graphql-go

The goal of this project is to provide full support of the GraphQL draft specification with a set of idiomatic, easy to use Go packages.

While still under heavy development (internal APIs are almost certainly subject to change), this library is safe for production use.

Features

• minimal API
• support for context.Context
• support for the OpenTelemetry and OpenTracing standards
• schema type-checking against resolvers
• resolvers are matched to the schema based on method sets (can resolve a GraphQL schema with a Go interface or Go struct).
• handles panics in resolvers
• parallel execution of resolvers
• subscriptions
  • sample WS transport

Roadmap

We're trying out the GitHub Project feature to manage graphql-go's development roadmap. Feedback is welcome and appreciated.

(Some) Documentation

Getting started

In order to run a simple GraphQL server locally create a main.go file with the following content:

package main

import (
        "log"
        "net/http"

        graphql "github.com/graph-gophers/graphql-go"
        "github.com/graph-gophers/graphql-go/relay"
)

type query struct{}

func (_ *query) Hello() string { return "Hello, world!" }

func main() {
        s := `
                type Query {
                        hello: String!
                }
        `
        schema := graphql.MustParseSchema(s, &query{})
        http.Handle("/query", &relay.Handler{Schema: schema})
        log.Fatal(http.ListenAndServe(":8080", nil))
}

Then run the file with go run main.go. To test:

curl -XPOST -d '{"query": "{ hello }"}' localhost:8080/query

For more realistic usecases check our examples section.

Resolvers

A resolver must have one method or field for each field of the GraphQL type it resolves. The method or field name has to be exported and match the schema's field's name in a non-case-sensitive way. You can use struct fields as resolvers by using SchemaOpt: UseFieldResolvers(). For example,

opts := []graphql.SchemaOpt{graphql.UseFieldResolvers()}
schema := graphql.MustParseSchema(s, &query{}, opts...)

When using UseFieldResolvers schema option, a struct field will be used only when:

• there is no method for a struct field
• a struct field does not implement an interface method
• a struct field does not have arguments

The method has up to two arguments:

• Optional context.Context argument.
• Mandatory *struct { ... } argument if the corresponding GraphQL field has arguments. The names of the struct fields have to be exported and have to match the names of the GraphQL arguments in a non-case-sensitive way.

The method has up to two results:

• The GraphQL field's value as determined by the resolver.
• Optional error result.

Example for a simple resolver method:

func (r *helloWorldResolver) Hello() string {
	return "Hello world!"
}

The following signature is also allowed:

func (r *helloWorldResolver) Hello(ctx context.Context) (string, error) {
	return "Hello world!", nil
}

Schema Options

• UseStringDescriptions() enables the usage of double quoted and triple quoted. When this is not enabled, comments are parsed as descriptions instead.
• UseFieldResolvers() specifies whether to use struct field resolvers.
• MaxDepth(n int) specifies the maximum field nesting depth in a query. The default is 0 which disables max depth checking.
• MaxParallelism(n int) specifies the maximum number of resolvers per request allowed to run in parallel. The default is 10.
• Tracer(tracer trace.Tracer) is used to trace queries and fields. It defaults to noop.Tracer.
• Logger(logger log.Logger) is used to log panics during query execution. It defaults to exec.DefaultLogger.
• PanicHandler(panicHandler errors.PanicHandler) is used to transform panics into errors during query execution. It defaults to errors.DefaultPanicHandler.
• DisableIntrospection() disables introspection queries.

Custom Errors

Errors returned by resolvers can include custom extensions by implementing the ResolverError interface:

type ResolverError interface {
	error
	Extensions() map[string]interface{}
}

Example of a simple custom error:

type droidNotFoundError struct {
	Code    string `json:"code"`
	Message string `json:"message"`
}

func (e droidNotFoundError) Error() string {
	return fmt.Sprintf("error [%s]: %s", e.Code, e.Message)
}

func (e droidNotFoundError) Extensions() map[string]interface{} {
	return map[string]interface{}{
		"code":    e.Code,
		"message": e.Message,
	}
}

Which could produce a GraphQL error such as:

{
  "errors": [
    {
      "message": "error [NotFound]: This is not the droid you are looking for",
      "path": [
        "droid"
      ],
      "extensions": {
        "code": "NotFound",
        "message": "This is not the droid you are looking for"
      }
    }
  ],
  "data": null
}

Tracing

By default the library uses noop.Tracer. If you want to change that you can use the OpenTelemetry or the OpenTracing implementations, respectively:

// OpenTelemetry tracer
package main

import (
	"github.com/graph-gophers/graphql-go"
	"github.com/graph-gophers/graphql-go/example/starwars"
	otelgraphql "github.com/graph-gophers/graphql-go/trace/otel"
	"github.com/graph-gophers/graphql-go/trace/tracer"
)
// ...
_, err := graphql.ParseSchema(starwars.Schema, nil, graphql.Tracer(otelgraphql.DefaultTracer()))
// ...

Alternatively you can pass an existing trace.Tracer instance:

tr := otel.Tracer("example")
_, err = graphql.ParseSchema(starwars.Schema, nil, graphql.Tracer(&otelgraphql.Tracer{Tracer: tr}))

// OpenTracing tracer
package main

import (
	"github.com/graph-gophers/graphql-go"
	"github.com/graph-gophers/graphql-go/example/starwars"
	"github.com/graph-gophers/graphql-go/trace/opentracing"
	"github.com/graph-gophers/graphql-go/trace/tracer"
)
// ...
_, err := graphql.ParseSchema(starwars.Schema, nil, graphql.Tracer(opentracing.Tracer{}))

// ...

If you need to implement a custom tracer the library would accept any tracer which implements the interface below:

type Tracer interface {
    TraceQuery(ctx context.Context, queryString string, operationName string, variables map[string]interface{}, varTypes map[string]*introspection.Type) (context.Context, func([]*errors.QueryError))
    TraceField(ctx context.Context, label, typeName, fieldName string, trivial bool, args map[string]interface{}) (context.Context, func(*errors.QueryError))
    TraceValidation(context.Context) func([]*errors.QueryError)
}

Examples