Re: [Json] Call for real-world examples of how parsers deal with duplicate keys

Bjoern Hoehrmann <derhoermi@gmx.net> Thu, 06 June 2013 18:18 UTC

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From: Bjoern Hoehrmann <derhoermi@gmx.net>
To: Paul Hoffman <paul.hoffman@vpnc.org>
Date: Thu, 06 Jun 2013 20:18:23 +0200
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Subject: Re: [Json] Call for real-world examples of how parsers deal with duplicate keys
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* Paul Hoffman wrote:
>Greetings again. Knowing what current parsers do with duplicate keys 
>might be useful to this discussion. Of course, some people will exclaim 
>"but that's wrong!" to some of what we see, but seeing it may be useful 
>nonetheless.
>
>I propose the following JSON text for the tests:
>
>{"a":1,"a":2}

I note that this test is insufficient for a conclusion like "takes the
last value", but it should be okay for concluding "does not reject the
input under default settings". With Perl, the JSON module on CPAN has
a pure-perl module JSON::PP, but would generally prefer a a C-based
module like JSON::XS when available (and `use JSON;` hides the choice).

  #!perl -w
  use JSON::PP;
  use Data::Dumper;
  print Dumper([ JSON::PP->new->decode('{"a":1,"a":2}') ]);

and the same with JSON::XS in place of JSON::PP will print

  $VAR1 = [
            {
              'a' => 2
            }
          ];

In Microsoft's .NET Framework the System.Runtime.Serialization.Json
reader abstracts JSON into XML...

  using System;
  using System.Text;
  using System.Runtime.Serialization.Json;
  
  class Program {
    static void Main(string[] args) {
      var json = "{\"a\":1,\"a\":2}";
      var bytes = UTF8Encoding.UTF8.GetBytes(json);
      var p = JsonReaderWriterFactory.CreateJsonReader(bytes,
        new System.Xml.XmlDictionaryReaderQuotas());
  
      while (p.Read()) {
        Console.WriteLine("{0}", p.ReadOuterXml());
      }
    }
  }

which results in

  <root type="object">
    <a type="number">1</a>
    <a type="number">2</a>
  </root>

This being a streaming parser it reports both instances as they are in
the document.
-- 
Björn Höhrmann · mailto:bjoern@hoehrmann.de · http://bjoern.hoehrmann.de
Am Badedeich 7 · Telefon: +49(0)160/4415681 · http://www.bjoernsworld.de
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