The example I was asked to use was to be able to use the FTP library to retrieve a file from a password-protected FTP server. Here we go.
N.B.: I use "to drill down" to mean something a bit hard to explain with words - it's the action of browsing the source code of a word in the Browser and progressively click each specified word to browse its source code in turn; this is interactive code spelunking.
- To brush up on FTP commands, I googled for: ftp unix tutorial password download. Turns out it's very simple.
- Switched right to the Factor docs, searched for FTP, clicked on ftp.client.
- Looked at the list of commands trying to try and make sense of it. A good way to make sense of libraries is to find the basic building blocks - the least abstract functions that provide the support for the higher level ones.
- Since the command to download a file is GET, I clicked on ftp-get and drilled down to both with-ftp-client and ftp-cwd.
- I saw that ftp-cwd calls ftp-command. This looks like the basic building block I was looking for. Its source confirms that this is very concrete (i.e. it does something I can promptly understand - namely, send a command and read the response).
- I'm done looking at ftp-get. I want to find something that has to do with passwords.
- ftp-password doesn't take a password, only a url, so the url must have the password already. I try "ftp://user:pwd@ftp.server.com/" >ftp-url inspect and verify that indeed the password is gotten from the URL itself.
- Tried "ftp://user:pwd@ftp.server.com/folder/file.ext" ftp-get - got an error saying it had trouble saving the file to disk - permission was denied. This makes sense since I never specified a local path to save the file to, but I see the error says it tried to save the file to my root folder. I suspect this is set in some dynamic variable, but I have no clue really. I need to find out where this function tries to save the files it GETs, or how it builds the local path.
- Drilled down ftp-get > (ftp-get) - saw it uses
but otherwise it's a dead-end. I'll have to walk the code to see exactly what is fed to . - Walked the code and found out it uses "file.ext" for the local-path. This doesn't look right, unless
does more than meets the eye. - Looked at the docs for
, it doesn't mention anything helpful to me. I look at the source for it down below and click on normalize-path - aha! The docs say this function prepends current-directory to its argument. I did suspect this was going to be implicitly handled by a dynamic variable. - Tried "/Users/user1/Desktop/" current-directory [ "ftp://user:pwd@ftp.server.com/folder/file.ext" ] with-variable and it worked fine.
I hope this helps.
