Problem
Incoming request payloads in JSON format often requires validation.
Validators might get complex and messy.
We don’t want our codebase to be messy - at least we try not to.
Solution
JSON schema
The best way is to convert our JSON representation of the incoming request into the JSON schema with the help of one of the multiple converters online. I was using the Free Online JSON to JSON Schema Converter.
From the input JSON payload:
{"id":"022eb326-6fa2-4932-8a5f-058a908616a4"}
We’re getting the JSON shema that looks like this for the mentioned input:
{
"$schema": "http://json-schema.org/draft-04/schema#",
"type": "object",
"properties": {
"id": {
"type": "string"
}
},
"required": [
"id"
]
}
Schema validation
Now let’s get to the code.
The validation function:
func ValidateSchema(payload map[string]any, schema string) error {
file, err := os.ReadFile(schema)
if err != nil {
return fmt.Errorf("os.ReadFile: %w", err)
}
schemaLoader := gojsonschema.NewStringLoader(string(file))
payloadLoader := gojsonschema.NewGoLoader(payload)
result, err := gojsonschema.Validate(schemaLoader, payloadLoader)
if err != nil {
return fmt.Errorf("gojsonschema.Validate: %w", err)
}
if !result.Valid() {
errMsg := "JSON validation failed:\n"
for _, desc := range result.Errors() {
errMsg += fmt.Sprintf("- %s\n", desc)
}
return fmt.Errorf("%w: %s", ErrInvalidPayload, errMsg)
}
return nil
}
Working application
Let’s put all the piecen together (file main.go):
package main
import (
"encoding/json"
"errors"
"fmt"
"log"
"os"
"github.com/google/uuid"
"github.com/xeipuuv/gojsonschema"
)
var ErrInvalidPayload = errors.New("invalid payload")
type RequestPayload struct {
ID uuid.UUID `json:"id"`
}
func main() {
p, err := payload()
if err != nil {
log.Fatal(err)
}
if err = ValidateSchema(p, "schema/payload.json"); err != nil {
log.Fatal(err)
}
fmt.Println("Schema validated")
}
func ValidateSchema(payload map[string]any, schema string) error {
file, err := os.ReadFile(schema)
if err != nil {
return fmt.Errorf("os.ReadFile: %w", err)
}
schemaLoader := gojsonschema.NewStringLoader(string(file))
payloadLoader := gojsonschema.NewGoLoader(payload)
result, err := gojsonschema.Validate(schemaLoader, payloadLoader)
if err != nil {
return fmt.Errorf("gojsonschema.Validate: %w", err)
}
if !result.Valid() {
errMsg := "JSON validation failed:\n"
for _, desc := range result.Errors() {
errMsg += fmt.Sprintf("- %s\n", desc)
}
return fmt.Errorf("%w: %s", ErrInvalidPayload, errMsg)
}
return nil
}
func payload() (map[string]any, error) {
r := &RequestPayload{ID: uuid.New()}
payload, err := json.Marshal(r)
if err != nil {
return nil, fmt.Errorf("json.Marshal: %w", err)
}
var data map[string]any
if err := json.Unmarshal(payload, &data); err != nil {
return nil, fmt.Errorf("json.Unmarshal: %w", err)
}
return data, nil
}
➜ payloadschema git:(main) ✗ go run main.go
Schema validated
Sources
