bdljsn_stringutil.h

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/// @file bdljsn_stringutil.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bdljsn_stringutil.h                                                -*-C++-*-
#ifndef INCLUDED_BDLJSN_STRINGUTIL
#define INCLUDED_BDLJSN_STRINGUTIL
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bdljsn_stringutil bdljsn_stringutil
/// @brief  Provide a utility functions for JSON strings.
/// @addtogroup bdl
/// @{
/// @addtogroup bdljsn
/// @{
/// @addtogroup bdljsn_stringutil
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bdljsn_stringutil-purpose"> Purpose</a>
/// * <a href="#bdljsn_stringutil-classes"> Classes </a>
/// * <a href="#bdljsn_stringutil-description"> Description </a>
///   * <a href="#bdljsn_stringutil-json-strings"> JSON Strings </a>
///     * <a href="#bdljsn_stringutil-guarantees-arbitrary-utf-8-to-json-string"> Guarantees: Arbitrary UTF-8 to JSON String </a>
///   * <a href="#bdljsn_stringutil-strictness"> Strictness </a>
///     * <a href="#bdljsn_stringutil-example-variance"> Example Variance </a>
///   * <a href="#bdljsn_stringutil-usage"> Usage </a>
///     * <a href="#bdljsn_stringutil-example-1-encoding-and-decoding-a-json-string"> Example 1: Encoding and Decoding a JSON String </a>
///
/// # Purpose {#bdljsn_stringutil-purpose}
/// Provide a utility functions for JSON strings.
///
/// # Classes {#bdljsn_stringutil-classes}
///
/// -  bdljsn::StringUtil: namespace for utility functions on JSON strings
///
/// # Description {#bdljsn_stringutil-description}
/// This component defines a utility `struct`,
/// `bdljsn::StringUtil`, that is a namespace for functions that convert
/// arbitrary UTF-8 codepoint sequences to JSON strings and vice versa.  The
/// rules for these conversions are outlined below in {JSON Strings} and
/// detailed in: https://www.rfc-editor.org/rfc/rfc8259#section-7 (RFC8259)
///
/// This utility provides two key functions:
///
/// * `writeString`: Given an arbitrary UTF-8 codepoint sequence, generate a
///   JSON string representing the same codepoints.
/// * `readString`: Given a JSON string (e.g., the output of `writeString`),
///   generate the equivalent sequence of UTF-8 code points.
///
/// When using these functions, a UTF-8 codepoint sequence is always preserved
/// on the round trip to JSON string and back; however, since there are
/// equivalent allowed representations of a JSON string, the converse is not
/// guaranteed.
///
/// ## JSON Strings {#bdljsn_stringutil-json-strings}
///
///
/// JSON strings consist of UTF-8 codepoints surround by double quotes (i.e.,
/// '\"') Within those double quotes certain characters *must* be escaped (i.e.,
/// replaced with some alternative, multi-byte representation).  Those
/// characters are:
///
/// * quotation marks
/// * backslashes (a.k.a., a "reverse solidus")
/// * the "control characters" in the range `U+0000` to `U+001F` (inclusive).
///
/// Each of the above characters can be escaped by replacing it with the six
/// byte sequence consisting of:
///
///   - a backslash,
///   - a lower-case `u`, and
///   - the Unicode value expressed as four hexadecimal digits.
///
/// For example, the character that rings the console bell is represented as
/// '\u0007'.  Note that the hexadecimal digits can use upper or lower case
/// letters but the lead `u` character must be lower case.  See {Strictness}.
///
/// Eight of the characters that must be escaped can be alternatively
/// represented by special, 2-byte sequences:
/// @code
/// +---------+-----------------+---------------+---------------+
/// | Unicode | Description     | 6-byte escape | 2-byte escape |
/// +---------+-----------------+---------------+---------------+
/// | U+0022  | quotation mark  | \u0022        |  \"           |
/// | U+005C  | backslash       | \u005c        |  \\           |
/// | U+002F  | slash           | \u002f        |  \/           |
/// | U+0008  | backspace       | \u0008        |  \b           |
/// | U+000C  | form feed       | \u000C        |  \f           |
/// | U+000A  | line feed       | \u000A        |  \n           |
/// | U+000D  | carriage return | \u000D        |  \r           |
/// | U+0009  | tab             | \u0009        |  \t           |
/// +---------+-----------------+---------------+---------------+
/// @endcode
/// Note that the above set is similar to but not identical to the set of two
/// byte `char` literals supported by C++.  For example, '\0' (null) and '\a'
/// (bell) are not included above.
///
/// ### Guarantees: Arbitrary UTF-8 to JSON String {#bdljsn_stringutil-guarantees-arbitrary-utf-8-to-json-string}
///
///
/// * No UTF-8 characters in the *Basic* *Multilingual* *Plane* are escaped
///   unless they are in the set that *must* be escaped.
/// * When a character must be escaped, the 6-byte (hexadecimal) representation
///   is used only if no 2-byte escape exists.
/// * When a 6-byte (hexadecimal) representation is used, hexadecimal letters
///   are in upper case.
/// * All UTF-8 characters outside of the *Basic* *Multilingual* *Plane*
///   are represented by two, adjacent 6-byte hexadecimal escape
///   sequences.  For details, see:
///   https://en.wikipedia.org/wiki/UTF-16#U+D800_to_U+DFFF
///
/// ## Strictness {#bdljsn_stringutil-strictness}
///
///
/// By default, the `bdljsn::StringUtil` read and write methods strictly follow
/// the RFC8259 standard.  Variances from those rules are expressed using
/// `bdljsn::StringUtil::FLags`, an `enum` of flag values that can be set in the
/// optional `flags` parameter of the decoding methods.  Multiple flags can be
/// bitwise set in `flags`; however, currently, just one variance flag is
/// defined.
///
/// ### Example Variance {#bdljsn_stringutil-example-variance}
///
///
/// RFC8259 specifies that the 6-byte Unicode escape sequence start with a
/// slash, `/`, and lower-case `u`.  However, if the
/// `bdljsn::StringUtil::e_ACCEPT_CAPITAL_UNICODE_ESCAPE` is set, an upper-case
/// `U` is accepted as well.  Thus, both '\u0007' and '\U0007' would be
/// interpreted as the BELL character.
///
/// ## Usage {#bdljsn_stringutil-usage}
///
///
/// This section illustrates intended use of this component.
///
/// ### Example 1: Encoding and Decoding a JSON String {#bdljsn_stringutil-example-1-encoding-and-decoding-a-json-string}
///
///
/// First, we initialize a string with a valid sequence of UTF-8 codepoints.
/// @code
/// bsl::string initial("Does the name \"Ivan Pavlov\" ring a bell\a?\n");
/// assert(bdlde::Utf8Util::isValid(initial));
/// @endcode
/// Notice that, as required by C++ syntax, several characters are represented
/// by their two-character escape sequence: double quote (twice), bell, and
/// newline.
///
/// Then, we examine the string as output:
/// @code
/// bsl::cout << initial << bsl::endl;
/// @endcode
/// and observe:
/// @code
/// Does the name "Ivan Pavlov" ring a bell?
///
/// @endcode
/// Notice that the backslash characters (having served their purpose of giving
/// special meaning to the subsequent character) are not shown.  The BELL and
/// NEWLINE characters are output but are not visible.
///
/// Now, we generate JSON string equivalent of the `initial` string.
/// @code
/// bsl::ostringstream oss;
///
/// int rcEncode = bdljsn::StringUtil::writeString(oss, initial);
/// assert(0 == rcEncode);
///
/// bsl::string  jsonCompatibleString = oss.str();
/// bsl::cout << jsonCompatibleString << bsl::endl;
/// @endcode
/// and observed how the `initial` string is represented for JSON:
/// @code
/// "Does the name \"Ivan Pavlov\" ring a bell\u0007?\n"
/// @endcode
/// Notice that:
/// * The entire string is delimited by double quotes.
/// * The interior double quotes and new line are represented by two character
///   escape sequences (as they were in the C++ string literal.
/// * Since JSON does not have a two character escape sequence for the BELL
///   character, '\u0007', the 6-byte Unicode representation is used.
///
/// Finally, we convert the `jsonCompatibleString` back to its original content:
/// @code
/// bsl::string fromJsonString;
/// const int   rcDecode = bdljsn::StringUtil::readString(
///                                                      &fromJsonString,
///                                                      jsonCompatibleString);
/// assert(0       == rcDecode);
/// assert(initial == fromJsonString);
///
/// bsl::cout << fromJsonString << bsl::endl;
/// @endcode
/// and observe (again):
/// @code
/// Does the name "Ivan Pavlov" ring a bell?
///
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bdl
 * @{
 */
/** @addtogroup bdljsn
 * @{
 */
/** @addtogroup bdljsn_stringutil
 * @{
 */
 
#include <bdlscm_version.h>
 
#include <bsls_assert.h>
 
#include <bsl_ostream.h>
#include <bsl_string.h>
#include <bsl_string_view.h>
 
 
namespace bdljsn {
 
                             // =================
                             // struct StringUtil
                             // =================
 
/// This class provides utility functions for converting arbitrary UTF-8
/// sequences into JSON strings and visa versa.  See {JSON Strings} in
/// {DESCRIPTION} for details of these transformations.
struct StringUtil {
 
  public:
    // TYPES
    enum Flags {
        e_NONE                          = 0
      , e_ACCEPT_CAPITAL_UNICODE_ESCAPE = 1 << 0
    };
 
    // CLASS METHODS
 
    /// Load to the specified `value` the UTF-8 codepoint sequence
    /// equivalent to the specified (JSON) `string` (see {JSON Strings}).
    /// Return 0 on success and a non-zero value otherwise.  Optionally
    /// specify `flags` to request variances from certain rules of JSON
    /// decoding (see {Strictness}).
    static int readString(bsl::string             *value,
                          const bsl::string_view&  string,
                          int                      flags = e_NONE);
 
    /// Load to the specified `value` the UTF-8 codepoint sequence
    /// equivalent to the specified `string`, that is JSON-compliant absent
    /// the leading and trailing double quote characters (see {JSON
    /// Strings}).  Return 0 on success and a non-zero value otherwise.
    /// Optionally specify `flags` to request variances from certain rules
    /// of JSON decoding (see {Strictness}).
    static int readUnquotedString(bsl::string             *value,
                                  const bsl::string_view&  string,
                                  int                      flags = e_NONE);
 
    /// Write to the specified `stream` a JSON-compliant string that is
    /// equivalent to the specified `string`, an arbitrary UTF-8 codepoint
    /// sequence.  Return 0 on success and a non-zero value otherwise.  The
    /// operation fails if `string` is not a sequence of UTF-8 codepoints or
    /// if there is an error writing to `stream`.  See {Conventions:
    /// Arbitrary UTF-8 to JSON String} for further details.
    static int writeString(bsl::ostream&           stream,
                           const bsl::string_view& string);
};
 
// ============================================================================
//                             INLINE DEFINITIONS
// ============================================================================
 
                             // -----------------
                             // struct StringUtil
                             // -----------------
 
// CLASS METHODS
inline
int StringUtil::readString(bsl::string             *value,
                           const bsl::string_view&  string,
                           int                      flags)
{
    BSLS_ASSERT(value);
 
    if (2 > string.size()) {
        return -1;                                                    // RETURN
    }
 
    if (string[0] != '"' && string[string.size() - 1] != '"') {
        return -1;                                                    // RETURN
    }
 
    const bsl::string_view contents = string.substr(1, string.size() - 2);
    return readUnquotedString(value, contents, flags);
}
 
}  // close package namespace
 
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2022 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------
 
/** @} */
/** @} */
/** @} */