These steps should be followed in order to establish a gameplay connection with an Archipelago session.
1. Client establishes WebSocket connection to Archipelago server.
2. Server accepts connection and responds with a [RoomInfo](#RoomInfo) packet.
3. Client may send a [GetDataPackage](#GetDataPackage) packet.
4. Server sends a [DataPackage](#DataPackage) packet in return. (If the client sent GetDataPackage.)
5. Client sends [Connect](#Connect) packet in order to authenticate with the server.
6. Server validates the client's packet and responds with [Connected](#Connected) or [ConnectionRefused](#ConnectionRefused).
7. Server may send [ReceivedItems](#ReceivedItems) to the client, in the case that the client is missing items that are queued up for it.
8. Server sends [Print](#Print) to all players to notify them of the new client connection.
In the case that the client does not authenticate properly and receives a [ConnectionRefused](#ConnectionRefused) then the server will maintain the connection and allow for follow-up [Connect](#Connect) packet.
There are libraries available that implement this network protocol in [Python](https://github.com/ArchipelagoMW/Archipelago/blob/main/CommonClient.py), [Java](https://github.com/ArchipelagoMW/Archipelago.MultiClient.Java), [.Net](https://github.com/ArchipelagoMW/Archipelago.MultiClient.Net) and [C++](https://github.com/black-sliver/apclientpp)
For Super Nintendo games there are clients available in either [Node](https://github.com/ArchipelagoMW/SuperNintendoClient) or [Python](https://github.com/ArchipelagoMW/Archipelago/blob/main/SNIClient.py), There are also game specific clients available for [The Legend of Zelda: Ocarina of Time](https://github.com/ArchipelagoMW/Z5Client) or [Final Fantasy 1](https://github.com/ArchipelagoMW/Archipelago/blob/main/FF1Client.py)
When the client receives a [ReceivedItems](#ReceivedItems) packet, if the `index` argument does not match the next index that the client expects then it is expected that the client will re-sync items with the server. This can be accomplished by sending the server a [Sync](#Sync) packet and then a [LocationChecks](#LocationChecks) packet.
Even if the client detects a desync, it can still accept the items provided in this packet to prevent gameplay interruption.
When the client receives a [ReceivedItems](#ReceivedItems) packet and the `index` arg is `0` (zero) then the client should accept the provided `items` list as its full inventory. (Abandon previous inventory.)
# Archipelago Protocol Packets
Packets are sent between the multiworld server and client in order to sync information between them. Below is a directory of each packet.
Packets are simple JSON lists in which any number of ordered network commands can be sent, which are objects. Each command has a "cmd" key, indicating its purpose. All packet argument types documented here refer to JSON types, unless otherwise specified.
An object can contain the "class" key, which will tell the content data type, such as "Version" in the following example.
| permissions | dict\[str, [Permission](#Permission)\[int\]\] | Mapping of permission name to [Permission](#Permission), keys are: "forfeit", "collect" and "remaining". |
| players | list\[[NetworkPlayer](#NetworkPlayer)\] | Sent only if the client is properly authenticated (see [Archipelago Connection Handshake](#Archipelago-Connection-Handshake)). Information on the players currently connected to the server. |
| datapackage_version | int | Data version of the [data package](#Data-Package-Contents) the server will send. Used to update the client's (optional) local cache. |
Dictates what is allowed when it comes to a player forfeiting their run. A forfeit is an action which distributes the rest of the items in a player's run to those other players awaiting them.
*`auto`: Distributes a player's items to other players when they complete their goal.
*`enabled`: Denotes that players may forfeit at any time in the game.
*`auto-enabled`: Both of the above options together.
*`disabled`: All forfeit modes disabled.
*`goal`: Allows for manual use of forfeit command once a player completes their goal. (Disabled until goal completion)
| errors | list\[str\] | Optional. When provided, should contain any one of: `InvalidSlot`, `InvalidGame`, `SlotAlreadyTaken`, `IncompatibleVersion`, `InvalidPassword`, or `InvalidItemsHandling`. |
| checked_locations | list\[int\] | Contains ids of all locations that have been checked. Useful for trackers, among other things. Location ids are in the range of ± 2<sup>53</sup>-1. |
| checked_locations | list\[int\] | May be a partial update, containing new locations that were checked, especially from a coop partner in the same slot. |
| missing_locations | list\[int\] | Should never be sent as an update, if needed is the inverse of checked_locations. |
Sent to clients purely to display a message to the player.
#### Arguments
| Name | Type | Notes |
| ---- | ---- | ----- |
| text | str | Message to display to player. |
### PrintJSON
Sent to clients purely to display a message to the player. This packet differs from [Print](#Print) in that the data being sent with this packet allows for more configurable or specific messaging.
Sent to clients to provide what is known as a 'data package' which contains information to enable a client to most easily communicate with the Archipelago server. Contents include things like location id to name mappings, among others; see [Data Package Contents](#Data-Package-Contents) for more info.
Sent to clients as a response the a [Get](#Get) package
#### Arguments
| Name | Type | Notes |
| ---- | ---- | ----- |
| keys | dict\[str\, any] | A key-value collection containing all the values for the keys requested in the [Get](#Get) package. |
Additional arguments added to the [Get](#Get) package that triggered this [Retrieved](#Retrieved) will also be passed along.
### SetReply
Sent to clients in response to a [Set](#Set) package if want_reply was set to true, or if the client has registered to receive updates for a certain key using the [SetNotify](#SetNotify) package. SetReply packages are sent even if a [Set](#Set) package did not alter the value for the key.
Many, if not all, other packets require a successfully authenticated client. This is described in more detail in [Archipelago Connection Handshake](#Archipelago-Connection-Handshake).
Sent to server to request a [ReceivedItems](#ReceivedItems) packet to synchronize items.
#### Arguments
No arguments necessary.
### LocationChecks
Sent to server to inform it of locations that the client has checked. Used to inform the server of new checks that are made, as well as to sync state.
#### Arguments
| Name | Type | Notes |
| ---- | ---- | ----- |
| locations | list\[int\] | The ids of the locations checked by the client. May contain any number of checks, even ones sent before; duplicates do not cause issues with the Archipelago server. |
### LocationScouts
Sent to the server to inform it of locations the client has seen, but not checked. Useful in cases in which the item may appear in the game world, such as 'ledge items' in A Link to the Past. The server will always respond with a [LocationInfo](#LocationInfo) packet with the items located in the scouted location.
#### Arguments
| Name | Type | Notes |
| ---- | ---- | ----- |
| locations | list\[int\] | The ids of the locations seen by the client. May contain any number of locations, even ones sent before; duplicates do not cause issues with the Archipelago server. |
| exclusions | list\[str\] | Optional. If specified, will not send back the specified data. Such as, \["Factorio"\] -> Datapackage without Factorio data.|
Used to request a single or multiple values from the server's data storage, see the [Set](#Set) package for how to write values to the data storage. A Get package will be answered with a [Retrieved](#Retrieved) package.
#### Arguments
| Name | Type | Notes |
| ------ | ----- | ------ |
| keys | list\[str\] | Keys to retrieve the values for. |
Additional arguments sent in this package will also be added to the [Retrieved](#Retrieved) package it triggers.
### Set
Used to write data to the server's data storage, that data can then be shared across worlds or just saved for later. Values for keys in the data storage can be retrieved with a [Get](#Get) package, or monitored with a [SetNotify](#SetNotify) package.
#### Arguments
| Name | Type | Notes |
| ------ | ----- | ------ |
| key | str | The key to manipulate. |
| default | any | The default value to use in case the key has no value on the server. |
| want_reply | bool | If set, the server will send a [SetReply](#SetReply) response back to the client. |
| operations | list\[[DataStorageOperation](#DataStorageOperation)\] | Operations to apply to the value, multiple operations can be present and they will be executed in order of appearance. |
Additional arguments sent in this package will also be added to the [SetReply](#SetReply) package it triggers.
#### DataStorageOperation
A DataStorageOperation manipulates or alters the value of a key in the data storage. If the operation transforms the value from one state to another then the current value of the key is used as the starting point otherwise the [Set](#Set)'s package `default` is used if the key does not exist on the server already.
DataStorageOperations consist of an object containing both the operation to be applied, provided in the form of a string, as well as the value to be used for that operation, Example:
```js
{"operation": "add", "value": 12}
```
The following operations can be applied to a datastorage key
| Operation | Effect |
| ------ | ----- |
| replace | Sets the current value of the key to `value`. |
| default | If the key has no value yet, sets the current value of the key to `default` of the [Set](#Set)'s package (`value` is ignored). |
| add | Adds `value` to the current value of the key, if both the current value and `value` are arrays then `value` will be appended to the current value. |
| mul | Multiplies the current value of the key by `value`. |
| pow | Multiplies the current value of the key to the power of `value`. |
| mod | Sets the current value of the key to the remainder after division by `value`. |
| max | Sets the current value of the key to `value` if `value` is bigger. |
| min | Sets the current value of the key to `value` if `value` is lower. |
| and | Applies a bitwise AND to the current value of the key with `value`. |
| or | Applies a bitwise OR to the current value of the key with `value`. |
| xor | Applies a bitwise Exclusive OR to the current value of the key with `value`. |
| left_shift | Applies a bitwise left-shift to the current value of the key by `value`. |
| right_shift | Applies a bitwise right-shift to the current value of the key by `value`. |
### SetNotify
Used to register your current session for receiving all [SetReply](#SetReply) packages of certain keys to allow your client to keep track of changes.
#### Arguments
| Name | Type | Notes |
| ------ | ----- | ------ |
| keys | list\[str\] | Keys to receive all [SetReply](#SetReply) packages for. |
A list of objects. Each object denotes one player. Each object has four fields about the player, in this order: `team`, `slot`, `alias`, and `name`. `team` and `slot` are ints, `alias` and `name` are strs.
Each player belongs to a `team` and has a `slot`. Team numbers start at `0`. Slot numbers are unique per team and start at `1`. Slot number `0` refers to the Archipelago server; this may appear in instances where the server grants the player an item.
`alias` represents the player's name in current time. `name` is the original name used when the session was generated. This is typically distinct in games which require baking names into ROMs or for async games.
`player` is the player slot of the world the item is located in, except when inside an [LocationInfo](#LocationInfo) Packet then it will be the slot of the player to receive the item
Message nodes sent along with [PrintJSON](#PrintJSON) packet to be reconstructed into a legible message. The nodes are intended to be read in the order they are listed in the packet.
`type` is used to denote the intent of the message part. This can be used to indicate special information which may be rendered differently depending on client. How these types are displayed in Archipelago's ALttP client is not the end-all be-all. Other clients may choose to interpret and display these messages differently.
| entrance_name | Entrance Name. No ID mapping exists. |
| color | Regular text that should be colored. Only `type` that will contain `color` data. |
`color` is used to denote a console color to display the message part with and is only send if the `type` is `color`. This is limited to console colors due to backwards compatibility needs with games such as ALttP. Although background colors as well as foreground colors are listed, only one may be applied to a [JSONMessagePart](#JSONMessagePart) at a time.
An object representing software versioning. Used in the [Connect](#Connect) packet to allow the client to inform the server of the Archipelago version it supports.
A data package is a JSON object which may contain arbitrary metadata to enable a client to interact with the Archipelago server most easily. Currently, this package is used to send ID to name mappings so that clients need not maintain their own mappings.
We encourage clients to cache the data package they receive on disk, or otherwise not tied to a session. You will know when your cache is outdated if the [RoomInfo](#RoomInfo) packet or the datapackage itself denote a different version. A special case is datapackage version 0, where it is expected the package is custom and should not be cached.
Note:
* Any ID is unique to its type across AP: Item 56 only exists once and Location 56 only exists once.
* Any Name is unique to its type across its own Game only: Single Arrow can exist in two games.
| Tracker | Tells the server that this client is actually a Tracker, will refuse new locations from this client and send all items as if they were remote items. |
| TextOnly | Tells the server that this client will not send locations and does not want to receive items. |
