Class JsonValueBoundaryScanner

Namespace

ShapeShift.Json

Assembly

ShapeShift.Json.dll

Recognizes the boundary of one complete, top-level JSON value using Utf8JsonReader's own incremental parsing support, without buffering more than that one value requires.

public sealed class JsonValueBoundaryScanner : IValueBoundaryScanner

Inheritance

object

JsonValueBoundaryScanner

Implements

IValueBoundaryScanner

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.ReferenceEquals(object, object)

object.ToString()

Remarks

Utf8JsonReader already supports incremental parsing of a growing buffer via JsonReaderState resumption, so this scanner does not reimplement any JSON grammar. It only drives the reader through exactly the calls required to recognize "one value has been fully read", which takes a small amount of care:

• TrySkip() requires the reader to already be positioned on a token; called on a reader that has never read a token (None) it returns true immediately without consuming anything, which would look like "boundary found at offset zero" if called blindly. So this type calls Read() first to position on the value's first token, and only afterward considers calling TrySkip().
• Once positioned, only StartObject and StartArray require a further TrySkip() call to consume the rest of the container; every other token type is itself already a complete, self-contained value after the single Read().
• Resuming a saved JsonReaderState correctly restores TokenType, so the same two checks above can simply be repeated on every call without tracking extra state of our own.

Constructors

JsonValueBoundaryScanner(JsonReaderOptions)

Initializes a new instance of the JsonValueBoundaryScanner class.

public JsonValueBoundaryScanner(JsonReaderOptions options = default)

Parameters

options JsonReaderOptions

The options that govern how the JSON is tokenized (e.g. comment handling, trailing commas).

Methods

TryScan(in ReadOnlySequence<byte>, bool, out SequencePosition, out SequencePosition)

Attempts to locate the end of the next complete top-level value at the start of buffer.

public bool TryScan(in ReadOnlySequence<byte> buffer, bool isFinalBlock, out SequencePosition end, out SequencePosition examined)

Parameters

buffer ReadOnlySequence<byte>

All input buffered so far and not yet consumed. Callers are expected to advance their underlying reader past examined after every call (whether it returns true or false), so on the next call for the same value, buffer begins exactly where the previous call's examined left off.

isFinalBlock bool

true if no further input will ever be appended to buffer (the source has reached its end).

end SequencePosition

Receives the position, within buffer, immediately after the complete value, if this method returns true; otherwise default.

examined SequencePosition

Receives the position, within buffer, up through which this instance guarantees it will never need to look again -- regardless of whether this call returns true or false. When this method returns true, this always equals end. When it returns false, this is buffer's start unless the implementation can prove the skipped-over bytes are not part of any value (for example, whitespace preceding the next JSON token) and therefore safe to discard even though the value itself has not yet been found. A caller that has reached isFinalBlock and finds this method returns false with examined equal to buffer's end may conclude that no further value begins here (a graceful end of a sequence of values), rather than that the input ended in the middle of one.

Returns

bool

true if buffer contains (starting at its start) one complete top-level value; false if more input is required before that can be determined.

Exceptions

DecoderException

Thrown when the buffered input is definitely malformed.