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ConfigTree.h 22.68 KiB
/**
* \copyright
* Copyright (c) 2012-2016, OpenGeoSys Community (http://www.opengeosys.org)
* Distributed under a Modified BSD License.
* See accompanying file LICENSE.txt or
* http://www.opengeosys.org/project/license
*
*/
#ifndef BASELIB_CONFIGTREE_H_
#define BASELIB_CONFIGTREE_H_
#include <typeindex>
#include <map>
#include <functional>
#include <memory>
#include <boost/property_tree/ptree.hpp>
extern template class boost::property_tree::basic_ptree<
std::string, std::string, std::less<std::string>>;
namespace BaseLib
{
class ConfigTree;
/*! Check if \c conf has been read entirely and invalidate it.
*
* This method can savely be called on \c nullptr's.
*
* \see ConfigTree::checkAndInvalidate()
*/
void checkAndInvalidate(ConfigTree* const conf);
//! \overload
void checkAndInvalidate(std::unique_ptr<ConfigTree> const& conf);
//! \overload
void checkAndInvalidate(ConfigTree& conf);
template<typename Iterator> class Range;
/*!
* Wrapper around a Boost Property Tree with some basic error reporting features.
*
* Features. This class:
* * makes sure that every configuration setting in a Property Tree is read
* exactly once. If some settings is not read (e.g. due to a typo), a warning message
* is generated. The message contains a hint where it occured.
* * enforces a naming scheme of settings: letters a-z, numbers 0-9, underscore
* * provides some functionality to read lists of values using range-based for loops.
* * has rather long method names that are easily greppable from the source code. So a list
* of supported configuration options can be easily obtained from the source code.
*
* The purpose of this class is to reduce or completely avoid the amount of error-handling
* code in routines that take configuration parameters.
*
* Most methods of this class check that they have not been called before for the same
* \c ConfigTree and the same parameter. This behaviour helps to enforce that every parameter
* is read exactly once during parsing of the configuration settings.
*
* The most notable restriction of this class when compared to plain tree traversal is, that
* one must know all the XML tags (i.e. configuration parameters) at compile time. It is not
* possible to read from this class, which configuration parameters are present in the tree.
* This restriction, however, is intended, because it provides the possibility to get all
* existing configuration parameters from the source code.
* * This class maintains a read counter for each parameter accessed through any of its methods.
* Read counters are increased with every read (the only exception being the peekConfParam() method).
* The destructor finally decreases the read counter for every tag/attribute it find on the
* current level of the XML tree. If the increases/decreases don't cancel each other, warning
* messages are generated. This check can also be enforced before destruction by using the
* BaseLib::checkAndInvalidate() functions.
*
* The design of this class entails some limitations compared to traversing a plain tree,
* e.g., it is not possible to obtain a list of tags or attributes from the tree,
* but one has to explicitly query the specific tags/attributes one is interested in.
* That way it is possible to get all used configuration parameters directly from the source
* code where this class is used, and to maintain the quality of the configuration parameter
* documentation.
*
* Instances of this class only keep a reference to the underlying <tt>boost::property_tree</tt>.
* Therefore it is necessary that the underlying property tree stays intact as long as any
* instance---i.e. the top level ConfigTree and any of its children---reference it.
* In order to simplify the handling of this dependence, the class ConfigTreeTopLevel can be used.
*
* The construction of a ConfigTree from the content of an XML file can be done with the
* function BaseLib::makeConfigTree(), which performs many error checks. For limitations
* of the used XML parser, please have a look at that function's documentation.
*/
class ConfigTree final
{
public:
/*! A wrapper around a Boost Iterator for iterating over ranges of subtrees.
*
* The methods of this class tell the associated (parent) \c ConfigTree object when
* a setting has been parsed.
*/
class SubtreeIterator
: public std::iterator<std::input_iterator_tag, ConfigTree>
{
public:
using Iterator = boost::property_tree::ptree::const_assoc_iterator;
explicit SubtreeIterator(Iterator it, std::string const& root,
ConfigTree const& parent)
: _it(it), _tagname(root), _parent(parent)
{}
SubtreeIterator& operator++() {
++_it;
_has_incremented = true;
return *this;
}
ConfigTree operator*() {
// if this iterator has been incremented since the last dereference,
// tell the _parent instance that a subtree now has been parsed.
if (_has_incremented) {
_has_incremented = false;
_parent.markVisited(_tagname, Attr::TAG, false);
}
return ConfigTree(_it->second, _parent, _tagname);
}
bool operator==(SubtreeIterator const& other) const {
return _it == other._it;
}
bool operator!=(SubtreeIterator const& other) const {
return _it != other._it;
}
private:
bool _has_incremented = true;
Iterator _it;
protected:
std::string const _tagname;
ConfigTree const& _parent;
};
/*! A wrapper around a Boost Iterator for iterating over ranges of parameters.
*
* The methods of this class tell the associated (parent) \c ConfigTree object when
* a setting has been parsed.
*/
class ParameterIterator : public SubtreeIterator
{
public:
#if defined(_MSC_VER) && _MSC_VER < 1900
// 1900 == MSCV 14.0 == Visual Studio 2015
// according to this post: http://stackoverflow.com/a/70630
// This table: http://en.cppreference.com/w/cpp/compiler_support
// says that since MSVC 14.0 inheriting of constructors is supported.
//! Inherit the constructor
explicit ParameterIterator(Iterator it, std::string const& root,
ConfigTree const& parent)
: SubtreeIterator(it, root, parent)
{}
#else
//! Inherit the constructor
using SubtreeIterator::SubtreeIterator;
#endif
ConfigTree operator*() {
auto st = SubtreeIterator::operator*();
if (st.hasChildren())
_parent.error("The requested parameter <" + _tagname + ">"
" has child elements.");
return st;
}
};
/*!
* A wrapper around a Boost Iterator for iterating over ranges of values.
*
* The methods of this class tell the associated (parent) \c ConfigTree object when
* a setting has been parsed.
*/
template<typename ValueType>
class ValueIterator
: public std::iterator<std::input_iterator_tag, ValueType>
{
public:
using Iterator = boost::property_tree::ptree::const_assoc_iterator;
explicit ValueIterator(Iterator it, std::string const& root,
ConfigTree const& parent)
: _it(it), _tagname(root), _parent(parent)
{}
ValueIterator<ValueType>& operator++() {
++_it;
_has_incremented = true;
return *this;
}
ValueType operator*() {
// if this iterator has been incremented since the last dereference,
// tell the _parent instance that a setting now has been parsed.
if (_has_incremented) {
_has_incremented = false;
_parent.markVisited<ValueType>(_tagname, Attr::TAG, false);
}
return ConfigTree(_it->second, _parent, _tagname).getValue<ValueType>(); }
bool operator==(ValueIterator<ValueType> const& other) const {
return _it == other._it;
}
bool operator!=(ValueIterator<ValueType> const& other) const {
return _it != other._it;
}
private:
bool _has_incremented = true;
Iterator _it;
std::string const _tagname;
ConfigTree const& _parent;
};
//! The tree being wrapped by this class.
using PTree = boost::property_tree::ptree;
/*! Type of the function objects used as callbacks.
*
* Arguments of the callback:
* \arg \c filename the file being from which this ConfigTree has been read.
* \arg \c path the path in the tree where the message was generated.
* \arg \c message the message to be printed.
*/
using Callback = std::function<void(const std::string& filename,
const std::string& path,
const std::string& message)>;
/*!
* Creates a new instance wrapping the given Boost Property Tree.
*
* \param tree the Boost Property Tree to be wrapped
* \param filename the file from which the \c tree has been read
* \param error_cb callback function to be called on error.
* \param warning_cb callback function to be called on warning.
*
* The callback functions must be valid callable functions, i.e. not nullptr's.
* They are configurable in order to make unit tests of this class easier.
* They should not be provided in production code!
*
* Defaults are strict: By default, both callbacks are set to the same function,
* i.e., warnings will also result in program abortion!
*/
explicit ConfigTree(PTree const& tree,
std::string const& filename,
Callback const& error_cb = onerror,
Callback const& warning_cb = onerror);
//! copying is not compatible with the semantics of this class
ConfigTree(ConfigTree const&) = delete;
//! After being moved from, \c other is in an undefined state and must not be
//! used anymore!
ConfigTree(ConfigTree && other);
//! copying is not compatible with the semantics of this class
ConfigTree& operator=(ConfigTree const&) = delete;
//! After being moved from, \c other is in an undefined state and must not be
//! used anymore!
ConfigTree& operator=(ConfigTree &&);
/*! \name Methods for directly accessing parameter values
*
*/
//!\{
/*! Get parameter \c param of type \c T from the configuration tree.
*
* \return the value looked for.
*
* \pre \c param must not have been read before from this ConfigTree.
*/
template<typename T> T
getConfParam(std::string const& param) const;
/*! Get parameter \c param of type \c T from the configuration tree or the \c default_value.
*
* This method has a similar behaviour as getConfParam(std::string const&) except in case
* of errors the \c default_value is returned.
*
* \pre \c param must not have been read before from this ConfigTree.
*/
template<typename T> T
getConfParam(std::string const& param, T const& default_value) const;
/*! Get parameter \c param of type \c T from the configuration tree if present
*
* This method has a similar behaviour as getConfParam(std::string const&) except
* no errors are raised. Rather it can be told from the return value if the
* parameter could be read.
*
* \pre \c param must not have been read before from this ConfigTree.
*/
template<typename T> boost::optional<T>
getConfParamOptional(std::string const& param) const;
/*! Fetches all parameters with name \c param from the current level of the tree.
*
* The return value is suitable to be used with range-base for-loops.
*
* \pre \c param must not have been read before from this ConfigTree.
*/
template<typename T> Range<ValueIterator<T> >
getConfParamList(std::string const& param) const;
//!\}
/*! \name Methods for accessing parameters that have attributes
*
* The <tt>getConfParam...()</tt> methods in this group---note: they do not have template
* parameters---check that the queried parameters do not have any children (apart from XML
* attributes); if they do, error() is called.
*
* The support for parameters with attributes is limited in the sense that it is not
* possible to peek/check them. However, such functionality can easily be added on demand.
*/
//!\{
/*! Get parameter \c param from the configuration tree.
*
* \return the subtree representing the requested parameter
*
* \pre \c param must not have been read before from this ConfigTree.
*/
ConfigTree
getConfParam(std::string const& param) const;
/*! Get parameter \c param from the configuration tree if present.
*
* \return the subtree representing the requested parameter
*
* \pre \c param must not have been read before from this ConfigTree.
*/
boost::optional<ConfigTree>
getConfParamOptional(std::string const& param) const;
/*! Fetches all parameters with name \c param from the current level of the tree.
*
* The return value is suitable to be used with range-base for-loops.
*
* \pre \c param must not have been read before from this ConfigTree.
*/
Range<ParameterIterator>
getConfParamList(std::string const& param) const;
/*! Get the plain data contained in the current level of the tree.
*
* \return the data converted to the type \c T
*
* \pre The data must not have been read before.
*/
template<typename T> T
getValue() const;
/*! Get XML attribute \c attr of type \c T for the current parameter.
*
* \return the requested attribute
*
* \pre \c param must not have been read before from this ConfigTree.
*/
template<typename T> T
getConfAttribute(std::string const& attr) const;
/*! Get XML attribute \c attr of type \c T for the current parameter if present.
*
* \return the requested attribute
*
* \pre \c param must not have been read before from this ConfigTree.
*/
template<typename T> boost::optional<T>
getConfAttributeOptional(std::string const& attr) const;
//!\}
/*! \name Methods for peeking and checking parameters
*
* To be used in builder/factory functions: E.g., one can peek a parameter denoting
* the type of an object to generate in the builder, and check the type parameter in
* the constructor of the generated object.
*/
//!\{
/*! Peek at a parameter \c param of type \c T from the configuration tree.
*
* This method is an exception to the single-read rule. It is meant to be used to
* tell from a ConfigTree instance where to pass that instance on for further processing.
*
* But in order that the requested parameter counts as "completely parsed", it has to be
* read through some other method, too.
*
* Return value and error behaviour are the same as for getConfParam<T>(std::string const&).
*/
template<typename T> T
peekConfParam(std::string const& param) const;
/*! Assert that \c param has the given \c value.
*
* Convenience method combining getConfParam(std::string const&) with a check.
*/
template<typename T> void
checkConfParam(std::string const& param, T const& value) const;
//! Make checkConfParam() work for string literals.
template<typename Ch> void
checkConfParam(std::string const& param, Ch const* value) const;
//!\}
/*! \name Methods for accessing subtrees
*
*/
//!\{
/*! Get the subtree rooted at \c root
*
* If \c root is not found error() is called.
*
* \pre \c root must not have been read before from this ConfigTree.
*/
ConfigTree
getConfSubtree(std::string const& root) const;
/*! Get the subtree rooted at \c root if present
*
* \pre \c root must not have been read before from this ConfigTree.
*/
boost::optional<ConfigTree>
getConfSubtreeOptional(std::string const& root) const;
/*! Get all subtrees that have a root \c root from the current level of the tree.
*
* The return value is suitable to be used with range-base for-loops.
*
* \pre \c root must not have been read before from this ConfigTree.
*/
Range<SubtreeIterator>
getConfSubtreeList(std::string const& root) const;
//!\}
/*! \name Methods for ignoring parameters
*
*/
//!\{
/*! Tell this instance to ignore parameter \c param.
*
* This method is used to avoid warning messages.
*
* \pre \c param must not have been read before from this ConfigTree.
*/
void ignoreConfParam(std::string const& param) const;
/*! Tell this instance to ignore all parameters \c param on the current level of the tree.
*
* This method is used to avoid warning messages.
*
* \pre \c param must not have been read before from this ConfigTree.
*/
void ignoreConfParamAll(std::string const& param) const;
/*! Tell this instance to ignore the XML attribute \c attr.
*
* This method is used to avoid warning messages.
*
* \pre \c attr must not have been read before from this ConfigTree.
*/
void ignoreConfAttribute(std::string const& attr) const;
//!\}
//! The destructor performs the check if all nodes at the current level of the tree
//! have been read.
~ConfigTree();
//! Default error callback function //! Will print an error message and call std::abort()
static void onerror(std::string const& filename, std::string const& path,
std::string const& message);
//! Default warning callback function
//! Will print a warning message
static void onwarning(std::string const& filename, std::string const& path,
std::string const& message);
private:
struct CountType
{
int count;
std::type_index type;
};
//! Used to indicate if dealing with XML tags or XML attributes
enum class Attr : bool
{
TAG = false, ATTR = true
};
//! Used for wrapping a subtree
explicit ConfigTree(PTree const& tree, ConfigTree const& parent, std::string const& root);
/*! Called if an error occurs. Will call the error callback.
*
* This method only acts as a helper method.
*
* This method finally calls <tt>std::abort()</tt>. In order to prevent that,
* a custom error callback that breaks out of the normal control flow---e.g., by throwing
* an exception---must be provided.
*/
#if defined(_MSC_VER) && _MSC_VER < 1900
// 1900 == MSCV 14.0 == Visual Studio 2015
// according to this post: http://stackoverflow.com/a/70630
// This table: http://en.cppreference.com/w/cpp/compiler_support
// says that since MSVC 14.0 attributes are supported.
__declspec(noreturn)
#else
[[noreturn]]
#endif
void error(std::string const& message) const;
//! Called for printing warning messages. Will call the warning callback.
//! This method only acts as a helper method.
void warning(std::string const& message) const;
//! Checks if \c key complies with the rules [a-z0-9_].
void checkKeyname(std::string const& key) const;
//! Used to generate the path of a subtree.
std::string joinPaths(std::string const& p1, std::string const& p2) const;
//! Asserts that the \c key has not been read yet.
void checkUnique(std::string const& key) const;
//! Asserts that the attribute \c attr has not been read yet.
void checkUniqueAttr(std::string const& attr) const;
/*! Keeps track of the key \c key and its value type \c T.
*
* This method asserts that a key is read always with the same type.
*
* \c param peek_only if true, do not change the read-count of the given key.
*/
template<typename T>
CountType& markVisited(std::string const& key, Attr const is_attr,
bool peek_only) const;
/*! Keeps track of the key \c key and its value type ConfigTree.
*
* This method asserts that a key is read always with the same type.
*
* \c param peek_only if true, do not change the read-count of the given key.
*/
CountType& markVisited(std::string const& key, Attr const is_attr,
bool const peek_only) const;
//! Used in the destructor to compute the difference between number of reads of a parameter
//! and the number of times it exists in the ConfigTree
void markVisitedDecrement(Attr const is_attr, std::string const& key) const;
//! Checks if this tree has any children.
bool hasChildren() const;
/*! Checks if the top level of this tree has been read entirely (and not too often).
*
* \post This method also invalidates the instance, i.e., afterwards it must not
* be used anymore!
*/
void checkAndInvalidate();
//! returns a short string at suitable for error/warning messages
static std::string shortString(std::string const& s);
//! The wrapped tree.
boost::property_tree::ptree const* _tree;
//! A path printed in error/warning messages.
std::string _path;
//! The path of the file from which this tree has been read.
std::string _filename;
//! A pair (is attribute, tag/attribute name).
using KeyType = std::pair<Attr, std::string>;
//! A map KeyType -> (count, type) keeping track which parameters have been read
//! how often and which datatype they have.
//!
//! This member will be written to when reading from the config tree.
//! Therefore it has to be mutable in order to be able to read from
//! constant instances, e.g., those passed as constant references to
//! temporaries.
mutable std::map<KeyType, CountType> _visited_params;
//! Indicates if the plain data contained in this tree has already been read.
mutable bool _have_read_data = false;
Callback _onerror; //!< Custom error callback.
Callback _onwarning; //!< Custom warning callback.
//! Character separating two path components.
static const char pathseparator;
//! Set of allowed characters as the first letter of a key name.
static const std::string key_chars_start;
//! Set of allowed characters in a key name.
static const std::string key_chars;
friend void checkAndInvalidate(ConfigTree* const conf);
friend void checkAndInvalidate(ConfigTree& conf);
friend void checkAndInvalidate(std::unique_ptr<ConfigTree> const& conf);
};
}
#include "ConfigTree-impl.h"
#endif // BASELIB_CONFIGTREE_H_