graphql.go

package graphql

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"

	"github.com/arvata-io/graphql/internal/jsonutil"
	"golang.org/x/net/context/ctxhttp"
)

// Client is a GraphQL client.
type Client struct {
	url        string // GraphQL server URL.
	httpClient *http.Client
}

// NewClient creates a GraphQL client targeting the specified GraphQL server URL.
// If httpClient is nil, then http.DefaultClient is used.
func NewClient(url string, httpClient *http.Client) *Client {
	if httpClient == nil {
		httpClient = http.DefaultClient
	}
	return &Client{
		url:        url,
		httpClient: httpClient,
	}
}

// Query executes a single GraphQL query request,
// with a query derived from q, populating the response into it.
// q should be a pointer to struct that corresponds to the GraphQL schema.
func (c *Client) Query(ctx context.Context, q interface{}, variables map[string]interface{}) error {
	return c.Run(ctx, &Query{
		Data:           q,
		Vars:           variables,
		RequestHandler: nil,
	})
}

// Mutate executes a single GraphQL mutation request,
// with a mutation derived from m, populating the response into it.
// m should be a pointer to struct that corresponds to the GraphQL schema.
func (c *Client) Mutate(ctx context.Context, m interface{}, variables map[string]interface{}) error {
	return c.Run(ctx, &Mutation{
		Data:           m,
		Vars:           variables,
		RequestHandler: nil,
	})
}

type request struct {
	Query     string                 `json:"query"`
	Variables map[string]interface{} `json:"variables,omitempty"`
}

// do executes a single GraphQL operation.
func (c *Client) Run(ctx context.Context, op Operation) error {
	in := request{
		Query:     op.Query(),
		Variables: op.Variables(),
	}
	var buf bytes.Buffer
	err := json.NewEncoder(&buf).Encode(in)
	if err != nil {
		return err
	}
	req, err := http.NewRequest(http.MethodPost, c.url, &buf)
	if err != nil {
		return err
	}
	req.Header.Set("Content-Type", "application/json")
	op.ModifyRequest(req)

	resp, err := ctxhttp.Do(ctx, c.httpClient, req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		body, _ := ioutil.ReadAll(resp.Body)
		return fmt.Errorf("non-200 OK status code: %v body: %q", resp.Status, body)
	}
	var out struct {
		Data   *json.RawMessage
		Errors errors
		//Extensions interface{} // Unused.
	}
	err = json.NewDecoder(resp.Body).Decode(&out)
	if err != nil {
		// TODO: Consider including response body in returned error, if deemed helpful.
		return err
	}
	if out.Data != nil {
		err := jsonutil.UnmarshalGraphQL(*out.Data, op.ResponsePtr())
		if err != nil {
			// TODO: Consider including response body in returned error, if deemed helpful.
			return err
		}
	}
	if len(out.Errors) > 0 {
		return out.Errors
	}
	return nil
}

// errors represents the "errors" array in a response from a GraphQL server.
// If returned via error interface, the slice is expected to contain at least 1 element.
//
// Specification: https://facebook.github.io/graphql/#sec-Errors.
type errors []struct {
	Message   string
	Locations []struct {
		Line   int
		Column int
	}
}

// Error implements error interface.
func (e errors) Error() string {
	return e[0].Message
}