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Added the termios crate to facilitate the changing of certain terminal
options. It is a wrapper around the termios C library, so 'man 3
termios' for more details.
Added the custom getchar() function, with retrieves characters from
STDIN as they are typed by the user (as opposed to waiting for a
newline, like io::stdin().read_line()). This is necessary, since keys
like <tab> and <up> have special functionality, which needs to be acted
on before command submission.
Added the custom getline() function, which uses getchar() to read
characters as they are typed. The getline() function contains the logic
for the various key presses. For most characters, we simply push the
byte to a buffer, and print it out to the screen (since getline()
assumes ECHO is off).
Signed-off-by: Rory Dudley <rory@netc.lu>
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This patch adds the following metadata fields to Cargo.toml, so that the
package can be published on https://crates.io:
- homepage: Our main website
- documentation: Also our main website (no docs for now, but they will
end up being hosted here in the near future)
- repository: A link to the git server with the source
Signed-off-by: Rory Dudley <rory@netc.lu>
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Removes the custom errors in src/recite/erro.rs, and replaces them with
std::io::Errors throughout (recite(), incant_, macros).
Fixed a bug with the way forking to the background is handled, where
registering the signal handler in main for all processes would break
couplets (i.e. pipes). Instead, this sets up a new signal handler each
time a process is forked into the background. It uses a Vec<i32> to keep
track of all the background processes.
Notes:
First off, there is some defunct code in the main repl loop, which is an
example of killing zombie processes after each prompt. This should be
removed, but I kept it in, just in case I go back to it for some reason.
To be honest, I have no clue why this code works. In theory, I should
have to remove the pid from the pids: Vec<i32> if waitpid returns a
positive integer. However, when I tried this, it completely broke the
program. ¯\_(ツ)_/¯
Also, it's worth noting that registering a signal handler with
signal_hook::low_level::register, is somewhat costly, according to their
docs. Given that this only occurs for background processes that are
forked, however, I think it is acceptable.
Finally, we never unregister the signal handler, so I'm not sure if
that's still hanging out in memory somewhere or no.
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First off, moved the giant match statements out of recite(), and into
macros in src/recite/ps.rs. There still needs to be two, since any verse
using the 'couplet' meter will need to redirect its STDOUT. Now the
recite() function returns a Result<(), Mishap>, which can be invoked
when calling the incant_ functions.
Custom errors were added in the form of 'Mishap''s. They are intended to
be returned from the incant_ functions, in the event that something goes
wrong with the Command::spawn() or Child::wait(). They each take a
String, which should be the verb or stanza that was entered by the user.
The incant_ functions separate the functionality of each type of meter
from the recite() function. They return a Result<i32, Mishap>, where
i32 is the exit code of the program that ran, and Mishap is a possible
error.
Before, the shell was cheating at forking a process to the background.
It would actually spawn a thread to wait for that process to finish.
Now, the program simply registers a handler for SIGCHLD, and uses libc's
waitpid() function to reap the child process, and print some output to
the user, indicating that it's finished.
Notes:
This was a huge patch which did some desperately needed cleanup of the
recite() function. Moving forward, will need to add more documentation,
and will probably scrap the custom errors, since this implementation is
a little half-baked. It's worth looking into in the future, but we can
probably live with io::Error's for the time being.
Fixing forking was a pretty big deal, though. In Linux, and other
u**x-like operating systems, parent processes need to reap their child
processes, otherwise they become zombies. Previously, the dwvsh did this
by spawning a separate thread to wait for child processes that were
forked to the background. Now, we are registering a handle for SIGCHLD,
which is a signal that gets sent to the parent when one of their
children finishes, or is killed. Using waitpid(2), we can determine
which process ended, and do something about it. In the case of a
processes that was forked into the background, when it finished,
waitpid(2) will return its PID. For foreground processes, it returns -1.
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Replaced the 'ctrlc' crate with 'signal-hook' for handling of SIGINT.
The 'signal_hook::low_level::register' function is actually unsafe.
However, according to
https://docs.rs/signal-hook/latest/signal_hook/low_level/fn.register.html,
it is only unsafe in the case of multithreaded applications. There are
some race conditions as well. For instance, it appears that even when we
fork to a child process, SIGINT is captured on both that process, as
well as the shell.
Notes:
The replacement was motivated by the fact that 'ctrlc' appears to use a
separate thread to handle interrupts. This is evident if you run:
ps aux | grep dwvsh
USER PID %CPU %MEM VSZ RSS TTY STAT START COMMAND
user pid 0.0 0.0 71500 3072 term Sl+ 20:08 target/debug/dwvsh
Further reading in 'man ps' under 'PROCESS STATE CODES', reveals that 'l'
is a process state referring to multithreaded applications.
Given the nature of interupts, this seems unnecessary.
The issue where SIGINT is captured by both the shell, and child process
will have to be addressed.
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Added logic to capture the interrupt signal. Using a rust crate called
'ctrlc' to do the heavy lifting. Program will simply reprint the prompt
on a new line if the interrup signal is detected.
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An extremely miniamal shell. It is capable of forking processes, and
passing arguments to them, but that's pretty much it.
Notes:
This is pretty much a prototype, to see how easily something like a
shell could be implemented in Rust.
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