Stream entries (#2582)

* Add entry streaming option

* Fix tests

* Remove obsolete comment

* Move entry stream functionality to struct w/ trait in order to test without i/o

src/entry_stream.rs

@@ -0,0 +1,57 @@
+//! The `entry_stream` module provides a method for streaming entries out via a
+//! local unix socket, to provide client services such as a block explorer with
+//! real-time access to entries.
+
+use crate::entry::Entry;
+use crate::result::Result;
+use std::io::prelude::*;
+use std::net::Shutdown;
+use std::os::unix::net::UnixStream;
+use std::path::Path;
+
+pub trait EntryStreamHandler {
+    fn stream_entries(&mut self, entries: &[Entry]) -> Result<()>;
+}
+
+pub struct EntryStream {
+    pub socket: String,
+}
+
+impl EntryStream {
+    pub fn new(socket: String) -> Self {
+        EntryStream { socket }
+    }
+}
+
+impl EntryStreamHandler for EntryStream {
+    fn stream_entries(&mut self, entries: &[Entry]) -> Result<()> {
+        let mut socket = UnixStream::connect(Path::new(&self.socket))?;
+        for entry in entries {
+            let result = serde_json::to_string(&entry)?;
+            socket.write_all(result.as_bytes())?;
+        }
+        socket.shutdown(Shutdown::Write)?;
+        Ok(())
+    }
+}
+
+pub struct MockEntryStream {
+    pub socket: Vec<String>,
+}
+
+impl MockEntryStream {
+    #[allow(clippy::needless_pass_by_value)]
+    pub fn new(_socket: String) -> Self {
+        MockEntryStream { socket: Vec::new() }
+    }
+}
+
+impl EntryStreamHandler for MockEntryStream {
+    fn stream_entries(&mut self, entries: &[Entry]) -> Result<()> {
+        for entry in entries {
+            let result = serde_json::to_string(&entry)?;
+            self.socket.push(result);
+        }
+        Ok(())
+    }
+}