Set up a local server with Go-File download-

at first

Make a request from the Android app and download the file on the local server where you set up the Web Server with Go

environment

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

Diagram

Specify the file name from the Android application, request to the server side, return the file and status code saved on the server side

Implementation

Local server

Server.go

package controllers

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

func apiSampleHandler(w http.ResponseWriter, r *http.Request) {
	switch r.Method {
	case "POST":
		fmt.Println("POST")
	case "GET":                                        //File DL with GET request
		fmt.Println("GET")
		name := fmt.Sprint(r.URL)                      // 「/Get "filename"
		fileName := strings.SplitAfter(name, "/")[1]   //Get "filename"
        //Check if the file exists on the server side
		if fileinfo, err := os.Stat("./" + fileName); os.IsNotExist(err) || fileinfo.IsDir() {
			fmt.Println("file is not exist")
			w.WriteHeader(http.StatusNotFound)
			return
		}
		buf, err := ioutil.ReadFile("./" + fileName)   //Read file
		if err != nil {
			fmt.Println("file could not be read")
			w.WriteHeader(http.StatusInternalServerError)
			return
		}
		w.Write(buf)                                   //Write to response
	}
	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

Prepare the file

Place the file for download in the same directory as main.go

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. Server access

Access the server by GET via http communication

Net.kt

   fun requestFileDownload(context: Context, requestUrl: String, fileName: String): Int {
        val url = URL("$requestUrl/$fileName.txt")     //URL object generation
        //UrlConnection object creation
        val urlConnection = url.openConnection() as HttpURLConnection 
        var result = ""
        var responseCode = 0
        try {
            urlConnection.requestMethod = "GET"         // POST,GET etc.
            urlConnection.doInput = true                //Reception of response body
            urlConnection.useCaches = false             //Use of cache
            urlConnection.connect()                     //Establish a connection

            responseCode = urlConnection.responseCode   //Get response code
            when (responseCode) {
                HttpURLConnection.HTTP_OK -> {          //Processed only when response code is 200: OK
                    val path = context.filesDir.toString() + "/" + fileName + FILE_EXPAND
                    //Read the contents of the response
                    DataInputStream(urlConnection.inputStream).use { fileInputStream ->
                        //Create and write a file
                        DataOutputStream(BufferedOutputStream(FileOutputStream(path))).use {
                            val buffer = ByteArray(BUFFER_SIZE)
                            var byteRead: Int
                            do {
                                byteRead = fileInputStream.read(buffer)
                                if (byteRead == -1) {
                                    break
                                }
                                it.write(buffer, 0, byteRead)
                            } while (true)
                        }
                    }
                }
            }
        } catch (e: Exception) {
            Log.e("Net", "#startConnection$e")
        } finally {
            urlConnection.disconnect()
        }
        return responseCode
    }
}

3. 3. 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

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

Five. Connect with Android

Set http: // {confirmed IP address}: 8080 in requestUrl of Net # requestFileDownload Set the file name to be downloaded in fileName of Net # requestFileDownload and execute

Confirm file download

Confirm that the file is generated in the application-specific area (under / data / data / {package_name} / files) View files on the device with Device File Explorer (https://developer.android.com/studio/debug/device-file-explorer?hl=ja )

Finally

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

Click here to upload files to the server (https://qiita.com/kurramkurram/items/262cd1d2f01dcb6fa8bd)

References

Go server side

Package http Check for the existence of Go language (golang) files and directories [Golang] File reading sample

Android application side

How to download and save a file over HTTP in Java