chore(storage): validates parts before completing multipart upload (#98)

Author: brennanMKE

AmplifyPlugins/Storage/AWSS3StoragePlugin/Support/Internal/StorageMultipartUpload.swift

@@ -11,6 +11,7 @@ import Amplify
 enum StorageMultipartUpload {
     enum Failure: Error {
         case invalidStateTransition(reason: String)
+        case invalidateParts(reason: String)
     }
 
     case none
@@ -152,6 +153,34 @@ enum StorageMultipartUpload {
         return part
     }
 
+    func validateForCompletion() throws {
+        guard case .parts(let uploadId, let uploadFile, let partSize, let parts) = self else {
+            throw Failure.invalidateParts(reason: "not prepared to complete")
+        }
+
+        if uploadId.isEmpty {
+            throw Failure.invalidateParts(reason: "uploadId is not valid")
+        }
+
+        if partSize.size < Bytes.megabytes(5).bytes {
+            throw Failure.invalidateParts(reason: "parts size is below minimim size")
+        }
+
+        for part in parts {
+            if part.eTag == nil || part.eTag?.isEmpty ?? false {
+                throw Failure.invalidateParts(reason: "Part has invalid eTag")
+            }
+        }
+
+        let totalBytes = parts.reduce(into: 0) { result, part in
+            result += part.bytes
+        }
+
+        if uploadFile.size != totalBytes {
+            throw Failure.invalidateParts(reason: "Total bytes uploaded does not match file size")
+        }
+    }
+
     // swiftlint:disable cyclomatic_complexity
     mutating func transition(multipartUploadEvent: StorageMultipartUploadEvent, logger: Logger = storageLogger) throws {
         switch multipartUploadEvent {

AmplifyPlugins/Storage/AWSS3StoragePlugin/Support/Internal/StorageMultipartUploadSession.swift

@@ -251,6 +251,13 @@ class StorageMultipartUploadSession {
                     fatalError("Invalid state")
                 }
             } else if partsCompleted {
+                do {
+                    try multipartUpload.validateForCompletion()
+                } catch {
+                    fail(error: error)
+                    return
+                }
+                
                 if let uploadId = multipartUpload.uploadId {
                     try client.completeMultipartUpload(uploadId: uploadId)
                 } else {