Adding test case for #687.

The test no longer repros after a lot of my recent channel work.

Closes #687.

src/test/run-pass/issue-687.rs

@@ -0,0 +1,62 @@
+// xfail-stage0
+
+use std;
+import std::ivec;
+
+tag msg {
+    closed;
+    received(u8[]);
+}
+
+fn producer(chan[u8[]] c) {
+    c <| ~[1u8, 2u8, 3u8, 4u8];
+    let u8[] empty = ~[];
+    c <| empty;
+}
+
+fn packager(chan[chan[u8[]]] cb, chan[msg] msg) {
+    let port[u8[]] p = port();
+    cb <| chan(p);
+    while (true) {
+        log "waiting for bytes";
+        let u8[] data;
+        p |> data;
+        log "got bytes";
+        if (ivec::len[u8](data) == 0u) {
+            log "got empty bytes, quitting";
+            break;
+        }
+        log "sending non-empty buffer of length";
+        log ivec::len[u8](data);
+        msg <| received(data);
+        log "sent non-empty buffer";
+    }
+    log "sending closed message";
+    msg <| closed;
+    log "sent closed message";
+}
+
+fn main() {
+    let port[msg] p = port();
+    let port[chan[u8[]]] recv_reader = port();
+    auto pack = spawn packager(chan(recv_reader), chan(p));
+
+    let chan[u8[]] source_chan;
+    recv_reader |> source_chan;
+    let task prod = spawn producer(source_chan);
+
+    while (true) {
+        let msg msg;
+        p |> msg;
+        alt (msg) {
+            case (closed) {
+                log "Got close message";
+                break;
+            }
+            case (received(?data)) {
+                log "Got data. Length is:";
+                log ivec::len[u8](data);
+            }
+        }
+    }
+}