Client checks environment string RAIN= for one of these values:
"SEG %i",segmentnumber
"FILE %s,%s",commandfile,replyfile
SEG %i tells us that communication buffer is in given segment in conventional memory, with RAIN server version string in TALK_REPORT and with TALK_CMD set to CMD_NONE, other fields not defined. All we have to do is to fill parameter fields, TALK_CMD as last one, do int 12h (registers are preserved, only ax is filled with some value, that is normal int 12h behaviour) and read reply. TALK_CMD is filled only by us and zeroed to CMD_NONE only by server after executing command. TALK_REPORT is filled only by server and zeroed to "" only by us after reading report. List of fields and commands from raindef.h or rain.pas:
#define TALK_BUFSIZE 1024 //buffer length #define TALK_STRSIZE 255 //max talk string length #define TALK_CMD (*(volatile int*)(talk+ 0)) //parameters for rain #define TALK_PARAM1 (*(volatile int*)(talk+ 4)) // #define TALK_PARAM2 (*(volatile int*)(talk+ 8)) // #define TALK_PARAM3 (*(volatile int*)(talk+12)) #define TALK_FILE_OFS (*(volatile int*)(talk+16)) #define TALK_FILE_SIZE (*(volatile int*)(talk+20)) #define TALK_FILE_NAME (( char*)(talk+24)) #define TALK_REPORT (( char*)(talk+512)) //reports from rain #define CMD_NONE 0 #define CMD_PLAY 1 // param1=loop,param2=type,filename,ofs,size #define CMD_STOP 2 // param1=handle #define CMD_VOL 3 // param1=handle,param2=vol #define CMD_PAN 4 // param1=handle,param2=pan #define CMD_AMPLIFY 5 // param1=amplification #define CMD_TERMINATE -1Rain version string looks like "Resident Audio Interface %i.%i (%s)", protocol_version_high, protocol_version_low, server_name.
FILE %s,%s gives us names of shared temporary files to write commands to and to read replies from. Files can be opened whole time. Each line in command file contains one command. Command has "%i %i %i %i %i %i %s", command,param1,param2,param3, fileofs,filesize,filename form or shorter when last parameters are not needed, command is one of CMD_xxxx constants. First line of reply file contains RAIN version string. Following lines contain reports and errors from server. All error messages start with " ". Just one non-error report is defined now: "end of %i",handle when sound stops or may not be played at all.
Command CMD_TERMINATE is last command sent by application, server terminates after receiving it. It is neccessary to report application end to server because it seems there is no way how NT server can detect end of DOS application running in DOS box (stdlib and winAPI functions detect only end of whole DOS box).