public async Task <Dictionary <string, object> > GetSyncResponse(int eventId, int teamId, int puzzleId, List <int> query_puzzle_ids,
int?min_solve_count, string annotations, string last_sync_time)
{
SyncResponse response = new SyncResponse();
// Get information for the puzzle that's being sync'ed.
Puzzle thisPuzzle = await context.Puzzles.Where(puz => puz.ID == puzzleId).FirstOrDefaultAsync();
if (thisPuzzle == null)
{
response.AddError("Could not find the puzzle you tried to sync.");
return(response.GetResult());
}
// Check to make sure that they're not trying to sync a puzzle and event that don't go together.
// That could be a security issue, allowing them to unlock pieces for a puzzle using the progress
// they made in a whole different event!
if (thisPuzzle.Event.ID != eventId)
{
response.AddError("That puzzle doesn't belong to that event.");
return(response.GetResult());
}
// Get the site version for this puzzle, so that if it's changed since the last time the
// requester sync'ed, the requester will know to reload itself.
response.SetSiteVersion(GetSiteVersion(thisPuzzle));
// Decode the request. If there are any errors, return an error response.
DecodedSyncRequest request = new DecodedSyncRequest(query_puzzle_ids, min_solve_count, annotations, last_sync_time,
thisPuzzle.MaxAnnotationKey, ref response);
// Do any processing that requires fetching the list of all puzzles this team has
// solved. Pass thisPuzzle.Group as the groupExcludedFromSolveCount parameter so that,
// when counting solves, we don't count solves in the same group as this puzzle as part
// of the solve count.
await HandleSyncAspectsRequiringListOfSolvedPuzzles(request, response, thisPuzzle.Group, teamId, eventId);
// Store any annotations the requester provided
await StoreAnnotations(request, response, thisPuzzle.ID, teamId);
// Fetch and return any annotations that the requester may not have yet
await GetAnnotationsRequesterLacks(request, response, thisPuzzle.ID, teamId);
return(response.GetResult());
}
/// <summary>
/// This routine updates a single existing annotation. As we do so, we increment
/// its version number and update its timestamp.
///
/// This routine is only meant to be called when we know an annotation exists
/// with the given puzzle ID, team ID, and key. In other words, this routine
/// is called when we need to update that annotation.
/// </summary>
private async Task UpdateOneAnnotation(SyncResponse response, int puzzleId, int teamId, int key, string contents)
{
// You may wonder why we're using ExecuteSqlCommandAsync instead of "normal"
// Entity Framework database functions. The answer is that we need to atomically
// update the Version field of the record, and Entity Framework has no way of
// expressing that directly.
//
// The reason we want to update the version number atomically is that we rely
// on the version number being a unique identifier of an annotation. We don't
// want the following scenario:
//
// Alice tries to set the annotation for key 17 to A, and simultaneously Bob
// tries to set it to B. Each reads the current version number, finds it to be
// 3, and updates the annotation to have version 4. Both of these updates may
// succeed, but one will overwrite the other; let's say Bob's write happens last
// and "wins". So Alice may believe that version 4 is A when actually version 4
// is B. When Alice asks for the current version, she'll be told it's version 4,
// and Alice will believe this means it's A. So Alice will believe that A is
// what's stored in the database even though it's not. Alice and Bob's computers
// will display different annotations for the same key, indefinitely.
//
// Note that we need a version number because the timestamp isn't guaranteed to
// be unique. So in the example above Alice and Bob might wind up updating with
// the same timestamp.
//
// You may also wonder why we use DateTime.Now instead of letting the database
// assign the timestamp itself. The reason is that the database might be running
// on a different machine than the puzzle server, and it might be using a different
// time zone.
try {
var sqlCommand = "UPDATE Annotations SET Version = Version + 1, Contents = @Contents, Timestamp = @Timestamp WHERE PuzzleID = @PuzzleID AND TeamID = @TeamID AND [Key] = @Key";
int result = await context.Database.ExecuteSqlRawAsync(sqlCommand,
new SqlParameter("@Contents", contents),
new SqlParameter("@Timestamp", DateTime.Now),
new SqlParameter("@PuzzleID", puzzleId),
new SqlParameter("@TeamID", teamId),
new SqlParameter("@Key", key));
if (result != 1)
{
response.AddError("Annotation update failed.");
}
}
catch (DbUpdateException) {
response.AddError("Encountered error while trying to update annotation.");
}
catch (Exception) {
response.AddError("Miscellaneous error while trying to update annotation.");
}
}
public DecodedSyncRequest(List <int> query_puzzle_ids, int?min_solve_count, string annotations, string last_sync_time,
int maxAnnotationKey, bool query_all_in_group, ref SyncResponse response)
{
// The query_puzzle_ids, min_solve_count, and query_all_in_group fields are already perfectly fine, so just copy them.
QueryPuzzleIds = query_puzzle_ids;
MinSolveCount = min_solve_count;
QueryAllInGroup = query_all_in_group;
// The last_sync_time field is a JSON-converted DateTime. Or at least, it's supposed to be;
// we need to check. Note that this string is one that we (the server) encoded. We do DateTime
// encoding and decoding on the server so as not to worry about different browsers encoding
// DateTimes differently.
if (last_sync_time == null)
{
LastSyncTime = null;
}
else
{
try {
LastSyncTime = JsonConvert.DeserializeObject <DateTime>(last_sync_time);
}
catch (JsonException) {
response.AddError("Could not deserialize last sync time.");
LastSyncTime = null;
}
}
// The annotations field is a JSON-converted list of objects, each with an integer key and
// string contents. Or at least, it's supposed to be; we have to check it carefully.
AnnotationRequests = new List <AnnotationRequest>();
if (annotations != null)
{
List <AnnotationRequest> uncheckedAnnotationRequests;
try {
// First, decode it into a list using the JSON deserializer.
uncheckedAnnotationRequests = JsonConvert.DeserializeObject <List <AnnotationRequest> >(annotations);
}
catch (JsonException) {
response.AddError("Could not deserialize annotations list.");
uncheckedAnnotationRequests = new List <AnnotationRequest>();
}
// Check each of the elements for validity.
foreach (var annotation in uncheckedAnnotationRequests)
{
if (annotation.key < 1)
{
response.AddError("Found non-positive key in annotation.");
continue;
}
if (annotation.key > maxAnnotationKey)
{
response.AddError("Found too-high key in annotation.");
continue;
}
if (annotation.contents.Length > 255)
{
response.AddError("Found contents in annotation longer than 255 bytes.");
continue;
}
AnnotationRequests.Add(annotation);
}
}
}
/// <summary>
/// This routine stores in the database any annotations the requester has uploaded.
/// </summary>
private async Task StoreAnnotations(DecodedSyncRequest request, SyncResponse response, int puzzleId, int teamId)
{
if (request.AnnotationRequests == null)
{
return;
}
foreach (var annotationRequest in request.AnnotationRequests)
{
// Try to generate this as a new annotation, with version 1.
Annotation annotation = new Annotation();
annotation.PuzzleID = puzzleId;
annotation.TeamID = teamId;
annotation.Key = annotationRequest.key;
annotation.Version = 1;
annotation.Contents = annotationRequest.contents;
annotation.Timestamp = DateTime.Now;
try {
context.Annotations.Add(annotation);
await context.SaveChangesAsync();
}
catch (DbUpdateException) {
// If the insert fails, there must already be an annotation there with the
// same puzzle ID, team ID, and key. So we need to update the existing one.
// As we do so, we increment its version number and update its timestamp.
//
// You may wonder why we're using ExecuteSqlCommandAsync instead of "normal"
// Entity Framework database functions. The answer is that we need to atomically
// update the Version field of the record, and Entity Framework has no way of
// expressing that directly.
//
// The reason we want to update the version number atomically is that we rely
// on the version number being a unique identifier of an annotation. We don't
// want the following scenario:
//
// Alice tries to set the annotation for key 17 to A, and simultaneously Bob
// tries to set it to B. Each reads the current version number, finds it to be
// 3, and updates the annotation to have version 4. Both of these updates may
// succeed, but one will overwrite the other; let's say Bob's write happens last
// and "wins". So Alice may believe that version 4 is A when actually version 4
// is B. When Alice asks for the current version, she'll be told it's version 4,
// and Alice will believe this means it's A. So Alice will believe that A is
// what's stored in the database even though it's not. Alice and Bob's computers
// will display different annotations for the same key, indefinitely.
//
// Note that we need a version number because the timestamp isn't guaranteed to
// be unique. So in the example above Alice and Bob might wind up updating with
// the same timestamp.
//
// You may also wonder why we use DateTime.Now instead of letting the database
// assign the timestamp itself. The reason is that the database might be running
// on a different machine than the puzzle server, and it might be using a different
// time zone.
// First, detach the annotation from the context so the context doesn't think the annotation is in the database.
context.Entry(annotation).State = EntityState.Detached;
try {
var sqlCommand = "UPDATE Annotations SET Version = Version + 1, Contents = @Contents, Timestamp = @Timestamp WHERE PuzzleID = @PuzzleID AND TeamID = @TeamID AND [Key] = @Key";
int result = await context.Database.ExecuteSqlCommandAsync(sqlCommand,
new SqlParameter("@Contents", annotationRequest.contents),
new SqlParameter("@Timestamp", DateTime.Now),
new SqlParameter("@PuzzleID", puzzleId),
new SqlParameter("@TeamID", teamId),
new SqlParameter("@Key", annotationRequest.key));
if (result != 1)
{
response.AddError("Annotation update failed.");
}
}
catch (DbUpdateException) {
response.AddError("Encountered error while trying to update annotation.");
}
catch (Exception) {
response.AddError("Miscellaneous error while trying to update annotation.");
}
}
}
}
