From 3f0d95fe8fe87cd3b3c6ba766e1ec643d6f7faa6 Mon Sep 17 00:00:00 2001
From: DTB <trinity@trinity.moe>
Date: Fri, 23 Feb 2024 20:49:24 -0700
Subject: [PATCH] swab(1): minimum viable program

---
 Makefile    |  7 +++++++
 src/swab.rs | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+)
 create mode 100644 src/swab.rs

diff --git a/Makefile b/Makefile
index 46fd88e..d8c0c59 100644
--- a/Makefile
+++ b/Makefile
@@ -101,6 +101,13 @@ strcmp: build/bin/strcmp
 build/bin/strcmp: src/strcmp.c build
 	$(CC) $(CFLAGS) -o $@ src/strcmp.c
 
+.PHONY: swab
+swab: build/bin/swab
+build/bin/swab: src/swab.rs build build/o/libsysexits.rlib
+	$(RUSTC) $(RUSTFLAGS) \
+		--extern sysexits=build/o/libsysexits.rlib \
+		-o $@ src/swab.rs
+
 .PHONY: true
 true: build/bin/true
 build/bin/true: src/true.c build
diff --git a/src/swab.rs b/src/swab.rs
new file mode 100644
index 0000000..26104eb
--- /dev/null
+++ b/src/swab.rs
@@ -0,0 +1,47 @@
+use std::{
+	env::args,
+	io::{ stdin, stdout, Error, ErrorKind, Read, Write },
+	process::ExitCode,
+	vec::Vec
+};
+
+extern crate sysexits;
+
+use sysexits::{ EX_OK, EX_OSERR };
+
+fn oserr(s: &str, e: Error) -> ExitCode {
+	eprintln!("{}: {}", s, e);
+	ExitCode::from(EX_OSERR as u8)
+}
+
+fn main() -> ExitCode {
+	let argv = args().collect::<Vec<String>>();
+	let mut buf: Vec<u8> = Vec::new();
+	let mut input = stdin();
+	let mut output = stdout().lock();
+
+	let wordsize: usize = 2;
+	let force = false;
+
+	buf.resize(wordsize, 0);
+
+	loop {
+		match input.read(&mut buf) {
+			Ok(0) => break ExitCode::from(EX_OK as u8),
+			Ok(v) if v == wordsize => {
+				let (left, right) = buf.split_at(v/2);
+				if let Err(e) = output.write(&right)
+						.and_then(|_| output.write(&left)) {
+					break oserr(&argv[0], e)
+				}
+			},
+			Ok(v) => {
+				if let Err(e) = output.write(&buf[..v]) {
+					break oserr(&argv[0], e)
+				}
+			},
+			Err(e) if e.kind() == ErrorKind::Interrupted && force => continue,
+			Err(e) => break oserr(&argv[0], e)
+		}
+	}
+}