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