sysutils: grep for stdin

userspace/sysutils/src/grep.rs

@@ -3,7 +3,7 @@
 
 use std::{
     fs::File,
-    io::{self, stdout, Seek, Write},
+    io::{self, stdout, Seek, Stdin, Write},
     path::{Path, PathBuf},
     process::ExitCode,
 };
@@ -29,6 +29,22 @@ struct FileInput {
     position: usize,
 }
 
+struct StdinInput {
+    stdin: Stdin,
+    buffer: String,
+    eof: bool,
+}
+
+impl StdinInput {
+    pub fn new() -> Self {
+        Self {
+            stdin: io::stdin(),
+            buffer: String::new(),
+            eof: false,
+        }
+    }
+}
+
 impl FileInput {
     pub fn open<P: AsRef<Path>>(path: P) -> io::Result<Self> {
         let mut file = File::open(path)?;
@@ -39,6 +55,22 @@ impl FileInput {
     }
 }
 
+impl Input for StdinInput {
+    fn next_line(&mut self) -> io::Result<Option<&[u8]>> {
+        if self.eof {
+            return Ok(None);
+        }
+
+        self.buffer.clear();
+        if self.stdin.read_line(&mut self.buffer)? == 0 {
+            self.eof = true;
+            return Ok(None);
+        }
+
+        Ok(Some(self.buffer.trim_end_matches('\n').as_bytes()))
+    }
+}
+
 impl Input for FileInput {
     fn next_line(&mut self) -> io::Result<Option<&[u8]>> {
         if self.position >= self.mmap.len() {
@@ -57,7 +89,7 @@ impl Input for FileInput {
     }
 }
 
-fn run_on<I: Input>(input: &mut I, regex: &Regex) -> io::Result<bool> {
+fn run_on<I: Input>(input: &mut I, regex: &Regex) -> Result<bool, Error> {
     let mut any = false;
     loop {
         let Some(line) = input.next_line()? else {
@@ -76,14 +108,18 @@ fn run_on<I: Input>(input: &mut I, regex: &Regex) -> io::Result<bool> {
 #[derive(Debug, Parser)]
 struct Args {
     expression: String,
-    filename: PathBuf,
+    filename: Option<PathBuf>,
 }
 
 fn run(args: &Args) -> Result<bool, Error> {
     let regex = Regex::new(&args.expression)?;
-    let mut input = FileInput::open(&args.filename)?;
-    let any = run_on(&mut input, &regex)?;
-    Ok(any)
+    if let Some(filename) = args.filename.as_deref() {
+        let mut input = FileInput::open(filename)?;
+        run_on(&mut input, &regex)
+    } else {
+        let mut input = StdinInput::new();
+        run_on(&mut input, &regex)
+    }
 }
 
 fn main() -> ExitCode {