Transferring a JSON array from Google App Engine to Cloud Storage using GO

Question

Transferring a JSON array from Google App Engine to Cloud Storage using GO

I am attempting to upload a JSON array to Google Cloud Storage, which is posted by an App Engine application using the code below:

saveData : function saveData() {
  var _this = this,
      save = this.shadowRoot.querySelector('#save-data'),
      subData = JSON.stringify(_this.app.userSession);

  save.url="url";
  save.body = subData;
  save.go();
}

The posted message is processed in the 'go' function with the following code. Currently, I can create a folder in the cloud storage bucket named after the user ID. However, my goal is to copy the entire JSON array (variable f in the code) into this folder. When I tried using io.Copy(wc, f), I encountered the error message below:

cannot use content (type userData) as type io.Reader in argument to io.Copy: userData does not implement io.Reader (missing Read method)

Clearly, there is something incorrect in my implementation, and as a newcomer to Go programming, I'm struggling to find a solution. Can anyone provide assistance?

package expt

import (
    "bytes"
    "encoding/json"
    "io/ioutil"
    "log"
    "net/http"
    "golang.org/x/net/context"
    "golang.org/x/oauth2"
    "golang.org/x/oauth2/google"
    "google.golang.org/appengine"
    "google.golang.org/appengine/file"
    "google.golang.org/appengine/urlfetch"
    "google.golang.org/cloud"
    "google.golang.org/cloud/storage"
)

var bucket = "expt"

func init() {
    http.HandleFunc("/", handleStatic)
    http.HandleFunc("/save", saveJson)
}

...

// Additional code continues here

javascript json google-app-engine go google-cloud-storage

Answer 1

Answer №1

This piece of code appears to be quite perplexing, but it seems like you are attempting to achieve the following:

func (d *saveData) createFile(fileName string, content userData) {
    wc := storage.NewWriter(d.ctx, bucket, fileName)
    wc.ContentType = "text/plain"
    d.cleanUp = append(d.cleanUp, fileName)

    //*** new code *******
    io.Copy(wc, content)
    //********************

    if err := wc.Close(); err != nil {
        d.errorf("createFile: unable to close bucket %q, file %q: %v", bucket, fileName, err)
        return
    }
}

You cannot directly write an object to a file; it must be encoded first. It seems like you intend to use JSON. You could approach it like this:

bs, err := json.Marshal(content)
if err != nil {
  return err
}
io.Copy(wc, bytes.NewReader(bs))

However, it would be more efficient to utilize json.NewEncoder:

json.NewEncoder(wc).Encode(content)

Simplifying your createUserFolder function is also possible (no need for a buffer to concatenate strings):

func (d *saveData) createUserFolder() {
    content := testA(d.r)
    d.createFile(content.id + "/")
}

Regarding testA, I am unsure of its intended purpose, but it can be streamlined as well:

type UserData {
  ID     string `json:"id"`
  Age    string `json:"age"`
  Gender string `json:"gender"`
}

func testA(r *http.Request) UserData {
  defer r.Body.Close()
  var obj struct {
    User UserData `json:"user"`
  }
  err := json.NewDecoder(r.Body).Decode(&obj)
  if err != nil {
      log.Println("Error: %s", err)
  }
  return obj.User
}

By using uppercase field names, JSON can handle the conversion for you.

There likely is more refactoring that can be done, but these suggestions should give you a good starting point.

Answer 2

This piece of code appears to be quite perplexing, but it seems like you are attempting to achieve the following:

func (d *saveData) createFile(fileName string, content userData) {
    wc := storage.NewWriter(d.ctx, bucket, fileName)
    wc.ContentType = "text/plain"
    d.cleanUp = append(d.cleanUp, fileName)

    //*** new code *******
    io.Copy(wc, content)
    //********************

    if err := wc.Close(); err != nil {
        d.errorf("createFile: unable to close bucket %q, file %q: %v", bucket, fileName, err)
        return
    }
}

You cannot directly write an object to a file; it must be encoded first. It seems like you intend to use JSON. You could approach it like this:

bs, err := json.Marshal(content)
if err != nil {
  return err
}
io.Copy(wc, bytes.NewReader(bs))

However, it would be more efficient to utilize json.NewEncoder:

json.NewEncoder(wc).Encode(content)

Simplifying your createUserFolder function is also possible (no need for a buffer to concatenate strings):

func (d *saveData) createUserFolder() {
    content := testA(d.r)
    d.createFile(content.id + "/")
}

Regarding testA, I am unsure of its intended purpose, but it can be streamlined as well:

type UserData {
  ID     string `json:"id"`
  Age    string `json:"age"`
  Gender string `json:"gender"`
}

func testA(r *http.Request) UserData {
  defer r.Body.Close()
  var obj struct {
    User UserData `json:"user"`
  }
  err := json.NewDecoder(r.Body).Decode(&obj)
  if err != nil {
      log.Println("Error: %s", err)
  }
  return obj.User
}

By using uppercase field names, JSON can handle the conversion for you.

There likely is more refactoring that can be done, but these suggestions should give you a good starting point.

Transferring a JSON array from Google App Engine to Cloud Storage using GO

Answer №1

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