Add the readrom binary

The readrom binary is similar to `readelf` from Linux and it will allow
to display information from an NES/Famicom ROM file. For now the
information being shown is just the header, but in the future we might
also include disassembling parts of the code, or retrieving the "CHARS"
section for a given ROM file, and similar.

In order to implement the header parsing part a new library has been
introduced, simply named "header" which abstracts everything away so you
just need to call `Header::try_from("my bytes")` to fetch the actual
information.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

2 files changed, 67 insertions, 0 deletions

diff --git a/crates/readrom/Cargo.toml b/crates/readrom/Cargo.toml
new file mode 100644
index 0000000..98a5106
--- /dev/null
+++ b/crates/readrom/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "readrom"
+version = "1.0.0"
+rust-version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+
+[dependencies]
+anyhow = "^1"
+clap = { version = "^4", features = ["derive"] }
+header.workspace = true
diff --git a/crates/readrom/src/main.rs b/crates/readrom/src/main.rs
new file mode 100644
index 0000000..56e60e0
--- /dev/null
+++ b/crates/readrom/src/main.rs
@@ -0,0 +1,55 @@
+use anyhow::{bail, Result};
+use clap::Parser as ClapParser;
+use header::{Header, Kind};
+use std::fs::File;
+use std::io::{ErrorKind, Read};
+
+/// Display information about NES/Famicom ROM files.
+#[derive(ClapParser, Debug)]
+#[command(version, about, long_about = None)]
+struct Args {
+    /// NES/Famicom ROM file from which to display information.
+    file: String,
+}
+
+fn print_header(header: &Header) {
+    println!("Header:");
+
+    match header.kind {
+        Kind::INes => println!("  Kind:\t\tiNES"),
+        Kind::Nes20 => println!("  Kind:\t\tNES 2.0"),
+    }
+
+    println!(
+        "  PRG ROM size:\t{} bytes ({}KB)",
+        header.prg_rom_size * 16 * 1024,
+        header.prg_rom_size * 16
+    );
+    println!(
+        "  CHR ROM size:\t{} bytes ({}KB)",
+        header.chr_rom_size * 8 * 1024,
+        header.chr_rom_size * 8
+    );
+    println!("  Mapper:\t{}", header.mapper);
+}
+
+fn main() -> Result<()> {
+    let args = Args::parse();
+    let mut input = File::open(args.file)?;
+
+    let mut buf = vec![0u8; 0x10];
+    if let Err(e) = input.read_exact(&mut buf) {
+        match e.kind() {
+            ErrorKind::UnexpectedEof => bail!("malformed ROM file."),
+            _ => return Err(e.into()),
+        }
+    }
+
+    let header = match Header::try_from(buf.as_slice()) {
+        Ok(h) => h,
+        Err(e) => bail!("{}.", e),
+    };
+    print_header(&header);
+
+    Ok(())
+}