.
+             * @param libName name of the library to load
+             */
+            public abstract void loadLibrary(String libName);
+        }
+
         // A hint that a host supports QUIC.
         static class QuicHint {
             // The host.
@@ -86,6 +101,7 @@ public abstract class CronetEngine {
         private String mUserAgent;
         private String mStoragePath;
         private boolean mLegacyModeEnabled;
+        private LibraryLoader mLibraryLoader;
         private String mLibraryName;
         private boolean mQuicEnabled;
         private boolean mHttp2Enabled;
@@ -187,8 +203,22 @@ public abstract class CronetEngine {
             return this;
         }
 
-        String libraryName() {
-            return mLibraryName;
+        /**
+         * Sets a {@link LibraryLoader} to be used to load the native library.
+         * If not set, the library will be loaded using {@link System#loadLibrary}.
+         * @return the builder to facilitate chaining.
+         */
+        public Builder setLibraryLoader(LibraryLoader loader) {
+            mLibraryLoader = loader;
+            return this;
+        }
+
+        void loadLibrary() {
+            if (mLibraryLoader == null) {
+                System.loadLibrary(mLibraryName);
+            } else {
+                mLibraryLoader.loadLibrary(mLibraryName);
+            }
         }
 
         /**

components/cronet/android/java/src/org/chromium/net/CronetLibraryLoader.java

@@ -32,7 +32,7 @@ class CronetLibraryLoader {
             if (sInitTaskPosted) {
                 return;
             }
-            System.loadLibrary(builder.libraryName());
+            builder.loadLibrary();
             if (!Version.CRONET_VERSION.equals(nativeGetCronetVersion())) {
                 throw new RuntimeException(String.format(
                       "Expected Cronet version number %s, "
@@ -74,7 +74,7 @@ class CronetLibraryLoader {
         nativeCronetInitOnMainThread();
     }
 
-    // Native methods are implemented in cronet_loader.cc.
+    // Native methods are implemented in cronet_library_loader.cc.
     private static native void nativeCronetInitOnMainThread();
     private static native String nativeGetCronetVersion();
 }

components/cronet/android/test/javatests/src/org/chromium/net/CronetUrlRequestContextTest.java

@@ -960,4 +960,33 @@ public class CronetUrlRequestContextTest extends CronetTestBase {
     // Verifies that CronetEngine.Builder config from testCronetEngineBuilderConfig() is properly
     // translated to a native UrlRequestContextConfig.
     private static native void nativeVerifyUrlRequestContextConfig(long config, String storagePath);
+
+    private static class TestBadLibraryLoader extends CronetEngine.Builder.LibraryLoader {
+        private boolean mWasCalled = false;
+
+        public void loadLibrary(String libName) {
+            // Report that this method was called, but don't load the library
+            mWasCalled = true;
+        }
+
+        boolean wasCalled() {
+            return mWasCalled;
+        }
+    }
+
+    @SmallTest
+    @Feature({"Cronet"})
+    public void testSkipLibraryLoading() throws Exception {
+        CronetEngine.Builder builder = new CronetEngine.Builder(getContext());
+        TestBadLibraryLoader loader = new TestBadLibraryLoader();
+        builder.setLibraryLoader(loader).setLibraryName("cronet_tests");
+        try {
+            // ensureInitialized() calls native code to check the version right after library load
+            // and will error with the message below if library loading was skipped
+            CronetLibraryLoader.ensureInitialized(getContext(), builder);
+            fail("Native library should not be loaded");
+        } catch (UnsatisfiedLinkError e) {
+            assertTrue(loader.wasCalled());
+        }
+    }
 }