From NSIS Wiki
Metadl - metalink downloading plugin for NSIS
Copyright (c) 2007 Hampus Wessman (email@example.com)
Metadl is a downloading plugin with support for both http and ftp, resuming and metalinks (including mirrors, hashes and chunk checksums). The progress display is based on code from NSISdl.
This readme describes how to use the plugin. It works almost the same as NSISdl, so it's easy to switch if you have used that plugin before. The downloading is handled by libcurl, xml parsing (for the metalinks) is handled by Expat and hashing is done by some code from XySSL. Metadl is open source and licensed under GNU LGPL.
For more information and current version see: http://hampus.vox.nu/metadl/
Using NSIS plugins
Before you can use the plugin NSIS must be able to find the dll file. One way to accomplish this is to put it in the plugin directory of NSIS. This will make it possible for all installers built on you computer to use metadl. Another way (that I like better) is to put it in a directory specific for your current installer and then add a line of code to your NSIS script that tells NSIS to look in this directory. You can for example create a subdirectory called "plugins" and add this line to your NSIS script:
metadl:download [options] [url] local-file
The return value is pushed to the stack:
- otherwise, an error string describing the error
If you don't want the progress window to appear, use
metadl::download_quiet (which isn't recommended, because you can't cancel the download then).
/RETRYTIME=5(the number of seconds between retries; default=5)
/MAXTRIES=0(max tries; 0=infinite, 1=no retries, ...; default=0)
/HASHTRIES=0(max tries when checksums fail, works as max tries; default=0)
/MD5 the-hash(use this hash to validate the download; no md5 as default)
/SHA1 the-hash(use this hash to validate the download; no sha1 as default)
- both md5 and sha1 can be used at the same time!
/CHECK(only checks hashes, won't download anything; disabled by default)
/MIRRORS=2 url1 url2(add these mirrors. You still need an "ordinary" url, so leave one mirror for that!)
It is also possible to translate the plugin (undocumented; not compatible with NSISdl!) and set all the other options from NSISdl (which aren't used anyway).
Local files and hash checking
If you don't enter an URL, the plugin won't try to download the file. This is useful if you want to use a local metalink, which will get parsed and used for downloading. Hashes are still being checked (if present) and an error will be returned if they don't match (instead of trying to download the file). If you don't want the files found in a metalink to be downloaded, you can add the option /CHECK (see above). Metalinks will still be parsed and all files described in them will be checked, but an error will be returned instead of trying to download any of them. "File check failed" will be returned when the hash checks fail or a file doesn't exist.
How it behaves
The plugin first looks for the local-file. If it exists it checks the hashes and if none fails it is done! Otherwise the old file is deleted (if there was one) and it looks for a file named local-file.partial. If there is one it continues at the end of the file, otherwise it creates one. Then the downloading begins. Mirrors are selected at random to begin with, but errors and in which order they was last tested is remember. After a while it picks the "best" server to try. I won't get into details about this, but it works quite well.
If errors occur then it updates the info about the mirrors (in memory) and checks if any more retries should be done (depends on 'max tries'). This is the total number of tries (not per mirror). When the file is downloaded the checksums are checked. If the file doesn't validate it is deleted and the process starts over again (depending on 'hash tries'). If the file is correct, then it is renamed to 'local-file'.
If the downloaded file ends with ".metalink" it is parsed and, if it is a metalink file, all the files described in the metalink will be downloaded as described above, to the same directory as the metalink. If any of these files also are metalinks, they won't get parsed though!
If not "cancel" or "success" is returned, an error message will always be returned instead, that explains what went wrong!
Compiling the plugin
I will describe how to cross compile the plugin in Ubuntu here. Compiling it in windows is more complex. Just follow these simple steps:
- Make sure you have the mingw32 package installed, otherwise run
sudo apt-get install mingw32
- Run "make prerequisites" to download expat and libcurl.
- Then run "make" to compile the plugin.
This will compile both metadl and its dependencies. You'll find the binary(ie metadl.dll) in the subdir "bin".
If you're using another platform than Ubuntu, then you will probably need to make some adjustments to the building process. The makefile included here is only made to work with Ubuntu. That's not great, but on the other hand it should be quite easy to make the necessary changes...