xeipuuv/gojsonschema
GitHub: xeipuuv/gojsonschema
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# gojsonschema
## Description
An implementation of JSON Schema for the Go programming language. Supports draft-04, draft-06 and draft-07.
References :
* http://json-schema.org
* http://json-schema.org/latest/json-schema-core.html
* http://json-schema.org/latest/json-schema-validation.html
## Installation
go get github.com/xeipuuv/gojsonschema
Dependencies :
* [github.com/xeipuuv/gojsonpointer](https://github.com/xeipuuv/gojsonpointer)
* [github.com/xeipuuv/gojsonreference](https://github.com/xeipuuv/gojsonreference)
* [github.com/stretchr/testify/assert](https://github.com/stretchr/testify#assert-package)
## Usage
### Example
package main
import (
"fmt"
"github.com/xeipuuv/gojsonschema"
)
func main() {
schemaLoader := gojsonschema.NewReferenceLoader("file:///home/me/schema.json")
documentLoader := gojsonschema.NewReferenceLoader("file:///home/me/document.json")
result, err := gojsonschema.Validate(schemaLoader, documentLoader)
if err != nil {
panic(err.Error())
}
if result.Valid() {
fmt.Printf("The document is valid\n")
} else {
fmt.Printf("The document is not valid. see errors :\n")
for _, desc := range result.Errors() {
fmt.Printf("- %s\n", desc)
}
}
}
#### Loaders
There are various ways to load your JSON data.
In order to load your schemas and documents,
first declare an appropriate loader :
* Web / HTTP, using a reference :
loader := gojsonschema.NewReferenceLoader("http://www.some_host.com/schema.json")
* Local file, using a reference :
loader := gojsonschema.NewReferenceLoader("file:///home/me/schema.json")
References use the URI scheme, the prefix (file://) and a full path to the file are required.
* JSON strings :
loader := gojsonschema.NewStringLoader(`{"type": "string"}`)
* Custom Go types :
m := map[string]interface{}{"type": "string"}
loader := gojsonschema.NewGoLoader(m)
And
type Root struct {
Users []User `json:"users"`
}
type User struct {
Name string `json:"name"`
}
...
data := Root{}
data.Users = append(data.Users, User{"John"})
data.Users = append(data.Users, User{"Sophia"})
data.Users = append(data.Users, User{"Bill"})
loader := gojsonschema.NewGoLoader(data)
#### Validation
Once the loaders are set, validation is easy :
result, err := gojsonschema.Validate(schemaLoader, documentLoader)
Alternatively, you might want to load a schema only once and process to multiple validations :
schema, err := gojsonschema.NewSchema(schemaLoader)
...
result1, err := schema.Validate(documentLoader1)
...
result2, err := schema.Validate(documentLoader2)
...
// etc ...
To check the result :
if result.Valid() {
fmt.Printf("The document is valid\n")
} else {
fmt.Printf("The document is not valid. see errors :\n")
for _, err := range result.Errors() {
// Err implements the ResultError interface
fmt.Printf("- %s\n", err)
}
}
## Loading local schemas
By default `file` and `http(s)` references to external schemas are loaded automatically via the file system or via http(s). An external schema can also be loaded using a `SchemaLoader`.
sl := gojsonschema.NewSchemaLoader()
loader1 := gojsonschema.NewStringLoader(`{ "type" : "string" }`)
err := sl.AddSchema("http://some_host.com/string.json", loader1)
Alternatively if your schema already has an `$id` you can use the `AddSchemas` function
loader2 := gojsonschema.NewStringLoader(`{
"$id" : "http://some_host.com/maxlength.json",
"maxLength" : 5
}`)
err = sl.AddSchemas(loader2)
The main schema should be passed to the `Compile` function. This main schema can then directly reference the added schemas without needing to download them.
loader3 := gojsonschema.NewStringLoader(`{
"$id" : "http://some_host.com/main.json",
"allOf" : [
{ "$ref" : "http://some_host.com/string.json" },
{ "$ref" : "http://some_host.com/maxlength.json" }
]
}`)
schema, err := sl.Compile(loader3)
documentLoader := gojsonschema.NewStringLoader(`"hello world"`)
result, err := schema.Validate(documentLoader)
It's also possible to pass a `ReferenceLoader` to the `Compile` function that references a loaded schema.
err = sl.AddSchemas(loader3)
schema, err := sl.Compile(gojsonschema.NewReferenceLoader("http://some_host.com/main.json"))
Schemas added by `AddSchema` and `AddSchemas` are only validated when the entire schema is compiled, unless meta-schema validation is used.
## Using a specific draft
By default `gojsonschema` will try to detect the draft of a schema by using the `$schema` keyword and parse it in a strict draft-04, draft-06 or draft-07 mode. If `$schema` is missing, or the draft version is not explicitely set, a hybrid mode is used which merges together functionality of all drafts into one mode.
Autodectection can be turned off with the `AutoDetect` property. Specific draft versions can be specified with the `Draft` property.
sl := gojsonschema.NewSchemaLoader()
sl.Draft = gojsonschema.Draft7
sl.AutoDetect = false
If autodetection is on (default), a draft-07 schema can savely reference draft-04 schemas and vice-versa, as long as `$schema` is specified in all schemas.
## Meta-schema validation
Schemas that are added using the `AddSchema`, `AddSchemas` and `Compile` can be validated against their meta-schema by setting the `Validate` property.
The following example will produce an error as `multipleOf` must be a number. If `Validate` is off (default), this error is only returned at the `Compile` step.
sl := gojsonschema.NewSchemaLoader()
sl.Validate = true
err := sl.AddSchemas(gojsonschema.NewStringLoader(`{
"$id" : "http://some_host.com/invalid.json",
"$schema": "http://json-schema.org/draft-07/schema#",
"multipleOf" : true
}`))
Errors returned by meta-schema validation are more readable and contain more information, which helps significantly if you are developing a schema.
Meta-schema validation also works with a custom `$schema`. In case `$schema` is missing, or `AutoDetect` is set to `false`, the meta-schema of the used draft is used.
## Working with Errors
The library handles string error codes which you can customize by creating your own gojsonschema.locale and setting it
gojsonschema.Locale = YourCustomLocale{}
However, each error contains additional contextual information.
Newer versions of `gojsonschema` may have new additional errors, so code that uses a custom locale will need to be updated when this happens.
**err.Type()**: *string* Returns the "type" of error that occurred. Note you can also type check. See below
Note: An error of RequiredType has an err.Type() return value of "required"
"required": RequiredError
"invalid_type": InvalidTypeError
"number_any_of": NumberAnyOfError
"number_one_of": NumberOneOfError
"number_all_of": NumberAllOfError
"number_not": NumberNotError
"missing_dependency": MissingDependencyError
"internal": InternalError
"const": ConstEror
"enum": EnumError
"array_no_additional_items": ArrayNoAdditionalItemsError
"array_min_items": ArrayMinItemsError
"array_max_items": ArrayMaxItemsError
"unique": ItemsMustBeUniqueError
"contains" : ArrayContainsError
"array_min_properties": ArrayMinPropertiesError
"array_max_properties": ArrayMaxPropertiesError
"additional_property_not_allowed": AdditionalPropertyNotAllowedError
"invalid_property_pattern": InvalidPropertyPatternError
"invalid_property_name": InvalidPropertyNameError
"string_gte": StringLengthGTEError
"string_lte": StringLengthLTEError
"pattern": DoesNotMatchPatternError
"multiple_of": MultipleOfError
"number_gte": NumberGTEError
"number_gt": NumberGTError
"number_lte": NumberLTEError
"number_lt": NumberLTError
"condition_then" : ConditionThenError
"condition_else" : ConditionElseError
**err.Value()**: *interface{}* Returns the value given
**err.Context()**: *gojsonschema.JsonContext* Returns the context. This has a String() method that will print something like this: (root).firstName
**err.Field()**: *string* Returns the fieldname in the format firstName, or for embedded properties, person.firstName. This returns the same as the String() method on *err.Context()* but removes the (root). prefix.
**err.Description()**: *string* The error description. This is based on the locale you are using. See the beginning of this section for overwriting the locale with a custom implementation.
**err.DescriptionFormat()**: *string* The error description format. This is relevant if you are adding custom validation errors afterwards to the result.
**err.Details()**: *gojsonschema.ErrorDetails* Returns a map[string]interface{} of additional error details specific to the error. For example, GTE errors will have a "min" value, LTE will have a "max" value. See errors.go for a full description of all the error details. Every error always contains a "field" key that holds the value of *err.Field()*
{{.field}} must be greater than or equal to {{.min}}
The library allows you to specify custom template functions, should you require more complex error message handling.
gojsonschema.ErrorTemplateFuncs = map[string]interface{}{
"allcaps": func(s string) string {
return strings.ToUpper(s)
},
}
Given the above definition, you can use the custom function `"allcaps"` in your localization templates:
{{allcaps .field}} must be greater than or equal to {{.min}}
The above error message would then be rendered with the `field` value in capital letters. For example:
"PASSWORD must be greater than or equal to 8"
Learn more about what types of template functions you can use in `ErrorTemplateFuncs` by referring to Go's [text/template FuncMap](https://golang.org/pkg/text/template/#FuncMap) type.
## Formats
JSON Schema allows for optional "format" property to validate instances against well-known formats. gojsonschema ships with all of the formats defined in the spec that you can use like this:
{"type": "string", "format": "email"}
Not all formats defined in draft-07 are available. Implemented formats are:
* `date`
* `time`
* `date-time`
* `hostname`. Subdomains that start with a number are also supported, but this means that it doesn't strictly follow [RFC1034](http://tools.ietf.org/html/rfc1034#section-3.5) and has the implication that ipv4 addresses are also recognized as valid hostnames.
* `email`. Go's email parser deviates slightly from [RFC5322](https://tools.ietf.org/html/rfc5322). Includes unicode support.
* `idn-email`. Same caveat as `email`.
* `ipv4`
* `ipv6`
* `uri`. Includes unicode support.
* `uri-reference`. Includes unicode support.
* `iri`
* `iri-reference`
* `uri-template`
* `uuid`
* `regex`. Go uses the [RE2](https://github.com/google/re2/wiki/Syntax) engine and is not [ECMA262](http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf) compatible.
* `json-pointer`
* `relative-json-pointer`
The validation code for `uri`, `idn-email` and their relatives use mostly standard library code.
For repetitive or more complex formats, you can create custom format checkers and add them to gojsonschema like this:
// Define the format checker
type RoleFormatChecker struct {}
// Ensure it meets the gojsonschema.FormatChecker interface
func (f RoleFormatChecker) IsFormat(input interface{}) bool {
asString, ok := input.(string)
if ok == false {
return false
}
return strings.HasPrefix("ROLE_", asString)
}
// Add it to the library
gojsonschema.FormatCheckers.Add("role", RoleFormatChecker{})
Now to use in your json schema:
{"type": "string", "format": "role"}
Another example would be to check if the provided integer matches an id on database:
JSON schema:
{"type": "integer", "format": "ValidUserId"}
// Define the format checker
type ValidUserIdFormatChecker struct {}
// Ensure it meets the gojsonschema.FormatChecker interface
func (f ValidUserIdFormatChecker) IsFormat(input interface{}) bool {
asFloat64, ok := input.(float64) // Numbers are always float64 here
if ok == false {
return false
}
// XXX
// do the magic on the database looking for the int(asFloat64)
return true
}
// Add it to the library
gojsonschema.FormatCheckers.Add("ValidUserId", ValidUserIdFormatChecker{})
Formats can also be removed, for example if you want to override one of the formats that is defined by default.
gojsonschema.FormatCheckers.Remove("hostname")
## Additional custom validation
After the validation has run and you have the results, you may add additional
errors using `Result.AddError`. This is useful to maintain the same format within the resultset instead
of having to add special exceptions for your own errors. Below is an example.
type AnswerInvalidError struct {
gojsonschema.ResultErrorFields
}
func newAnswerInvalidError(context *gojsonschema.JsonContext, value interface{}, details gojsonschema.ErrorDetails) *AnswerInvalidError {
err := AnswerInvalidError{}
err.SetContext(context)
err.SetType("custom_invalid_error")
// it is important to use SetDescriptionFormat() as this is used to call SetDescription() after it has been parsed
// using the description of err will be overridden by this.
err.SetDescriptionFormat("Answer to the Ultimate Question of Life, the Universe, and Everything is {{.answer}}")
err.SetValue(value)
err.SetDetails(details)
return &err
}
func main() {
// ...
schema, err := gojsonschema.NewSchema(schemaLoader)
result, err := gojsonschema.Validate(schemaLoader, documentLoader)
if true { // some validation
jsonContext := gojsonschema.NewJsonContext("question", nil)
errDetail := gojsonschema.ErrorDetails{
"answer": 42,
}
result.AddError(
newAnswerInvalidError(
gojsonschema.NewJsonContext("answer", jsonContext),
52,
errDetail,
),
errDetail,
)
}
return result, err
}
This is especially useful if you want to add validation beyond what the
json schema drafts can provide such business specific logic.
## Uses
gojsonschema uses the following test suite :
https://github.com/json-schema/JSON-Schema-Test-Suite
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