view vamp-client/ProcessQtTransport.h @ 116:d15cb1151d76

Add JSON support directly to the server. Had hoped to avoid this (using Capnp as canonical in the server and then converting externally as necessary) but it's just too useful for debugging purposes when bundled with client app

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */
 
#ifndef PIPER_PROCESS_QT_TRANSPORT_H
#define PIPER_PROCESS_QT_TRANSPORT_H

#include "SynchronousTransport.h"

#include <QProcess>
#include <QString>
#include <QMutex>

#include <iostream>

namespace piper_vamp {
namespace client {

/**
 * A SynchronousTransport implementation that spawns a sub-process
 * using Qt's QProcess abstraction and talks to it via stdin/stdout
 * channels. Calls are completely serialized; the protocol only
 * supports one call in process at a time, and therefore the transport
 * only allows one at a time. This class is thread-safe because it
 * serializes explicitly using a mutex.
 */
class ProcessQtTransport : public SynchronousTransport
{
public:
    ProcessQtTransport(std::string processName) :
        m_completenessChecker(0) {
        m_process = new QProcess();
        m_process->setReadChannel(QProcess::StandardOutput);
        m_process->setProcessChannelMode(QProcess::ForwardedErrorChannel);
        QString name(QString::fromStdString(processName));

        // The second argument here is vital, otherwise we get a
        // different start() overload which parses all command args
        // out of its first argument only and therefore fails when
        // name has a space in it. This is such a gotcha that Qt5.6
        // even introduced a QT_NO_PROCESS_COMBINED_ARGUMENT_START
        // build flag to disable that overload. Unfortunately I only
        // discovered that after wasting almost a day on it.
        m_process->start(name, QStringList());
        
        if (!m_process->waitForStarted()) {
            if (m_process->state() == QProcess::NotRunning) {
                QProcess::ProcessError err = m_process->error();
                if (err == QProcess::FailedToStart) {
                    std::cerr << "Unable to start server process "
                              << processName << std::endl;
                } else if (err == QProcess::Crashed) {
                    std::cerr << "Server process " << processName
                              << " crashed on startup" << std::endl;
                } else {
                    std::cerr << "Server process " << processName
                              << " failed on startup with error code "
                              << err << std::endl;
                }
                delete m_process;
                m_process = nullptr;
            }
        }
    }

    ~ProcessQtTransport() {
        if (m_process) {
            if (m_process->state() != QProcess::NotRunning) {
		m_process->closeWriteChannel();
                m_process->waitForFinished(200);
                m_process->close();
                m_process->waitForFinished();
                std::cerr << "server exited" << std::endl;
            }
            delete m_process;
        }
    }

    void
    setCompletenessChecker(MessageCompletenessChecker *checker) override {
        //!!! ownership?
        m_completenessChecker = checker;
    }
    
    bool
    isOK() const override {
        return m_process != nullptr;
    }
    
    std::vector<char>
    call(const char *ptr, size_t size) override {

	QMutexLocker locker(&m_mutex);
	
        if (!m_completenessChecker) {
            throw std::logic_error("No completeness checker set on transport");
        }
        
        std::cerr << "writing " << size << " bytes to server" << std::endl;
        m_process->write(ptr, size);
        
        std::vector<char> buffer;
        bool complete = false;
        
        while (!complete) {

            qint64 byteCount = m_process->bytesAvailable();

	    if (!byteCount) {
		std::cerr << "waiting for data from server..." << std::endl;
		m_process->waitForReadyRead(1000);
                if (m_process->state() == QProcess::NotRunning) {
                    QProcess::ProcessError err = m_process->error();
                    if (err == QProcess::Crashed) {
                        std::cerr << "Server crashed during request" << std::endl;
                    } else {
                        std::cerr << "Server failed during request with error code "
                                  << err << std::endl;
                    }
                    //!!! + catch
                    throw std::runtime_error("Piper server exited unexpectedly");
                }
            } else {
                size_t formerSize = buffer.size();
                buffer.resize(formerSize + byteCount);
                m_process->read(buffer.data() + formerSize, byteCount);
                complete = m_completenessChecker->isComplete(buffer);
            }
        }

        return buffer;
    }
    
private:
    MessageCompletenessChecker *m_completenessChecker; //!!! I don't own this (currently)
    QProcess *m_process; // I own this
    QMutex m_mutex;
};

}
}

#endif