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#region Copyright notice and license
// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#endregion
using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Text;
namespace Google.Protobuf
{
/// <summary>
/// Simple but strict JSON tokenizer, rigidly following RFC 7159.
/// </summary>
/// <remarks>
/// <para>
/// This tokenizer is stateful, and only returns "useful" tokens - names, values etc.
/// It does not create tokens for the separator between names and values, or for the comma
/// between values. It validates the token stream as it goes - so callers can assume that the
/// tokens it produces are appropriate. For example, it would never produce "start object, end array."
/// </para>
/// <para>Implementation details: the base class handles single token push-back and </para>
/// <para>Not thread-safe.</para>
/// </remarks>
internal abstract class JsonTokenizer
{
private JsonToken bufferedToken;
/// <summary>
/// Creates a tokenizer that reads from the given text reader.
/// </summary>
internal static JsonTokenizer FromTextReader(TextReader reader)
{
return new JsonTextTokenizer(reader);
}
/// <summary>
/// Creates a tokenizer that first replays the given list of tokens, then continues reading
/// from another tokenizer. Note that if the returned tokenizer is "pushed back", that does not push back
/// on the continuation tokenizer, or vice versa. Care should be taken when using this method - it was
/// created for the sake of Any parsing.
/// </summary>
internal static JsonTokenizer FromReplayedTokens(IList<JsonToken> tokens, JsonTokenizer continuation)
{
return new JsonReplayTokenizer(tokens, continuation);
}
/// <summary>
/// Returns the depth of the stack, purely in objects (not collections).
/// Informally, this is the number of remaining unclosed '{' characters we have.
/// </summary>
internal int ObjectDepth { get; private set; }
// TODO: Why do we allow a different token to be pushed back? It might be better to always remember the previous
// token returned, and allow a parameterless Rewind() method (which could only be called once, just like the current PushBack).
internal void PushBack(JsonToken token)
{
if (bufferedToken != null)
{
throw new InvalidOperationException("Can't push back twice");
}
bufferedToken = token;
if (token.Type == JsonToken.TokenType.StartObject)
{
ObjectDepth--;
}
else if (token.Type == JsonToken.TokenType.EndObject)
{
ObjectDepth++;
}
}
/// <summary>
/// Returns the next JSON token in the stream. An EndDocument token is returned to indicate the end of the stream,
/// after which point <c>Next()</c> should not be called again.
/// </summary>
/// <remarks>This implementation provides single-token buffering, and calls <see cref="NextImpl"/> if there is no buffered token.</remarks>
/// <returns>The next token in the stream. This is never null.</returns>
/// <exception cref="InvalidOperationException">This method is called after an EndDocument token has been returned</exception>
/// <exception cref="InvalidJsonException">The input text does not comply with RFC 7159</exception>
internal JsonToken Next()
{
JsonToken tokenToReturn;
if (bufferedToken != null)
{
tokenToReturn = bufferedToken;
bufferedToken = null;
}
else
{
tokenToReturn = NextImpl();
}
if (tokenToReturn.Type == JsonToken.TokenType.StartObject)
{
ObjectDepth++;
}
else if (tokenToReturn.Type == JsonToken.TokenType.EndObject)
{
ObjectDepth--;
}
return tokenToReturn;
}
/// <summary>
/// Returns the next JSON token in the stream, when requested by the base class. (The <see cref="Next"/> method delegates
/// to this if it doesn't have a buffered token.)
/// </summary>
/// <exception cref="InvalidOperationException">This method is called after an EndDocument token has been returned</exception>
/// <exception cref="InvalidJsonException">The input text does not comply with RFC 7159</exception>
protected abstract JsonToken NextImpl();
/// <summary>
/// Skips the value we're about to read. This must only be called immediately after reading a property name.
/// If the value is an object or an array, the complete object/array is skipped.
/// </summary>
internal void SkipValue()
{
// We'll assume that Next() makes sure that the end objects and end arrays are all valid.
// All we care about is the total nesting depth we need to close.
int depth = 0;
// do/while rather than while loop so that we read at least one token.
do
{
var token = Next();
switch (token.Type)
{
case JsonToken.TokenType.EndArray:
case JsonToken.TokenType.EndObject:
depth--;
break;
case JsonToken.TokenType.StartArray:
case JsonToken.TokenType.StartObject:
depth++;
break;
}
} while (depth != 0);
}
/// <summary>
/// Tokenizer which first exhausts a list of tokens, then consults another tokenizer.
/// </summary>
private class JsonReplayTokenizer : JsonTokenizer
{
private readonly IList<JsonToken> tokens;
private readonly JsonTokenizer nextTokenizer;
private int nextTokenIndex;
internal JsonReplayTokenizer(IList<JsonToken> tokens, JsonTokenizer nextTokenizer)
{
this.tokens = tokens;
this.nextTokenizer = nextTokenizer;
}
// FIXME: Object depth not maintained...
protected override JsonToken NextImpl()
{
if (nextTokenIndex >= tokens.Count)
{
return nextTokenizer.Next();
}
return tokens[nextTokenIndex++];
}
}
/// <summary>
/// Tokenizer which does all the *real* work of parsing JSON.
/// </summary>
private sealed class JsonTextTokenizer : JsonTokenizer
{
// The set of states in which a value is valid next token.
private static readonly State ValueStates = State.ArrayStart | State.ArrayAfterComma | State.ObjectAfterColon | State.StartOfDocument;
private readonly Stack<ContainerType> containerStack = new Stack<ContainerType>();
private readonly PushBackReader reader;
private State state;
internal JsonTextTokenizer(TextReader reader)
{
this.reader = new PushBackReader(reader);
state = State.StartOfDocument;
containerStack.Push(ContainerType.Document);
}
/// <remarks>
/// This method essentially just loops through characters skipping whitespace, validating and
/// changing state (e.g. from ObjectBeforeColon to ObjectAfterColon)
/// until it reaches something which will be a genuine token (e.g. a start object, or a value) at which point
/// it returns the token. Although the method is large, it would be relatively hard to break down further... most
/// of it is the large switch statement, which sometimes returns and sometimes doesn't.
/// </remarks>
protected override JsonToken NextImpl()
{
if (state == State.ReaderExhausted)
{
throw new InvalidOperationException("Next() called after end of document");
}
while (true)
{
var next = reader.Read();
if (next == null)
{
ValidateState(State.ExpectedEndOfDocument, "Unexpected end of document in state: ");
state = State.ReaderExhausted;
return JsonToken.EndDocument;
}
switch (next.Value)
{
// Skip whitespace between tokens
case ' ':
case '\t':
case '\r':
case '\n':
break;
case ':':
ValidateState(State.ObjectBeforeColon, "Invalid state to read a colon: ");
state = State.ObjectAfterColon;
break;
case ',':
ValidateState(State.ObjectAfterProperty | State.ArrayAfterValue, "Invalid state to read a comma: ");
state = state == State.ObjectAfterProperty ? State.ObjectAfterComma : State.ArrayAfterComma;
break;
case '"':
string stringValue = ReadString();
if ((state & (State.ObjectStart | State.ObjectAfterComma)) != 0)
{
state = State.ObjectBeforeColon;
return JsonToken.Name(stringValue);
}
else
{
ValidateAndModifyStateForValue("Invalid state to read a double quote: ");
return JsonToken.Value(stringValue);
}
case '{':
ValidateState(ValueStates, "Invalid state to read an open brace: ");
state = State.ObjectStart;
containerStack.Push(ContainerType.Object);
return JsonToken.StartObject;
case '}':
ValidateState(State.ObjectAfterProperty | State.ObjectStart, "Invalid state to read a close brace: ");
PopContainer();
return JsonToken.EndObject;
case '[':
ValidateState(ValueStates, "Invalid state to read an open square bracket: ");
state = State.ArrayStart;
containerStack.Push(ContainerType.Array);
return JsonToken.StartArray;
case ']':
ValidateState(State.ArrayAfterValue | State.ArrayStart, "Invalid state to read a close square bracket: ");
PopContainer();
return JsonToken.EndArray;
case 'n': // Start of null
ConsumeLiteral("null");
ValidateAndModifyStateForValue("Invalid state to read a null literal: ");
return JsonToken.Null;
case 't': // Start of true
ConsumeLiteral("true");
ValidateAndModifyStateForValue("Invalid state to read a true literal: ");
return JsonToken.True;
case 'f': // Start of false
ConsumeLiteral("false");
ValidateAndModifyStateForValue("Invalid state to read a false literal: ");
return JsonToken.False;
case '-': // Start of a number
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
double number = ReadNumber(next.Value);
ValidateAndModifyStateForValue("Invalid state to read a number token: ");
return JsonToken.Value(number);
default:
throw new InvalidJsonException("Invalid first character of token: " + next.Value);
}
}
}
private void ValidateState(State validStates, string errorPrefix)
{
if ((validStates & state) == 0)
{
throw reader.CreateException(errorPrefix + state);
}
}
/// <summary>
/// Reads a string token. It is assumed that the opening " has already been read.
/// </summary>
private string ReadString()
{
var value = new StringBuilder();
bool haveHighSurrogate = false;
while (true)
{
char c = reader.ReadOrFail("Unexpected end of text while reading string");
if (c < ' ')
{
throw reader.CreateException(string.Format(CultureInfo.InvariantCulture, "Invalid character in string literal: U+{0:x4}", (int) c));
}
if (c == '"')
{
if (haveHighSurrogate)
{
throw reader.CreateException("Invalid use of surrogate pair code units");
}
return value.ToString();
}
if (c == '\\')
{
c = ReadEscapedCharacter();
}
// TODO: Consider only allowing surrogate pairs that are either both escaped,
// or both not escaped. It would be a very odd text stream that contained a "lone" high surrogate
// followed by an escaped low surrogate or vice versa... and that couldn't even be represented in UTF-8.
if (haveHighSurrogate != char.IsLowSurrogate(c))
{
throw reader.CreateException("Invalid use of surrogate pair code units");
}
haveHighSurrogate = char.IsHighSurrogate(c);
value.Append(c);
}
}
/// <summary>
/// Reads an escaped character. It is assumed that the leading backslash has already been read.
/// </summary>
private char ReadEscapedCharacter()
{
char c = reader.ReadOrFail("Unexpected end of text while reading character escape sequence");
switch (c)
{
case 'n':
return '\n';
case '\\':
return '\\';
case 'b':
return '\b';
case 'f':
return '\f';
case 'r':
return '\r';
case 't':
return '\t';
case '"':
return '"';
case '/':
return '/';
case 'u':
return ReadUnicodeEscape();
default:
throw reader.CreateException(string.Format(CultureInfo.InvariantCulture, "Invalid character in character escape sequence: U+{0:x4}", (int) c));
}
}
/// <summary>
/// Reads an escaped Unicode 4-nybble hex sequence. It is assumed that the leading \u has already been read.
/// </summary>
private char ReadUnicodeEscape()
{
int result = 0;
for (int i = 0; i < 4; i++)
{
char c = reader.ReadOrFail("Unexpected end of text while reading Unicode escape sequence");
int nybble;
if (c >= '0' && c <= '9')
{
nybble = c - '0';
}
else if (c >= 'a' && c <= 'f')
{
nybble = c - 'a' + 10;
}
else if (c >= 'A' && c <= 'F')
{
nybble = c - 'A' + 10;
}
else
{
throw reader.CreateException(string.Format(CultureInfo.InvariantCulture, "Invalid character in character escape sequence: U+{0:x4}", (int) c));
}
result = (result << 4) + nybble;
}
return (char) result;
}
/// <summary>
/// Consumes a text-only literal, throwing an exception if the read text doesn't match it.
/// It is assumed that the first letter of the literal has already been read.
/// </summary>
private void ConsumeLiteral(string text)
{
for (int i = 1; i < text.Length; i++)
{
char? next = reader.Read();
if (next == null)
{
throw reader.CreateException("Unexpected end of text while reading literal token " + text);
}
if (next.Value != text[i])
{
throw reader.CreateException("Unexpected character while reading literal token " + text);
}
}
}
private double ReadNumber(char initialCharacter)
{
StringBuilder builder = new StringBuilder();
if (initialCharacter == '-')
{
builder.Append("-");
}
else
{
reader.PushBack(initialCharacter);
}
// Each method returns the character it read that doesn't belong in that part,
// so we know what to do next, including pushing the character back at the end.
// null is returned for "end of text".
char? next = ReadInt(builder);
if (next == '.')
{
next = ReadFrac(builder);
}
if (next == 'e' || next == 'E')
{
next = ReadExp(builder);
}
// If we read a character which wasn't part of the number, push it back so we can read it again
// to parse the next token.
if (next != null)
{
reader.PushBack(next.Value);
}
// TODO: What exception should we throw if the value can't be represented as a double?
try
{
return double.Parse(builder.ToString(),
NumberStyles.AllowLeadingSign | NumberStyles.AllowDecimalPoint | NumberStyles.AllowExponent,
CultureInfo.InvariantCulture);
}
catch (OverflowException)
{
throw reader.CreateException("Numeric value out of range: " + builder);
}
}
private char? ReadInt(StringBuilder builder)
{
char first = reader.ReadOrFail("Invalid numeric literal");
if (first < '0' || first > '9')
{
throw reader.CreateException("Invalid numeric literal");
}
builder.Append(first);
int digitCount;
char? next = ConsumeDigits(builder, out digitCount);
if (first == '0' && digitCount != 0)
{
throw reader.CreateException("Invalid numeric literal: leading 0 for non-zero value.");
}
return next;
}
private char? ReadFrac(StringBuilder builder)
{
builder.Append('.'); // Already consumed this
int digitCount;
char? next = ConsumeDigits(builder, out digitCount);
if (digitCount == 0)
{
throw reader.CreateException("Invalid numeric literal: fraction with no trailing digits");
}
return next;
}
private char? ReadExp(StringBuilder builder)
{
builder.Append('E'); // Already consumed this (or 'e')
char? next = reader.Read();
if (next == null)
{
throw reader.CreateException("Invalid numeric literal: exponent with no trailing digits");
}
if (next == '-' || next == '+')
{
builder.Append(next.Value);
}
else
{
reader.PushBack(next.Value);
}
int digitCount;
next = ConsumeDigits(builder, out digitCount);
if (digitCount == 0)
{
throw reader.CreateException("Invalid numeric literal: exponent without value");
}
return next;
}
private char? ConsumeDigits(StringBuilder builder, out int count)
{
count = 0;
while (true)
{
char? next = reader.Read();
if (next == null || next.Value < '0' || next.Value > '9')
{
return next;
}
count++;
builder.Append(next.Value);
}
}
/// <summary>
/// Validates that we're in a valid state to read a value (using the given error prefix if necessary)
/// and changes the state to the appropriate one, e.g. ObjectAfterColon to ObjectAfterProperty.
/// </summary>
private void ValidateAndModifyStateForValue(string errorPrefix)
{
ValidateState(ValueStates, errorPrefix);
switch (state)
{
case State.StartOfDocument:
state = State.ExpectedEndOfDocument;
return;
case State.ObjectAfterColon:
state = State.ObjectAfterProperty;
return;
case State.ArrayStart:
case State.ArrayAfterComma:
state = State.ArrayAfterValue;
return;
default:
throw new InvalidOperationException("ValidateAndModifyStateForValue does not handle all value states (and should)");
}
}
/// <summary>
/// Pops the top-most container, and sets the state to the appropriate one for the end of a value
/// in the parent container.
/// </summary>
private void PopContainer()
{
containerStack.Pop();
var parent = containerStack.Peek();
switch (parent)
{
case ContainerType.Object:
state = State.ObjectAfterProperty;
break;
case ContainerType.Array:
state = State.ArrayAfterValue;
break;
case ContainerType.Document:
state = State.ExpectedEndOfDocument;
break;
default:
throw new InvalidOperationException("Unexpected container type: " + parent);
}
}
private enum ContainerType
{
Document, Object, Array
}
/// <summary>
/// Possible states of the tokenizer.
/// </summary>
/// <remarks>
/// <para>This is a flags enum purely so we can simply and efficiently represent a set of valid states
/// for checking.</para>
/// <para>
/// Each is documented with an example,
/// where ^ represents the current position within the text stream. The examples all use string values,
/// but could be any value, including nested objects/arrays.
/// The complete state of the tokenizer also includes a stack to indicate the contexts (arrays/objects).
/// Any additional notional state of "AfterValue" indicates that a value has been completed, at which
/// point there's an immediate transition to ExpectedEndOfDocument, ObjectAfterProperty or ArrayAfterValue.
/// </para>
/// <para>
/// These states were derived manually by reading RFC 7159 carefully.
/// </para>
/// </remarks>
[Flags]
private enum State
{
/// <summary>
/// ^ { "foo": "bar" }
/// Before the value in a document. Next states: ObjectStart, ArrayStart, "AfterValue"
/// </summary>
StartOfDocument = 1 << 0,
/// <summary>
/// { "foo": "bar" } ^
/// After the value in a document. Next states: ReaderExhausted
/// </summary>
ExpectedEndOfDocument = 1 << 1,
/// <summary>
/// { "foo": "bar" } ^ (and already read to the end of the reader)
/// Terminal state.
/// </summary>
ReaderExhausted = 1 << 2,
/// <summary>
/// { ^ "foo": "bar" }
/// Before the *first* property in an object.
/// Next states:
/// "AfterValue" (empty object)
/// ObjectBeforeColon (read a name)
/// </summary>
ObjectStart = 1 << 3,
/// <summary>
/// { "foo" ^ : "bar", "x": "y" }
/// Next state: ObjectAfterColon
/// </summary>
ObjectBeforeColon = 1 << 4,
/// <summary>
/// { "foo" : ^ "bar", "x": "y" }
/// Before any property other than the first in an object.
/// (Equivalently: after any property in an object)
/// Next states:
/// "AfterValue" (value is simple)
/// ObjectStart (value is object)
/// ArrayStart (value is array)
/// </summary>
ObjectAfterColon = 1 << 5,
/// <summary>
/// { "foo" : "bar" ^ , "x" : "y" }
/// At the end of a property, so expecting either a comma or end-of-object
/// Next states: ObjectAfterComma or "AfterValue"
/// </summary>
ObjectAfterProperty = 1 << 6,
/// <summary>
/// { "foo":"bar", ^ "x":"y" }
/// Read the comma after the previous property, so expecting another property.
/// This is like ObjectStart, but closing brace isn't valid here
/// Next state: ObjectBeforeColon.
/// </summary>
ObjectAfterComma = 1 << 7,
/// <summary>
/// [ ^ "foo", "bar" ]
/// Before the *first* value in an array.
/// Next states:
/// "AfterValue" (read a value)
/// "AfterValue" (end of array; will pop stack)
/// </summary>
ArrayStart = 1 << 8,
/// <summary>
/// [ "foo" ^ , "bar" ]
/// After any value in an array, so expecting either a comma or end-of-array
/// Next states: ArrayAfterComma or "AfterValue"
/// </summary>
ArrayAfterValue = 1 << 9,
/// <summary>
/// [ "foo", ^ "bar" ]
/// After a comma in an array, so there *must* be another value (simple or complex).
/// Next states: "AfterValue" (simple value), StartObject, StartArray
/// </summary>
ArrayAfterComma = 1 << 10
}
/// <summary>
/// Wrapper around a text reader allowing small amounts of buffering and location handling.
/// </summary>
private class PushBackReader
{
// TODO: Add locations for errors etc.
private readonly TextReader reader;
internal PushBackReader(TextReader reader)
{
// TODO: Wrap the reader in a BufferedReader?
this.reader = reader;
}
/// <summary>
/// The buffered next character, if we have one.
/// </summary>
private char? nextChar;
/// <summary>
/// Returns the next character in the stream, or null if we have reached the end.
/// </summary>
/// <returns></returns>
internal char? Read()
{
if (nextChar != null)
{
char? tmp = nextChar;
nextChar = null;
return tmp;
}
int next = reader.Read();
return next == -1 ? null : (char?) next;
}
internal char ReadOrFail(string messageOnFailure)
{
char? next = Read();
if (next == null)
{
throw CreateException(messageOnFailure);
}
return next.Value;
}
internal void PushBack(char c)
{
if (nextChar != null)
{
throw new InvalidOperationException("Cannot push back when already buffering a character");
}
nextChar = c;
}
/// <summary>
/// Creates a new exception appropriate for the current state of the reader.
/// </summary>
internal InvalidJsonException CreateException(string message)
{
// TODO: Keep track of and use the location.
return new InvalidJsonException(message);
}
}
}
}
}