Introduce a basic client for the language server protocol

The language server protocol is used to transport language specific
information needed to efficiently edit source files. For example
completion, go to operations and symbol information. These information
are transferred via JSON-RPC. The complete definition can be found under
https://microsoft.github.io/language-server-protocol/specification.

This language server protocol support consists of two major parts, the
C++ representation of the language server protocol, and the client part
for the communication with an external language server.

The TypeScript definitions of the protocol interfaces are transferred to
C++ classes. Those classes have getter and setter for every interface
value. Optional values from the protocol are represented by
Utils::optional<ValueType>. The JSON objects that are used to transfer
the data between client and server are hidden by a specialized
JsonObject class derived from QJsonObject. Additionally this JsonObject
provides a validity check that is capable of creating a detailed error
message for malformed, or at least unexpected JSON representation of the
protocol.

The client is the interface between Qt Creator and language server
functionality, like completion, diagnostics, document and workspace
synchronization. The base client converts the data that is sent from/to
the server between the raw byte array and the corresponding C++ objects.
The transportat layer is defined in a specialized base client (this
initial change will only support stdio language server). The running
clients are handled inside the language client manager, which is also
used to connect global and exclusive Qt Creator functionality to the
clients.

Task-number: QTCREATORBUG-20284
Change-Id: I8e123e20c3f14ff7055c505319696d5096fe1704
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

1 files changed, 211 insertions, 0 deletions

diff --git a/src/libs/languageserverprotocol/basemessage.cpp b/src/libs/languageserverprotocol/basemessage.cpp
new file mode 100644
index 0000000000..7c92e8732e
--- /dev/null
+++ b/src/libs/languageserverprotocol/basemessage.cpp
@@ -0,0 +1,211 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#include "basemessage.h"
+
+#include "jsonrpcmessages.h"
+
+#include <utils/mimetypes/mimedatabase.h>
+
+#include <QBuffer>
+#include <QTextCodec>
+
+#include <cstring>
+#include <utility>
+
+namespace LanguageServerProtocol {
+
+BaseMessage::BaseMessage()
+    : mimeType(JsonRpcMessageHandler::jsonRpcMimeType())
+{ }
+
+BaseMessage::BaseMessage(const QByteArray &mimeType, const QByteArray &content,
+                         int expectedLength, QTextCodec *codec)
+    : mimeType(mimeType.isEmpty() ? JsonRpcMessageHandler::jsonRpcMimeType() : mimeType)
+    , content(content)
+    , contentLength(expectedLength)
+    , codec(codec)
+{ }
+
+BaseMessage::BaseMessage(const QByteArray &mimeType, const QByteArray &content)
+    : BaseMessage(mimeType, content, content.length(), defaultCodec())
+{ }
+
+bool BaseMessage::operator==(const BaseMessage &other) const
+{
+    if (mimeType != other.mimeType || content != other.content)
+        return false;
+    if (codec) {
+        if (other.codec)
+            return codec->mibEnum() == other.codec->mibEnum();
+        return codec->mibEnum() == defaultCodec()->mibEnum();
+    }
+    if (other.codec)
+        return other.codec->mibEnum() == defaultCodec()->mibEnum();
+
+    return true;
+}
+
+static QPair<QByteArray, QByteArray> splitHeaderFieldLine(
+        const QByteArray &headerFieldLine, QString &parseError)
+{
+    static const int fieldSeparatorLength = std::strlen(headerFieldSeparator);
+    int assignmentIndex = headerFieldLine.indexOf(headerFieldSeparator);
+    if (assignmentIndex >= 0) {
+        return {headerFieldLine.mid(0, assignmentIndex),
+                    headerFieldLine.mid(assignmentIndex + fieldSeparatorLength)};
+    }
+    parseError = BaseMessage::tr("Unexpected header line \"%1\"")
+            .arg(QLatin1String(headerFieldLine));
+    return {};
+}
+
+static void parseContentType(BaseMessage &message, QByteArray contentType, QString &parseError)
+{
+    if (contentType.startsWith('"') && contentType.endsWith('"'))
+        contentType = contentType.mid(1, contentType.length() - 2);
+    QList<QByteArray> contentTypeElements = contentType.split(';');
+    QByteArray mimeTypeName = contentTypeElements.takeFirst();
+    QTextCodec *codec = nullptr;
+    for (const QByteArray &_contentTypeElement : contentTypeElements) {
+        const QByteArray &contentTypeElement = _contentTypeElement.trimmed();
+        if (contentTypeElement.startsWith(contentCharsetName)) {
+            const int equalindex = contentTypeElement.indexOf('=');
+            const QByteArray charset = contentTypeElement.mid(equalindex + 1);
+            if (equalindex > 0)
+                codec = QTextCodec::codecForName(charset);
+            if (!codec) {
+                parseError = BaseMessage::tr("Cannot decode content with \"%1\" "
+                                "falling back to \"%2\"")
+                        .arg(QLatin1String(charset),
+                             QLatin1String(defaultCharset));
+            }
+        }
+    }
+    message.mimeType = mimeTypeName;
+    message.codec = codec ? codec : BaseMessage::defaultCodec();
+}
+
+static void parseContentLength(BaseMessage &message, QByteArray contentLength, QString &parseError)
+{
+    bool ok = true;
+    message.contentLength = QString::fromLatin1(contentLength).toInt(&ok);
+    if (!ok) {
+        parseError = BaseMessage::tr("Expected an integer in \"%1\", but got \"%2\"")
+                .arg(contentLengthFieldName, QLatin1String(contentLength));
+    }
+}
+
+void BaseMessage::parse(QBuffer *data, QString &parseError, BaseMessage &message)
+{
+    const qint64 startPos = data->pos();
+
+    if (message.isValid()) { // incomplete message from last parse
+        message.content.append(data->read(message.contentLength - message.content.length()));
+        return;
+    }
+
+    while (!data->atEnd()) {
+        const QByteArray &headerFieldLine = data->readLine();
+        if (headerFieldLine == headerSeparator) {
+            if (message.isValid())
+                message.content = data->read(message.contentLength);
+            return;
+        }
+        const QPair<QByteArray, QByteArray> nameAndValue =
+                splitHeaderFieldLine(headerFieldLine, parseError);
+        const QByteArray &headerFieldName = nameAndValue.first.trimmed();
+        const QByteArray &headerFieldValue = nameAndValue.second.trimmed();
+
+        if (headerFieldName.isEmpty())
+            continue;
+        if (headerFieldName == contentLengthFieldName) {
+            parseContentLength(message, headerFieldValue, parseError);
+        } else if (headerFieldName == contentTypeFieldName) {
+            parseContentType(message, headerFieldValue, parseError);
+        } else {
+            parseError = tr("Unexpected header field \"%1\" in \"%2\"")
+                    .arg(QLatin1String(headerFieldName),
+                         QLatin1String(headerFieldLine));
+        }
+    }
+
+    // the complete header wasn't received jet, waiting for the rest of it and reparse
+    data->seek(startPos);
+}
+
+QTextCodec *BaseMessage::defaultCodec()
+{
+    static QTextCodec *codec = QTextCodec::codecForName(defaultCharset);
+    return codec;
+}
+
+bool BaseMessage::isComplete() const
+{
+    if (!isValid())
+        return false;
+    QTC_ASSERT(content.length() <= contentLength, return true);
+    return content.length() == contentLength;
+}
+
+bool BaseMessage::isValid() const
+{
+    return contentLength >= 0;
+}
+
+QByteArray BaseMessage::toData()
+{
+    return header() + content;
+}
+
+QByteArray BaseMessage::header() const
+{
+    QByteArray header;
+    header.append(lengthHeader());
+    if (codec != defaultCodec()
+            || (!mimeType.isEmpty() && mimeType != JsonRpcMessageHandler::jsonRpcMimeType())) {
+        header.append(typeHeader());
+    }
+    header.append(headerSeparator);
+    return header;
+}
+
+QByteArray BaseMessage::lengthHeader() const
+{
+    return QByteArray(contentLengthFieldName)
+            + QByteArray(headerFieldSeparator)
+            + QString::number(content.size()).toLatin1()
+            + QByteArray(headerSeparator);
+}
+
+QByteArray BaseMessage::typeHeader() const
+{
+    return QByteArray(contentTypeFieldName)
+            + QByteArray(headerFieldSeparator)
+            + mimeType + "; " + contentCharsetName + "=" + codec->name()
+            + QByteArray(headerSeparator);
+}
+
+} // namespace LanguageServerProtocol