encoding/json: Unmarshal of json elements into struct with variable "uuid" in lower case does not work

[Geekgasm]

Please answer these questions before submitting your issue. Thanks!

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

go version go1.10.1 darwin/amd64

Does this issue reproduce with the latest release?

yes

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

GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/d037698/Library/Caches/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/d037698/go"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.10.1/libexec"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.10.1/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
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/xp/4bmz5sv10cd8hp6r9frr9__80000gn/T/go-build330651932=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Run this program to unmarshal a json blob with a key "uuid":

package main

import (
  "fmt"
  "encoding/json"
)

func main() {
  var jsonBlob = []byte(`[
    {"UUID": "C5FA164A3F4C11E88B5406B45C771ECC"},
    {"uuid": "C5FA164A3F4C11E88B5406B45C771ECC"}
  ]`)

  type BiglyUUID struct {
    UUID  string
  }
  var bigUuids []BiglyUUID
  err := json.Unmarshal(jsonBlob, &bigUuids)
  if err != nil {
    fmt.Println("error:", err)
  }
  fmt.Printf("%+v", bigUuids)
  fmt.Println()

  type tinyUuid struct {
    uuid string
  }
  var smallUuids []tinyUuid
  err2 := json.Unmarshal(jsonBlob, &smallUuids)
  if err2 != nil {
    fmt.Println("error:", err2)
  }
  fmt.Printf("%+v", smallUuids)
  fmt.Println()
}

Go Playground link: https://play.golang.org/p/pVDWjEWgCCQ

What did you expect to see?

[{UUID:C5FA164A3F4C11E88B5406B45C771ECC} {UUID:C5FA164A3F4C11E88B5406B45C771ECC}]
[{uuid:C5FA164A3F4C11E88B5406B45C771ECC} {uuid:C5FA164A3F4C11E88B5406B45C771ECC}]

What did you see instead?

[{UUID:C5FA164A3F4C11E88B5406B45C771ECC} {UUID:C5FA164A3F4C11E88B5406B45C771ECC}]
[{uuid:} {uuid:}]

[bradfitz]

This is working as documented. Read the encoding/json docs for details.

For questions about Go, see https://golang.org/wiki/Questions.