See
PostgreSQL message formats
Describe (F)
Byte1('D')
Identifies the message as a Describe command.
Int32
Length of message contents in bytes, including self.
Byte1
'S' to describe a prepared statement; or 'P' to describe a portal.
String
The name of the prepared statement or portal to describe (an empty string selects the unnamed prepared statement or portal).
Execute (F)
Byte1('E')
Identifies the message as an Execute command.
Int32
Length of message contents in bytes, including self.
String
The name of the portal to execute (an empty string selects the unnamed portal).
Int32
Maximum number of rows to return, if portal contains a query that returns rows (ignored otherwise). Zero denotes "no limit".
Sync (F)
Byte1('S')
Identifies the message as a Sync command.
Int32(4)
Length of message contents in bytes, including self.