Read json object from stdin in golang

Question

How to read a json object from stdin? I want to copy and paste a json object into the stdin, read it and unmarshal it. Here is the code:

    var input string
    _, err := fmt.Scan(&input)
    if err != nil {
        fmt.Println(err)
        continue
    }

    var record MedicalRecord
    if err := json.Unmarshal([]byte(input), &record); err != nil {
        log.Println(err)
        continue
    }

And the errors are printed to console.

> 2018/06/26 00:26:32 invalid character ':' after top-level value
> 2018/06/26 00:26:32 unexpected end of JSON input
> 2018/06/26 00:26:32 invalid character ':' after top-level value
> 2018/06/26 00:26:32 invalid character ',' after top-level value
> 2018/06/26 00:26:32 invalid character ':' after top-level value
> 2018/06/26 00:26:32 invalid character ',' after top-level value
> 2018/06/26 00:26:32 invalid character ':' after top-level value
> 2018/06/26 00:26:32 invalid character ',' after top-level value
> 2018/06/26 00:26:32 invalid character ':' after top-level value
> 2018/06/26 00:26:32 invalid character ',' after top-level value

If I'm not mistaken, Go is reading until it finds '\n' . How can I solve this problem?

Answer 1

Use a *json.Decoder to consume JSON from an io.Reader:

package main

import (
    "encoding/json"
    "log"
    "os"
)

type MedicalRecord struct{}

func main() {
    var record MedicalRecord

    err := json.NewDecoder(os.Stdin).Decode(&record)
    if err != nil {
        log.Fatal(err)
    }
}

You can consume multiple consecutive JSON documents by calling Decode repeatedly:

package main

import (
    "encoding/json"
    "io"
    "log"
    "os"
)

type MedicalRecord struct{}

func main() {
    var record MedicalRecord

    dec := json.NewDecoder(os.Stdin)
    for {
        err := dec.Decode(&record)
        if err == io.EOF {
            return
        }
        if err != nil {
            log.Fatal(err)
        }
    }
}