Set up a local server with Go-File upload-

at first

Set up a Web Server with Go and upload files from the Android application

environment

PC Windows10 Android Studio 4.0 Kotlin 1.3.72 Android device Emulator (API Level 29) Go 1.11.1

Diagram

Send a file from the Android app, save it on the server side, and return the status code from the server to the app

Implementation

Local server

Server.go

package controllers

import (
	"fmt"
	"net/http"
	"io/ioutil"
	"os"
)

func apiSampleHandler(w http.ResponseWriter, r *http.Request) {
	switch(r.Method) {
		case "POST":
			fmt.Println("POST")
            //Get uploaded files and headers
			file, fileHeader, _ := r.FormFile ("upload_file")　
			fileName := fileHeader.Filename //Get the filename from the header
			defer file.Close()              //Close the file at the end
			data, _ := ioutil.ReadAll(file) //Read file
			saveFile, _ := os.Create(fileName) //Generate a file for saving
			defer saveFile.Close()          //Close the file for saving at the end
			_, err = saveFile.Write(data)   //Write to file
			if err != nil {
				fmt.Println("can not write file")
				w.WriteHeader(http.StatusBadRequest)
				return
			}
		case "GET":
			fmt.Println("GET")
	}
    // 200:Returns OK
	w.WriteHeader(http.StatusOK)
}

// main.Call from go to start the server
func StartWebServer() error {
	http.HandleFunc("/", apiSampleHandler)
	return http.ListenAndServe(":8080", nil)
}

Run main.go and start the server Go to http: // localhost: 8080 and make sure the server is up

Android app

1．Androidmanifest.xml

Define Permission to access the Internet

AndroidManifest.xml

<uses-permission android:name="android.permission.INTERNET" />

Since the http communication setting is turned off from Android 9.0, set uses CleartextTrafic to true

AndroidManifest.xml

<application
abridgement
    android:usesCleartextTraffic="true">
    <activity android:name=".MainActivity">
abridgement
    </activity>
</application>

2. Generate file

Generate a text file in the application-specific area of the Android device (under `` `/ data / data / {package_name} / files```)

File.kt

const val FILE_EXPAND = ".txt"

class File {
    fun makeTxtFile(context: Context, fileName: String, str: String) {
        try {
            context.openFileOutput(fileName + FILE_EXPAND, Context.MODE_PRIVATE).use {
                it.write(str.toByteArray())
            }
        } catch (e: IOException) {
            Log.e("File", "#makeTxtFile $e")
        }
    }
}

Confirm file generation View files on the device with Device File Explorer (https://developer.android.com/studio/debug/device-file-explorer?hl=ja )

3. 3. Server access

Read the file and send the file via http communication

Net.kt

 fun startConnection(context: Context, requestUrl: String, requestMethod: String, fileName: String): Pair<Int, String> {
        val url = URL(requestUrl)                      //URL object generation
        //UrlConnection object creation
        val urlConnection = url.openConnection() as HttpURLConnection 
        var result = ""
        var responseCode = 0
        try {
            val boundary = "--------------------------" 
            urlConnection.requestMethod = requestMethod // POST,GET etc.
            urlConnection.doOutput = true               //Send request body
            urlConnection.doInput = true                //Reception of response body
            urlConnection.useCaches = false             //Use of cache
            // multipart/form-data: Send multiple data, boundary: Separation between multiple data
            urlConnection.setRequestProperty(
                "Content-Type",
                "multipart/form-data; boundary=$boundary" 
            )
            val filePath = context.filesDir             //App-specific area path
            val file = File("$filePath/$fileName$FILE_EXPAND") //Create a file object
            FileInputStream(file).use { fileInputStream ->
                urlConnection.connect()                 //Establish a connection
                DataOutputStream(urlConnection.outputStream).use {
                   it.writeBytes(                       //Set header
                       TWO_HYPHEN + boundary + LINE_END +
                               "Content-Disposition: form-data; name=\"upload_file\"; " +
                               "filename=\"$fileName$FILE_EXPAND\"$LINE_END" +
                               "Content-Type: application/octet-stream$LINE_END$LINE_END"
                   )
                   //File writing
                   val buffer = ByteArray(BUFFER_SIZE)
                   var bytesRead: Int
                   do {
                       bytesRead = fileInputStream.read(buffer)
                       if (bytesRead == -1) break
                       it.write(buffer, 0, bytesRead)
                   } while (true)
                   it.writeBytes(                       //footer settings
                        LINE_END + TWO_HYPHEN + boundary + TWO_HYPHEN + LINE_END
                   )
                   it.flush()
                }
            }
            responseCode = urlConnection.responseCode   //Get response code
 
            BufferedReader(InputStreamReader(urlConnection.inputStream)).use {
                val sb = StringBuffer()
                for (line in it.readLines()) {
                    line.let { sb.append(line) }
                }
                result = sb.toString()
            }
        } catch (e: Exception) {
            Log.e("Net", "#startConnection$e")
        } finally {
            urlConnection.disconnect()
        }
        return responseCode to result
    }
}

Four. Confirmation of IP address

Confirm the IP address of the server (PC) you want to access by executing the following with the command prompt

>ipconfig

Five. Connect your PC and Android device to the same network environment

6. Connect with Android

Set http: // {confirmed IP address}: 8080 in requestUrl of Net # startConnection and execute the application

Confirm file upload

Check the same directory as main.go on your PC Complete if the file has been created

Finally

The whole source is here The access destination, RequestMethod, and file name can be changed dynamically by the application.

References

Go server side

File upload in Go language

Android application side

[Android] Save files in the app FileOutputStream, FileInputStream Upload File To Server - Android Example [Android] while-FileInputStream.read error in kotlin [Kotlin] I want to return multiple values!