JSON Validator

Yao He

JSON Validator

XML表达信息比较详尽，格式清晰。其实做代码的generator等脚本的时候，也会通过JSON来传递用户的定制参数的。比如cfg.json的内容如下: 

{
    "timescale":"1ns/1ps",
    "dut":{
	"name":"mydut",
	"top_file":"~/mydut.v",
	"filelist":"~/mydut.f"
    },
    "tbp":"demo",
    "env":{
	"name":"bus",
	"agent":[
	    {
		"name":"abc",
		"active":1,
		"off":0,
		"interface":{
		    "ifclk":"clk",
		    "ifrst":"rst",
		    "signal":[
			{
			    "name":"ahb_burst",
			    "bind":"ahb_burst_o"
			},
			{
			    "name":"ahb_valid",
			    "bind":"ahb_valid_o"
			}
		    ]
		}
	    }
	]
    }   
}

同样的，如何在第一时间去check用户输入的json信息是否是正确的？这时候就用到了json-schema文件作为一种validation的标准。假设top.schema.json的内容如下: 

{
    "type": "object",
    "properties":{
	"timescale":{
	    "type": "string"
	},
	"dut":{
	    "type":"object",
	    "properties":{
		"name":{
		    "type":"string"
		},
		"top_file":{
		    "type":"string"
		},
		"filelist":{
		    "type":"string"
		}
	    },
	    "required":["name","top_file","filelist"]
	},
	"env":{
	    "type":"object",
	    "properties":{
		"name":{
		    "type":"string"
		},
		"agent":{
		    "type":"array",
		    "items":{
			"type":"object",
			"properties":{
			    "name":{
				"type":"string"
			    },
			    "active":{
				"type":"integer"
			    },
			    "off":{
				"type":"integer"
			    },
			    "interface":{
				"type":"object",
				"properties":{
				    "ifclk":{
					"type":"string"
				    },
				    "ifrst":{
					"type":"string"
				    },
				    "signal":{
					"type":"array",
					"items":{
					    "type":"object",
					    "properties":{
						"name":{
						    "type":"string"
						},
						"bind":{
						    "type":"string"
						}
					    },
					    "required":["name"]
					},
					"minItems":1
				    }
				},
				"required":["signal"]
			    }
			},
			"required":["name"]
		    },
		    "minItems":1
		}
	    }
	}			
    },
    "required":["dut"]
}

我们用perl来处理JSON文件的validation过程，如下: 

use JSON qw(decode_json);
use JSON::Validator qw(validate_json);

my $validator = JSON::Validator->new;

open(FILE, "top.schema.json") or die "Can not open file top.schema.json";
my @lines = <FILE>;

my $schema = decode_json(join("\n",@lines));

close(FILE); 
$validator->schema($schema);

open(FILE, "cfg.json") or die "Can not open file cfg.json";
@lines = <FILE>;
close(FILE);
my $json_to_be_validated = decode_json(join("\n",@lines));

# Validate your data
@errors = $validator->validate($json_to_be_validated);

# Do something if any errors was found
die "@errors" if @errors;

通过对比可以发现虽然json数据格式简单，但是json的validation格式很不友好，比XML的DTD格式杂乱的多。