Ensure consistency with headers

Some Box APIs support headers used to ensure consistency between your application and Box.

etag, if-match, and if-none-match

Many of the file system items (files or folders) that can be requested via the API return an etag value for the item.

For example, a file resource returns an etag in the JSON response.

curl https://api.box.com/2.0/files/12345 \
    -H "authorization: Bearer ACCESS_TOKEN"

{
  "id": 12345,
  "etag": 1,
  "type": "file",
  "sequence_id": 3,
  "name": "Contract.pdf",
  ...
}

This etag can be used as the value of a if-match or if-none-match header to either ensure a resource hasn’t changed since the etag value was received, or to prevent unnecessary downloads for items that haven’t changed.

For example, to fetch the same file only if it has changed, pass in the etag value in a if-none-match header.

curl https://api.box.com/2.0/files/12345 \
    -H "authorization: Bearer ACCESS_TOKEN" \
    -H "if-none-match: 1"

This API call would result in an empty response if the file had not changed.

Ensure consistent changes

The if-match header allows your application to ensure that no changes are made to items when another application or a user has made changes to the item since your application last inspected it. This helps ensure that changes aren’t lost when two applications or users are changing items at the same time.

The following endpoints support this header.

if-match capable endpoints
	Upload a new file version
	Update a file’s information
	Delete a file
	Update a folder’s information
	Delete a folder
	Update a web link’s information
	Delete a web link

The response of these APIs calls depends on the existence of the item, and whether the etag value matches the most recent version.

Item found?	Etag match?	HTTP status
Yes	Yes	200
Yes	No	412
No	Yes	412
No	No	404

Moving items

The if-match header cannot be used to prevent moving of files, folders, or web links. Instead, Box always ensures that the latest item is moved to the new location.

Prevent unnecessary request downloads

The if-none-match header allows your application to ensure that no information is downloaded for items that have not changed since your application last inspected it. This helps ensure no unnecessary information is downloaded, speeding up your application and saving on bandwidth.

if-none-match capable endpoints
	Get a file’s information
	Get a folder’s information
	Get a web link’s information
	Get a shared item’s information

The response of these APIs calls depends on the existence of the item, and whether the etag value matches the most recent version.

Item found?	Etag match?	HTTP Status
Yes	Yes	304
Yes	No	200
No	Yes	404
No	No	404