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Documentation for XPRZModem.library Version 1.0, 29 July 1989, by Rick Huebner 1. Introduction (or "What is this thing, anyway?") --------------------------------------------------- XPRZModem.library is an Amiga shared library (with full Manx C source code) which provides ZModem file transfer capability to any XPR-compatible communications program. The XPR external protocol standard describes an interface method which allows various file transfer protocols to be implemented as Amiga shared libraries which may then be used interchangeably in any compatible communications program. This takes a heavy load off of the comm program author, who no longer has to support scads of different file transfer protocols (many of which are quite tricky to code) in their program in order to make it widely useful and popular. The comm program is also smaller and more efficient as a result, since all those obscure protocols (you know, the ones *you* don't need) are no longer taking up space. The XPR standard also helps users, who can mix and match their favorite file transfer protocols (and implementations thereof) with their favorite comm programs. And when new protocols are invented, the user simply plugs in a new library, and voila!, it's ready to use. Hopefully, making protocols easy to support will allow more and better comm programs to be written, as authors can concentrate on their programs instead of constantly re-inventing the wheel. Of course, for all of this wonderful stuff to happen, there needs to be a good selection of these XPR protocol libraries available to the public. It's the classic chicken-and-egg problem; comm program authors won't be motivated to support the XPR standard unless there are a goodly number of protocols available for it. And other programmers won't be motivated to write XPR protocol libraries until there are a goodly number of comm programs which can use them. In an effort to do my bit [ B^) ] for the Amiga community, which has given me so many neat toys to play with over the past few years, I decided to try and help get the ball rolling. It just so happens that I run a BBS (see ad at end of file B-)), and I help work on the BBS software I use (Opus, a popular MS-DOS program [don't boo and hiss, that's something PClones are well suited for; why waste a neat machine like an Amiga on sitting around being a BBS all day?]). And in that capacity, I wrote the ZModem implementation for Opus back when ZModem first came out, around 1986. I went through a period of serious frustration in the early days of Amiga comm programs, since I'd gone to the trouble of writing ZModem for my BBS program, and none of my users had a program which could handle it. I wasn't yet knowledgeable enough about programming the Amiga to fix the problem myself, and comm program authors weren't interested in my ZModem code since it was so MS-DOS-dependant (I *tried* to give it away), so I had to wait quite a long time before my own BBS users were able to take advantage of my own ZModem implementation. Anyway, this means that when I saw the XPR standard published, I was in a good position to help out. I had this perfectly good, heavily tested ZModem code sitting around, and it wasn't very hard to convert that code into an XPR-type ZModem library. Hopefully, the early availability of a ZModem library will help stimulate interest in the XPR standard, resulting in better Amiga telecomms for all of us. And by making my source code PD, I hope to help others interested in writing XPR protocol libraries by giving them some serious example code. Also, having ZModem library code readily available to John Q. Hacker should help ensure a steady stream of new lemon-fresh enhanced ZModem libraries (with enzymes) for all of us to use in the future. Of course, no discussion of the XPR standard would be complete without giving proper credit to the author, Willy Langeveld of the Stanford Linear Accelerator Center. Many thanks are due him for this effort. If you have any further questions about the XPR standard, be sure and download the spec; it should be available on BIX (since he's a sysop there), or on most other major systems. And I'll try to keep the current version available on my BBS, as well. All files in this archive which are not copyrighted are hereby released to the public domain (which they were anyway, by way of not being copyrighted, but I want to make sure YOU realize that). Do as you like with them. Please make lots of copies and distribute them all over the place, and make lots of derivative works, and everything! Heck, you can even publicly perform and/or display this code if you can figure out how... 2. Installation (OK, enough chatter; let's get to work) -------------------------------------------------------- Couldn't be easier. Just copy the xprzmodem.library file into your LIBS: directory. All XPR-compatible comm programs should provide a way for you to select which XPR protocol you wish to use, either by giving you a file requester showing LIBS:xpr*.library, or by automatically detecting these libraries and adding them into their menus. WARNING: VLT 4.058 appears to have a bug in its xpr_sflush() routine which causes random Guru 3 crashes (at least on my stock A2000). Luckily, the sflush() routine isn't that crucial, so I've included a version of the library with the sflush() calls commented out for VLT users. The only problem caused by not using sflush() is that error recovery and resync when sending files will be a bit erratic, possibly causing extra timeouts. The data should still get sent just fine; the transfer just won't be as efficient as usual. 3. Options ----------- The XPR standard lays out a way for the comm program user to specify options for the XPR protocol. The comm program is supposed to provide some method of passing an option string to the XPR library before transferring files. The precise format and usage of this option string is left up to the XPR protocol author; the comm program just sends it verbatim. If an environment variable is found with the same name as the XPR protocol (i.e. there's a file in the ENV: directory called "xprzmodem"), the comm program is supposed to use this string (contents of file) to initialize the protocol options. Also, a menu option or some such should normally be provided which will allow the user to be prompted for the option string interactively. In any case, no matter how your particular comm program feels like handling it, these are the options supported by this implementation of ZModem: T{Y|N|?} Text translation mode: TY = Text Yes; if receiving, translate CR/LF pairs or solo CR chars to normal Amiga LF chars. Ignore data past ^Z. If sending, suggests to receiver that they should receive this file in text mode. TN = Text No; receive file verbatim, without changes. If sending, suggest to receiver that they receive this file verbatim, without translations. T? = Text status unknown; if receiving, use sender's suggestion as to whether to do EOL translations or not. If sending, tell receiver to use default mode, 'cause we don't know either. O{Y|N|R|S} Overwrite mode: OY = Overwrite Yes; if about to receive file with same name as one which already exists, delete the old file and receive the new file in its place. ON = Overwrite No; if about to receive file with same name as one which already exists, append ".dup" onto the name of the new file to keep them separate. OR = Overwrite Resume; if about to receive file with same name as one which already exists, resume receiving file data from the current end of the existing file. OS = Overwrite Skip; if (etc.), tell sender never mind, skip this file, we don't want it. Batch transfers will move on to the next file in the set, if any. Bnnn Buffer size: XPRZModem.library adds a layer of file I/O buffering in addition to whatever the comm program may or may not provide. This option sets the size of XPRZModem's file I/O buffer in kilobytes. The minimum value is 1 KB, for those using RAM drives or fast hard drives, or those whose comm programs already provide sufficient buffering. The maximum value is as much contiguous RAM as you have available in your Amiga. If you specify more than is actually available, XPRZModem will keep decrementing the buffer size requested by 1 KB until the memory allocation works. That way, if your RAM is too fragmented to use the amount you request, XPRZModem simply uses the largest block available. Buffering is especially helpful for floppy drive users; it keeps your drive from continuously gronking and slowing things down all through the transfer. Fnnn Frame size: Although normally avoided, ZModem has the ability to require an ACK to be sent from the receiver to the sender every X-many data bytes. Normally you don't want to use this feature, because not waiting for ACKs is part of how ZModem works so fast. However, this feature can be very useful in conjunction with file I/O buffering on slow devices (namely those floppy drives). If you set up a large I/O buffer to avoid gronking your floppy so often, you'll find that when the buffer finally *does* get around to being flushed that it can take a looonng time; so long, in fact, that the delay can cause timeouts and errors. But if you set your ZModem to require the sender to wait for an ACK every buffer's-worth of data, the sender will politely wait for you to flush your buffer to the slow floppy and send it an ACK saying it's OK to continue now. This value should be set to 0 to disable ACKs (normal mode), or set it to the actual number of data bytes allowed between ACKs. For example, if you set B64 because of your floppy, you should also set F65536. Note that the setting for the option must immediately follow the option character with no intervening characters ("TY", not "T Y" or "T=Y"). When setting multiple options at once, separate the options from each other with commas and/or spaces; for example, "TN,OR,F0". You don't have to specify all options every time; the options you specify will be merged into the current option settings, replacing their old values. Upper/lower case is not significant. The default option settings if you don't change anything are "T?,ON,B16,F0". 4. Serial port settings ------------------------ ZModem (at least this implementation of it) requires that your serial port be set to 8 data bits, no parity, 1 stop bit. This allows ZModem to send full 8-bit binary data bytes without having them munged on the way through the modem. If your comm program supports the xpr_setserial() function, XPRZModem will use it to set your serial port to 8N1 before doing a transfer, and will set your port back the way it was again after it's done. If your comm program doesn't support xpr_setserial(), you'll need to make sure it's in 8N1 mode yourself. ZModem works well in all serial port handshaking modes; none, XON/XOFF, or 7-wire/RTS/CTS. Since any or all of those handshaking modes may be appropriate at different times, with different modems or remote systems, XPRZModem lets you set the handshaking mode and doesn't mess with it. 5. Receiving files ------------------- Once you get the ZModem options and your serial port configuration set up properly, you're ready to actually use this thing (gasp!). Receiving files via ZModem is quite simple. First, get the file sender going by using whatever command it wants. ZModem is a batch file transfer protocol, meaning that it's capable of transferring several files in a single exchange, so the remote system may allow you to specify multiple files to be sent to you at one time. It may also allow you to use wildcard characters in the filename(s); this is all system dependant. Once you've gotten the sender going, use whatever option your comm program provides to begin receiving files with ZModem; this will usually be a menu option or button gadget. The comm program should now prompt you for the name of the file to be received. Here's the only non-obvious part of receiving files; because of the interchangeability of XPR libraries, the comm program has no way of knowing whether your chosen protocol is a batch protocol or a single file protocol. Batch protocols send the names of the files being transferred along with the data, so the receiving program doesn't choose the name; you just tell the comm program what directory to receive the files into, and they are automatically named correctly. However, single-file protocols like good ol' XModem don't send the filename with the data, and the receiving comm program has to name the file. So... the upshot of all this is that your comm program will probably ask you for the name of the file to be received, whereas all you need to tell a ZModem receiver is the name of the directory to put the files into. The way XPRZModem handles this is for you to just specify a dummy filename in the directory which you want to put the files in. XPRZModem will use the directory portion of the filename you specify, and will append the actual names of the received files onto this directory path in order to create the received files. So if you want your received files to go into "HD:Uploads", tell your comm program the name of the file being received is "HD:Uploads/x" or something similar. Once you enter the dummy filename, ZModem should automatically transfer all of the files you specified into that directory. Make sure that you have set the ZModem options properly before starting the transfer; especially, make sure you only use TY if you know that all of the files being transferred in this batch are printable ASCII text files. If you use TY on normal binary files like .ARCs or .ZOOs, they'll be mangled beyond use. 6. Sending files ----------------- Sending files using ZModem is fairly straightforward. First, activate the file receiver with whatever command the remote system requires. You may or may not need to specify a filename or directory to the remote system; this depends on their implementation of ZModem. Once the remote system is ready to receive files, activate your comm program's ZModem send function. Your comm program will prompt you for which file(s) to send. Although ZModem is a batch protocol, your comm program may or may not allow you to specify multiple file names to be sent; also, wildcards may or may not be supported. These decisions are up to the comm program author; ZModem will handle multiple files and wildcards if the comm program allows them. Once you've specified the file name(s), the file(s) will be sent to the remote system. Note that the directory paths of the files you send will not be included in the filenames sent to the other system; only the filename portion will be sent. Also, note that the T option serves only as a suggestion to the receiving system when sending files; the receiver makes the final decision as to whether to take your advice or to force the files to be received in text or binary mode. If errors occur while sending the file(s), you'll probably notice a small enhancement I made to the normal ZModem error recovery procedures. Normally, file transfer protocols have to compromise between efficient data transmission on good, clean phone lines and quick error recovery on bad, noisy phone lines. If you pick a large packet size, you get high throughput on clean lines due to low packet overhead, but you have slow recovery times and large amounts of retransmitted data on noisy lines. If you've used YModem on noisy lines you've seen this problem. But, if you use small packets to reduce retransmitted data on noisy lines, you increase the amount of time the protocol spends sending packet overhead, and your throughput suffers. The solution is to vary the block size according to the experienced error rate during the transfer. That way you aren't stuck with a rigid packet length which will sometimes be the wrong size no matter what. I came up with this idea back when I first wrote the ZModem code for Opus, and cleared it for future compatibility with ZModem's designer, Chuck Forsberg, back then. Since then the basic concept has been extensively tested in the Opus BBS system, and has proven quite effective; it has also been incorporated into various other ZModem implementations over time. The actual algorithm for deciding what size packets to use when is pretty much up to the protocol author; XPRZModem uses a modified version of the Opus algorithm which prevents locking the packet size at a small value when a large one-time burst of errors occurs. 7. Notes for comm program authors ---------------------------------- That's pretty much everything you need to know in order to use XPRZModem properly. Here are some notes for the "other" XPR standard users, namely the comm program authors: Certain XPR callback functions *must* be implemented by the comm program author in order for XPRZModem to be used. If any of these functions are not supported by your comm program, XPRZModem will display an error message and abort when invoked. These required functions are: xpr_fopen(), xpr_fclose(), xpr_fread(), xpr_fwrite(), xpr_fseek(), xpr_sread(), xpr_swrite(), and xpr_update() The xpr_update() function provides many data fields for your comm program to potentially display to the user. These are the XPR_UPDATE struct elements which XPRZModem will keep updated during transfers: xpru_protocol, xpru_filename, xpru_filesize, xpru_msg, xpru_errormsg, xpru_blocks, xpru_blocksize, xpru_bytes, xpru_errors, xpru_timeouts, xpru_blockcheck, xpru_expecttime, xpru_elapsedtime, and xpru_datarate As you can see, XPRZModem tries to provide as many status fields as possible. Although all of them are useful, the ones which are most important to ZModem users are filename, filesize, msg and/or errormsg, and bytes. Please try to provide at least these fields in your status display, plus as many of the rest as you can manage. Although only the XPR callback functions listed above are crucial for XPRZModem, all of them are used if they are provided. Although XPRZModem will function without any of the other routines, its performance or capabilities may be degraded somewhat. Specifically, this is what you give up if you choose not to supply any of these other XPR callback functions: xpr_sflush(): Used when performing error recovery and resync when sending files. If not provided, extra timeout errors and delayed error recovery will be likely. The files will still be transferred properly, but errors will degrade overall throughput more than usual. xpr_chkabort(): Called between sending or receiving packets. If not provided, there's no way for your comm program user to abort a transfer in progress except by trying to somehow force it to decide to give up and abort on its own, such as by turning off the modem and hoping the protocol will abort after enough timeouts. xpr_chkmisc(): Also called between sending or receiving packets. Actually, this is the one routine which doesn't cause any problems if missing. If you don't need a timeslice while the transfer is going, don't provide it. xpr_gets(): Called to prompt the user interactively for options when your comm program invokes XProtocolSetup() with a null xpr_filename field. If not provided, you'll have to prompt the user for the options string yourself, and pass this string in xpr_filename when invoking XProtocolSetup(). xpr_setserial(): Called to obtain the current serial port settings, and to change the serial port to 8N1 if it's not already set that way. If not provided, XPRZModem will assume all transfers are being done at 2400 bps, which won't hurt anything, and your users will have to make sure that the serial port is set to 8N1 themselves. xpr_ffirst() and xpr_fnext(): If either of these routines are missing, XPRZModem will lose the ability to send multiple files in a batch. The xpr_filename pointer passed to XProtocolSend() will be assumed to point to the actual full filename of the single file to be sent in this batch. If both of these routines are provided, XPRZModem will rely upon them completely to obtain the names of the files to send, and the xpr_filename pointer will not be used for any purpose by XPRZModem except to be passed to ffirst/fnext. This gives your comm program a way to send not just a single filename template's worth of files in a batch, but a list of different filenames. If, for example, you set xpr_filename to point to the first node of a linked list of filenames and/or templates to be sent, rather than just having it point to a string, you can have your ffirst and fnext routines traverse this linked list in order to determine the next file to be sent. Or you could have xpr_filename point to a buffer containing a list of filenames separated by commas, and your ffirst/fnext routines could return each filename in this list in turn. The key here is that if you provide these two routines, you're in complete control over the series of names fed to XProtocolSend. If you omit these routines, XPRZModem is stuck with single-file mode. Once again, if these two routines are provided, XPRZModem will *always* call them; it makes no attempt to use the xpr_filename pointer for anything itself. This is not explicitly spelled out in the XPR standard, but it seems the only reasonable way to handle batch protocols to me. Hopefully other XPR library authors will follow this precedent as well, so that comm program authors will be able to count on multiple-filename batch sessions being handled properly. xpr_finfo(): Used to determine the filesize of files being sent, in order to tell the receiving system how big they are. Also used to determine the size of a file which already exists when in Overwrite Resume mode; XPRZModem must be able to get the size of the current portion of the file in order to be able to tell the sender where to resume sending from. If this routine isn't provided, Overwrite Resume mode is not allowed. 8. The future -------------- I don't want or expect this to be the last or only XPR ZModem library available. There are a lot of less-commonly-used ZModem features which have popped up over the past few years, and many people might like to see some of them made available. Such as 32-bit CRC (although I consider CRC-16 perfectly adequate for the max 1K packets sent by ZModem), full control-character escaping, or maybe 8th bit escaping to allow use of 7-bit serial channels. I didn't want to add a bunch of rarely-used bells and whistles to this version of the library, because I want it to be able to serve as comprehensible example code. I just want to provide a good solid ZModem which reliably handles the majority of people's needs. Hopefully, this will serve as a foundation for future enhanced versions, while providing a safe fallback for people to come back to if that fancy new enhanced version (with neo-maxi zoomed weebies) turns out to need some more debugging. Bug reports, questions, or comments may be sent to me at: BIX: rahuebner Usenet: rhuebner@cup.portal.com Compu$erve: 73105,1022 Or, if you think it's important, and you want an answer in less than a week or two, call my BBS: Amiga++ 1-402-291-3636 1200-9600 bps, HST or V.32 FidoNet node 1:285/614 I check the messages on my BBS at least once a day, so that's where to get ahold of me quick. I'll also try and stock the latest XPR standard spec and XPR libraries there, in addition to the best collection of Amiga PD software in the MidWest ( <- blatant ad ).