private void ReadStringIntoBuffer()

in src/Elastic.Apm/Libraries/Newtonsoft.Json/JsonTextReader.cs [1048:1202]
129 lines of code
30 McCabe index (conditional complexity)

		private void ReadStringIntoBuffer(char quote)
		{
			MiscellaneousUtils.Assert(CharBuffer != null);

			var charPos = CharPos;
			var initialPosition = CharPos;
			var lastWritePosition = CharPos;
			_stringBuffer.Position = 0;

			while (true)
			{
				switch (CharBuffer[charPos++])
				{
					case '\0':
						if (_charsUsed == charPos - 1)
						{
							charPos--;

							if (ReadData(true) == 0)
							{
								CharPos = charPos;
								throw JsonReaderException.Create(this,
									"Unterminated string. Expected delimiter: {0}.".FormatWith(CultureInfo.InvariantCulture, quote));
							}
						}
						break;
					case '\\':
						CharPos = charPos;
						if (!EnsureChars(0, true))
							throw JsonReaderException.Create(this,
								"Unterminated string. Expected delimiter: {0}.".FormatWith(CultureInfo.InvariantCulture, quote));

						// start of escape sequence
						var escapeStartPos = charPos - 1;

						var currentChar = CharBuffer[charPos];
						charPos++;

						char writeChar;

						switch (currentChar)
						{
							case 'b':
								writeChar = '\b';
								break;
							case 't':
								writeChar = '\t';
								break;
							case 'n':
								writeChar = '\n';
								break;
							case 'f':
								writeChar = '\f';
								break;
							case 'r':
								writeChar = '\r';
								break;
							case '\\':
								writeChar = '\\';
								break;
							case '"':
							case '\'':
							case '/':
								writeChar = currentChar;
								break;
							case 'u':
								CharPos = charPos;
								writeChar = ParseUnicode();

								if (StringUtils.IsLowSurrogate(writeChar))
								{
									// low surrogate with no preceding high surrogate; this char is replaced
									writeChar = UnicodeReplacementChar;
								}
								else if (StringUtils.IsHighSurrogate(writeChar))
								{
									bool anotherHighSurrogate;

									// loop for handling situations where there are multiple consecutive high surrogates
									do
									{
										anotherHighSurrogate = false;

										// potential start of a surrogate pair
										if (EnsureChars(2, true) && CharBuffer[CharPos] == '\\' && CharBuffer[CharPos + 1] == 'u')
										{
											var highSurrogate = writeChar;

											CharPos += 2;
											writeChar = ParseUnicode();

											if (StringUtils.IsLowSurrogate(writeChar))
											{
												// a valid surrogate pair!
											}
											else if (StringUtils.IsHighSurrogate(writeChar))
											{
												// another high surrogate; replace current and start check over
												highSurrogate = UnicodeReplacementChar;
												anotherHighSurrogate = true;
											}
											else
											{
												// high surrogate not followed by low surrogate; original char is replaced
												highSurrogate = UnicodeReplacementChar;
											}

											EnsureBufferNotEmpty();

											WriteCharToBuffer(highSurrogate, lastWritePosition, escapeStartPos);
											lastWritePosition = CharPos;
										}
										else
										{
											// there are not enough remaining chars for the low surrogate or is not follow by unicode sequence
											// replace high surrogate and continue on as usual
											writeChar = UnicodeReplacementChar;
										}
									} while (anotherHighSurrogate);
								}

								charPos = CharPos;
								break;
							default:
								CharPos = charPos;
								throw JsonReaderException.Create(this,
									"Bad JSON escape sequence: {0}.".FormatWith(CultureInfo.InvariantCulture, @"\" + currentChar));
						}

						EnsureBufferNotEmpty();
						WriteCharToBuffer(writeChar, lastWritePosition, escapeStartPos);

						lastWritePosition = charPos;
						break;
					case StringUtils.CarriageReturn:
						CharPos = charPos - 1;
						ProcessCarriageReturn(true);
						charPos = CharPos;
						break;
					case StringUtils.LineFeed:
						CharPos = charPos - 1;
						ProcessLineFeed();
						charPos = CharPos;
						break;
					case '"':
					case '\'':
						if (CharBuffer[charPos - 1] == quote)
						{
							FinishReadStringIntoBuffer(charPos - 1, initialPosition, lastWritePosition);
							return;
						}
						break;
				}
			}
		}