解码数组括号不包围的JSON流吗？

Question

I'm trying to decode a JSON stream from a file. The file is newline separated JSON objects. But it's not formatted with array brackets surrounding the objects, so I can't figure out how to use encoding/json stream decoder.

I get the error not at beginning of value because there is no opening bracket.

package main

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

func main() {

    // My data is missing opening and closing brackets around the jsonStream string.
    // [
    const jsonStream = `
        {"Name": "Ed", "Text": "Knock knock."},
        {"Name": "Sam", "Text": "Who's there?"},
        {"Name": "Ed", "Text": "Go fmt."},
        {"Name": "Sam", "Text": "Go fmt who?"},
        {"Name": "Ed", "Text": "Go fmt yourself!"}
    `
    // ]
    type Message struct {
        Name, Text string
    }
    dec := json.NewDecoder(strings.NewReader(jsonStream))

    // read open bracket -- this fails (no bracket)
    t, err := dec.Token()
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("%T: %v
", t, t)

    // while the array contains values
    for dec.More() {
        var m Message
        // decode an array value (Message)
        err := dec.Decode(&m)
        if err != nil {
            log.Fatal(err)
        }

        fmt.Printf("%v: %v
", m.Name, m.Text)
    }

    // read closing bracket -- this also would fail (no bracket)
    t, err = dec.Token()
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("%T: %v
", t, t)

}

Removing the dec.Token() error checks doesn't work either. I guess the parser doesn't expect to see objects before it has seen an array open bracket?

Is there some workaround?

Answer 1

One suggestion is to use a pipe, and prepend and append the [].

reader := strings.NewReader(jsonStream)

pr, pw := io.Pipe()

go func() {
    pw.Write([]byte(`[`))
    io.Copy(pw, reader)
    pw.Write([]byte(`]`))
}()

dec := json.NewDecoder(pr)

You should add some error handling.

See https://play.golang.org/p/Oogu_NdAUyR for the whole thing.