Change URL of DigitalCD radio station?

Does anybody know if it is possible to change the URL of a radio station in the DigitalCD playlist in a programmatic manner (without hacking the file directly, that is).

I ask because 96.4 Eagle is at http://str1.sad.ukrd.com/eagle but this is a redirect which DigitalCD can’t handle, so I’ve written a short program to retrieve the HTTP header which provides the new data location (seems to vary domain prefix for load balancing, and to suffix a value which may be based upon the IP address; if the IP changes, a new value is required).
To give an example – the current data URL (which I’m currently listening to) is http://fg1.sad.ukrd.com/eagle?ts=1457036187 and for now I’ve set the variable Eagle$URL to this but it’ll get “annoying” to update this manually too often. ;-)

Before I go the whole hog and pull the playlist file apart, I thought I’d ask, in case there’s a SWI or WimpMessage or something that I didn’t find in the docs…

I suspect the correct answer to your problem is to send your code to André so that he can incorporate it into the next DigitalCD release :-) (Disclaimer: I’m not actually sure which part handles streaming radio, so maybe it’s a third-party module that would need modifying)

All my code does is pluck “Location:” out of the HTTP header (302, IIRC). There is probably already suitable code already present as it understands and reports on a 404, so all it needs is to understand a redirection.

I rewrote my socket code in BASIC and then threw together an app to run just before DigitalCD starts and directly modify the playlist (discard the existing Eagle entry and write out the new URL). There’s a lot of string operations and such and I really didn’t feel like wrestling with C for a simple MID$ so I just figured it was less grief to do it all in BASIC.
Then, for the hell of it, compiled it with ABC. ;-)

I’d drop a copy on my site, but RISC OS is lacking an SFTP client that supports public key authentication.¹

¹ This means even if you manage to discover my password (which is unlikely as it is a long string of line noise that most people on the planet don’t have a hope of remembering), you still won’t be able to log in. It requires an RSA key – of which two copies exist in the world. One is on my computer (in WinSCP) and the other is a backup on a floppy disc.

In case anybody else in the Guildford/Aldershot/Camberley area wants to listen using DigitalCD… put this in the same directory as DigitalCD and add an entry to !Run to run this just before starting DigitalCD itself.

The “value” changes after a little while of inactivity, so if trying to play The Eagle gets you a 404, quit DigitalCD and restart it to refresh.

This process may work for other UKRD streams – I’ve not tested this though.

REM >EagleFinder
REM
REM Find where 96.4 The Eagle is, and patch the DigitalCD playlist
REM
REM By Rick Murray, 2016/03/03
REM
REM If it works, the playlist is updated and the previous copied as "PrevPlaylist".
REM If it fails, we just exit...

ON ERROR PRINT REPORT$+" at "+STR$(ERL) : END
REM TRACE ON

DIM buffy% 4095                : REM 4K buffer
domain$ = "str1.sad.ukrd.com"  : REM Domain to fetch from
path$   = "/eagle"             : REM What to fetch (path)
port%   = 80                   : REM Port (80 = HTTP)
handle% = 0                    : REM Socket handle
ip% = 0                        : REM IP address
rb% = 0                        : REM Resolver data block
edited% = FALSE                : REM Existing entry edited?

REM Ensure Stack is loaded
SYS "XOS_SWINumberFromString", 0, "Socket_Creat" TO swi%
IF swi% <> &41200 THEN END                           : REM No stack loaded

REM Ensure Resolver is loaded. This is a little different because the
REM various resolvers share SWI numbers but have different names.
SYS "XOS_SWINumberToString", &46000, buffy%, 64
swi$ = FNGetStringAtAddress(buffy%, 0)
IF swi$ = "User" THEN END                            : REM No resolver loaded

REM Resolve the domain
REPEAT
  SYS "XResolver_GetHost", domain$ TO stat%, rb% ; flag%
  IF (flag% AND 1) = 1 THEN END
UNTIL stat% <> 36                                    : REM "EINPROGRESS"
REM ##TODO## Timeout?
IF rb% = 0 THEN END                                  : REM Unable to resolve domain
ip% = !(!(rb%!16))                                   : REM Yikes!

REM Create socket
SYS "Socket_Creat", 2, 1, 0 TO handle%
IF handle% = -1 THEN END                             : REM Unable to connect socket (ish...)

REM Connect to the remote machine
buffy%!0  = 2 OR ((port% DIV 256) << 16) OR ((port% MOD 256) << 24)
buffy%!4  = ip%
buffy%!8  = 0
buffy%!12 = 0
SYS "XSocket_Connect", handle%, buffy%, 16, 0 TO ; flag%
IF ((flag% AND 1) = 1) THEN
  SYS "Socket_Close", handle%
  handle% = 0
  END                                                : REM Connection refused (most likely)
ENDIF

REM Send our request
$buffy% = "GET "+path$+" HTTP/1.0"+CHR$(10)
$buffy%+= "Host: "+domain$+CHR$(10)
$buffy%+= "Accept: */*"+CHR$(10)
$buffy%+= "User-Agent: EagleFinder/0.1; RISC OS 5"+CHR$(10)+CHR$(10)
SYS "Socket_Write", handle%, buffy%, LEN($buffy%)

REM We don't poll (as we're running prior to DigitalCD starting up)
REM so waste a second to give time for the server to reply.
SYS "Hourglass_Start", 1
t% = TIME
REPEAT : UNTIL ((t% + 100) < TIME)
SYS "Hourglass_Off"

REM Read the first 160 bytes and discard them (early HTTP header stuff)
SYS "XSocket_Read", handle%, buffy%, 160 TO size% ; flag%

REM Now read 255 bytes. This part contains what we want to look at
FOR t% = 0 TO 255 : buffy%?t% = 0 : NEXT             : REM Ensure buffer is empty
SYS "XSocket_Read", handle%, buffy%, 255 TO size% ; flag%
IF ( (flag% AND 1) OR (size% = -1) ) THEN
  REM Failed!
  SYS "Socket_Shutdown", handle%, 2
  SYS "Socket_Close", handle%
  END
ENDIF

reply$ = FNGetStringAtAddress(buffy%, 0)
PRINT reply$

posn% = INSTR(reply$, "Location:")
IF (posn% = 0) THEN END                              : REM No "Location:" found

posn% += 10                                          : REM Skip "Location:"
reply$ = MID$(reply$, posn%)
$buffy% = reply$
reply$ = FNGetStringAtAddress(buffy%, 13)            : REM Lame-ass way to trim line ;-)
REM PRINT reply$                : REM ^^ Server appears to reply <13><10>!

REM At this stage, reply$ will contain the "new" URL.

REM Back-up current playlist.
OSCLI("%Copy <Choices$Dir>.DigitalCD.PlayList <Choices$Dir>.DigitalCD.PrevPlayList ~C~DF~N~P~Q~S~V")
REM Don't confirm, don't delete original, force, not 'only if newer',
REM don't prompt, not quick, don't stamp, not verbose.
REM In other words, shuddup and copy it.

REM Open the files (Prev for reading from, main for writing to)
REM This is accessing Choices incorrectly (Choices: / Choices$Write)
REM because I know the file has read/write access AND I want to be
REM sure to edit the original...
in% = OPENIN("<Choices$Dir>.DigitalCD.PrevPlayList")
out% = OPENOUT("<Choices$Dir>.DigitalCD.PlayList")

REM Copy line by line, checking for "ukrd"
REPEAT
  inline$ = GET$#in%
  IF (INSTR(inline$, "ukrd") <> 0) THEN
    REM Found, so update with it
    inline$ = GET$#in%                               : REM Discard next line
    posn% = INSTR(reply$, "eagle")                   : REM Find the split point
    BPUT#out%, LEFT$(reply$, (posn% - 1))            : REM Line1 - domain
    BPUT#out%, MID$(reply$, posn%);                  : REM Line2 - path + check value
    BPUT#out%, "*aUKRD,f257,r128,t96.4 Eagle,v85"    : REM Line2 - other stuff
    edited% = TRUE
    PRINT "Eagle edited."
  ELSE
    REM Just copy the line to the output
    BPUT#out%, inline$
  ENDIF
UNTIL EOF#in%

IF (edited% = FALSE) THEN
  REM There wasn't a copy to edit, so append new...
  posn% = INSTR(reply$, "eagle")                     : REM Find the split point
  BPUT#out%, LEFT$(reply$, (posn% - 1))              : REM Line1 - domain
  BPUT#out%, MID$(reply$, posn%);                    : REM Line2 - path + check value
  BPUT#out%, "*aUKRD,f257,r128,t96.4 Eagle,v85"      : REM Line2 - other stuff
  PRINT "Eagle appended."
ENDIF

REM Close files
CLOSE#in%
CLOSE#out%

REM And the socket...
SYS "Socket_Close", hande%

REM We're done.
SYS "Wimp_CommandWindow", -1
END

:

DEFFNGetStringAtAddress(array%, term%)
  LOCAL s$
  s$ = ""
  WHILE (?array% <> term%)
    s$ += CHR$(?array%)
    array% += 1
  ENDWHILE
=s$