feat: add preview update channel

1 files changed, 67 insertions, 0 deletions

diff --git a/src/checksum.rs b/src/checksum.rs
new file mode 100644
index 00000000..4f61a33c
--- /dev/null
+++ b/src/checksum.rs
@@ -0,0 +1,67 @@
+use std::{
+    fs::File,
+    io::{self, Read},
+    path::Path,
+};
+
+use sha2::{Digest, Sha256};
+
+pub(crate) fn verify_sha256(path: &Path, expected: &str) -> io::Result<()> {
+    let expected = expected.trim().to_ascii_lowercase();
+    if expected.len() != 64 || !expected.chars().all(|ch| ch.is_ascii_hexdigit()) {
+        return Err(io::Error::new(
+            io::ErrorKind::InvalidData,
+            "expected sha256 must be 64 hexadecimal characters",
+        ));
+    }
+
+    let actual = file_sha256(path)?;
+    if actual != expected {
+        return Err(io::Error::new(
+            io::ErrorKind::InvalidData,
+            format!("sha256 mismatch: expected {expected}, got {actual}"),
+        ));
+    }
+    Ok(())
+}
+
+fn file_sha256(path: &Path) -> io::Result<String> {
+    let mut file = File::open(path)?;
+    let mut hasher = Sha256::new();
+    let mut buffer = [0u8; 64 * 1024];
+    loop {
+        let read = file.read(&mut buffer)?;
+        if read == 0 {
+            break;
+        }
+        hasher.update(&buffer[..read]);
+    }
+    Ok(to_lower_hex(&hasher.finalize()))
+}
+
+fn to_lower_hex(bytes: &[u8]) -> String {
+    const HEX: &[u8; 16] = b"0123456789abcdef";
+    let mut output = String::with_capacity(bytes.len() * 2);
+    for &byte in bytes {
+        output.push(HEX[(byte >> 4) as usize] as char);
+        output.push(HEX[(byte & 0x0f) as usize] as char);
+    }
+    output
+}
+
+#[cfg(test)]
+mod tests {
+    use std::fs;
+
+    #[test]
+    fn verifies_matching_sha256() {
+        let path = std::env::temp_dir().join(format!("herdr-checksum-test-{}", std::process::id()));
+        fs::write(&path, b"herdr").unwrap();
+        let result = super::verify_sha256(
+            &path,
+            "78193ef266c1e3c2ce4ea2a86d7fc87e8c52799653faaac8536533a1c9300f82",
+        );
+        let _ = fs::remove_file(&path);
+        assert!(result.is_ok());
+    }
+}