streetrelay-3ds

Sources that helped tremendously while building this:

• Gist by wwylele
• Docs by NarcolepticK
• libctru-cecd by NarcolepticK
• CECTool by FlagBrew

If you're interested in building your own homebrew that works with StreetRelay, I would recommend checking these sources out!

Basics

File Structure

CEC
+- MBoxList____
+- <typically 8 char id>
|  +- MBoxInfo____
|  +- MBoxData.001
|  +- MBoxData.010
|  +- MBoxData.050
|  +- InBox___
|  |  +- BoxInfo_____
|  |  +- _<12 char id>
|  |  +- ...
|  +- OutBox__
|     +- BoxInfo_____
|     +- OBIndex_____
|     +- _<12 char id>
+- <typically 8 char id>
   +- ...

1. MBoxList____ contains a list of all the games that have StreetPass enabled currently, in the form of 16 byte IDs. These games are saved in folders, named the ASCII representation of their IDs.
2. <typically 8 char ID> is a folder containing all StreetPass-related information for a game, including:
   1. MBoxInfo____ contains basic information about the mailbox
   2. MBoxData.001 ICN encoded game icon for the title
   3. MBoxData.010 UTF encoded game title
   4. MBoxData.050 Title ID
   5. InBox___ contains all current incoming StreetPass tags (i.e. a visitor in StreetPass Mii Plaza)
      1. BoxInfo_____ contains information about the current box (inbox in this case), including an index of all messages and their headers.
      2. _<12 char id> is a StreetPass tag. (hurray) This file has a 0x70 length header, zero or more extra headers, and the actual tag data. The ID is the first 8 bytes of the message ID converted to a custom base64
   6. OutBox__ contains all? (never seen more than one) your outgoing StreetPass data. (i.e. your data as a visitor in StreetPass Mii Plaza)
      1. BoxInfo_____ same as above, contains information about the outbox, and a list of all included messages' headers.
      2. OBIndex_____ Only found in the OutBox__, contains a list of how many outbox items there are and a list of their IDs. Simplified version of BoxInfo____
      3. _<12 char id> outgoing StreetPass tag. Exactly the same as in the InBox__

Workflow

1. Upload profile data (not relevant)
2. Get StreetPass games in MBoxList___
3. For each game in MBoxList___:
   1. Get outbox data
   2. Upload data in outbox
   3. Get list of tags available
   4. If server requests game public data:
      1. Upload MBoxData.001 and MBoxData.010 (icon and title)
   5. If inbox is not full:
      1. Download first tag
      2. Add tag to BoxData____
      3. Change tag dates