/* -*- Mode: protobuf; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

// # Core Dumps
//
// A core dump is a serialized snapshot of the heap graph. We serialize the heap
// as a series of protobuf messages with each message prefixed by its Varint32
// byte size so we can delimit individual protobuf messages (protobuf parsers
// cannot determine where a message ends on their own).
//
// The first protobuf message is an instance of the `Metadata` message. All
// subsequent messages will be instances of the `Node` message. The first of
// these `Node` messages is the root node of the serialized heap graph. Here is
// a diagram of our core dump format:
//
//     +-----------------------------------------------------------------------+
//     | Varint32: The size of following `Metadata` message.                   |
//     +-----------------------------------------------------------------------+
//     | message: The core dump `Metadata` message.                            |
//     +-----------------------------------------------------------------------+
//     | Varint32: The size of the following `Node` message.                   |
//     +-----------------------------------------------------------------------+
//     | message: The first `Node` message. This is the root node.             |
//     +-----------------------------------------------------------------------+
//     | Varint32: The size of the following `Node` message.                   |
//     +-----------------------------------------------------------------------+
//     | message: A `Node` message.                                            |
//     +-----------------------------------------------------------------------+
//     | Varint32: The size of the following `Node` message.                   |
//     +-----------------------------------------------------------------------+
//     | message: A `Node` message.                                            |
//     +-----------------------------------------------------------------------+
//     | .                                                                     |
//     | .                                                                     |
//     | .                                                                     |
//     +-----------------------------------------------------------------------+
//
// Core dumps should always be written with a
// `google::protobuf::io::GzipOutputStream` and read from a
// `google::protobuf::io::GzipInputStream`.
//
// Note that all strings are de-duplicated. The first time the N^th unique
// string is encountered, the full string is serialized. Subsequent times that
// same string is encountered, it is referenced by N. This de-duplication
// happens across string properties, not on a per-property basis. For example,
// if the same K^th unique string is first used as an Edge::EdgeNameOrRef and
// then as a StackFrame::Data::FunctionDisplayNameOrRef, the first will be the
// actual string as the functionDisplayName oneof property, and the second will
// be a reference to the first as the edgeNameRef oneof property whose value is
// K.
//
// We would ordinarily abstract these de-duplicated strings with messages of
// their own, but unfortunately, the protobuf compiler does not have a way to
// inline a messsage within another message and the child message must be
// referenced by pointer. This leads to extra mallocs that we wish to avoid.


package mozilla.devtools.protobuf;

// A collection of metadata about this core dump.
message Metadata {
    // Number of microseconds since midnight (00:00:00) 1 January 1970 UTC.
    optional uint64 timeStamp = 1;
}

// A serialized version of `JS::ubi::StackFrame`. Older parent frame tails are
// de-duplicated to cut down on [de]serialization and size costs.
message StackFrame {
    oneof StackFrameType {
        // This is the first time this stack frame has been serialized, and so
        // here is all of its data.
        Data   data = 1;
        // A reference to a stack frame that has already been serialized and has
        // the given number as its id.
        uint64 ref  = 2;
    }

    message Data {
        optional uint64        id           = 1;
        optional StackFrame    parent       = 2;
        optional uint32        line         = 3;
        optional uint32        column       = 4;

        // De-duplicated two-byte string.
        oneof SourceOrRef {
            bytes  source                   = 5;
            uint64 sourceRef                = 6;
        }

        // De-duplicated two-byte string.
        oneof FunctionDisplayNameOrRef {
            bytes  functionDisplayName      = 7;
            uint64 functionDisplayNameRef   = 8;
        }

        optional bool          isSystem     = 9;
        optional bool          isSelfHosted = 10;
    }
}

// A serialized version of `JS::ubi::Node` and its outgoing edges.
message Node {
    optional uint64     id                   = 1;

    // De-duplicated two-byte string.
    oneof TypeNameOrRef {
        bytes           typeName             = 2;
        uint64          typeNameRef          = 3;
    }

    optional uint64     size                 = 4;
    repeated Edge       edges                = 5;
    optional StackFrame allocationStack      = 6;

    // De-duplicated one-byte string.
    oneof JSObjectClassNameOrRef {
        bytes           jsObjectClassName    = 7;
        uint64          jsObjectClassNameRef = 8;
    }

    // JS::ubi::CoarseType. Defaults to Other.
    optional uint32     coarseType           = 9 [default = 0];

    // De-duplicated one-byte string.
    oneof ScriptFilenameOrRef {
        bytes           scriptFilename       = 10;
        uint64          scriptFilenameRef    = 11;
    }
}

// A serialized edge from the heap graph.
message Edge {
    optional uint64 referent    = 1;

    // De-duplicated two-byte string.
    oneof EdgeNameOrRef {
        bytes       name    = 2;
        uint64      nameRef = 3;
    }
}
