chore(examples): Add tagdump helper tool

examples/tagdump.rs

@@ -0,0 +1,52 @@
+//! This is not actually an example that uses the `id3` crate, but helps dumping entire ID3 tags
+//! from MP3 files to stdout. These files can then be used as testdata for this crate.
+
+use std::env::args;
+use std::error::Error;
+use std::fs::File;
+use std::io::{self, Read, Write};
+
+const CHUNK_SIZE: usize = 2048;
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let Some(path) = args().nth(1) else {
+        return Err("No path specified!".into());
+    };
+
+    let mut file = File::open(&path)?;
+
+    let mut header = [0u8; 10];
+    file.read_exact(&mut header)?;
+    assert!(&header[..3] == b"ID3");
+    let tag_size: u32 = u32::from(header[9])
+        | u32::from(header[8]) << 7
+        | u32::from(header[7]) << 14
+        | u32::from(header[6]) << 21;
+    eprintln!("Tag size: {tag_size}");
+    let has_footer = (header[5] & 0x10) != 0;
+
+    let mut bytes_left: usize = tag_size.try_into()?;
+    if has_footer {
+        // Footer is present, add 10 bytes to the size.
+        eprintln!("Footer: yes");
+        bytes_left += 10;
+    } else {
+        eprintln!("Footer: no");
+    }
+
+    eprintln!("Writing {bytes_left} bytes to stdout...");
+    let mut stdout = io::stdout().lock();
+    stdout.write_all(&header)?;
+
+    let mut buffer: [u8; CHUNK_SIZE] = [0; CHUNK_SIZE];
+    while bytes_left > 0 {
+        let bytes_to_read = bytes_left.min(CHUNK_SIZE);
+        file.read_exact(&mut buffer[..bytes_to_read])?;
+        stdout.write_all(&buffer[..bytes_to_read])?;
+        bytes_left -= bytes_to_read;
+    }
+    stdout.flush()?;
+    eprintln!("Done.");
+
+    Ok(())
+}