Use object contexts

Console

1. In the Google Cloud console, go to the Cloud Storage Buckets page.
   

   Go to Buckets

2. Upload the object.

3. Follow the steps to attach contexts to the object.

Command line

To attach contexts when you upload objects with the gcloud storage cp command, use the --custom-contexts flag:

gcloud storage cp OBJECT_LOCATION gs://DESTINATION_BUCKET_NAME --custom-contexts=KEY=VALUE,...

Where:

• OBJECT_LOCATION is the local path to your object. For example, Desktop/employees.txt.
• DESTINATION_BUCKET_NAME is the name of the bucket to which you are uploading your object. For example, my-bucket.
• KEY is the context key to attach to an object. For example, Department. You can specify multiple key-value pairs separated by commas.
• VALUE is the value to associate with the context key. For example, Human resources.

Alternatively, create a JSON file that contains the contexts you want to attach to the objects, and use the --custom-contexts-file flag:

  {
    "KEY": {
      "value": "VALUE"
    },
    ...
  }

Where:

• KEY is the context key to attach to an object. For example, Department. You can specify multiple key-value pairs.
• VALUE is the value to associate with the context key. For example, Human resources.

To attach contexts when you upload directories with the gcloud storage rsync command, use the --custom-contexts flag or the --custom-contexts-file flag:

gcloud storage rsync DIRECTORY_LOCATION gs://DESTINATION_BUCKET_NAME --recursive --custom-contexts=KEY=VALUE,...

Where:

• DIRECTORY_LOCATION is the local path to your directory. For example, ~/my_directory.
• DESTINATION_BUCKET_NAME is the name of the bucket to which you are uploading your directory. For example, my-bucket.
• KEY is the context key to attach to objects. For example, Department. You can specify multiple key-value pairs separated by commas.
• VALUE is the value to associate with the context key. For example, Human resources.

JSON API

To attach contexts to objects when you upload new objects, use any of the following methods:

• Multipart uploads

• Resumable uploads

As part of the object metadata in JSON format, include the contexts field:

  {
    "contexts": {
      "custom": {
        "KEY": {
          "value": "VALUE"
        },
        ...
      }
    }
  }

Where:

• KEY is the context key to attach to an object. For example, Department. You can specify multiple key-value pairs in the custom object.
• VALUE is the value to associate with the context key. For example, Human resources.

Console

1. In the Google Cloud console, go to the Cloud Storage Buckets page.
   

   Go to Buckets

2. In the list of buckets, click the name of the bucket containing the object.

3. Navigate to the object, and then click more_vert Open object overflow menu.

4. Click Edit contexts.

5. In the Edit contexts panel, do any of the following:

   • Add a new object context:

     1. Click Add a custom context.

     2. In the Object context key and Object context value fields, enter a new key-value pair.

     3. Click Done.

     4. Optional: To add additional object contexts, click Add a custom context, repeat the previous steps, and then click Save.

   • Edit an object context:

     1. Click the object context.

     2. Update the Object context key field, the Object context value field, or both.

     3. Click Done, and then click Save.

   • Delete an object context:

     Click delete Delete, and then click Save.

Command line

Use the gcloud storage objects update command:

gcloud storage objects update gs://BUCKET_NAME/OBJECT_NAME CUSTOM_CONTEXTS_FLAG

Where:

• BUCKET_NAME is the name of the bucket that contains the object for which you want to edit context. For example, my-bucket.
• OBJECT_NAME is the name of the object. For example, employees.txt.

• CUSTOM_CONTEXTS_FLAG is any of the following flags:

  • To replace all existing contexts, use --custom-contexts=KEY=VALUE,... or --custom-contexts-file=CUSTOM_CONTEXTS_FILE

    Where:

    • KEY is the context key to attach to an object. For example, Department. You can specify multiple key-value pairs separated by commas.
    • VALUE is the value to associate with the context key. For example, Human resources.
    • CUSTOM_CONTEXTS_FILE is the path to the JSON or YAML file that contains the contexts you want to attach to the object.

  • To delete all existing contexts, use the --clear-custom-contexts flag.

  • To add, modify, or delete individual contexts, use a combination of --update-custom-contexts=KEY=VALUE,... and --remove-custom-contexts=KEY,...

    Where:

    • KEY is the context key that you want to attach to or delete from an object. For example, Department.
    • VALUE is the value to associate with the context key that you want to attach to or delete from an object. For example, Human resources.

If successful, the response looks like the following example:

Patching gs://my-bucket/employees.txt#1560574162144861...
  Completed 1

Client libraries

import com.google.cloud.storage.Blob;
import com.google.cloud.storage.BlobId;
import com.google.cloud.storage.BlobInfo;
import com.google.cloud.storage.BlobInfo.ObjectContexts;
import com.google.cloud.storage.BlobInfo.ObjectCustomContextPayload;
import com.google.cloud.storage.Storage;
import com.google.cloud.storage.StorageOptions;
import com.google.common.collect.Maps;
import java.util.Map;

public class SetObjectContexts {
  public static void setObjectContexts(
      String projectId, String bucketName, String objectName, String key, String value)
      throws Exception {
    // The ID of your GCP project
    // String projectId = "your-project-id";

    // The ID of your GCS bucket
    // String bucketName = "your-unique-bucket-name";

    // The ID of your GCS object
    // String objectName = "your-object-name";

    // The context key-value you want to add
    // String key = "your-context-key";
    // String value = "your-context-value";

    try (Storage storage =
        StorageOptions.newBuilder().setProjectId(projectId).build().getService()) {
      BlobId blobId = BlobId.of(bucketName, objectName);
      Blob blob = storage.get(blobId);
      if (blob == null) {
        System.out.println("The object " + objectName + " was not found in " + bucketName);
        return;
      }

      // Recommended: Set a generation-match precondition to avoid potential race
      // conditions and data corruptions. The request to update returns a 412 error if
      // the object's generation number does not match your precondition.
      Storage.BlobTargetOption precondition = Storage.BlobTargetOption.generationMatch();

      // This section demonstrates how to upsert, delete all, and delete a specific context.

      // To upsert a context (if the key already exists, its value is replaced;
      // otherwise, a new key-value pair is added):
      ObjectCustomContextPayload payload =
          ObjectCustomContextPayload.newBuilder().setValue(value).build();
      Map<String, ObjectCustomContextPayload> custom = Maps.newHashMap();
      custom.put(key, payload);
      ObjectContexts contexts = ObjectContexts.newBuilder().setCustom(custom).build();

      /*
       * To delete all existing contexts:
       * ObjectContexts contexts = ObjectContexts.newBuilder().setCustom(null).build();
       */

      /*
       * To delete a specific key from the context:
       * Map<String, ObjectCustomContextPayload> custom = Maps.newHashMap();
       * custom.put(key, null);
       * ObjectContexts contexts = ObjectContexts.newBuilder().setCustom(custom).build();
       */
      BlobInfo pendingUpdate = blob.toBuilder().setContexts(contexts).build();
      storage.update(pendingUpdate, precondition);

      System.out.println(
          "Updated custom contexts for object " + objectName + " in bucket " + bucketName);
    }
  }
}

use google_cloud_storage::client::StorageControl;
use google_cloud_storage::model::ObjectContexts;
use google_cloud_wkt::FieldMask;

pub async fn sample(client: &StorageControl, bucket_id: &str) -> anyhow::Result<()> {
    const NAME: &str = "object-with-contexts";
    let object = client
        .get_object()
        .set_bucket(format!("projects/_/buckets/{bucket_id}"))
        .set_object(NAME)
        .send()
        .await?;

    let metageneration = object.metageneration;
    let mut custom = object.contexts.clone().unwrap_or_default().custom;
    custom.entry("example".to_string()).or_default().value = "true".into();

    let updated = client
        .update_object()
        .set_if_metageneration_match(metageneration)
        .set_object(object.set_contexts(ObjectContexts::new().set_custom(custom)))
        .set_update_mask(FieldMask::default().set_paths(["contexts.custom.example"]))
        .send()
        .await?;
    println!(
        "successfully set contexts for object {NAME} in bucket {bucket_id}: {:?}",
        updated.contexts
    );
    Ok(())
}

JSON API

1. Have gcloud CLI installed and initialized, which lets you generate an access token for the Authorization header.

2. Create a JSON file that contains the settings for the object, which must include the contexts configuration fields for the object.

   To add, modify, or overwrite existing contexts, use the following format:

     {
       "contexts": {
         "custom": {
           "KEY": {
             "value": "VALUE"
           },
           ...
         }
       }
     }

   Where:

   • KEY is the context key to attach to an object. For example, Department. You can specify multiple key-value pairs in the custom object.
   • VALUE is the value to associate with the context key. For example, Human resources.

   To delete all existing contexts, use the following format:

     {
       "contexts": {
         "custom": null
       }
     }

   To delete a specific key from the context, use the following format:

     {
       "contexts": {
         "custom": {
           "KEY": null,
           ...
         }
       }
     }

   Where:

   KEY is the context key that you want to delete from an object. For example, Department. You can specify multiple keys to delete from the custom object.

3. Use cURL to call the JSON API with a PATCH Object request:

   curl -X PATCH --data-binary @JSON_FILE_NAME \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json" \
     "https://storage.googleapis.com/storage/v1/b/BUCKET_NAME/o/OBJECT_NAME"

   Where:

   • JSON_FILE_NAME is the path to the file that includes the object contexts information.
   • BUCKET_NAME is the name of the bucket that contains the object for which you want to edit context. For example, my-bucket.
   • OBJECT_NAME is the URL-encoded name of the object. For example, employees.txt.

Alternatively, you can replace an object's context with a PUT Object request. The PUT object request also replaces other object metadata. Therefore, we don't recommend using the PUT object request.

Console

1. In the Google Cloud console, go to the Cloud Storage Buckets page.
   

   Go to Buckets

2. In the list of buckets, click the name of the bucket that contains the object with the contexts you want to view.

3. Navigate to the object, and then click the object's name.

   On the Object details page, the key-value pairs for any attached contexts are listed in the Object contexts section.

Command line

Use the gcloud storage objects describe command:

gcloud storage objects describe gs://BUCKET_NAME/OBJECT_NAME

Where:

• BUCKET_NAME is the name of the bucket containing the object. For example, my-bucket.
• OBJECT_NAME is the name of the object. For example, employees.txt.

If successful, the response looks similar to the following example:

bucket: my-bucket
contexts:
  custom:
    Department:
      createTime: '2023-01-01T00:00:00.000000+00:00'
      type: CUSTOM
      updateTime: '2023-01-01T00:00:00.000000+00:00'
      value: Human resources
    google:annotation:face-detector-v1:
      createTime: '2025-09-29T17:20:00.000000+00:00'
      extendedDataTypeUrl: type.googleapis.com/google.protobuf.Struct
      type: CUSTOM
      updateTime: '2025-09-29T17:20:00.000000+00:00'
      value: SUCCESS
name: employees.txt

Client libraries

import com.google.cloud.storage.Blob;
import com.google.cloud.storage.BlobInfo.ObjectContexts;
import com.google.cloud.storage.BlobInfo.ObjectCustomContextPayload;
import com.google.cloud.storage.Storage;
import com.google.cloud.storage.StorageOptions;
import java.util.Map;

public class GetObjectContexts {
  public static void getObjectContexts(String projectId, String bucketName, String objectName)
      throws Exception {
    // The ID of your GCP project
    // String projectId = "your-project-id";

    // The ID of your GCS bucket
    // String bucketName = "your-unique-bucket-name";

    // The ID of your GCS object
    // String objectName = "your-object-name";

    try (Storage storage =
        StorageOptions.newBuilder().setProjectId(projectId).build().getService()) {

      Blob blob = storage.get(bucketName, objectName);
      if (blob == null) {
        System.out.println("The object " + objectName + " was not found in " + bucketName);
        return;
      }
      ObjectContexts objectContexts = blob.getContexts();

      if (objectContexts != null) {
        Map<String, ObjectCustomContextPayload> customContexts = objectContexts.getCustom();
        if (customContexts == null) {
          System.out.println("No custom contexts found for object: " + objectName);
          return;
        }
        // Print blob's object contexts
        System.out.println("\nCustom Contexts:");
        for (Map.Entry<String, ObjectCustomContextPayload> custom : customContexts.entrySet()) {
          System.out.println(custom.getKey() + "=" + custom.getValue());
        }
      }
    }
  }
}

use google_cloud_storage::client::StorageControl;

pub async fn sample(client: &StorageControl, bucket_id: &str) -> anyhow::Result<()> {
    const NAME: &str = "object-with-contexts";
    let object = client
        .get_object()
        .set_bucket(format!("projects/_/buckets/{bucket_id}"))
        .set_object(NAME)
        .send()
        .await?;
    println!(
        "The contexts field for object {NAME} in bucket {bucket_id} is: {:?}",
        object.contexts
    );
    Ok(())
}

JSON API

1. Have gcloud CLI installed and initialized, which lets you generate an access token for the Authorization header.

2. Use cURL to call the JSON API with a GET Object request:

   curl -X GET \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     "https://storage.googleapis.com/storage/v1/b/BUCKET_NAME/o/OBJECT_NAME"

   Where:

   • BUCKET_NAME is the name of the bucket containing the object. For example, my-bucket.
   • OBJECT_NAME is the URL-encoded name of the object. For example, employees.txt.

   If successful, the response looks similar to the following example:

     {
       "kind": "storage#object",
       "name": "employees.txt",
       "bucket": "my-bucket",
       "contexts": {
         "custom": {
           "Department": {
             "value": "Human resources",
             "createTime": "2023-01-01T00:00:00.000Z",
             "updateTime": "2023-01-01T00:00:00.000Z"
           },
           "google:annotation:face-detector-v1": {
             "value": "SUCCESS",
             "createTime": "2025-09-29T17:20:00.000Z",
             "updateTime": "2025-09-29T17:20:00.000Z",
             "extendedDataTypeUrl": "type.googleapis.com/google.protobuf.Struct"
           }
         }
       }
     }
     

JSON API

To retrieve a single full context (including extended data) by key:

1. Have gcloud CLI installed and initialized, which lets you generate an access token for the Authorization header.

2. Use cURL to call the JSON API with a GET View Full Context request:

   curl -X GET \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     "https://storage.googleapis.com/storage/v1/b/BUCKET_NAME/o/OBJECT_NAME/viewFullContext?contextKey=KEY"

   Where:

   • BUCKET_NAME is the name of the bucket containing the object. For example, my-bucket.
   • OBJECT_NAME is the URL-encoded name of the object. For example, employees.txt.
   • KEY is the specific context key to retrieve. For example, google:annotation:face-detector-v1.

   If successful, the response looks similar to the following example:

   {
     "kind": "storage#objectFullContext",
     "type": "CUSTOM",
     "key": "google:annotation:face-detector-v1",
     "value": "SUCCESS",
     "createTime": "2025-09-29T17:20:00.000Z",
     "updateTime": "2025-09-29T17:20:00.000Z",
     "extendedData": {
       "@type": "type.googleapis.com/google.protobuf.Struct",
       "value": {
         "modelName": "face-detector",
         "modelVersion": "v1",
         "faceAnnotationGroup": {
           "faceAnnotations": [
             {
               "detectionConfidence": 0.9,
               "landmarkingConfidence": 0.8
             }
           ]
         }
       }
     }
   }

Command line

The gcloud storage cp command, gcloud storage rsync command, and gcloud storage mv command preserve contexts from the source object by default. To modify contexts during these operations, use any of the following flags:

• The --custom-contexts flag to set new contexts for the destination object.

• The --clear-custom-contexts flag to prevent contexts from the source object from being attached to the destination object.

• A combination of the --update-custom-contexts and --remove-custom-contexts flags to modify individual contexts from the source object before attaching them to the destination object.

To set new contexts when you copy an object, use the gcloud storage cp command:

gcloud storage cp gs://SOURCE_BUCKET_NAME/SOURCE_OBJECT_NAME gs://DESTINATION_BUCKET_NAME/DESTINATION_OBJECT_NAME --custom-contexts=KEY=VALUE,...

Where:

• SOURCE_BUCKET_NAME is the name of the bucket containing the object to copy. For example, my-source-bucket.
• SOURCE_OBJECT_NAME is the name of the object to copy. For example, employees.txt.
• DESTINATION_BUCKET_NAME is the name of the bucket to copy the object to. For example, my-destination-bucket.
• DESTINATION_OBJECT_NAME is the name of the destination object. For example, employees-backup.txt.
• KEY is the context key to attach to an object. For example, Department. You can specify multiple key-value pairs separated by commas.
• VALUE is the value to associate with the context key. For example, Human resources.

To remove all contexts from the source object when you copy an object, use the gcloud storage cp command:

gcloud storage cp gs://SOURCE_BUCKET_NAME/SOURCE_OBJECT_NAME gs://DESTINATION_BUCKET_NAME/DESTINATION_OBJECT_NAME --clear-custom-contexts

Where:

• SOURCE_BUCKET_NAME is the name of the bucket containing the object to copy. For example, my-source-bucket.
• SOURCE_OBJECT_NAME is the name of the object to copy. For example, pets/dog.png.
• DESTINATION_BUCKET_NAME is the name of the bucket to copy the object to. For example, my-destination-bucket.
• DESTINATION_OBJECT_NAME is the name of the destination object. For example, pets/cat.png.

To modify individual contexts from the source object when you copy an object, use the gcloud storage cp command with --update-custom-contexts and --remove-custom-contexts:

gcloud storage cp gs://SOURCE_BUCKET_NAME/SOURCE_OBJECT_NAME gs://DESTINATION_BUCKET_NAME/DESTINATION_OBJECT_NAME --update-custom-contexts=KEY=VALUE,... --remove-custom-contexts=KEY,...

Where:

• SOURCE_BUCKET_NAME is the name of the bucket containing the object to copy. For example, my-source-bucket.
• SOURCE_OBJECT_NAME is the name of the object to copy. For example, pets/dog.png.
• DESTINATION_BUCKET_NAME is the name of the bucket to copy the object to. For example, my-destination-bucket.
• DESTINATION_OBJECT_NAME is the name of the destination object. For example, pets/cat.png.
• KEY is the context key to attach to an object. For example, Department. You can specify multiple key-value pairs or keys separated by commas.
• VALUE is the value to associate with the context key. For example, Human resources.

JSON API

To override contexts when copying an object, include the contexts.custom property in the request body:

1. Have gcloud CLI installed and initialized, which lets you generate an access token for the Authorization header.

2. Create a JSON file that contains the contexts to attach to the destination object:

     {
       "contexts": {
         "custom": {
           "KEY": {
             "value": "VALUE"
           }
         }
       }
     }

   Where:

   • KEY is the context key to attach to an object. For example, Department.
   • VALUE is the value to associate with the context key. For example, Human resources.

3. Use cURL to call the JSON API with a POST Object request:

   curl -X POST --data-binary @JSON_FILE_NAME \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json" \
     "https://storage.googleapis.com/storage/v1/b/SOURCE_BUCKET_NAME/o/SOURCE_OBJECT_NAME/copyTo/b/DESTINATION_BUCKET_NAME/o/DESTINATION_OBJECT_NAME"

   Where:

   • JSON_FILE_NAME is the path to the JSON file that includes the object contexts information.
   • SOURCE_BUCKET_NAME is the name of the bucket that contains the object to copy. For example, my-source-bucket.
   • SOURCE_OBJECT_NAME is the URL-encoded name of the object to copy. For example, employees.txt.
   • DESTINATION_BUCKET_NAME is the name of the bucket to copy the object to. For example, my-destination-bucket.
   • DESTINATION_OBJECT_NAME is the URL-encoded name of the destination object. For example, employees-backup.txt.

To discard source contexts during a copy operation, use the dropContextGroups=custom query parameter in your request:

curl -X POST \
  -H "Authorization: Bearer $(gcloud auth print-access-token)" \
  "https://storage.googleapis.com/storage/v1/b/SOURCE_BUCKET_NAME/o/SOURCE_OBJECT_NAME/copyTo/b/DESTINATION_BUCKET_NAME/o/DESTINATION_OBJECT_NAME?dropContextGroups=custom"

If the request body contains contexts with the google: prefix, you can retain existing keys and values from the source object, but Cloud Storage rejects new google: keys or modified values.

To preserve contexts, omit the contexts property from the request body and exclude the dropContextGroups query parameter.

Command line

The gcloud storage cp command, gcloud storage rsync command, and gcloud storage mv commands perform rewrites automatically when necessary, for example, when copying objects between different locations or storage classes. gcloud storage cp and gcloud storage rsync result in a source and destination object, while gcloud storage mv creates the destination object and removes the source object. Because these operations create a new object, you can also modify or attach contexts as part of the same command by using any of the following flags:

• The --custom-contexts flag to set new contexts for the destination object.

• The --clear-custom-contexts flag to prevent contexts from the source object from being attached to the destination object.

• A combination of the --update-custom-contexts and --remove-custom-contexts flags to modify individual contexts from the source object before attaching them to the destination object.

To set new contexts when you copy an object, use the gcloud storage cp command:

gcloud storage cp gs://SOURCE_BUCKET_NAME/SOURCE_OBJECT_NAME gs://DESTINATION_BUCKET_NAME/DESTINATION_OBJECT_NAME --custom-contexts=KEY=VALUE,...

Where:

• SOURCE_BUCKET_NAME is the name of the bucket containing the object to copy. For example, my-source-bucket.
• SOURCE_OBJECT_NAME is the name of the object to copy. For example, employees.txt.
• DESTINATION_BUCKET_NAME is the name of the bucket to copy the object to. For example, my-destination-bucket.
• DESTINATION_OBJECT_NAME is the name of the destination object. For example, employees-backup.txt.
• KEY is the context key to attach to an object. For example, Department. You can specify multiple key-value pairs separated by commas.
• VALUE is the value to associate with the context key. For example, Human resources.

To remove all contexts from the source object when you copy an object, use the gcloud storage cp command:

gcloud storage cp gs://SOURCE_BUCKET_NAME/SOURCE_OBJECT_NAME gs://DESTINATION_BUCKET_NAME/DESTINATION_OBJECT_NAME --clear-custom-contexts

Where:

• SOURCE_BUCKET_NAME is the name of the bucket containing the object to copy. For example, my-source-bucket.
• SOURCE_OBJECT_NAME is the name of the object to copy. For example, pets/dog.png.
• DESTINATION_BUCKET_NAME is the name of the bucket to copy the object to. For example, my-destination-bucket.
• DESTINATION_OBJECT_NAME is the name of the destination object. For example, pets/cat.png.

To modify individual contexts from the source object when you copy an object, use the gcloud storage cp command with --update-custom-contexts and --remove-custom-contexts:

gcloud storage cp gs://SOURCE_BUCKET_NAME/SOURCE_OBJECT_NAME gs://DESTINATION_BUCKET_NAME/DESTINATION_OBJECT_NAME --update-custom-contexts=KEY=VALUE,... --remove-custom-contexts=KEY,...

Where:

• SOURCE_BUCKET_NAME is the name of the bucket containing the object to copy. For example, my-source-bucket.
• SOURCE_OBJECT_NAME is the name of the object to copy. For example, pets/dog.png.
• DESTINATION_BUCKET_NAME is the name of the bucket to copy the object to. For example, my-destination-bucket.
• DESTINATION_OBJECT_NAME is the name of the destination object. For example, pets/cat.png.
• KEY is the context key to attach to an object. For example, Department. You can specify multiple key-value pairs or keys separated by commas.
• VALUE is the value to associate with the context key. For example, Human resources.

JSON API

To override contexts when rewriting an object, include the contexts.custom property in the request body:

1. Have gcloud CLI installed and initialized, which lets you generate an access token for the Authorization header.

2. Create a JSON file that contains the contexts to attach to the destination object:

     {
       "contexts": {
         "custom": {
           "KEY": {
             "value": "VALUE"
           }
         }
       }
     }

   Where:

   • KEY is the context key to attach to an object. For example, Department.
   • VALUE is the value to associate with the context key. For example, Human resources.

3. Use cURL to call the JSON API with a POST rewrite Object request:

   curl -X POST --data-binary @JSON_FILE_NAME \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json" \
     "https://storage.googleapis.com/storage/v1/b/SOURCE_BUCKET_NAME/o/SOURCE_OBJECT_NAME/rewriteTo/b/DESTINATION_BUCKET_NAME/o/DESTINATION_OBJECT_NAME"

   Where:

   • JSON_FILE_NAME is the path to the JSON file that includes the object contexts information.
   • SOURCE_BUCKET_NAME is the name of the bucket that contains the object to rewrite. For example, my-source-bucket.
   • SOURCE_OBJECT_NAME is the URL-encoded name of the object to rewrite. For example, employees.txt.
   • DESTINATION_BUCKET_NAME is the name of the bucket to rewrite the object to. For example, my-destination-bucket.
   • DESTINATION_OBJECT_NAME is the URL-encoded name of the destination object. For example, employees-backup.txt.

To discard source contexts during a rewrite operation, use the dropContextGroups=custom query parameter in your request:

curl -X POST \
  -H "Authorization: Bearer $(gcloud auth print-access-token)" \
  "https://storage.googleapis.com/storage/v1/b/SOURCE_BUCKET_NAME/o/SOURCE_OBJECT_NAME/rewriteTo/b/DESTINATION_BUCKET_NAME/o/DESTINATION_OBJECT_NAME?dropContextGroups=custom"

If the request body contains contexts with the google: prefix, you can retain existing keys and values from the source object, but Cloud Storage rejects new google: keys or modified values.

To preserve contexts, omit the contexts property from the request body and exclude the dropContextGroups query parameter.

Command line

To specify new contexts for the destination object when composing objects, use the --contexts flag:

gcloud storage objects compose gs://BUCKET_NAME/SOURCE_OBJECT_1 gs://BUCKET_NAME/SOURCE_OBJECT_2 gs://BUCKET_NAME/DESTINATION_OBJECT_NAME --contexts=KEY=VALUE,...

Where:

• BUCKET_NAME is the name of the bucket that contains the source objects and where the destination object is created. For example, my-bucket.
• SOURCE_OBJECT_1 and SOURCE_OBJECT_2 are source objects to compose.
• DESTINATION_OBJECT_NAME is the name of the destination object to be created. For example, my-composite-object.
• KEY is the context key to attach to an object. For example, Department. You can specify multiple key-value pairs separated by commas.
• VALUE is the value to associate with the context key. For example, Human resources.

To prevent source contexts from being attached to composite objects, use the --clear-custom-contexts flag:

gcloud storage objects compose gs://BUCKET_NAME/SOURCE_OBJECT_1 gs://BUCKET_NAME/SOURCE_OBJECT_2 gs://BUCKET_NAME/DESTINATION_OBJECT_NAME --clear-custom-contexts

Where:

• BUCKET_NAME is the name of the bucket that contains source objects and where the destination object is created. For example, my-bucket.
• SOURCE_OBJECT_1 and SOURCE_OBJECT_2 are the source objects to compose.
• DESTINATION_OBJECT_NAME is the name of the destination object to be created. For example, my-composite-object.

JSON API

To specify new contexts for the destination object when composing objects, include contexts in the destination property of the request body.

1. Have gcloud CLI installed and initialized, which lets you generate an access token for the Authorization header.

2. Create a JSON file that contains the request body:

   {
     "sourceObjects": [
       {"name": "SOURCE_OBJECT_1"},
       {"name": "SOURCE_OBJECT_2"}
     ],
     "destination": {
       "contentType": "text/plain",
       "contexts": {
         "custom": {
           "KEY": {
             "value": "VALUE"
           }
         }
       }
     }
   }

   Where:

   • SOURCE_OBJECT_1 and SOURCE_OBJECT_2 are source objects to compose.
   • KEY is the context key to attach to an object. For example, Department.
   • VALUE is the value to associate with the context key. For example, Human resources.

3. Use cURL to call the JSON API with a POST compose Object request:

   curl -X POST --data-binary @JSON_FILE_NAME \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json" \
     "https://storage.googleapis.com/storage/v1/b/BUCKET_NAME/o/DESTINATION_OBJECT_NAME/compose"

   Where:

   • JSON_FILE_NAME is the path to the JSON file that includes the request body.
   • BUCKET_NAME is the name of the bucket that contains source objects and where the destination object is created. For example, my-bucket.
   • DESTINATION_OBJECT_NAME is the name of the destination object to be created. For example, my-composite-object.

To prevent source contexts from being attached to composite objects, use the dropContextGroups=custom query parameter in your request:

1. Have gcloud CLI installed and initialized, which lets you generate an access token for the Authorization header.

2. Create a JSON file that contains the request body:

   {
     "sourceObjects": [
       {"name": "SOURCE_OBJECT_1"},
       {"name": "SOURCE_OBJECT_2"}
     ],
     "destination": {
       "contentType": "text/plain"
   }
   }

   Where:

   • SOURCE_OBJECT_1 and SOURCE_OBJECT_2 are source objects to compose.

3. Use cURL to call the JSON API with a POST compose Object request:

   curl -X POST --data-binary @JSON_FILE_NAME \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json" \
     "https://storage.googleapis.com/storage/v1/b/BUCKET_NAME/o/DESTINATION_OBJECT_NAME/compose?dropContextGroups=custom"

   Where:

   • JSON_FILE_NAME is the path to the JSON file that includes the request body.
   • BUCKET_NAME is the name of the bucket that contains source objects and where the destination object is created. For example, my-bucket.
   • DESTINATION_OBJECT_NAME is the name of the destination object to be created. For example, my-composite-object.