feat: add write-large-file example to show how to write huge files.

This requires DEFLATE64 support, which is seemingly present in the
default rust backend.

examples/write-large-file.rs

@@ -0,0 +1,36 @@
+//! Write a huge file with lots of zeros, that should compress perfectly.
+
+use std::io::Write;
+
+use zip::write::FileOptions;
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let args: Vec<_> = std::env::args().collect();
+    if args.len() < 2 {
+        return Err(format!("Usage: {} <filename>", args[0]).into());
+    }
+
+    let filename = &*args[1];
+    doit(filename)?;
+    Ok(())
+}
+
+fn doit(filename: &str) -> zip::result::ZipResult<()> {
+    let file = std::fs::File::create(filename)?;
+    let mut zip = zip::ZipWriter::new(file);
+
+    let options = FileOptions::default()
+        .compression_method(zip::CompressionMethod::Deflated)
+        // files over u32::MAX require this flag set.
+        .large_file(true)
+        .unix_permissions(0o755);
+    zip.start_file("huge-file-of-zeroes", options)?;
+    let content: Vec<_> = std::iter::repeat(0_u8).take(65 * 1024).collect();
+    let mut bytes_written = 0_u64;
+    while bytes_written < u32::MAX as u64 {
+        zip.write_all(&content)?;
+        bytes_written += content.len() as u64;
+    }
+    zip.finish()?;
+    Ok(())
+}
+