SP works on top of
@url{http://noiseprotocol.org/noise.html#interactive-patterns,
-@verb{|Noise_IK_25519_ChaChaPoly_BLAKE2b|}} protocol. Each Noise packet
-are sent inside XDR envelope:
+@code{Noise_IK_25519_ChaChaPoly_BLAKE2b}} protocol. Each Noise packet
+is sent inside an @url{https://tools.ietf.org/html/rfc4506, XDR} envelope:
@verbatim
+-----------------+
@end verbatim
@multitable @columnfractions 0.2 0.3 0.5
-@headitem @tab XDR type @tab Value
+@headitem @tab XDR type @tab Value
@item Magic number @tab
8-byte, fixed length opaque data @tab
- @verb{|NNCPS0x00x00x01|}
+ @verb{|N N C P S 0x00 0x00 0x01|}
@item Payload @tab
variable length opaque data @tab
Noise packet itself
Peers static keys are specified as @ref{Configuration, @emph{noisepub}}
configuration entry.
-Payload inside Noise packets has maximum size of @emph{65 KiB - 256 B =
+Payload inside Noise packets has maximum size of @emph{64 KiB - 256 B =
65280 B}. It is sent immediately in the first message by each side. The
very first payload (that is carried inside handshake messages) is always
padded to the maximum size with @emph{HALT} packets (read below), for
+------+--------------------+
@end verbatim
@multitable @columnfractions 0.2 0.3 0.5
- @headitem @tab XDR type @tab Value
+ @headitem @tab XDR type @tab Value
@item Niceness @tab
unsigned integer @tab
1-255, file niceness level
+------+---------------+
@end verbatim
@multitable @columnfractions 0.2 0.3 0.5
- @headitem @tab XDR type @tab Value
+ @headitem @tab XDR type @tab Value
@item Hash @tab
32-byte, fixed length opaque data @tab
Unique file identifier, its checksum
+------+-------------------------+
@end verbatim
@multitable @columnfractions 0.2 0.3 0.5
- @headitem @tab XDR type @tab Value
+ @headitem @tab XDR type @tab Value
@item Hash @tab
32-byte, fixed length opaque data @tab
Unique file identifier, its checksum
+------+------+
@end verbatim
@multitable @columnfractions 0.2 0.3 0.5
- @headitem @tab XDR type @tab Value
+ @headitem @tab XDR type @tab Value
@item Hash @tab
32-byte, fixed length opaque data @tab
Unique file identifier, its checksum
@end multitable
@end table
+
+Typical peer's behaviour is following:
+
+@verbatiminclude sp.utxt
+
+@enumerate
+@item Perform @emph{Noise-IK} handshake:
+
+ @table @strong
+ @item Initiator
+ Collects all @emph{tx}-related files information and prepares
+ payload filled with @emph{INFO}s for including in the @strong{first}
+ handshake message.
+ @item Responder
+ After receiving the first handshake message, it gains remote
+ identity knowledge and similarly prepares the payload for including
+ in the @strong{second} handshake message.
+ @end table
+
+ All payloads are padded to maximal message size with @emph{HALT}s.
+
+@item If queued @emph{INFO}s are not sent completely in handshake
+payloads, then send all of remaining in the transport stage.
+
+@item When @emph{INFO} packet received:
+
+ @itemize
+ @item Check that it has an acceptable niceness level.
+ Ignore it if it is too nice.
+ @item If already downloaded file exists, then queue @emph{DONE}
+ sending.
+ @item If @file{.seen} exists, then queue @emph{DONE} sending.
+ @item If @file{.part} exists, then queue @emph{FREQ} sending with
+ corresponding offset.
+ @end itemize
+
+@item When @emph{FREQ} packet received, append it to current sending
+queue. Sending queue contains files with offsets that are needed to be
+sent.
+
+@item While sending queue is not empty, send @emph{FILE} packets.
+@emph{FREQ} could contain offset equal to size -- anyway sent
+@emph{FILE} packet with an empty payload. @emph{FILE} sending is
+performed only if no other outgoing packets are queued: @emph{INFO}s
+have higher priority.
+
+@item When @emph{FILE} packet received, check if it is completely
+downloaded (comparing to @emph{INFO}'s packet size information). If so,
+then run background integrity checker on it. If check succeeds, then
+delete @file{.part} suffix from file's name and send @emph{DONE} packet.
+
+@item When @emph{DONE} packet received, delete corresponding file.
+@item When @emph{HALT} packet received, empty file sending queue.
+
+@item Each second, node checks: are there any new @emph{tx} packets
+appeared and queues corresponding @emph{INFO} packets.
+
+@item If no packets are sent and received during @ref{CfgOnlineDeadline,
+onlinedeadline} duration, then close the connection. There is no
+explicit indication that session is over.
+
+@end enumerate