sprintf not happenin we go prefix/postfix now with templating

src/config.rs

@@ -77,7 +77,7 @@ fn build_config_std() -> Config {
             },
          },
          output: Stream {
-            format: None,
+            format: Some(String::from("%s")),
             engine: Engine{
                name: String::from("stdout"),
                kafka: None,

src/stream.rs

@@ -3,6 +3,8 @@ use crate::config::Stream;
 use hidapi::HidApi;
 use rusb::UsbContext;
 use gilrs::{Gilrs, Button, Event};
+use printf;
+use std::os::raw::c_void;
 
 pub trait InputStream {
    fn get(&mut self) -> Vec<char>;
@@ -192,7 +194,37 @@ pub trait OutputStream {
 }
 
 pub fn build_output_stream(cfg: &Stream) -> Box<dyn OutputStream> {
-   return _build_output_stream(cfg)
+   return build_formatted_output_stream(cfg, _build_output_stream(cfg))
+}
+
+pub struct OutputStreamFormatted {
+   format: Option<String>,
+   stream: Box<dyn OutputStream>,
+}
+
+pub fn build_formatted_output_stream(cfg: &Stream, stream: Box<dyn OutputStream>) -> Box<dyn OutputStream> {
+   return Box::new(OutputStreamFormatted{
+      format: cfg.format.clone(),
+      stream: stream,
+   });
+}
+
+impl OutputStream for OutputStreamFormatted {
+   fn put(&mut self, v: Vec<char>) {
+      match self.format.as_ref() {
+         Some(x) => self.stream.put(sprintf(x, v)),
+         None => self.stream.put(v),
+      };
+   }
+}
+
+fn sprintf(format: &String, arg: Vec<char>) -> Vec<char> {
+   unsafe {
+      return printf::printf(
+         format.as_bytes().as_ptr() as *const i8,
+         arg.iter().cloned().collect::<String>().as_bytes().as_ptr() as *mut c_void,
+      ).chars().collect();
+   }
 }
 
 pub fn _build_output_stream(cfg: &Stream) -> Box<dyn OutputStream> {
@@ -232,6 +264,17 @@ mod test_output {
    fn _test_output_stream_impl(engine: &mut dyn OutputStream) {
       engine.put("teehee".to_string().chars().collect());
    }
+
+   #[test]
+   fn test_sprintf() {
+      assert_eq!(
+         "hello world".to_string().chars().collect::<Vec<char>>(),
+         sprintf(
+            &String::from("hello %s"),
+            String::from("world").chars().collect(),
+         ),
+      );
+   }
 }
 
 pub struct OutputStreamUDP {