[sword-devel] InstallMgr details.

[Troy A. Griffitts]

"Until you understand the details, design always sounds simple."
   --I'm sure, some famous architect near retirement.


There is a basic and practical difference between a local and a remote 
installation, however abstract you want to get.

Remote repositories have concepts like 'refresh from remote source' 
(apt-get update)

Local repositories usually aren't 'entered' in a list by a user, though 
I suppose they could be if it was useful.  Practically there is usually 
1 local source (a CD or USB drive) and the user can Browse... to the 
location.  This is not easily replicated for remote sources.  They are 
typically 'configured' and their configuration stored for future reference.

So, while the difference between local and remote is there, a remote FTP 
source and a remote HTTP source will likely be much less different.
Some I can think of:  We now have just added support in 1.6.0 for 
non-anonymous FTP, so the user can input username/password if 
necessary-- useful for access to a private beta repository.  We have 
supported Passive FTP as an option.  With HTTP access, we might also add 
HTTP proxy features.  These all require frontend user preferences.

There will almost certainly be additional work for the frontends when we 
add HTTP support, though not as different as you fear might be.


To understand the design decisions for InstallMgr, you have to have a 
basic understanding of the SWORD API:

Libraries of modules are exposed as SWMgr objects.
An SWMgr object can be easily created from a local path:

SWMgr localLibrary("/path");

So for local sources, you don't need InstallMgr to obtain an SWMgr object.

InstallMgr has a new object: InstallSource which houses the 
configuration information for a remote source and can give back an SWMgr 
object which represents that remote library.

InstallMgr provides new SWMgr features useful when writing an install 
client like: compare 2 SWMgr objects and tell you which books are new, 
old, updated, etc.

InstallMgr can install TO an SWMgr.  This sounded like a clever idea, as 
an SWMgr has the concept of a 'primary path', but in hindsite, we only 
will probably ever support installing TO a local directory, so this has 
added confusion.  The use case was:

SWMgr defaultLocalSWORDLibrary;
installMgr.installModule(&defaultLocalSWORDLibrary, "D:\\", "KJV");

But this is too simplistic a use case to be practical.


Due to backward compatibility, my least favourite interface in 
InstallMgr is:

(for history, it used to be, at a time we only supported CD (well, 
local) installations:

int InstallMgr::installModule(SWMgr *destMgr, const char *fromLocation, 
const char *modName);
// which I don't hate

)


/** call to install a module from a local path (fromLocation) or remote 
InstallSource (is) (leave the other 0)
  */
int InstallMgr::installModule(SWMgr *destMgr, const char *fromLocation, 
const char *modName, InstallSource *is = 0);


So, InstallMgr can either install FROM a local path (historically the 
initial impl), or remote InstallSource.

When we decide to majorly break backward compatibility for the interface 
cleanup and remove all deprecated methods, InstallSource will probably 
get a c-tor(const char *path), and the 2nd parameter will just go away.


Hope this alleviates some of your design concerns and helps you 
understand the historical thinking behind the decisions.


	-Troy.



Greg Hellings wrote:
> On Thu, May 14, 2009 at 11:29 PM, Matthew Talbert <ransom1982 at gmail.com> wrote:
>>> Does it require a difference (for the C++ front ends) to add support
>>> for FTP InstallMgr methods than it does for them to add a file://
>>> version?  It seems that, if so, this is a problem with the design of
>>> InstallMgr.  I would imagine that the interface between SWORD and the
>>> application would be identical in all those cases -- all the
>>> application needs is to retrieve the information and provide a way for
>>> the user to input new locations.  I get the impression from your
>>> previous messages that the front ends will need to change when you add
>>> HTTP support to the library then front ends will need to add another
>>> portion to their install manager that allows the user to create HTTP
>>> install locations separate from FTP or file:// ones -- is that the
>>> case?
>> The interface is different for local installations than it is for FTP
>> installations. For local installations, you must create an SWMgr that
>> points to the location of the modules to be installed, then you can
>> get a listing of the modules available (but you must be careful to not
>> augment the path with HOME/.sword or other locations or it won't
>> work). For FTP, it also creates an SWMgr, but it does it itself, and
>> exposes the list of available modules. This difference is why Xiphos
>> couldn't really use a local source until 3.0. No one had figured out
>> how it was supposed to work :)
> 
> I see -- it seems to me that method doesn't take nearly as much
> abstraction as it should.  I should imagine that a client application
> could simply create an InstallMgr object and pass it the string that
> it ought to search for.  If the string is file://, ftp://, http://,
> cifs:// or \\host or whatever shouldn't much matter in my mind.  The
> URI should be parsed and the proper actions taken within InstallMgr.
> Why was it done with a different class for each type, forcing the
> client app to handle the parsing and take each experience differently?
>  Inherently that will lead to different apps supporting or not
> supporting certain of the features (the example that you just
> mentioned, for instance).  If there was just the matter of "Create an
> InstallMgr object, ask it what's available, tell it to install to
> such-and-such a writable location" then as the library expanded
> support for HTTP, SFTP, SomeFutureTP the applications would not even
> need to know or care.
> 
> --Greg
> 
>> Matthew
>>
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