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Concatenates a list of existing objects into a new object in the same bucket. The existing source objects are unaffected by this operation.
See Composite objects for a general discussion of object composition, and see Compose objects for tool-specific guides to performing a composition.
Required permissionsThe authenticated user must have the storage.objects.create and storage.objects.get IAM permissions to use this method. If the new composite object overwrites an existing object, the authenticated user must also have the storage.objects.delete permission. If the request body includes the retention property, the authenticated user must also have the storage.objects.setRetention IAM permission.
POST https://storage.googleapis.com/storage/v1/b/bucket/o/destinationObject/compose
In addition to standard query parameters, the following query parameters apply to this method.
To see an example of how to include query parameters in a request, see the JSON API Overview page.
Parameters Parameter name Value Description Path parametersbucket string Name of the bucket containing the source objects. The destination object is stored in this bucket. destinationObject string Name of the new object. For information about how to URL encode object names to be path safe, see Encoding URI path parts. Optional query parameters destinationPredefinedAcl string Apply a predefined set of access controls to the destination object.
Acceptable values are:
authenticatedRead: Object owner gets OWNER access, and allAuthenticatedUsers get READER access.bucketOwnerFullControl: Object owner gets OWNER access, and project team owners get OWNER access.bucketOwnerRead: Object owner gets OWNER access, and project team owners get READER access.private: Object owner gets OWNER access.projectPrivate: Object owner gets OWNER access, and project team members get access according to their roles.publicRead: Object owner gets OWNER access, and allUsers get READER access.iamConfiguration.uniformBucketLevelAccess.enabled is set to true, requests that include this parameter fail with a 400 Bad Request response.
ifGenerationMatch long Makes the operation conditional on there being a live destination object with a generation number that matches the given value. Setting ifGenerationMatch to 0 makes the operation succeed only if there is no live destination object. ifMetagenerationMatch long Makes the operation conditional on there being a live destination object with a metageneration number that matches the given value. kmsKeyName string Resource name of the Cloud KMS key that will be used to encrypt the composed object. If not specified, the request uses the bucket's default Cloud KMS key, if any, or else it uses standard Cloud Storage encryption. X-Goog-Encryption-Algorithm string The encryption algorithm to use, which must be AES256. Used when encrypting the composed object with a customer-supplied encryption key. X-Goog-Encryption-Key string An RFC 4648 Base64-encoded string of your AES-256 encryption key. Used when encrypting the composed object with a customer-supplied encryption key. X-Goog-Encryption-Key-Sha256 string An RFC 4648 Base64-encoded string of the SHA256 hash of your encryption key. Used when encrypting the composed object with a customer-supplied encryption key. Request body
In the request body, supply data with the following structure:
{
"kind": "storage#composeRequest",
"sourceObjects": [
{
"name": string,
"generation": "long",
"objectPreconditions": {
"ifGenerationMatch": "long"
}
}
],
"destination": objects Resource
} Property name Value Description Notes kind string The kind of item this is. destination nested object Properties of the resulting object. writable sourceObjects[] list The list of source objects that will be concatenated into a single object. There is a limit of 32 components that can be composed in a single operation. sourceObjects[].name string The source object's name. All source objects must reside in the same bucket and use the same storage class. writable sourceObjects[].generation long1 The generation of this object to use as the source. writable sourceObjects[].objectPreconditions object Conditions that must be met for this operation to execute. sourceObjects[].objectPreconditions.ifGenerationMatch long1 Only perform the composition if the generation of the source object that would be used matches this value. If this value and a generation are both specified, they must be the same value or the call will fail. writable 1 This property is a string formatted as the specified value type. Response
If successful, this method returns an object resource in the response body, with the owner and acl properties omitted.
For information about status and error codes returned by this API, see the reference page.
Try it!Use the APIs Explorer below to call this method on live data and see the response.
Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.
Last updated 2025-08-07 UTC.
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