single-threaded

2 files changed, 74 insertions, 1 deletions

diff --git a/Cargo.toml b/Cargo.toml
index f0d7824..dffbe19 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,3 +6,6 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+anyhow = "1.0.56"
+clap = { version = "3.1.6", features = ["derive"] }
+sha2 = "0.10.2"
diff --git a/src/main.rs b/src/main.rs
index e7a11a9..408b697 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,73 @@
+use clap::Parser;
+use sha2::{Digest, Sha256};
+use std::fs::File;
+use std::io::{BufReader, Read};
+use std::path::{Path, PathBuf};
+
+const BUF_SIZE: usize = 4096;
+
 fn main() {
-    println!("Hello, world!");
+    let args = Args::parse();
+    if let Err(e) = checksums_main(&args.filenames) {
+        eprintln!("ERROR: {e}");
+        std::process::exit(1);
+    }
+}
+
+fn checksums_main(filenames: &[PathBuf]) -> anyhow::Result<()> {
+    let x: Result<Vec<()>, std::io::Error> = filenames
+        .iter()
+        .map(|filename| checksum(filename))
+        .map(|x| print_checksum_result(x))
+        .collect();
+    let _ = x?;
+    Ok(())
+}
+
+fn checksum(filename: &Path) -> Result<FileChecksum, std::io::Error> {
+    let mut checksum = Sha256::new();
+
+    let file = File::open(filename)?;
+    let mut reader = BufReader::new(file);
+    loop {
+        let mut buf = vec![0; BUF_SIZE];
+        let n = reader.read(&mut buf)?;
+        if n == 0 {
+            break;
+        }
+        checksum.update(&buf[..n]);
+    }
+
+    let checksum = checksum.finalize();
+    let checksum = format!("{checksum:x}");
+    Ok(FileChecksum::new(filename, checksum))
+}
+
+#[derive(Parser)]
+struct Args {
+    filenames: Vec<PathBuf>,
+}
+
+#[derive(Debug)]
+struct FileChecksum {
+    filename: PathBuf,
+    checksum: String,
+}
+
+impl FileChecksum {
+    fn new(filename: &Path, checksum: String) -> Self {
+        Self {
+            filename: filename.to_path_buf(),
+            checksum,
+        }
+    }
+}
+
+fn print_checksum_result(x: Result<FileChecksum, std::io::Error>) -> Result<(), std::io::Error> {
+    if let Ok(x) = x {
+        println!("{} {}", x.checksum, x.filename.display());
+        Ok(())
+    } else {
+        Err(x.unwrap_err())
+    }
 }