NowAttachment structure - iOS

The NowAttachment structure provides functions that enable you to validate attachments by comparing their computed hash.

Table 1. Properties

Name	Type	Description
data	Data	Attachment data.
hash	String	Computed digest for the attachment data. This computed digest is used to validate the attachment by comparing it to the known digest stored in the attachment metadata. Calculating the computed digest is expensive; avoid using it in the UI. Instead, consider using the hash property in the NowAttachmentMetadata class. If you must use the computed hash, use it sparingly, and consider caching it.
metadata	NowAttachmentMetadata	Metadata associated with the attachment.

NowAttachment - validate()

Validates the attachment by comparing the computed hash for the attachment data to the digest stored in the attachment metadata.

Table 2. Parameters

Name	Type	Description
None

Table 3. Returns

Type	Description
Boolean	Flag that indicates whether the attachment is valid. Possible values: true: Attachment is valid. false: Attachment is invalid.

The following code example shows how to call this function.

guard 
  let metadataHeader = response.httpResponse?.value(forHTTPHeaderField: NowAttachment.attachmentMetadataHeaderKey),
  let metadataHeaderData = metadataHeader.data(using: .utf8) else {
    throw NowDataError.missingAttachmentMetadata
  }
            
let metadata = try coder.decode(NowAttachmentMetadata.self, from: metadataHeaderData)
let attachment = NowAttachment(metadata: metadata, data: response.data)
            
if !attachment.validate() {
  throw NowDataError.attachmentValidation
}
// Attachment is valid
return attachment