fix(camera_android_camerax): write exposure time to EXIF when missing

Some devices (e.g. Honor) omit exposure time in JPEG EXIF when using CameraX
ImageCapture.takePicture. Use Camera2Interop session capture callback to
record SENSOR_EXPOSURE_TIME and patch EXIF after save via ExifInterface when
TAG_EXPOSURE_TIME is absent.

Adds androidx.exifinterface dependency and unit tests for patchExifExposureTime.

Made-with: Cursor

Author: vodemn

packages/camera/camera_android_camerax/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.6.25+1
+
+* Writes exposure time to EXIF metadata when the device's JPEG encoder omits it. Uses Camera2 interop to capture `SENSOR_EXPOSURE_TIME` and patches EXIF after CameraX saves the file.
+
 ## 0.6.25
 
 * Adds support for `MediaSettings.fps` for camera preview, image streaming, and video recording.

packages/camera/camera_android_camerax/android/build.gradle

@@ -78,6 +78,7 @@ dependencies {
     implementation("androidx.camera:camera-lifecycle:${camerax_version}")
     implementation("androidx.camera:camera-video:${camerax_version}")
     implementation("com.google.guava:guava:33.5.0-android")
+    implementation("androidx.exifinterface:exifinterface:1.3.7")
     testImplementation("junit:junit:4.13.2")
     testImplementation("org.mockito:mockito-core:5.20.0")
     testImplementation("org.mockito:mockito-inline:5.2.0")

packages/camera/camera_android_camerax/android/src/main/java/io/flutter/plugins/camerax/ImageCaptureProxyApi.java

@@ -4,14 +4,25 @@
 
 package io.flutter.plugins.camerax;
 
+import android.hardware.camera2.CameraCaptureSession;
+import android.hardware.camera2.CaptureRequest;
+import android.hardware.camera2.CaptureResult;
+import android.hardware.camera2.TotalCaptureResult;
+import android.util.Log;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
+import androidx.annotation.OptIn;
+import androidx.annotation.VisibleForTesting;
+import androidx.camera.camera2.interop.Camera2Interop;
+import androidx.camera.camera2.interop.ExperimentalCamera2Interop;
 import androidx.camera.core.ImageCapture;
 import androidx.camera.core.ImageCaptureException;
 import androidx.camera.core.resolutionselector.ResolutionSelector;
+import androidx.exifinterface.media.ExifInterface;
 import java.io.File;
 import java.io.IOException;
 import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicReference;
 import kotlin.Result;
 import kotlin.Unit;
 import kotlin.jvm.functions.Function1;
@@ -22,9 +33,14 @@
  * native class or an instance of that class.
  */
 class ImageCaptureProxyApi extends PigeonApiImageCapture {
+  private static final String TAG = "ImageCaptureProxyApi";
+
   static final String TEMPORARY_FILE_NAME = "CAP";
   static final String JPG_FILE_TYPE = ".jpg";
 
+  @VisibleForTesting
+  final AtomicReference<Long> lastExposureTimeNs = new AtomicReference<>();
+
   ImageCaptureProxyApi(@NonNull ProxyApiRegistrar pigeonRegistrar) {
     super(pigeonRegistrar);
   }
@@ -35,6 +51,7 @@ public ProxyApiRegistrar getPigeonRegistrar() {
     return (ProxyApiRegistrar) super.getPigeonRegistrar();
   }
 
+  @OptIn(markerClass = ExperimentalCamera2Interop.class)
   @NonNull
   @Override
   public ImageCapture pigeon_defaultConstructor(
@@ -62,6 +79,22 @@ public ImageCapture pigeon_defaultConstructor(
     if (resolutionSelector != null) {
       builder.setResolutionSelector(resolutionSelector);
     }
+
+    Camera2Interop.Extender<ImageCapture> extender = new Camera2Interop.Extender<>(builder);
+    extender.setSessionCaptureCallback(
+        new CameraCaptureSession.CaptureCallback() {
+          @Override
+          public void onCaptureCompleted(
+              @NonNull CameraCaptureSession session,
+              @NonNull CaptureRequest request,
+              @NonNull TotalCaptureResult result) {
+            Long exposureTime = result.get(CaptureResult.SENSOR_EXPOSURE_TIME);
+            if (exposureTime != null) {
+              lastExposureTimeNs.set(exposureTime);
+            }
+          }
+        });
+
     return builder.build();
   }
 
@@ -125,6 +158,7 @@ ImageCapture.OnImageSavedCallback createOnImageSavedCallback(
     return new ImageCapture.OnImageSavedCallback() {
       @Override
       public void onImageSaved(@NonNull ImageCapture.OutputFileResults outputFileResults) {
+        patchExifExposureTime(file, lastExposureTimeNs.get());
         ResultCompat.success(file.getAbsolutePath(), callback);
       }
 
@@ -134,4 +168,22 @@ public void onError(@NonNull ImageCaptureException exception) {
       }
     };
   }
+
+  @VisibleForTesting
+  static void patchExifExposureTime(@NonNull File file, @Nullable Long exposureTimeNs) {
+    if (exposureTimeNs == null) {
+      return;
+    }
+    try {
+      ExifInterface exif = new ExifInterface(file.getAbsolutePath());
+      String existingExposureTime = exif.getAttribute(ExifInterface.TAG_EXPOSURE_TIME);
+      if (existingExposureTime == null || existingExposureTime.isEmpty()) {
+        double exposureTimeInSeconds = exposureTimeNs / 1_000_000_000.0;
+        exif.setAttribute(ExifInterface.TAG_EXPOSURE_TIME, String.valueOf(exposureTimeInSeconds));
+        exif.saveAttributes();
+      }
+    } catch (IOException e) {
+      Log.w(TAG, "Failed to write exposure time to EXIF", e);
+    }
+  }
 }

packages/camera/camera_android_camerax/android/src/test/java/io/flutter/plugins/camerax/ImageCaptureTest.java

@@ -6,8 +6,11 @@
 
 import static org.junit.Assert.assertEquals;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.mockConstruction;
 import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoInteractions;
 import static org.mockito.Mockito.when;
@@ -18,19 +21,25 @@
 import androidx.camera.core.ImageCapture;
 import androidx.camera.core.ImageCaptureException;
 import androidx.camera.core.resolutionselector.ResolutionSelector;
+import androidx.exifinterface.media.ExifInterface;
 import java.io.File;
 import java.io.IOException;
 import java.util.concurrent.Executor;
 import kotlin.Result;
 import kotlin.Unit;
 import kotlin.jvm.functions.Function1;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
 import org.junit.runner.RunWith;
+import org.mockito.MockedConstruction;
 import org.mockito.MockedStatic;
 import org.robolectric.RobolectricTestRunner;
 
 @RunWith(RobolectricTestRunner.class)
 public class ImageCaptureTest {
+  @Rule public TemporaryFolder tempFolder = new TemporaryFolder();
+
   @Test
   public void pigeon_defaultConstructor_createsImageCaptureWithCorrectConfiguration() {
     final PigeonApiImageCapture api = new TestProxyApiRegistrar().getPigeonApiImageCapture();
@@ -234,4 +243,80 @@ public void setTargetRotation_makesCallToSetTargetRotation() {
 
     verify(instance).setTargetRotation((int) rotation);
   }
+
+  @Test
+  public void patchExifExposureTime_writesExposureTimeWhenMissing() throws IOException {
+    final File file = tempFolder.newFile("test.jpg");
+    try (MockedConstruction<ExifInterface> mockedExif =
+        mockConstruction(
+            ExifInterface.class,
+            (mock, ctx) ->
+                when(mock.getAttribute(ExifInterface.TAG_EXPOSURE_TIME)).thenReturn(null))) {
+      ImageCaptureProxyApi.patchExifExposureTime(file, 500_000_000L);
+      ExifInterface exif = mockedExif.constructed().get(0);
+      verify(exif).setAttribute(ExifInterface.TAG_EXPOSURE_TIME, String.valueOf(0.5));
+      verify(exif).saveAttributes();
+    }
+  }
+
+  @Test
+  public void patchExifExposureTime_doesNotOverwriteExistingExposureTime() throws IOException {
+    final File file = tempFolder.newFile("test.jpg");
+    try (MockedConstruction<ExifInterface> mockedExif =
+        mockConstruction(
+            ExifInterface.class,
+            (mock, ctx) ->
+                when(mock.getAttribute(ExifInterface.TAG_EXPOSURE_TIME)).thenReturn("0.8"))) {
+      ImageCaptureProxyApi.patchExifExposureTime(file, 1_000_000_000L);
+      ExifInterface exif = mockedExif.constructed().get(0);
+      verify(exif).getAttribute(ExifInterface.TAG_EXPOSURE_TIME);
+      verify(exif, never()).setAttribute(eq(ExifInterface.TAG_EXPOSURE_TIME), any());
+      verify(exif, never()).saveAttributes();
+    }
+  }
+
+  @Test
+  public void patchExifExposureTime_doesNothingWhenExposureTimeIsNull() throws IOException {
+    final File file = tempFolder.newFile("test.jpg");
+    try (MockedConstruction<ExifInterface> mockedExif =
+        mockConstruction(ExifInterface.class)) {
+      ImageCaptureProxyApi.patchExifExposureTime(file, null);
+      assertEquals(0, mockedExif.constructed().size());
+    }
+  }
+
+  @Test
+  public void patchExifExposureTime_continuesOnExifError() {
+    final File nonExistentFile = new File("/non/existent/path.jpg");
+    // Should not throw even when ExifInterface fails to open the file
+    ImageCaptureProxyApi.patchExifExposureTime(nonExistentFile, 1_000_000_000L);
+  }
+
+  @Test
+  public void onImageSaved_callsPatchExifExposureTime() {
+    final ProxyApiRegistrar mockApiRegistrar = mock(ProxyApiRegistrar.class);
+    final ImageCaptureProxyApi api = new ImageCaptureProxyApi(mockApiRegistrar);
+    api.lastExposureTimeNs.set(123_000_000L);
+
+    final File mockFile = mock(File.class);
+    when(mockFile.getAbsolutePath()).thenReturn("test/path.jpg");
+
+    final String[] result = {null};
+    final ImageCapture.OnImageSavedCallback callback =
+        api.createOnImageSavedCallback(
+            mockFile,
+            ResultCompat.asCompatCallback(
+                reply -> {
+                  result[0] = reply.getOrNull();
+                  return null;
+                }));
+
+    try (MockedStatic<ImageCaptureProxyApi> mockedApi =
+        mockStatic(ImageCaptureProxyApi.class)) {
+      callback.onImageSaved(mock(ImageCapture.OutputFileResults.class));
+      mockedApi.verify(
+          () -> ImageCaptureProxyApi.patchExifExposureTime(mockFile, 123_000_000L));
+    }
+    assertEquals("test/path.jpg", result[0]);
+  }
 }

packages/camera/camera_android_camerax/pubspec.yaml

@@ -2,7 +2,7 @@ name: camera_android_camerax
 description: Android implementation of the camera plugin using the CameraX library.
 repository: https://github.com/flutter/packages/tree/main/packages/camera/camera_android_camerax
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+camera%22
-version: 0.6.25
+version: 0.6.25+1
 
 environment:
   sdk: ^3.9.0