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| -rw-r--r-- | src/lib/dns/labelsequence.h | 456 |
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diff --git a/src/lib/dns/labelsequence.h b/src/lib/dns/labelsequence.h new file mode 100644 index 0000000..91dbe59 --- /dev/null +++ b/src/lib/dns/labelsequence.h @@ -0,0 +1,456 @@ +// Copyright (C) 2012-2020 Internet Systems Consortium, Inc. ("ISC") +// +// 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/. + +#ifndef LABELSEQUENCE_H +#define LABELSEQUENCE_H 1 + +#include <dns/name.h> +#include <util/buffer.h> + +namespace isc { +namespace dns { + +/// \brief Light-weight Accessor to Name data. +/// +/// The purpose of this class is to easily match Names and parts of Names, +/// without needing to copy the underlying data on each label strip. +/// +/// It can only work on existing Name objects, or data as provided by the +/// Name object or another LabelSequence, and the data or Name MUST +/// remain in scope during the entire lifetime of its associated +/// LabelSequence(s). +/// +/// Upon creation of a LabelSequence, it records the offsets of the +/// labels in the wireformat data of the Name. When stripLeft() or +/// stripRight() is called on the LabelSequence, no changes in the +/// original data occur, but the internal pointers of the +/// LabelSequence are modified. +/// +/// LabelSequences can be compared to other LabelSequences, and their +/// data can be requested (which then points to part of the original +/// data of the original Name object). +class LabelSequence { + // Name calls the private toText(bool) method of LabelSequence. + friend std::string Name::toText(bool) const; + +public: + /// \brief Max possible size of serialized image generated by \c serialize + /// + /// A fixed length buffer of this size can be always passed to + /// \c serialize() safely. (But the application shouldn't use the + /// specific size value; it must use this constant variable). + static const size_t MAX_SERIALIZED_LENGTH = + Name::MAX_WIRE + Name::MAX_LABELS + 1; + + /// + /// \name Well-known LabelSequence constants + /// + //@{ + /// Wildcard label ("*") + static const LabelSequence& WILDCARD(); + //@} + + /// \brief Constructs a LabelSequence for the given name + /// + /// \note The associated Name MUST remain in scope during the lifetime + /// of this LabelSequence, since getData() refers to data from the + /// Name object (the only data the LabelSequence stores are pointers + /// to the labels in the Name object). + /// + /// \param name The Name to construct a LabelSequence for + explicit LabelSequence(const Name& name): + data_(&name.ndata_[0]), + offsets_(&name.offsets_[0]), + first_label_(0), + last_label_(name.getLabelCount() - 1) + {} + + /// \brief Constructor from serialized image. + /// + /// This constructor restores a \c LabelSequence object from a serialized + /// binary image previously generated by \c serialize(). Any other input + /// to this constructor will result in undefined behavior. + /// + /// The binary data passed to this constructor MUST remain in scope and + /// MUST NOT be modified during the lifetime of this LabelSequence. + /// + /// As long as the data were previously generated by a call to + /// \c serialize() on a valid \c LabelSequence object, this constructor + /// should succeed. While any other case is undefined, this constructor + /// may perform some validity checks internally for safety. Nevertheless, + /// applications must not rely on such checks. + /// + /// \param buf Pointer to the serialized image generated by \c serialize(). + explicit LabelSequence(const void* buf); + + /// \brief Construct 'extendable' LabelSequence + /// + /// This form of LabelSequence copies the data from the given + /// labelsequence into the given external buffer, which is subsequently + /// extendable by calling extend() + /// + /// The data is placed into the given buffer as follows: + /// - binary sequence of name data, starting at position 0, + /// length determined by source LabelSequence + /// - offsets, starting at position Name::MAX_WIRE, length + /// determined by source LabelSequence + /// The offsets are updated to be correct for the potentially partial + /// name data (as stripLeft() and stripRight may have been called on + /// the source LabelSequence). + /// + /// \note The given buf MUST remain in scope during the lifetime of + /// the LabelSequence created here. + /// \note The buffer should never be modified except through + /// calls to extend(). + /// \note Also, only associate the buffer with at most one + /// LabelSequence. Behaviour is undefined if two LabelSequences are + /// using the same buffer. + /// + /// \param src LabelSequence to copy the initial data from + /// \param buf external buffer to store this labelsequence's data in + LabelSequence(const LabelSequence& src, uint8_t buf[MAX_SERIALIZED_LENGTH]); + + /// \brief Copy constructor. + /// + /// \note The associated data MUST remain in scope during the lifetime + /// of this LabelSequence, since only the pointers are copied. + /// + /// \note No validation is done on the given data upon construction; + /// use with care. + /// + /// \param ls The LabelSequence to construct a LabelSequence from + LabelSequence(const LabelSequence& ls): + data_(ls.data_), + offsets_(ls.offsets_), + first_label_(ls.first_label_), + last_label_(ls.last_label_) + {} + + /// \brief Assignment operator. + /// + /// \note The associated data MUST remain in scope during the lifetime + /// of this LabelSequence, since only the pointers are copied. + /// + /// \note No validation is done on the given data upon construction; + /// use with care. + /// + /// \param other The LabelSequence to assign a LabelSequence from + LabelSequence& operator=(const LabelSequence& other) { + if (this != &other) { + // Not self-assignment. + data_ = other.data_; + offsets_ = other.offsets_; + first_label_ = other.first_label_; + last_label_ = other.last_label_; + } + return (*this); + } + + /// \brief Return the wire-format data for this LabelSequence + /// + /// The data is returned as a pointer to (the part of) the original + /// wireformat data, from either the original Name object, or the + /// raw data given in the constructor, and the given len value is + /// set to the number of octets that match this labelsequence. + /// + /// \note The data pointed to is only valid if the original Name + /// object or data is still in scope + /// + /// \param len Pointer to a size_t where the length of the data + /// will be stored (in number of octets) + /// \return Pointer to the wire-format data of this label sequence + const uint8_t* getData(size_t* len) const; + + /// \brief Return the length of the wire-format data of this LabelSequence + /// + /// This method returns the number of octets for the data that would + /// be returned by the \c getData() method. + /// + /// Note that the return value of this method is always positive. + /// Note also that if the return value of this method is 1, it means the + /// sequence consists of the null label, i.e., a single "dot", and vice + /// versa. + /// + /// \note The data pointed to is only valid if the original Name + /// object or data is still in scope + /// + /// \return The length of the data of the label sequence in octets. + size_t getDataLength() const; + + /// \brief Return the size of serialized image of the \c LabelSequence. + /// + /// This method calculates the size of necessary storage to store + /// serialized image of this \c LabelSequence (which would be dumped by + /// \c serialize()) and returns it. The size is in bytes. + /// + /// \throw none. + /// + /// \return The size of serialized image of the \c LabelSequence. + size_t getSerializedLength() const; + + /// \brief Serialize the \c LabelSequence object in to a buffer. + /// + /// This method dumps a serialized image of this \c LabelSequence + /// that would be restored by the corresponding constructor into the + /// given buffer. The buffer size must be at least equal to + /// the value returned by getSerializedLength() (it can be larger than + /// that). + /// + /// Be careful about where the buffer is located; due to the nature + /// of the buffer, it's quite possible that the memory region is being used + /// to construct another active \c LabelSequence. In such a case + /// the serialization would silently break that sequence object, and + /// it will be very difficult to identify the cause. This method + /// has minimal level checks to avoid such disruption: If the serialization + /// would break "this" \c LabelSequence object, it doesn't write anything + /// to the given buffer and throw a \c isc::BadValue exception. + /// + /// In general, it should be safe to call this method on a + /// \c LabelSequence object constructed from a \c Name object or + /// a copy of such \c LabelSequence. When you construct \c LabelSequence + /// from pre-serialized data, calling this method on it can be unsafe. + /// One safe (but a bit less efficient) way in such a case is to make + /// the source \c LabelSequence temporary and immediately create a + /// local copy using an explicit buffer, and call this method on the + /// latter: + /// \code + /// // don't do this, it's not safe (and would result in exception): + /// // LabelSequence(buf).serialize(buf, buf_len); + /// + /// // The following are the safe way: + /// uint8_t ext_buf[LabelSequence::MAX_SERIALIZED_LENGTH]; + /// LabelSequence seq(LabelSequence(buf), ext_buf); + /// ... (strip the labels, etc) + /// seq.serialize(buf, buf_len); // it's safe to override buf here + /// \endcode + /// + /// The serialized image would be as follows: + /// - olen: number of offsets (1 byte) + /// - binary sequence of offsets (olen bytes, verbatim copy of offsets_ + /// of this size) + /// - binary sequence of name data (length determined by itself, verbatim + /// copy of data_ of the corresponding size) + /// + /// Applications must use the resulting image as opaque value and must not + /// use it for other purposes than input to the corresponding constructor + /// to restore it. Application behavior that assumes the specific + /// organization of the image is not guaranteed. + /// + /// \throw isc::BadValue buf_len is too short (this method never throws + /// otherwise) or the serialization would override internal data of + /// of the source LabelSequence. + /// + /// \param buf Pointer to the placeholder to dump the serialized image + /// \param buf_len The size of available region in \c buf + void serialize(void* buf, size_t buf_len) const; + + /// \brief Compares two label sequences for equality. + /// + /// Performs a (optionally case-sensitive) comparison between this + /// LabelSequence and another LabelSequence for equality. + /// + /// \param other The LabelSequence to compare with + /// \param case_sensitive If true, comparison is case-sensitive + /// \return true if The label sequences consist are the same length, + /// and contain the same data. + bool equals(const LabelSequence& other, bool case_sensitive = false) const; + + /// \brief Compares two label sequences for equality (case ignored). + /// + /// This is equivalent to <code>this->equals(other)</code>. + /// + /// The operator version is convenient some specific cases such as in + /// unit tests. + bool operator==(const LabelSequence& other) const { + return (equals(other)); + } + + /// \brief Compares two label sequences. + /// + /// Performs a (optionally case-insensitive) comparison between this + /// LabelSequence and another LabelSequence. + /// + /// \param other The LabelSequence to compare with + /// \param case_sensitive If true, comparison is case-insensitive + /// \return a <code>NameComparisonResult</code> object representing the + /// comparison result. + NameComparisonResult compare(const LabelSequence& other, + bool case_sensitive = false) const; + + /// \brief Remove labels from the front of this LabelSequence + /// + /// \note No actual memory is changed, this operation merely updates the + /// internal pointers based on the offsets in the Name object. + /// + /// \exception OutOfRange if i is greater than or equal to the number + /// of labels currently pointed to by this LabelSequence + /// + /// \param i The number of labels to remove. + void stripLeft(size_t i); + + /// \brief Remove labels from the end of this LabelSequence + /// + /// \note No actual memory is changed, this operation merely updates the + /// internal pointers based on the offsets originally provided. + /// + /// \exception OutOfRange if i is greater than or equal to the number + /// of labels currently pointed to by this LabelSequence + /// + /// \param i The number of labels to remove. + void stripRight(size_t i); + + /// \brief Returns the current number of labels for this LabelSequence + /// + /// \return The number of labels + size_t getLabelCount() const { + return (last_label_ - first_label_ + 1); + } + + /// \brief Convert the LabelSequence to a string. + /// + /// This method returns a <code>std::string</code> object representing the + /// LabelSequence as a string. The returned string ends with a dot + /// '.' if the label sequence is absolute. + /// + /// This function assumes the underlying data is in proper + /// uncompressed wire format. If it finds an unexpected label + /// character including compression pointer, an exception of class + /// \c BadLabelType will be thrown. In addition, if resource + /// allocation for the result string fails, a corresponding standard + /// exception will be thrown. + /// + /// \return a string representation of the <code>LabelSequence</code>. + std::string toText() const; + + /// \brief Convert the LabelSequence to a string without escape sequences. + /// + /// The string returned will contain a single character value for any + /// escape sequences in the label(s). + /// + /// \param omit_final_dot whether to omit the trailing dot in the output. + /// \return a string representation of the <code>LabelSequence</code> + /// that does not contain escape sequences. + std::string toRawText(bool omit_final_dot) const; + + /// \brief Extend this LabelSequence with the given labelsequence + /// + /// The given labels are appended to the name data, and internal + /// offset data is updated accordingly. + /// + /// The data from the given LabelSequence is copied into the buffer + /// associated with this LabelSequence; the appended LabelSequence + /// (the 'labels' argument) can be released if it is not needed for + /// other operations anymore. + /// + /// If this LabelSequence is absolute, its root label will be stripped + /// before the given LabelSequence is appended; after extend(), + /// this LabelSequence will be absolute if, and only if, the appended + /// LabelSequence was. A side-effect of this property is that adding + /// the root label to an absolute LabelSequence has no effect (the + /// root label is stripped, then added again). + /// + /// Some minimal checking is done on the data, but internal integrity + /// is not assumed. Do NOT modify the given buffer except through calls + /// to this method, and do NOT call this method if the buffer is + /// associated to another LabelSequence (behaviour of the other + /// LabelSequence is undefined in that scenario). + /// + /// \exception BadValue If the buffer does not appear to be associated + /// with this LabelSequence, or if the maximum wire length or maximum + /// number of labels would be exceeded by this operation + /// + /// \param labels The labels to append to this LabelSequence + /// \param buf The buffer associated with this LabelSequence + void extend(const LabelSequence& labels, + uint8_t buf[MAX_SERIALIZED_LENGTH]); + +private: + /// \brief Convert the LabelSequence to a string. + /// + /// This method is a version of the zero-argument toText() method, + /// that accepts a <code>omit_final_dot</code> argument. The + /// returned string ends with a dot '.' if + /// <code>omit_final_dot</code> is <code>false</code>. + /// + /// This method is used as a helper for <code>Name::toText()</code> + /// only. + /// + /// \param omit_final_dot whether to omit the trailing dot in the output. + /// \return a string representation of the <code>LabelSequence</code>. + std::string toText(bool omit_final_dot) const; +public: + /// \brief Calculate a simple hash for the label sequence. + /// + /// This method calculates a hash value for the label sequence as binary + /// data. If \c case_sensitive is false, it ignores the case stored in + /// the labels; specifically, it normalizes the labels by converting all + /// upper case characters to lower case ones and calculates the hash value + /// for the result. + /// + /// This method is intended to provide a lightweight way to store a + /// relatively small number of label sequences in a hash table. + /// For this reason it only takes into account data up to 16 octets + /// (16 was derived from BIND 9's implementation). Also, the function does + /// not provide any unpredictability; a specific sequence will always have + /// the same hash value. It should therefore not be used in the context + /// where an untrusted third party can mount a denial of service attack by + /// forcing the application to create a very large number of label + /// sequences that have the same hash value and expected to be stored in + /// a hash table. + /// + /// \exception None + /// + /// \param case_sensitive + /// \return A hash value for this label sequence. + size_t getHash(bool case_sensitive) const; + + /// \brief Checks whether the label sequence is absolute + /// + /// \return true if the last label is the root label + bool isAbsolute() const; + +private: + const uint8_t* data_; // wire-format name data + const uint8_t* offsets_; // an array of offsets in data_ for the labels + size_t first_label_; // index of offsets_ for the first label + size_t last_label_; // index of offsets_ for the last label. + // can be equal to first_label_, but must not + // be smaller (the class ensures that) +}; + + +/// +/// \brief Insert the label sequence as a string into stream. +/// +/// This method convert the \c label_sequence into a string and inserts +/// it into the output stream \c os. +/// +/// This function overloads the global operator<< to behave as described in +/// ostream::operator<< but applied to \c LabelSequence objects. +/// +/// \param os A \c std::ostream object on which the insertion operation is +/// performed. +/// \param label_sequence The \c LabelSequence object output by the operation. +/// \return A reference to the same \c std::ostream object referenced by +/// parameter \c os after the insertion operation. +std::ostream& +operator<<(std::ostream& os, const LabelSequence& label_sequence); + +inline const LabelSequence& +LabelSequence::WILDCARD() { + static const uint8_t wildcard_buf[4] = { 0x01, 0x00, 0x01, '*' }; + static const LabelSequence wild_ls(wildcard_buf); + return (wild_ls); +} + +} // end namespace dns +} // end namespace isc + +#endif + +// Local Variables: +// mode: c++ +// End: |