json: Use segmentio/encoding/json for unmarshaling

For maximum compatibility it's used only for unmarshaling at the
moment. The existing unit tests look good, benchmarks are promising.

name \ time/op     bench_encoding_json.txt  bench_go_json.txt  bench_jsoniter.txt  bench_segmentio.txt
UnmarshalOrders-8               185ms ± 0%          89ms ± 0%          116ms ± 0%            97ms ± 0%

name \ alloc/op    bench_encoding_json.txt  bench_go_json.txt  bench_jsoniter.txt  bench_segmentio.txt
UnmarshalOrders-8              19.1MB ± 0%        30.7MB ± 0%         27.2MB ± 0%          28.3MB ± 0%

name \ allocs/op   bench_encoding_json.txt  bench_go_json.txt  bench_jsoniter.txt  bench_segmentio.txt
UnmarshalOrders-8                388k ± 0%          335k ± 0%           686k ± 0%            332k ± 0%

Using this library for marshaling produces different results from
encoding/json due tue the handling of embedded pointers. See
segmentio/encoding#63

code-generate/generate_types.go

@@ -271,7 +271,7 @@ func generateStructUnmarshalJSON(object *RamlType, discriminatedAttributes []*Ra
 	c = c.Block(
 		jen.Type().Id("Alias").Id(object.CodeName),
 		jen.If(
-			jen.Err().Op(":=").Qual("encoding/json", "Unmarshal").Call(
+			jen.Err().Op(":=").Qual("github.com/segmentio/encoding/json", "Unmarshal").Call(
 				jen.Id("data"),
 				jen.Parens(jen.Op("*").Id("Alias")).Parens(jen.Id("obj")),
 			),

commercetools/client.go

@@ -3,7 +3,6 @@ package commercetools
 import (
 	"bytes"
 	"context"
-	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -15,6 +14,7 @@ import (
 	"github.com/opentracing-contrib/go-stdlib/nethttp"
 	"github.com/opentracing/opentracing-go"
 	"github.com/pkg/errors"
+	"github.com/segmentio/encoding/json"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/clientcredentials"
 )

commercetools/client_graphql.go

@@ -3,13 +3,13 @@ package commercetools
 import (
 	"bytes"
 	"context"
-	"encoding/json"
 	"fmt"
 	"io/ioutil"
 	"net/http"
 
 	mapstructure "github.com/mitchellh/mapstructure"
 	"github.com/pkg/errors"
+	"github.com/segmentio/encoding/json"
 )
 
 type GraphQLQuery struct {

commercetools/client_test.go

@@ -26,7 +26,7 @@ func TestClientGetBadRequestJson(t *testing.T) {
 	defer server.Close()
 
 	_, err := client.ProductGetWithID(context.TODO(), "fake-id")
-	assert.Equal(t, "invalid character ',' looking for beginning of value", err.Error())
+	assert.Equal(t, "json: invalid character ',' looking for beginning of value: ,", err.Error())
 	assert.IsType(t, commercetools.ErrorResponse{}, err)
 }
 

commercetools/date.go

@@ -1,10 +1,11 @@
 package commercetools
 
 import (
-	"encoding/json"
 	"fmt"
 	"strconv"
 	"time"
+
+	"github.com/segmentio/encoding/json"
 )
 
 // Date holds date information for Commercetools API format