Flush output after *out-limit* characters

Defaults to 1024, but can be rebound on any message with :out-limit.

src/main/clojure/clojure/tools/nrepl/middleware/session.clj

@@ -18,6 +18,8 @@
 ;; depending upon the expectations of the client/user.  I'm not sure at the moment
 ;; how best to make it configurable though...
 
+(def ^{:dynamic true} *out-limit* 1024)
+
 (defn- session-out
   "Returns a PrintWriter suitable for binding as *out* or *err*.  All of
    the content written to that PrintWriter will (when .flush-ed) be sent on the
@@ -33,7 +35,9 @@
                           (number? x) (.append buf (char x))
                           (not off) (.append buf x)
                           (instance? CharSequence x) (.append buf ^CharSequence x off len)
-                          :else (.append buf ^chars x off len))))
+                          :else (.append buf ^chars x off len))
+                        (when (<= *out-limit* (.length buf))
+                          (.flush ^Writer this))))
                     (flush []
                       (let [text (locking buf (let [text (str buf)]
                                                 (.setLength buf 0)
@@ -89,6 +93,7 @@
                   *err* (session-out :err id transport)
                   *in* in
                   *ns* (create-ns 'user)
+                  *out-limit* (or (baseline-bindings #'*out-limit*) 1024)
                   ; clojure.test captures *out* at load-time, so we need to make sure
                   ; runtime output of test status/results is redirected properly
                   ; TODO is this something we need to consider in general, or is this
@@ -139,13 +144,14 @@
    *msg* to the currently-evaluated message so that session-specific *out*
    and *err* content can be associated with the originating message)."
   [h]
-  (fn [{:keys [op session transport] :as msg}]
+  (fn [{:keys [op session transport out-limit] :as msg}]
     (let [the-session (if session
                         (@sessions session)
                         (create-session transport))]
       (if-not the-session
         (t/send transport (response-for msg :status #{:error :unknown-session}))
         (let [msg (assoc msg :session the-session)]
+          (when out-limit (swap! the-session assoc #'*out-limit* out-limit))
           (case op
             "clone" (register-session msg)
             "close" (close-session msg)

src/main/java/clojure/tools/nrepl/StdOutBuffer.java

@@ -3,9 +3,9 @@
 /**
  * This class exists solely so that the clojure side can call .setLength under JDK 1.5.
  * Doing so with a StringBuilder/StringBuffer fails with:
- * 
+ *
  * Can't call public method of non-public class: public void java.lang.AbstractStringBuilder.setLength(int)
- * 
+ *
  * ...as documented in these outstanding bugs:
  * http://dev.clojure.org/jira/browse/CLJ-126
  * http://dev.clojure.org/jira/browse/CLJ-259
@@ -16,7 +16,11 @@ public class StdOutBuffer {
     public void setLength (int x) {
         sb.setLength(x);
     }
-
+
+    public int length () {
+        return sb.length();
+    }
+
     public void append(Object x) {
         sb.append(x);
     }

src/test/clojure/clojure/tools/nrepl_test.clj

@@ -94,6 +94,21 @@
           (map :out)
           (remove nil?)))))
 
+(def-repl-test streaming-out-without-explicit-flushing
+  (is (= ["(0 1 "
+          "2 3 4"
+          " 5 6 "
+          "7 8 9"
+          " 10)"]
+         ; new session
+         (->> (message client {:op :eval :out-limit 5 :code "(print (range 11))"})
+              (map :out)
+              (remove nil?))
+         ; existing session
+         (->> (message session {:op :eval :out-limit 5 :code "(print (range 11))"})
+              (map :out)
+              (remove nil?)))))
+
 (def-repl-test ensure-whitespace-prints
   (is (= " \t \n \f \n" (->> (repl-eval client "(println \" \t \n \f \")")
                           combine-responses