Implement ExternalPrinterWriter

To enable duplex output of log messages

Fixes kkawakam#797

examples/external_print.rs

@@ -1,5 +1,11 @@
+extern crate env_logger;
+extern crate log;
+
+use std::io::Write;
 use std::thread;
 use std::time::Duration;
+use env_logger::Target;
+use log::LevelFilter;
 
 use rand::{thread_rng, Rng};
 
@@ -8,10 +14,24 @@ use rustyline::{DefaultEditor, ExternalPrinter, Result};
 fn main() -> Result<()> {
     let mut rl = DefaultEditor::new()?;
     let mut printer = rl.create_external_printer()?;
+
+    env_logger::builder()
+        .filter_level(LevelFilter::Info)
+        .target(Target::Pipe(rl.create_external_writer()?))
+        .init();
+    thread::spawn(move || {
+        loop {
+            log::info!("Log Message");
+            thread::sleep(Duration::from_secs(3));
+        }
+    });
+
+    let mut writer = rl.create_external_writer().unwrap();
     thread::spawn(move || {
         let mut rng = thread_rng();
         let mut i = 0usize;
         loop {
+            writer.write("writing without newline".as_bytes());
             printer
                 .print(format!("External message #{i}"))
                 .expect("External print failure");
@@ -23,7 +43,6 @@ fn main() -> Result<()> {
 
     loop {
         let line = rl.readline("> ")?;
-        rl.add_history_entry(line.as_str())?;
-        println!("Line: {line}");
+        println!("Read Line: {line}");
     }
-}
+}

src/lib.rs

@@ -41,7 +41,7 @@ mod undo;
 pub mod validate;
 
 use std::fmt;
-use std::io::{self, BufRead, Write};
+use std::io::{self, BufRead, Read, Write};
 use std::path::Path;
 use std::result;
 
@@ -923,6 +923,12 @@ impl<H: Helper, I: History> Editor<H, I> {
         self.term.create_external_printer()
     }
 
+    /// Create a wrapper for the external printer implementing std::io::Write
+    pub fn create_external_writer(&mut self) -> Result<Box<dyn Write + Send>> {
+        self.create_external_printer().map(|printer|
+            Box::new(ExternalPrinterWriter(Box::new(printer))) as Box<dyn Write + Send>)
+    }
+
     /// Change cursor visibility
     pub fn set_cursor_visibility(
         &mut self,
@@ -932,6 +938,23 @@ impl<H: Helper, I: History> Editor<H, I> {
     }
 }
 
+struct ExternalPrinterWriter<P>(Box<P>);
+
+impl<P> Write for ExternalPrinterWriter<P>
+where P: ExternalPrinter + Send {
+    fn write(&mut self, mut buf: &[u8]) -> io::Result<usize> {
+        let mut string = String::with_capacity(buf.len());
+        buf.read_to_string(&mut string).inspect(|_| {
+            self.0.print(string); //.strip_suffix('\n').map(|s| s.to_string()).unwrap_or(string));
+        })
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}
+
+
 impl<H: Helper, I: History> config::Configurer for Editor<H, I> {
     fn config_mut(&mut self) -> &mut Config {
         &mut self.config