sonata: add PostgreSQL protocol cheatsheet

POSTGRESQL_PROTOCOL

@@ -0,0 +1,126 @@
+
+###PostgreSQL protocol 3.0 cheatsheet.
+
+**startup packet**
+
+	u32 len  *len including len*
+	data[]
+
+**header**
+
+	u8  type *readable char*
+	u32 len  *len including len*
+	data[]
+
+**Startup**
+
+	C: SSLRequest
+	S: # one byte: 'S', 'N'
+	S: 'S' # proceed with SSL
+	S: 'N' # not supported
+		- maybe close connection
+
+	C: StartupMessage # or CancelRequest
+	# { len, version: 0x30000, user...database...options..}
+
+	S: # AUTH require message
+	S: AuthenticationClearTextPassword # {'R', 8, 3 }
+	C: PasswordMessage # { 'p', len, data }
+
+	S: ErrorResponce # { 'E', len, 'S' ... ,  } 
+		- close connection
+	S: AuthenticationOk # {'R', 8, 0 }
+
+
+	# new backend created; server tries to apply startup options
+	S: ErrorResponce
+		- close connection
+	
+	S: BackendKeyData # { 'K', 12, u32 pid, u32 key }
+		- cancel key
+
+	S: ParameterStatus # { 'S', len, name, value }
+		- client_encoding, etc...
+
+	S: NoticeResponce # { 'N', len, ... } same as error
+		- just print the message
+	
+	S: ReadyForQuery # { 'Z', 5, tx }  tx: 'I' inactive, 'T' in tx, 'E' cancelled tx
+
+**Terminate**
+
+	C: Terminate # { 'F', 4 }
+		- no wait, close connection
+
+
+**Cancel**
+	*- new connection required*
+	*- no reply from server*
+
+	C: CancelRequest # { 16, 80877102, pid, key }
+
+**Query**
+
+	C: Query # { 'Q', len, text }
+
+	S: RowDescription
+	S: DataRow
+	S: CommandComplete #  can be several
+
+	#  can be repeated several time for reach stmt;stmt
+
+	S: EmptyQueryResponce # in case if text=""
+	S: NoticeResponce
+	S: ErrorResponce
+
+	# all text stmts processed, ready for next command
+	S: ReadyForQuery
+
+**Extended query**
+
+	C: Parse # { 'P', len, operator_name, query, u16 types_count, ... u32 type }
+
+	           #                can be 0                 can be 0         can be 0
+	           #
+	           # Parse can have only one query, no ';'.
+	           #
+	           # Nameless operator exists till next query.
+			   #
+	           # Named operator exists till end of a session, or explicitly destroyed.
+		       # Named operator available for SQL Prepare and Execute calls.
+
+	S: ParseComplete # { '1', len }
+	S: ErrorResponce
+
+	C: Bind # { 'B', len, portal_name, operator_name,
+	          #	   16  argc_call_arg_types_count, u16[] types,
+	          #                                   0 or 1
+			  #    u16 argc, [ i32 len,  bytes],
+              #
+	          #    u16 argc_result_cols_types_count, u16[] types }
+
+			  # Named/Nameless Portal exists till transaction ends
+	          #
+	          # Named portal avail for SQL Declare, Cursor, Fetch
+
+	S: BindComplete # { '2', len }
+
+	C: Describe # { 'D', len, u8 'S'/'P', operator_or_portal_name }
+	C: Execute # { 'E', len, portal_name, u32 limit } 0 - limitless
+
+	S: PortalSuspended # { 's', len }   on execute limit reach
+
+	S: NoData  # { 'n', len } on Describe, when portal has no query
+	S: RowDescription  # answer for Describe
+	S: DataRow
+
+	S: CommandComplete
+	S: EmptyQueryResponce
+	S ErrorResponce # Skips all commands till Sync
+
+	C: Close # { 'C', len, u8 'S'/'P', operator_or_portal }
+	C: Sync # { 'S', len }
+
+	S: ReadyForQuery
+
+**function call, copy, async**