Whats the best way to read Unix Socket response from server in Golang if there is no EOF

Question

I want to read full response from the server, but I don't know precise size of it.

I would expect this to work:

message, err := ioutil.ReadAll(conn)

But server is not sending EOF, so this statement just hangs.

I know its a JSON response, so I could read data until the last }, but that seems not the best way how it could be done.

What is the best practice to read full response?

update:

after some while I found out that it's possible this way:

var m map[string]interface{}
d := json.NewDecoder(conn)
d.Decode(&m)

for key, value := range m {
    fmt.Print(key)
    fmt.Print(" : ")
    fmt.Print(value)
    fmt.Print("\n")
    switch vv := value.(type) {
    case map[string]interface{}:
        for k, v := range vv {
            fmt.Print(k)
            fmt.Print(" : ")
            fmt.Print(v)
            fmt.Print("\n")
        }
    }
}

user5728991 · Accepted Answer · 2018-06-21 00:53:10Z

2

Use a json.Decoder. Here's how to read multiple messages:

 d := json.NewDecoder(conn)
 for {
     var m message // <-- use whatever type is appropriate for your app
     err := d.Decode(&m)
     if err == io.EOF {
         break
     } else if err != nil {
         // handle error
     }
     // do something with m
}

Remove the loop if you expect exactly one message.

answered Jun 21, 2018 at 0:53

user5728991

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5 Comments

user9946708 Over a year ago

Unable to make it work. Just to be sure its a Json string coming from conn, _ := net.Dial("unix", "/var/run/some.sock"). The programm don't hang anymore, but m is empty. Getting this error: json: cannot unmarshal object into Go value of type string

user5728991 Over a year ago

Declare m to match the type of the data. It sounds like you declared m as a string, but the JSON value is an object. Try var m map[string]interface{} (which will handle a JSON object) or var m interface{} (which will handle any JSON value).

user9946708 Over a year ago

Ok it reads data in m, but now how to access data in the interface?

user5728991 Over a year ago

Edit the question to show what you actually tried and examples of the JSON. Without that information, it's impossible to help further.

user9946708 Over a year ago

I was thinking of generic working with json responses, added an update in question.

phemmer · Accepted Answer · 2018-06-21 00:51:47Z

1

You want a json.Decoder. The decoder is meant to read a stream of JSON objects. It reads from the stream until it receives a complete object, and then unmarshals it onto the provided object pointer.

Example:

package main

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

func main() {
    pr, pw := io.Pipe()
    go pw.Write([]byte(`{"foo":"bar"}`))
    var data map[string]string
    json.NewDecoder(pr).Decode(&data)
    fmt.Printf("Data: %v\n", data)
}

^{https://play.golang.org/p/JQMXGzrDAH-}

Which outputs:

Data: map[foo:bar]

answered Jun 21, 2018 at 0:51

phemmer

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