add example to use Easy2 in downloading files

examples/file_download.rs

@@ -0,0 +1,51 @@
+/// This is an example how to use Easy2 to download a file.
+/// Can able to resume a download and control download speed.
+use std::{fs::OpenOptions, io::Write, path::PathBuf};
+
+use curl::easy::{Easy2, Handler, WriteError};
+
+enum Collector {
+    File(PathBuf),
+    // You can add what type of storage you want
+}
+
+impl Handler for Collector {
+    fn write(&mut self, data: &[u8]) -> Result<usize, WriteError> {
+        match self {
+            Collector::File(download_path) => {
+                println!("File chunk size: {}", data.len());
+                let mut file = OpenOptions::new()
+                    .create(true)
+                    .append(true)
+                    .open(download_path)
+                    .map_err(|e| {
+                        eprintln!("{}", e);
+                        WriteError::Pause
+                    })?;
+
+                file.write_all(data).map_err(|e| {
+                    eprintln!("{}", e);
+                    WriteError::Pause
+                })?;
+                Ok(data.len())
+            }
+        }
+    }
+}
+fn main() {
+    let collector = Collector::File(PathBuf::from("<Your target path>"));
+    let mut easy2 = Easy2::new(collector);
+
+    easy2.url("https://www.rust-lang.org/").unwrap();
+    easy2.get(true).unwrap();
+    // Setting of download speed control in bytes per second
+    easy2.max_recv_speed(2000).unwrap();
+    // Can resume download by giving a byte offset
+    easy2.resume_from(0).unwrap();
+    easy2.perform().unwrap();
+
+    let status_code = easy2.response_code().unwrap();
+    let content_type = easy2.content_type().unwrap();
+    eprintln!("Content Type: {:?}", content_type);
+    eprintln!("Status Code: {}", status_code);
+}