Stream isolates.

sdk/lib/isolate/mangler.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+class _IsolateEncoder {
+  final manglingToken;
+  final Map _encoded = new Map();
+  final Map _visiting = new Map();
+  final Function _mangle;
+  static const int _REFERENCE = 0;
+  static const int _DECLARATION = 1;
+  static const int _ESCAPED = 2;
+  static const int _MANGLED = 3;
+
+  _IsolateEncoder(this.manglingToken, mangle(data))
+      : this._mangle = mangle;
+
+  encode(var data) {
+    if (data is num || data is String || data is bool || data == null) {
+      return data;
+    }
+
+    if (_encoded.containsKey(data)) return _encoded[data];

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

This uses equality, not identiity. We should use an IdentityMap for this (when
we have one).

[floitsch, 2012/11/22 20:06:12]

Added TODO.

+    if (_visiting.containsKey(data)) {
+      // Self reference.
+      var selfReference = _visiting[data];
+      if (selfReference == data) {
+        // Nobody used the self-reference yet.
+        selfReference = _createReference();
+        _visiting[data] = selfReference;
+      }
+      return selfReference;
+    }
+
+    var result;
+
+    if (data is List) {
+      bool hasBeenDuplicated = false;
+      result = data;
+      for (int i = 0; i < data.length; i++) {
+        var mangled = encode(data[i]);
+        if (mangled != data[i] && !hasBeenDuplicated) {
+          result = new List(data.length);
+          for (int j = 0; j < i; j++) {
+            result[j] = data[j];
+          }

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

hasBeenDuplicated = true; ?

[floitsch, 2012/11/22 20:06:12]

Done.

+        }
+        if (hasBeenDuplicated) {
+          result[i] = mangled;
+        }
+      }
+      result = _escapeIfNecessary(result);
+    } else if (data is Set) {
+      bool needsCopy = false;
+      data.forEach((entry) {
+        var encoded = encode(entry);
+        if (encoded != entry) needsCopy = true;

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

and break. No need to test more after the first modifying encoding was hit.
If you want to avoid duplicate encoding, you can even store entry and encoded,
and don't bother trying to encode until after you've seen entry in the next
iteration.

[floitsch, 2012/11/22 20:06:12]

Duplicate encoding is not a problem since they are cached anyways. (in the
_encoded map).
done for the break.

+      });
+      result = data;
+      if (needsCopy) {
+        result = new Set();
+        data.forEach((entry) {
+          result.add(encode(entry));
+        });
+      }
+    } else if (data is Map) {
+      bool needsCopy = false;
+      data.forEach((key, value) {
+        var encodedKey = encode(key);
+        var encodedValue = encode(value);
+        if (encodedKey != key) needsCopy = true;
+        if (encodedValue != value) needsCopy = true;

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

And break after the first encoding is found.

[floitsch, 2012/11/22 20:06:12]

cannot. This is a map.forEach.

[Lasse Reichstein Nielsen, 2012/11/23 12:12:38]

True. You would need to iterate the keys instead.

+      });
+      result = data;
+      if (needsCopy) {
+        result = new Map();
+        data.forEach((key, value) {
+          result[encode(key)] = encode(value);
+        });
+      }
+    } else {
+      // We don't handle self-references for user data.
+      _visiting.remove(data);

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

Consider keeping it and throwing if you see the same data again. Unless the
mangling can give different results for the same data, you're in an infinite
recursion.

[floitsch, 2012/11/22 20:06:12]

Added TODO.

+      result = _mangle(data);
+      if (result != data) {
+        result = _wrapMangled(encode(result));
+      }
+    }
+
+    var selfReference = _visiting[data];
+    if (selfReference != null && selfReference != data) {
+      // A self-reference has been used.
+      result = encode(_declareReference(selfReference, data));
+    }
+    _encoded[data] = result;
+
+    _visiting.remove(data);
+    return result;
+  }
+
+  _createReference() => [manglingToken, _REFERENCE];

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

What is it a reference to? I.e., how can you tell two references apart, if you
have multiple self-referencing objects?
Try sending:
 var x = [1,2,[4,5],3];
 x[2].add(x);
 x[2].add(x[2]);
and see what you get when mangling/unmangling.

[floitsch, 2012/11/22 20:06:12]

Done.

+  _declareReference(reference, data) {
+    return [manglingToken, _DECLARATION, reference, data];
+  }
+
+  _wrapMangled(data) => [manglingToken, _MANGLED, data];
+  _escapeIfNecessary(List list) {
+    if (!list.isEmpty && list[0] == manglingToken) {
+      return [manglingToken, _ESCAPED, list];

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

Then the list contents are not encoded. You should encode the remaining list
elements into this list, effectively only replacing the first element with two
elements (and reverse when decoding ofcourse).

[floitsch, 2012/11/22 20:06:12]

_escapeIfNecessary is only called on a encoded list.

[Lasse Reichstein Nielsen, 2012/11/23 12:12:38]

Ah, true.

+    } else {
+      return list;
+    }
+  }
+}
+
+class _IsolateDecoder {
+  final manglingToken;
+  final Map _decoded = new Map();
+  final Function _unmangle;
+  static const int _REFERENCE = IsolateEncoder._REFERENCE;
+  static const int _DECLARATION = IsolateEncoder._DECLARATION;
+  static const int _ESCAPED = IsolateEncoder._ESCAPED;
+  static const int _MANGLED = IsolateEncoder._MANGLED;
+
+  _IsolateDecoder(this.manglingToken, unmangle(data))
+      : this._unmangle = unmangle;
+
+  decode(var data) {
+    if (data is num || data is String || data is bool || data == null) {
+      return data;
+    }
+
+    if (_decoded.containsKey(data)) return _decoded[data];

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

if 'data' comes from a JSON.parse, it's not equal to something with the same
structure. When will this match?

[floitsch, 2012/11/22 20:06:12]

data comes from the isolate-communication. These guarantee that DAGs stay DAGs.
In other words: we can get the same list (or any other instance) multiple times.

+
+    if (_isDeclaration(data)) {
+      var reference = _extractReference(data);
+      var declared = _extractDeclared(data);
+      return _decodeObject(declared, reference);

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

So the reference is just a list: [magic#, REFERENCE].
It's equality is identity equality. How will that be used?

[floitsch, 2012/11/22 20:06:12]

This works because of the guarantees of the send/receive port communication.

+    } else {
+      return _decodeObject(data, null);
+    }
+  }
+
+  _decodeObject(data, reference) {
+    if (_decoded.containsKey(data)) {

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

I don't think this lookup will ever succeed if the data has been JSON
stringified and then parsed.

[floitsch, 2012/11/22 20:06:12]

which it hasn't.

+      assert(reference == null);
+      return _decoded[data];
+    }
+
+    // If the data was a reference then we would have found it in the _decoded
+    // map.

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

I find that unlikely.

[floitsch, 2012/11/22 20:06:12]

see above.

+    assert(!_isReference(data));
+
+    var result;
+    if (_isMangled(data)) {
+      assert(reference == null);
+      List mangled = _extractMangled(data);
+      var decoded = decode(mangled);
+      result = _unmangle(decoded);
+    } else if (data is List) {
+      if (_isEscaped(data)) data = _extractEscaped(data);

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

Here you decode the escaped data, even if it wasn't encoded.
Except that you don't get here because _isMangled returns true on escapes?

[floitsch, 2012/11/22 20:06:12]

data cannot be mangled and escaped at the same time.

[Lasse Reichstein Nielsen, 2012/11/23 12:12:38]

Ack, isMangled is not the same as isMarked.

+      assert(!_isMarked(data));
+      result = data;
+      bool hasBeenDuplicated = false;
+      List duplicate() {
+        assert(!hasBeenDuplicated);
+        result = new List();
+        result.length = data.length;
+        if (reference != null) _decoded[reference] = result;
+        hasBeenDuplicated = true;
+      }
+
+      if (reference != null) duplicate();
+      for (int i = 0; i < data.length; i++) {
+        var decoded = decode(data[i]);
+        if (decoded != data[i] && !hasBeenDuplicated) {
+          duplicate();
+          for (int j = 0; j < i; j++) {
+            result[j] = data[j];
+          }
+        }
+        if (hasBeenDuplicated) {
+          result[i] = decoded;
+        }
+      }
+    } else if (data is Set) {
+      bool needsCopy = reference != null;
+      if (!needsCopy) {
+        data.forEach((entry) {
+          var decoded = decode(entry);
+          if (decoded != entry) needsCopy = true;

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

and break.

[floitsch, 2012/11/22 20:06:12]

Done.

+        });
+      }
+      result = data;
+      if (needsCopy) {
+        result = new Set();
+        if (reference != null) _decoded[reference] = result;
+        data.forEach((entry) {
+          result.add(decode(entry));
+        });
+      }
+    } else if (data is Map) {
+      bool needsCopy = reference != null;
+      if (!needsCopy) {
+        data.forEach((key, value) {
+          var decodedKey = decode(key);
+          var decodedValue = decode(value);
+          if (decodedKey != key) needsCopy = true;
+          if (decodedValue != value) needsCopy = true;
+        });
+      }
+      result = data;
+      if (needsCopy) {
+        result = new Map();
+        if (reference != null) _decoded[reference] = result;
+        data.forEach((key, value) {
+          result[decode(key)] = decode(value);
+        });
+      }
+    } else {
+      result = data;
+    }
+    _decoded[data] = result;
+    return result;
+  }
+
+  _isMarked(data)
+      => data is List && !data.isEmpty && data[0] == manglingToken;

[Lasse Reichstein Nielsen, 2012/11/22 10:23:15]

'!data.isEmpty' -> 'data.length >= 2' or you can't safely test data[1] in the
following tests. 
Or is that an assert? If a list contains manglingToken as first, it's never a
single-element list, because then it would be escaped anyway?

[floitsch, 2012/11/22 20:06:12]

added assert.

+  _isReference(data) => _isMarked(data) && data[1] == _REFERENCE;
+  _isDeclaration(data) => _isMarked(data) && data[1] == _DECLARATION;
+  _isMangled(data) => _isMarked(data) && data[1] == _MANGLED;
+  _isEscaped(data) => _isMarked(data) && data[1] == _ESCAPED;
+
+  _extractReference(declaration) {
+    assert(_isDeclaration(declaration));
+    return declaration[2];
+  }
+  _extractDeclared(declaration) {
+    assert(_isDeclaration(declaration));
+    return declaration[3];
+  }
+  _extractMangled(wrappedMangled) {
+    assert(_isMangled(wrappedMangled));
+    return wrappedMangled[2];
+  }
+  _extractEscaped(data) {
+    assert(_isEscaped(data));
+    return data[2];
+  }
+}