core/command: add log --follow

Author: outfoxxed

src/core/logging.cpp

@@ -1,10 +1,14 @@
 #include "logging.hpp"
 #include <array>
+#include <cerrno>
 #include <cstdio>
 
+#include <fcntl.h>
 #include <qbytearrayview.h>
+#include <qcoreapplication.h>
 #include <qdatetime.h>
 #include <qendian.h>
+#include <qfilesystemwatcher.h>
 #include <qhash.h>
 #include <qhashfunctions.h>
 #include <qlist.h>
@@ -356,6 +360,18 @@ void ThreadLogging::initFs() {
 		delete detailedFile;
 		detailedFile = nullptr;
 	} else {
+		auto lock = flock {
+		    .l_type = F_WRLCK,
+		    .l_whence = SEEK_SET,
+		    .l_start = 0,
+		    .l_len = 0,
+		};
+
+		if (fcntl(detailedFile->handle(), F_SETLK, &lock) != 0) { // NOLINT
+			qCWarning(logLogging) << "Unable to set lock marker on detailed log file. --follow from "
+			                         "other instances will not work.";
+		}
+
 		qCInfo(logLogging) << "Saving detailed logs to" << path;
 	}
 
@@ -737,22 +753,13 @@ bool EncodedLogReader::registerCategory() {
 	return true;
 }
 
-bool readEncodedLogs(QIODevice* device, bool timestamps, int tail, const QString& rulespec) {
-	QList<QLoggingRule> rules;
-
-	{
-		QLoggingSettingsParser parser;
-		parser.setContent(rulespec);
-		rules = parser.rules();
-	}
-
-	auto reader = EncodedLogReader();
-	reader.setDevice(device);
+bool LogReader::initialize() {
+	this->reader.setDevice(this->file);
 
 	bool readable = false;
 	quint8 logVersion = 0;
 	quint8 readerVersion = 0;
-	if (!reader.readHeader(&readable, &logVersion, &readerVersion)) {
+	if (!this->reader.readHeader(&readable, &logVersion, &readerVersion)) {
 		qCritical() << "Failed to read log header.";
 		return false;
 	}
@@ -765,49 +772,131 @@ bool readEncodedLogs(QIODevice* device, bool timestamps, int tail, const QString
 		return false;
 	}
 
-	auto color = LogManager::instance()->colorLogs;
-
-	auto filters = QHash<quint16, CategoryFilter>();
+	return true;
+}
 
-	auto tailRing = RingBuffer<LogMessage>(tail);
+bool LogReader::continueReading() {
+	auto color = LogManager::instance()->colorLogs;
+	auto tailRing = RingBuffer<LogMessage>(this->remainingTail);
 
 	LogMessage message;
 	auto stream = QTextStream(stdout);
-	while (reader.read(&message)) {
+	auto readCursor = this->file->pos();
+	while (this->reader.read(&message)) {
+		readCursor = this->file->pos();
+
 		CategoryFilter filter;
-		if (filters.contains(message.readCategoryId)) {
-			filter = filters.value(message.readCategoryId);
+		if (this->filters.contains(message.readCategoryId)) {
+			filter = this->filters.value(message.readCategoryId);
 		} else {
-			for (const auto& rule: rules) {
+			for (const auto& rule: this->rules) {
 				filter.applyRule(message.category, rule);
 			}
 
-			filters.insert(message.readCategoryId, filter);
+			this->filters.insert(message.readCategoryId, filter);
 		}
 
 		if (filter.shouldDisplay(message.type)) {
-			if (tail == 0) {
-				LogMessage::formatMessage(stream, message, color, timestamps);
+			if (this->remainingTail == 0) {
+				LogMessage::formatMessage(stream, message, color, this->timestamps);
 				stream << '\n';
 			} else {
 				tailRing.emplace(message);
 			}
 		}
 	}
 
-	if (tail != 0) {
+	if (this->remainingTail != 0) {
 		for (auto i = tailRing.size() - 1; i != -1; i--) {
 			auto& message = tailRing.at(i);
-			LogMessage::formatMessage(stream, message, color, timestamps);
+			LogMessage::formatMessage(stream, message, color, this->timestamps);
 			stream << '\n';
 		}
 	}
 
 	stream << Qt::flush;
 
-	if (!device->atEnd()) {
+	if (this->file->pos() != readCursor) {
 		qCritical() << "An error occurred parsing the end of this log file.";
-		qCritical() << "Remaining data:" << device->readAll();
+		qCritical() << "Remaining data:" << this->file->readAll();
+		return false;
+	}
+
+	return true;
+}
+
+void LogFollower::FcntlWaitThread::run() {
+	auto lock = flock {
+	    .l_type = F_RDLCK, // won't block other read locks when we take it
+	    .l_whence = SEEK_SET,
+	    .l_start = 0,
+	    .l_len = 0,
+	};
+
+	auto r = fcntl(this->follower->reader->file->handle(), F_SETLKW, &lock); // NOLINT
+
+	if (r != 0) {
+		qCWarning(logLogging).nospace()
+		    << "Failed to wait for write locks to be removed from log file with error code " << errno
+		    << ": " << qt_error_string();
+	}
+}
+
+bool LogFollower::follow() {
+	QObject::connect(&this->waitThread, &QThread::finished, this, &LogFollower::onFileLocked);
+
+	QObject::connect(
+	    &this->fileWatcher,
+	    &QFileSystemWatcher::fileChanged,
+	    this,
+	    &LogFollower::onFileChanged
+	);
+
+	this->fileWatcher.addPath(this->path);
+	this->waitThread.start();
+
+	auto r = QCoreApplication::exec();
+	return r == 0;
+}
+
+void LogFollower::onFileChanged() {
+	if (!this->reader->continueReading()) {
+		QCoreApplication::exit(1);
+	}
+}
+
+void LogFollower::onFileLocked() {
+	if (!this->reader->continueReading()) {
+		QCoreApplication::exit(1);
+	} else {
+		QCoreApplication::exit(0);
+	}
+}
+
+bool readEncodedLogs(
+    QFile* file,
+    const QString& path,
+    bool timestamps,
+    int tail,
+    bool follow,
+    const QString& rulespec
+) {
+	QList<QLoggingRule> rules;
+
+	{
+		QLoggingSettingsParser parser;
+		parser.setContent(rulespec);
+		rules = parser.rules();
+	}
+
+	auto reader = LogReader(file, timestamps, tail, rules);
+
+	if (!reader.initialize()) return false;
+	if (!reader.continueReading()) return false;
+
+	if (follow) {
+		auto follower = LogFollower(&reader, path);
+		return follower.follow();
 	}
 
 	return true;

src/core/logging.hpp

@@ -4,6 +4,7 @@
 
 #include <qcontainerfwd.h>
 #include <qdatetime.h>
+#include <qfile.h>
 #include <qhash.h>
 #include <qlatin1stringview.h>
 #include <qlogging.h>
@@ -130,7 +131,14 @@ class LogManager: public QObject {
 	LoggingThreadProxy threadProxy;
 };
 
-bool readEncodedLogs(QIODevice* device, bool timestamps, int tail, const QString& rulespec);
+bool readEncodedLogs(
+    QFile* file,
+    const QString& path,
+    bool timestamps,
+    int tail,
+    bool follow,
+    const QString& rulespec
+);
 
 } // namespace qs::log
 

src/core/logging_p.hpp

@@ -1,12 +1,18 @@
 #pragma once
+#include <utility>
+
 #include <qbytearrayview.h>
 #include <qcontainerfwd.h>
 #include <qfile.h>
+#include <qfilesystemwatcher.h>
 #include <qlogging.h>
+#include <qobject.h>
+#include <qthread.h>
 #include <qtmetamacros.h>
 #include <qtypes.h>
 
 #include "logging.hpp"
+#include "logging_qtprivate.hpp"
 #include "ringbuf.hpp"
 
 namespace qs::log {
@@ -120,4 +126,64 @@ private slots:
 	EncodedLogWriter detailedWriter;
 };
 
+class LogFollower;
+
+class LogReader {
+public:
+	explicit LogReader(
+	    QFile* file,
+	    bool timestamps,
+	    int tail,
+	    QList<qt_logging_registry::QLoggingRule> rules
+	)
+	    : file(file)
+	    , timestamps(timestamps)
+	    , remainingTail(tail)
+	    , rules(std::move(rules)) {}
+
+	bool initialize();
+	bool continueReading();
+
+private:
+	QFile* file;
+	EncodedLogReader reader;
+	bool timestamps;
+	int remainingTail;
+	QHash<quint16, CategoryFilter> filters;
+	QList<qt_logging_registry::QLoggingRule> rules;
+
+	friend class LogFollower;
+};
+
+class LogFollower: public QObject {
+	Q_OBJECT;
+
+public:
+	explicit LogFollower(LogReader* reader, QString path): reader(reader), path(std::move(path)) {}
+
+	bool follow();
+
+private slots:
+	void onFileChanged();
+	void onFileLocked();
+
+private:
+	LogReader* reader;
+	QString path;
+	QFileSystemWatcher fileWatcher;
+
+	class FcntlWaitThread: public QThread {
+	public:
+		explicit FcntlWaitThread(LogFollower* follower): follower(follower) {}
+
+	protected:
+		void run() override;
+
+	private:
+		LogFollower* follower;
+	};
+
+	FcntlWaitThread waitThread {this};
+};
+
 } // namespace qs::log

src/core/logging_qtprivate.cpp

@@ -16,34 +16,13 @@
 #include <qstringview.h>
 #include <qtypes.h>
 
+#include "logging_qtprivate.hpp"
+
 namespace qs::log {
 Q_DECLARE_LOGGING_CATEGORY(logLogging);
 
 namespace qt_logging_registry {
 
-class QLoggingRule {
-public:
-	QLoggingRule();
-	QLoggingRule(QStringView pattern, bool enabled);
-	[[nodiscard]] int pass(QLatin1StringView categoryName, QtMsgType type) const;
-
-	enum PatternFlag {
-		FullText = 0x1,
-		LeftFilter = 0x2,
-		RightFilter = 0x4,
-		MidFilter = LeftFilter | RightFilter
-	};
-	Q_DECLARE_FLAGS(PatternFlags, PatternFlag)
-
-	QString category;
-	int messageType;
-	PatternFlags flags;
-	bool enabled;
-
-private:
-	void parse(QStringView pattern);
-};
-
 class QLoggingSettingsParser {
 public:
 	void setContent(QStringView content);

src/core/logging_qtprivate.hpp

@@ -0,0 +1,44 @@
+#pragma once
+
+// The logging rule parser from qloggingregistry_p.h and qloggingregistry.cpp.
+
+// Was unable to properly link the functions when directly using the headers (which we depend
+// on anyway), so below is a slightly stripped down copy. Making the originals link would
+// be preferable.
+
+#include <qflags.h>
+#include <qlogging.h>
+#include <qloggingcategory.h>
+#include <qstringview.h>
+
+namespace qs::log {
+Q_DECLARE_LOGGING_CATEGORY(logLogging);
+
+namespace qt_logging_registry {
+
+class QLoggingRule {
+public:
+	QLoggingRule();
+	QLoggingRule(QStringView pattern, bool enabled);
+	[[nodiscard]] int pass(QLatin1StringView categoryName, QtMsgType type) const;
+
+	enum PatternFlag {
+		FullText = 0x1,
+		LeftFilter = 0x2,
+		RightFilter = 0x4,
+		MidFilter = LeftFilter | RightFilter
+	};
+	Q_DECLARE_FLAGS(PatternFlags, PatternFlag)
+
+	QString category;
+	int messageType;
+	PatternFlags flags;
+	bool enabled;
+
+private:
+	void parse(QStringView pattern);
+};
+
+} // namespace qt_logging_registry
+
+} // namespace qs::log