Add string stream and binary stream, add text decoding (#570)

* WIP

* Add binary/string streams and text decoding

* Make string collection fallible

* Oops, forgot pretty hex

* Oops, forgot pretty hex

* clippy

crates/nu-protocol/src/value/stream.rs

@@ -7,6 +7,94 @@ use std::{
     },
 };
 
+/// A single buffer of binary data streamed over multiple parts. Optionally contains ctrl-c that can be used
+/// to break the stream.
+pub struct ByteStream {
+    pub stream: Box<dyn Iterator<Item = Vec<u8>> + Send + 'static>,
+    pub ctrlc: Option<Arc<AtomicBool>>,
+}
+impl ByteStream {
+    pub fn into_vec(self) -> Vec<u8> {
+        self.flatten().collect::<Vec<u8>>()
+    }
+}
+impl Debug for ByteStream {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("ByteStream").finish()
+    }
+}
+
+impl Iterator for ByteStream {
+    type Item = Vec<u8>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(ctrlc) = &self.ctrlc {
+            if ctrlc.load(Ordering::SeqCst) {
+                None
+            } else {
+                self.stream.next()
+            }
+        } else {
+            self.stream.next()
+        }
+    }
+}
+
+/// A single string streamed over multiple parts. Optionally contains ctrl-c that can be used
+/// to break the stream.
+pub struct StringStream {
+    pub stream: Box<dyn Iterator<Item = Result<String, ShellError>> + Send + 'static>,
+    pub ctrlc: Option<Arc<AtomicBool>>,
+}
+impl StringStream {
+    pub fn into_string(self, separator: &str) -> Result<String, ShellError> {
+        let mut output = String::new();
+
+        let mut first = true;
+        for s in self.stream {
+            output.push_str(&s?);
+
+            if !first {
+                output.push_str(separator);
+            } else {
+                first = false;
+            }
+        }
+        Ok(output)
+    }
+
+    pub fn from_stream(
+        input: impl Iterator<Item = Result<String, ShellError>> + Send + 'static,
+        ctrlc: Option<Arc<AtomicBool>>,
+    ) -> StringStream {
+        StringStream {
+            stream: Box::new(input),
+            ctrlc,
+        }
+    }
+}
+impl Debug for StringStream {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("StringStream").finish()
+    }
+}
+
+impl Iterator for StringStream {
+    type Item = Result<String, ShellError>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(ctrlc) = &self.ctrlc {
+            if ctrlc.load(Ordering::SeqCst) {
+                None
+            } else {
+                self.stream.next()
+            }
+        } else {
+            self.stream.next()
+        }
+    }
+}
+
 /// A potentially infinite stream of values, optinally with a mean to send a Ctrl-C signal to stop
 /// the stream from continuing.
 ///