encoding/json: encoding.UnmarshalText() produces unexpected values when json.Unmarshaling.

[rkolp]

What version of Go are you using (go version)?

$ go version
go version go1.14 darwin/amd64

Does this issue reproduce with the latest release?

Yes, however it seems v1.13.X is working properly.

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users//Library/Caches/go-build"
GOENV="/Users//Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users//develop/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users//develop/go/src/github.com//go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/2w/0n_2xt5x51sbnz4__k1slqnw0000gn/T/go-build451039144=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I tried to implement encoding.TextUnmarshaler for unmarshaling JSON. However when escaped characters are added to the end of a JSON value the unmarshaled value becomes mangled and includes JSON formatting characters.

package main

import (
	"encoding/json"
	"fmt"
	"strings"
)

type RC string

func (r *RC) UnmarshalText(b []byte) error {
	*r = RC(fmt.Sprintf("RC_%s", strings.ToUpper(string(b))))
	return nil
}

type incident struct {
	Regions map[RC]Region `json:"regions"`
}

type Region struct {
	Facets []Facet `json:"facets"`
}

type Facet struct {
	SOE string `json:"sensitivity_override_explanation"`
}

func main() {
	r := `
	{
		"regions": {
			"US": {
				"facets": [{
				"sensitivity_override_explanation": "43423432423\\r"
				}]
			}
		}
	}
	`
	i := new(incident)

	if err := json.Unmarshal([]byte(r), &i); err != nil {
		fmt.Println(err)
		return
	}

	for k := range i.Regions {
		fmt.Printf("key: %q\n", k)
	}
}

What did you expect to see?

key: "RC_US"

What did you see instead?

key: "RC_US\": {\n\t\t\t"

[andybons]

@mvdan

[rkolp]

Looks like someone else ran into this issue as well: #38105

[mvdan]

Thanks @rkolp. It looks like @dsnet already did a bisect and a backport issue there, so let's consolidate both issues into that one. I realise this issue is older, so apologies for the mishap.