Recently I revived my husband's Nintendo 2DS XL and flashed custom firmware to it. This lets me install custom games and applications via a multitude of installers, including one called FBI. FBI accepts files in the CIA format, an installable 3DS format that's the same as used in the eShop.
Because the DS is a fun little portable console I decided to use it as the main vehicle for learning new Japanese words. Recently I remembered how much I've forgotten how to write in Japanese, and a portable console with a stylus is a nice way to practice. Plus there are lots of games on the DS I can learn from while I practice writing. While I researched what games are heavy on dialogue on the DS I remembered that the PC98 was a thing and had so, so many adventure games that were heavy on text. And I love its color palette. As it happens there is a port of Neko Project 2 for the DS, a PC98 emulator.
To install a game typically I can find a QR code online which encodes a link to a CIA file, which I can scan with the DS via FBI and it handles the download and install for me. For NP2 I had access to the CIA file from my computer but no QR code. My solution was to use ftpd, which my hacked DS already had, to transfer the CIA file from my computer to the DS.
FTP is weird and old and really insecure, but it's really convenient. The commands I used to transfer this file from my computer to the DS were.
wesl-ee@particle-arts np2for3ds/np2 > ftp 10.0.0.238 5000
Connected to 10.0.0.238.
220 Hello!
Name (10.0.0.238:wesl-ee):
230 OK
ftp> put NP21.cia /NP21.cia
200 OK
150 Ready
ftp>
Opening FBI, clicking "SD Card" and then clicking "A" on the file did not give me an option to install the game, it only gave the filetype as "Archive" and presented options to rename, copy, or delete the file. According to what I read online, I expected to see an "Install CIA File" option.
I ruminated on the possibilities and figued the file was corrupted somehow. There were two options: (1) bad download or (2) corruption during network transfer. Because FTP uses TCP for transfers, the possibility of experiencing actual file corruption during this step were slim. And I trusted the download I had found was legit.
This seemed to be a very niche issue but I had some ideas. Looking online I found no immediately relevant information and FBI was not being very helpful.
I tapped my knowledge of FTP and remembered a fact buried in the back of my mind
somewhere, that FTP has two different transfer modes: ASCII and binary. ASCII
mode is used for text files and will convert all line-ending characters (LF,
\n on Unix-like systems and \r\n on Windows) when transfering to an
operating system that uses the other. This is the default mode according to RFC
specs and the default mode of almost all distributions of the ftp binary,
which I was using. In order to not induce this behavior, any session should
begin with the command binary, switching the mode from ASCII to binary. Binary
transfer mode does not modify any of the underlying data being transfered.
This was the issue affecting my CIA file: all of the characters which would
have been \r\n were being converted to \n. This was corrupting the file.
Running binary fixed that issue, and I was able to install the file normally
in FBI. Moving the CIA file to the DS via SD card would have worked too!