FIX: Gap Of Uploading The Same File Key Twice

cms/internal/handlers/videos.go

@@ -113,8 +113,9 @@ func PresignVideoUpload(w http.ResponseWriter, r *http.Request) {
 //	@Success		201		{object}	api.CompleteResponse
 //	@Failure		400		{object}	api.ProblemDetails	"Request body was not valid JSON"
 //	@Failure		404		{object}	api.ProblemDetails	"categoryIds referenced a category that does not exist"
+//	@Failure		409		{object}	api.ProblemDetails	"key has already been registered by an earlier request"
 //	@Failure		422		{object}	api.ProblemDetails	"title was empty, key was missing or not a key issued by this API, or categoryIds was empty"
-//	@Failure		500		{object}	api.ProblemDetails	"Categories could not be read, the transcoding job could not be queued, or the video record could not be saved"
+//	@Failure		500		{object}	api.ProblemDetails	"Categories could not be read, the key could not be checked, the transcoding job could not be queued, or the video record could not be saved"
 //	@Router			/api/videos [post]
 func CompleteVideoUpload(w http.ResponseWriter, r *http.Request) {
 	r.Body = http.MaxBytesReader(w, r.Body, maxJSONBodySize)
@@ -166,6 +167,24 @@ func CompleteVideoUpload(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Ahead of queueing, because a key that is already registered would
+	// otherwise get a second transcoding job before the insert failed on the
+	// storage_key UNIQUE constraint. That constraint is still the backstop:
+	// this check and the insert are not one atomic step, so two concurrent
+	// requests carrying the same key can both get past here.
+	alreadyRegistered, err := repositories.VideoRepo.VideoExistsWithStorageKey(r.Context(), key)
+	if err != nil {
+		log.Printf("Something Went Wrong Checking Whether The Video Was Already Registered: %s", err)
+		writeProblem(w, http.StatusInternalServerError, "Something Went Wrong Checking Whether The Video Was Already Registered",
+			"The submitted key could not be checked against the existing video records, so no video record was created and no transcoding job was queued. This is a server-side fault; the uploaded file is still in storage, so retry this request with the same 'key'.")
+		return
+	}
+	if alreadyRegistered {
+		writeProblem(w, http.StatusConflict, "Video Already Registered",
+			fmt.Sprintf("The 'key' %q has already been registered, so a video record and a transcoding job exist for that file. Registering it a second time would queue a duplicate job. If you meant to add a different video, request a fresh key from POST /api/videos/presign and upload the file to it.", key))
+		return
+	}
+
 	jobID, err := services.MediaConvertClient.QueueEncodingJob(r.Context(), key)
 	if err != nil {
 		log.Printf("Something Went Wrong On Creation Of Transcoding Job: %s", err)