Add an initial implementation of xargs

This includes much of the core xargs functionality, with the following
notable exceptions:

- Parallel execution (`-P`): This option currently just does
  nothing, that way anything that passes -P can at least run without a
  notable behavior shift (other than simply being slower).
- Replacement strings (`-I`): This can easily be worked around via an
  intermediate shell invocation (e.g. `xargs -L1 sh -c 'do-things-with
  $@' --`).
- EOF strings (`-E`): I've honestly never seen this actually used,
  though it would not be particularly difficult to implement given the
  current architecture.

Closes uutils#37

Signed-off-by: Ryan Gonzalez <ryan.gonzalez@collabora.com>

Cargo.toml

@@ -11,6 +11,7 @@ authors = ["uutils developers"]
 
 [dependencies]
 chrono = "0.4"
+clap = "2.34"
 glob = "0.3"
 walkdir = "2.3"
 tempfile = "3"
@@ -28,6 +29,10 @@ serial_test = "0.5"
 name = "find"
 path = "src/find/main.rs"
 
+[[bin]]
+name = "xargs"
+path = "src/xargs/main.rs"
+
 [[bin]]
 name = "testing-commandline"
 path = "src/testing/commandline/main.rs"

src/lib.rs

@@ -12,3 +12,4 @@ extern crate walkdir;
 extern crate tempfile;
 
 pub mod find;
+pub mod xargs;

src/testing/commandline/main.rs

@@ -6,18 +6,27 @@
 
 use std::env;
 use std::fs::{self, File, OpenOptions};
-use std::io::Write;
+use std::io::{stdin, stdout, Read, Write};
 use std::path::PathBuf;
 
 fn usage() -> ! {
     println!("Simple command-line app just used for testing -exec flags!");
     std::process::exit(2);
 }
 
+enum ExitWith {
+    Failure,
+    UrgentFailure,
+    #[cfg(unix)]
+    Signal,
+}
+
 #[derive(Default)]
 struct Config {
-    exit_with_failure: bool,
-    destination_dir: String,
+    exit_with: Option<ExitWith>,
+    print_stdin: bool,
+    no_print_cwd: bool,
+    destination_dir: Option<String>,
 }
 
 fn open_file(destination_dir: &str) -> File {
@@ -39,20 +48,61 @@ fn open_file(destination_dir: &str) -> File {
     }
 }
 
+fn write_content(mut f: impl Write, config: &Config, args: &[String]) {
+    if !config.no_print_cwd {
+        writeln!(f, "cwd={}", env::current_dir().unwrap().to_string_lossy())
+            .expect("failed to write to file");
+    }
+
+    if config.print_stdin {
+        let mut s = String::new();
+        stdin()
+            .read_to_string(&mut s)
+            .expect("failed to read from stdin");
+        writeln!(f, "stdin={}", s.trim()).expect("failed to write to file");
+    }
+
+    writeln!(f, "args=").expect("failed to write to file");
+
+    // first two args are going to be the path to this executable and
+    // the destination_dir we want to write to. Don't write either of those
+    // as they'll be non-deterministic.
+    for arg in &args[2..] {
+        writeln!(f, "{}", arg).expect("failed to write to file");
+    }
+}
+
 fn main() {
     let args = env::args().collect::<Vec<String>>();
     if args.len() < 2 || args[1] == "-h" || args[1] == "--help" {
         usage();
     }
     let mut config = Config {
-        destination_dir: args[1].clone(),
+        destination_dir: if args[1] != "-" {
+            Some(args[1].clone())
+        } else {
+            None
+        },
         ..Default::default()
     };
     for arg in &args[2..] {
         if arg.starts_with("--") {
             match arg.as_ref() {
                 "--exit_with_failure" => {
-                    config.exit_with_failure = true;
+                    config.exit_with = Some(ExitWith::Failure);
+                }
+                "--exit_with_urgent_failure" => {
+                    config.exit_with = Some(ExitWith::UrgentFailure);
+                }
+                #[cfg(unix)]
+                "--exit_with_signal" => {
+                    config.exit_with = Some(ExitWith::Signal);
+                }
+                "--no_print_cwd" => {
+                    config.no_print_cwd = true;
+                }
+                "--print_stdin" => {
+                    config.print_stdin = true;
                 }
                 _ => {
                     usage();
@@ -61,20 +111,19 @@ fn main() {
         }
     }
 
-    {
-        let mut f = open_file(&config.destination_dir);
-        // first two args are going to be the path to this executable and
-        // the destination_dir we want to write to. Don't write either of those
-        // as they'll be non-deterministic.
-        f.write_fmt(format_args!(
-            "cwd={}\nargs=\n",
-            env::current_dir().unwrap().to_string_lossy()
-        ))
-        .expect("failed to write to file");
-        for arg in &args[2..] {
-            f.write_fmt(format_args!("{}\n", arg))
-                .expect("failed to write to file");
-        }
+    if let Some(destination_dir) = &config.destination_dir {
+        write_content(open_file(destination_dir), &config, &args);
+    } else {
+        write_content(stdout(), &config, &args);
+    }
+
+    match config.exit_with {
+        None => std::process::exit(0),
+        Some(ExitWith::Failure) => std::process::exit(2),
+        Some(ExitWith::UrgentFailure) => std::process::exit(255),
+        #[cfg(unix)]
+        Some(ExitWith::Signal) => unsafe {
+            uucore::libc::raise(uucore::libc::SIGINT);
+        },
     }
-    std::process::exit(if config.exit_with_failure { 2 } else { 0 });
 }

src/xargs/main.rs

@@ -0,0 +1,12 @@
+// Copyright 2021 Collabora, Ltd.
+//
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+fn main() {
+    let args = std::env::args().collect::<Vec<String>>();
+    std::process::exit(findutils::xargs::xargs_main(
+        &args.iter().map(|s| s.as_ref()).collect::<Vec<&str>>(),
+    ))
+}