buffer.js for precise control over packet reading

packages/driver-streams-node/src/buffer.js

@@ -0,0 +1,68 @@
+//---------------------------------------------------------------------------
+// @syndicate-lang/driver-streams-node, Stream support for Syndicate/js
+// Copyright (C) 2016-2018 Tony Garnock-Jones <tonyg@leastfixedpoint.com>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//---------------------------------------------------------------------------
+
+import { currentFacet, Observe, genUuid, Bytes, List } from "@syndicate-lang/core";
+const S = activate require("./streams");
+
+message type PacketRequest(id, size);
+
+export {
+  PacketRequest,
+};
+
+export function spawnBufferStream() {
+  const id = genUuid('buffer-stream');
+  spawn named id {
+    stop on retracted Observe(S.Duplex(id));
+    assert S.Duplex(id);
+    assert S.StreamInfo(id, 'Duplex', null);
+
+    field this.buffer = Bytes();
+    field this.queue = List();
+
+    on message S.Push(id, $chunk, $ack) {
+      this.buffer = Bytes.concat([this.buffer, chunk]);
+      if (ack !== null) send ack;
+    }
+
+    stop on message S.Close(id, $ack) {
+      if (ack !== null) send ack;
+    }
+
+    on message PacketRequest(id, $size) {
+      if (size === 0) {
+        // Signal to terminate.
+        currentFacet().stop(() => { send S.Data(id, this.buffer); });
+      } else {
+        this.queue = this.queue.push(size);
+      }
+    }
+
+    dataflow {
+      if (!this.queue.isEmpty()) {
+        const expected = this.queue.first();
+        if (this.buffer.size >= expected) {
+          send S.Data(id, this.buffer.slice(0, expected));
+          this.buffer = this.buffer.slice(expected);
+          this.queue = this.queue.shift();
+        }
+      }
+    }
+  }
+  return id;
+}

packages/driver-streams-node/src/index.js

@@ -20,3 +20,4 @@
 Object.assign(module.exports, activate require('./streams.js'));
 Object.assign(module.exports, activate require('./net.js'));
 Object.assign(module.exports, activate require('./subprocess.js'));
+Object.assign(module.exports, activate require('./buffer.js'));