(Go) Download Binary File to In-Memory Bytes

This example demonstrates how to download the binary content of a file from Google Drive directly into local memory.

Chilkat Go Downloads Go Package for Windows, MacOS, Linux, Alpine Linux, Solaris

    success := true

    // It requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // This example uses a previously obtained access token having permission for the 
    // Google Drive scope.

    gAuth := chilkat.NewAuthGoogle()
    gAuth.SetAccessToken("GOOGLE-DRIVE-ACCESS-TOKEN")

    rest := chilkat.NewRest()

    // Connect using TLS.
    // A single REST object, once connected, can be used for many Google Drive REST API calls.
    // The auto-reconnect indicates that if the already-established HTTPS connection is closed,
    // then it will be automatically re-established as needed.
    bAutoReconnect := true
    success = rest.Connect("www.googleapis.com",443,true,bAutoReconnect)

    // Provide the authentication credentials (i.e. the access token)
    rest.SetAuthGoogle(gAuth)

    // ------------------------------------------------------------------------------
    // To download a file, we must know the file ID.
    // In a previous example (see Build Local Metadata Cache
    // we built a local cache to make it easy to lookup file IDs given a file path.
    // Let's say we want to download "testFolder/abc/123/penguins.jpg".
    // First we lookup the fileId in the cache.  With the fileId, we can download the file.
    gdCache := chilkat.NewCache()
    gdCache.SetLevel(0)
    gdCache.AddRoot("C:/ckCache/googleDrive")

    fileId := gdCache.FetchText("testFolder/abc/123/penguins.jpg")
    if gdCache.LastMethodSuccess() != true {
        fmt.Println("Filepath not found in cache.")
        gAuth.DisposeAuthGoogle()
        rest.DisposeRest()
        gdCache.DisposeCache()
        return
    }

    // We need to send a GET request like this:
    // GET https://www.googleapis.com/drive/v3/files/fileId?alt=media
    // The fileId is part of the path.
    sbPath := chilkat.NewStringBuilder()
    sbPath.Append("/drive/v3/files/")
    sbPath.Append(*fileId)
    rest.AddQueryParam("alt","media")

    // To download to memory, we'll send the request in one call, then receive
    // the response header, and then the response body.
    // If the response header indicates failure or an unexpected response, then the
    // body is not the data we desire.

    // First send the HTTP request.
    success = rest.SendReqNoBody("GET",*sbPath.GetAsString())
    if success != true {
        fmt.Println(rest.LastErrorText())
        gAuth.DisposeAuthGoogle()
        rest.DisposeRest()
        gdCache.DisposeCache()
        sbPath.DisposeStringBuilder()
        return
    }

    // Get the response header.
    statusCode := rest.ReadResponseHeader()
    if statusCode != 200 {
        fmt.Println("response status code = ", rest.ResponseStatusCode())
        fmt.Println("response status text = ", rest.ResponseStatusText())
        fmt.Println("response header: ", rest.ResponseHeader())

        // Read the response body (which should be error text or HTML)
        errResponseBody := rest.ReadRespBodyString()
        if rest.LastMethodSuccess() == true {
            fmt.Println("response body: ", *errResponseBody)
        }

        gAuth.DisposeAuthGoogle()
        rest.DisposeRest()
        gdCache.DisposeCache()
        sbPath.DisposeStringBuilder()
        return
    }

    // Read the response body, which should contain the file data.
    var jpgBytes []byte
    jpgBytes = rest.ReadRespBodyBinary()
    if rest.LastMethodSuccess() != true {
        fmt.Println(rest.LastErrorText())
        gAuth.DisposeAuthGoogle()
        rest.DisposeRest()
        gdCache.DisposeCache()
        sbPath.DisposeStringBuilder()
        return
    }

    // Save jpgBytes to a file so we can examine the file to verify that it worked.
    fac := chilkat.NewFileAccess()
    fac.WriteEntireFile("qa_output/penguins_out.jpg",jpgBytes)

    fmt.Println("File downloaded.")

    gAuth.DisposeAuthGoogle()
    rest.DisposeRest()
    gdCache.DisposeCache()
    sbPath.DisposeStringBuilder()
    fac.DisposeFileAccess()