X-Git-Url: http://www.git.cypherpunks.ru/?p=nncp.git;a=blobdiff_plain;f=doc%2Fsp.texi;h=36f5cc794d32ced78508a4e99c718fa45cfea69a;hp=ab8390e6bbb85e5c98d10fe3bb5c4802052b1d6f;hb=203dfe36da7adf2b3089e4fa4017a67409cbad70;hpb=c6fc64da2b9ab1be9cc809b0d455d35998cde45a

diff --git a/doc/sp.texi b/doc/sp.texi
index ab8390e..36f5cc7 100644
--- a/doc/sp.texi
+++ b/doc/sp.texi
@@ -1,10 +1,14 @@
 @node Sync
+@cindex sync protocol
+@cindex online protocol
+@cindex synchronization
 @unnumbered Synchronization protocol
 
 So-called synchronization protocol (SP) is used in current TCP daemon's
 implementation. It is used for synchronizing @ref{Spool, spool}
 directory contents between two nodes.
 
+@cindex XMODEM
 It is aimed to be very simple and effective. It uses reliable transport
 like TCP connections. It must be effective both on single-duplex and
 full-duplex links: for example satellites have very high throughput but
@@ -12,10 +16,17 @@ high-delay links, so acknowledging of each received packet, like
 @url{https://en.wikipedia.org/wiki/XMODEM, XMODEM} does, causes
 unacceptable performance degradation.
 
+@vindex NNCPDEADLINE
+Internally it uses various timeouts and deadlines. One of them used
+extensively is 10 seconds default deadline timeout. You can override it
+with @env{$NNCPDEADLINE} environment variable, that could be useful with
+very high delay links.
+
+@cindex Noise-IK
 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
 +-----------------+
@@ -24,10 +35,10 @@ are sent inside XDR envelope:
 @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
@@ -36,7 +47,7 @@ are sent inside XDR envelope:
 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
@@ -49,26 +60,41 @@ just an unsigned integer telling what body structure follows.
 
 @table @emph
 
+@cindex HALT payload
 @item HALT
     Stop file transmission, empty sending queue on the remote side.
     Actually @emph{HALT} packet does not have any body, only the header
     with the type. It is also used in the first payload for padding to
     the maximum size.
+
 @verbatim
 +------+
 | HALT |
 +------+
 @end verbatim
 
+@cindex PING payload
+@item PING
+    Dummy packet only used for determining workability of the connection.
+
+@verbatim
++------+
+| PING |
++------+
+@end verbatim
+
+@cindex INFO payload
 @item INFO
     Information about the file we have for transmission.
+
 @verbatim
 +------+--------------------+
 | INFO | NICE | SIZE | HASH |
 +------+--------------------+
 @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
@@ -80,16 +106,19 @@ just an unsigned integer telling what body structure follows.
         Unique file identifier, its checksum
     @end multitable
 
+@cindex FREQ payload
 @item FREQ
     File transmission request. Ask remote side to queue the file for
     transmission.
+
 @verbatim
 +------+---------------+
 | FREQ | HASH | OFFSET |
 +------+---------------+
 @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
@@ -98,15 +127,18 @@ just an unsigned integer telling what body structure follows.
         Offset from which remote side must transmit the file
     @end multitable
 
+@cindex FILE payload
 @item FILE
     Chunk of file.
+
 @verbatim
 +------+-------------------------+
 | FILE | HASH | OFFSET | PAYLOAD |
 +------+-------------------------+
 @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
@@ -118,18 +150,91 @@ just an unsigned integer telling what body structure follows.
         Chunk of file itself
     @end multitable
 
+@cindex DONE payload
 @item DONE
     Signal remote side that we have successfully downloaded the file.
+
 @verbatim
 +------+------+
 | DONE | HASH |
 +------+------+
 @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.plantuml.txt
+
+@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/XXX} 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, insert it to current sending
+queue with niceness level sort: higher priority packets will be sent
+first. 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 Each minute, if no packets were sent, node sends @emph{PING}
+packet.
+
+@item If no non-PING packets are sent and received during
+@ref{CfgOnlineDeadline, onlinedeadline} duration, then close the
+connection. There is no explicit indication that session is over.
+
+@item If no packets are received during two minutes (two PING timeouts),
+then close the connection.
+
+@end enumerate