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ngc_group_history_sync.md

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Spec for NGC group history sync

use only for public groups, not for private groups!

Send history sync request

  • trigger: tox_group_peer_join_cb()

each time a peer joins we ask that peer to send all non-private group chat messages from 130 minutes ago up to now.

to make sure that peer is actually really online (tox has a bit of an issue there), wait n seconds before sending ngch_request

n = 5 + random(0 .. 6)

  • ngch_request packet data:
what Length in bytes Contents
magic 6 0x667788113435
version 1 0x01
pkt id 1 0x01
sync delta 1 how many minutes back from now() to get messages
allowed values from 5 to 130 minutes (both inclusive)

send the data to the peer with: tox_group_send_custom_private_packet() and specifiy lossless paramter as true

Respond to history sync request

  • trigger: tox_group_custom_private_packet_cb() and it's the ngch_request packet

the tox client needs to get authorization from the user that it's ok to share group chat history with the requesting peer

then we send all non-private group chats messages from 130 minutes ago up to now sorted by oldest (first) to newest (last) each message is sent as a seperate lossless custom packet

wait n milliseconds seconds before sending the next message.

n = 300 + random(0 .. 300)

  • ngch_syncmsg packet data:

for text messages:

MAX_GC_CUSTOM_PACKET_SIZE 40000
header_size = 6 + 1 + 1 + 4 + 32 + 4 + 25 = 73
max sync message text bytes = MAX_GC_CUSTOM_PACKET_SIZE - header_size = 39927

what Length in bytes Contents
magic 6 0x667788113435
version 1 0x01
pkt id 1 0x02 <-- text
msg id 4 4 bytes message id for this group message
sender 32 32 bytes pubkey of the original sender in the ngc group
timestamp 4 uint32_t unixtimestamp in UTC of local wall clock (in bigendian) when the message was originally sent
name 25 sender name 25 bytes (cut off if longer, or right padded with 0x0 bytes)
message [1, 39927] message text, zero length message not allowed!

send the data to the peer with: tox_group_send_custom_private_packet() and specifiy lossless paramter as true

for files:

MAX_GC_CUSTOM_PACKET_SIZE 40000
header_size = 6 + 1 + 1 + 32 + 32 + 4 + 25 = 356
max sync message file bytes = MAX_GC_CUSTOM_PACKET_SIZE - header_size = 39644
max group file bytes is 36701

what Length in bytes Contents
magic 6 0x667788113435
version 1 0x01
pkt id 1 0x03 <-- file
msg id 32 *uint8_t to uniquely identify the message (the original value that is saved in history)
sender 32 32 bytes pubkey of the original sender in the ngc group
timestamp 4 uint32_t unixtimestamp in UTC of local wall clock (in bigendian) when the message was originally sent
name 25 sender name 25 bytes (cut off if longer, or right padded with 0x0 bytes)
filename 255 len TOX_MAX_FILENAME_LENGTH data first, then pad with NULL bytes
data [1, 36701] bytes of file data, zero length files not allowed!

send the data to the peer with: tox_group_send_custom_private_packet() and specifiy lossless paramter as true

Receive history sync data

  • trigger: tox_group_custom_private_packet_cb() and it's the ngch_syncmsg packet

the tox client needs to sort these messages into the group chat view since the dates can be in the past and newer messages can already be present in the current uservisible view.

  • duplicate message check:

if a message with that msg id for this group chat and this sender within the last 300 days already exists, then assume it is a duplicate and keep the current message and discard the incoming sync message.

  • cutoff UTF-8

since name could have been cut at the maximum byte limit, the tox client needs to check for cut off UTF-8 and handle this accordingly.