CBOR

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A C# implementation of Concise Binary Object Representation, a general-purpose binary data format defined in RFC 8949. According to that RFC, CBOR’s data model “is an extended version of the JSON data model”, supporting many more types of data than JSON. “CBOR was inspired by MessagePack”, but “is not intended as a version of or replacement for MessagePack.”

This implementation was written by Peter O. and is released to the Public Domain under the CC0 Declaration.

This implementation also doubles as a reader and writer of JSON, and can convert data from JSON to CBOR and back.

Finally, this implementation supports arbitrary-precision binary and decimal floating-point numbers and rational numbers with arbitrary-precision components.

Source code is available in the project page.

Note that after version 4.5x, the CBOR library’s repository will stop including special projects for .NET 2.0 and .NET 4.0, leaving the .NET-Standard project for building the library.

How to Install

Starting with version 0.21.0, the C# implementation is available in the NuGet Package Gallery under the name PeterO.Cbor. To install this library as a NuGet package, enter Install-Package PeterO.Cbor in the NuGet Package Manager Console.

Documentation

This library defines one class, called CBORObject, that allows you to read and write CBOR objects to and from data streams and byte arrays, and to convert JSON text to CBOR objects and back.

See the C# (.NET) API documentation.

The C# implementation is designed as a Portable Class Library.

Other Sites

Examples

The following shows certain use examples of this library. Additional examples can be found in the API documentation.

Creating a map and converting that map to CBOR bytes and a JSON string:

c# // The following creates a CBOR map and adds // several kinds of objects to it var cbor = CBORObject.NewMap() .Add("item", "any string") .Add("number", 42) .Add("map", CBORObject.NewMap().Add("number", 42)) .Add("array", CBORObject.NewArray().Add(999f).Add("xyz")) .Add("bytes", new byte[] { 0, 1, 2 }); // The following converts the map to CBOR byte[] bytes = cbor.EncodeToBytes(); // The following converts the map to JSON string json = cbor.ToJSONString(); Console.WriteLine(json);

Creating a map and converting that map to canonical CBOR bytes (for WebAuthn and other purposes) and a .NET dictionary:

c# // The following creates a CBOR map and adds // several kinds of objects to it var cbor = CBORObject.NewMap() .Add("item", "any string") .Add("foo", "another string") .Add("quux", "a third string"); // The following converts the map to canonical CBOR byte[] bytes = cbor.EncodeToBytes(CBOREncodeOptions.DefaultCtap2Canonical); // The following converts the map to a dictionary var dict = cbor.ToObject<IDictionary<string,string>>(); Console.WriteLine(dict.Count);

Reading data from a file (C#). Note that all the examples for reading and writing to files assume that the platform supports file I/O; the portable class library doesn’t make that assumption.

c# // Read all the bytes from a file and decode the CBOR object // from it. However, there are two disadvantages to this approach: // 1. The byte array might be very huge, so a lot of memory to store // the array may be needed. // 2. The decoding will succeed only if the entire array, // not just the start of the array, consists of a CBOR object. var cbor = CBORObject.DecodeFromBytes( File.ReadAllBytes("object.cbor"), CBOREncodeOptions.Default);

Another example of reading data from a file:

c# // C# // Open the file stream using (var stream = new FileStream("object.cbor", FileMode.Open)) { // Read the CBOR object from the stream var cbor = CBORObject.Read(stream); // At this point, the object is read, but the file stream might // not have ended yet. Here, the code may choose to read another // CBOR object, check for the end of the stream, or just ignore the // rest of the file. The following is an example of checking for the // end of the stream. if (stream.Position != stream.Length) { // The end of the stream wasn't reached yet. } else { // The end of the stream was reached. } }

If a byte array contains multiple CBOR objects, the byte array should be wrapped in a MemoryStream and the stream used to read the objects, as DecodeFromBytes assumes the array contains only one CBOR object. Here is an example.

c# // C# // Create a memory stream with a view of the byte array using (var stream = new MemoryStream(byteArray)) { // Read the CBOR object from the stream var cbor = CBORObject.Read(stream); // The rest of the example follows the one given above. }

Writing CBOR data to a file (C#):

c# // This example assumes that the variable "cbor" refers // to a CBORObject object. using (var stream = new FileStream("object.cbor", FileMode.Create)) { cbor.WriteTo(stream); }

Writing multiple objects to a file, including arbitrary objects (the resulting file is also called a CBOR sequence):

c# // C# // This example writes a sequence of objects in CBOR // format to the same file. using (var stream = new FileStream("object.cborseq", FileMode.Create)) { CBORObject.Write(true, stream); CBORObject.Write(422.5, stream); CBORObject.Write("some string", stream); CBORObject.Write(CBORObject.Undefined, stream); CBORObject.NewArray().Add(42).WriteTo(stream); }

Reading JSON from a file:

c# // Open the file stream using (var stream = new FileStream("object.json", FileMode.Open)) { // Read the JSON object from the stream // as a CBOR object var cbor = CBORObject.ReadJSON(stream); }

Writing a CBOR object as JSON:

```c# // This example assumes that the variable “cbor” refers // to a CBORObject object. // NOTE: Specifying Encoding.UTF8 as the third parameter // would add a byte order mark to the beginning of the text, // but conforming JSON implementations are forbidden from // adding it this way in JSON texts they generate. File.WriteAllText( “object.json”, cbor.ToJSONString(), new System.Text.Encoding.UTF8Encoding(false));

// This is an alternative way to write the CBOR object // and is supported since version 1.2. using (var stream = new FileStream(“object2.json”, FileMode.Create)) { // Write the CBOR object as JSON; here, a byte order // mark won’t be added cbor.WriteJSONTo(stream); } // Version 1.2 and later support a third way to write // objects to JSON: the CBORObject.WriteJSON method using (var stream = new FileStream(“object3.json”, FileMode.Create)) { CBORObject.WriteJSON(“some string”, stream); } using (var stream = new FileStream(“object4.json”, FileMode.Create)) { CBORObject.WriteJSON(cbor, stream); } using (var stream = new FileStream(“object5.json”, FileMode.Create)) { CBORObject.WriteJSON(true, stream); } using (var stream = new FileStream(“object6.json”, FileMode.Create)) { CBORObject.WriteJSON(42, stream); } ```

There are several ways to check whether a CBOR object is a 32-bit integer. Which one to use depends on the application’s needs. Some of them follow (written in C#).

c# /* Accept any untagged CBOR integer that can fit the Int32 range */ if(!cbor.IsTagged && cbor.Type==CBORType.Integer && cbor.CanValueFitInInt32()) { return cbor.AsInt32(); } /* Accept any CBOR integer, tagged or not, that can fit the Int32 range */ if(cbor.Type==CBORType.Integer && cbor.CanValueFitInInt32()) { return cbor.AsInt32(); } /* Accept any CBOR integer or floating-point number, tagged or not, that is an integer within the Int32 range */ if((cbor.Type==CBORType.Integer || cborType==CBORType.FloatingPoint) || cbor.Untag().AsNumber().CanValueFitInInt32()) { return cbor.AsInt32(); } /* Accept any CBOR object representing an integer number that can fit the Int32 range */ if(cbor.IsNumber && cbor.AsNumber().CanValueFitInInt32()) { return cbor.AsInt32(); }

The following example illustrates a custom strategy for converting objects of a given class into CBOR objects. ``` public class CPOD3 { public string Aa { get; set; } public string Bb { get; set; } public string Cc { get; set; } }

private class CPOD3Converter : ICBORToFromConverter<CPOD3> {
   public CBORObject ToCBORObject(CPOD3 cpod) {
      return CBORObject.NewMap()
         .Add(0,cpod.Aa)
         .Add(1,cpod.Bb)
         .Add(2,cpod.Cc);
   }
   public CPOD3 FromCBORObject(CBORObject obj) {
      if (obj.Type!=CBORType.Map) {
         throw new CBORException();
      }
      var ret=new CPOD3();
      ret.Aa=obj[0].AsString();
      ret.Bb=obj[1].AsString();
      ret.Cc=obj[2].AsString();
      return ret;
   }
}

//////////
//  And in the code...

   var cp2=new CPOD3();
   cp2.Aa="AA";
   cp2.Bb="BB";
   cp2.Cc="CC";
   var conv=new CPOD3Converter();
   // Serialize CBOR object, passing the type mapper
   var cbor=conv.ToCBORObject(cp2);
   // Deserialize CBOR object, passing the type mapper
   cp2=conv.FromCBORObject(cbor); ```

NOTE: All code samples in this section are released under the Unlicense.

Demo

Go to https://github.com/peteroupc/Calculator for source code to a demo of the CBOR library in the form of a calculator.

About

Written by Peter O.

Any copyright to this work is released to the Public Domain. In case this is not possible, this work is also licensed under the Unlicense: https://unlicense.org/

Release Notes

See History.md for release notes.

Specifications

Here are specifications by this implementation’s author on certain CBOR tags:

Acknowledgments

I thank all users who sent issues to this repository.