Consolidate ledger serialization code

The new read_entries() works, but is overly-contrained. Not
using that function yet, but adding it here in the hopes some
Rust guru will tell us how to get that lifetime constraint out
of there.

Fixes #517

src/bank.rs

@@ -519,10 +519,9 @@ mod tests {
     use super::*;
     use bincode::serialize;
     use entry::next_entry;
-    use entry_writer::EntryWriter;
+    use entry_writer::{self, EntryWriter};
     use hash::hash;
     use ledger::next_entries;
-    use serde_json;
     use signature::KeyPairUtil;
     use std::io::{BufRead, BufReader, Seek, SeekFrom};
 
@@ -800,12 +799,12 @@ mod tests {
 
         let mut file = tempfile().unwrap();
         EntryWriter::write_entries(&mut file, &entries).unwrap();
-
         file.seek(SeekFrom::Start(0)).unwrap();
+
         let reader = BufReader::new(file);
         reader
             .lines()
-            .map(|line| serde_json::from_str(&line.unwrap()).unwrap())
+            .map(|line| entry_writer::read_entry(line.unwrap()).unwrap())
     }
 
     #[test]

src/bin/fullnode.rs

@@ -9,7 +9,7 @@ use atty::{is, Stream};
 use getopts::Options;
 use solana::bank::Bank;
 use solana::crdt::ReplicatedData;
-use solana::entry::Entry;
+use solana::entry_writer;
 use solana::server::Server;
 use std::env;
 use std::fs::File;
@@ -68,11 +68,10 @@ fn main() {
     eprintln!("Initializing...");
     let stdin = stdin();
     let entries = stdin.lock().lines().map(|line| {
-        let entry: Entry = serde_json::from_str(&line.unwrap()).unwrap_or_else(|e| {
+        entry_writer::read_entry(line.unwrap()).unwrap_or_else(|e| {
             eprintln!("failed to parse json: {}", e);
             exit(1);
-        });
-        entry
+        })
     });
     eprintln!("done parsing...");
 

src/entry_writer.rs

@@ -5,7 +5,7 @@
 use bank::Bank;
 use entry::Entry;
 use serde_json;
-use std::io::{self, Write};
+use std::io::{self, BufRead, Error, ErrorKind, Write};
 
 pub struct EntryWriter<'a, W> {
     bank: &'a Bank,
@@ -46,6 +46,17 @@ impl<'a, W: Write> EntryWriter<'a, W> {
     }
 }
 
+pub fn read_entry(s: String) -> io::Result<Entry> {
+    serde_json::from_str(&s).map_err(|e| Error::new(ErrorKind::Other, e.to_string()))
+}
+
+// TODO: How to implement this without attaching the input's lifetime to the output?
+pub fn read_entries<'a, R: BufRead>(
+    reader: &'a mut R,
+) -> impl Iterator<Item = io::Result<Entry>> + 'a {
+    reader.lines().map(|s| read_entry(s?))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;