JavaScript

var base64 = "base64 content";
let pdfWindow = window.open("");
pdfWindow.document.write("<iframe width='100%' height='100%' src='data:application/pdf;base64, " + base64 + "'></iframe>");

[EnableCors("AnotherPolicy")]
    [HttpPost]
    public FileStreamResult Post([FromForm] string communityName, [FromForm] string files) //byte[]
    {
    	var removedInvalidCharsFromFileName = removeInvalidCharsFromFileName(files);
    	var tFiles = removedInvalidCharsFromFileName.Split(',');
    	string rootPath = Configuration.GetValue<string>("ROOT_PATH");
    	string communityPath = rootPath + "\\" + communityName;

	byte[] theZipFile = null;
	FileStreamResult result = null;
	

	using (MemoryStream zipStream = new MemoryStream())
	{
		using (ZipArchive zip = new ZipArchive(zipStream, ZipArchiveMode.Create, true))
		{
			foreach (string attachment in tFiles)
			{
				var zipEntry = zip.CreateEntry(attachment);

				using (FileStream fileStream = new FileStream(communityPath + "\\" + attachment, FileMode.Open))
				using (Stream entryStream = zipEntry.Open())
				{
					fileStream.CopyTo(entryStream);
				}
			}
		}

		theZipFile = zipStream.ToArray();
		result = new FileStreamResult(zipStream, "application/zip") { FileDownloadName = $"{communityName}.zip" };
	}

	//return theZipFile;
	return result;
    }

handleDownload = (e) => {
	e.preventDefault();

	var formData = new FormData();
	formData.append('communityname', this.state.selectedCommunity);
	formData.append('files', JSON.stringify(this.state['checkedFiles']));

	//let env='local';        
	let url = clientConfiguration['filesApi.local'];
	//let tempFiles = clientConfiguration[`tempFiles.${env}`];
	//alert(tempFiles);

	axios({
		method: 'post',
		responseType: 'application/blob',
		contentType: 'application/blob',
		url: url,
		data: formData
	})
		.then(res => {
			console.log(res);
			console.log(res.data);
			let fileName = `${this.state['selectedCommunity']}`
			const arrayBuffer = base64ToArrayBuffer(res.data);
			createAndDownloadBlobFile(arrayBuffer, fileName, 'zip');
		})
		.catch(error => {
			console.log(error.message);
		});
    };

export function createAndDownloadBlobFile(body, filename, extension = 'pdf') {
    const blob = new Blob([body]);
    const fileName = `${filename}.${extension}`;
    if (navigator.msSaveBlob) {
        // IE 10+
        navigator.msSaveBlob(blob, fileName);
    } else {
        const link = document.createElement('a');
        // Browsers that support HTML5 download attribute
        if (link.download !== undefined) {
            const url = URL.createObjectURL(blob);
            link.setAttribute('href', url);
            link.setAttribute('download', fileName);
            link.style.visibility = 'hidden';
            document.body.appendChild(link);
            link.click();
            document.body.removeChild(link);
        }
    }
    }

    export function base64ToArrayBuffer(base64) {
        const binaryString = window.atob(base64); // Comment this if not using base64
        const bytes = new Uint8Array(binaryString.length);
        return bytes.map((byte, i) => binaryString.charCodeAt(i));
    }

componentDidMount() {
        console.log(clientConfiguration)
        
        fetch(clientConfiguration['communitiesApi.local'])
            .then((response) => {
                return response.json();                
            })
            .then(data => {
                console.log(data);
                let communitiesFromApi = data.map(community => { return { value: community, display: community } });
                this.setState({ communities: [{ value: '', display: 'Select a Community...' }].concat(communitiesFromApi) });    
                            
            }).catch(error => {
                console.log(error);
            });
    };

handleDownload = (e) => {
        e.preventDefault();

        var formData = new FormData();
        formData.append('communityname', this.state.selectedCommunity);
        formData.append('files', JSON.stringify(this.state['checkedFiles']));

        let url = clientConfiguration['filesApi.local'];
        let tempFiles = clientConfiguration['tempFiles.local'];

        axios({
            method: 'post',
            responseType: 'application/zip',
            contentType: 'application/zip',
            url: url,
            data: formData
        })
            .then(res => {       
                var fileName = `${this.state['selectedCommunity']}.zip`;
                saveAs(`https://localhost:44352/TempFiles/${res.data}`, fileName);
            });
    };

[HttpGet("{communityName}")]
public string Get(string communityName)
{
    string rootPath = Configuration.GetValue<string>("ROOT_PATH");
    string communityPath = rootPath + "\\" + communityName;

    string[] files = Directory.GetFiles(communityPath);

    List<string> strippedFiles = new List<string>();
    foreach (string file in files)
    {
        strippedFiles.Add(file.Replace(communityPath + "\\", ""));
    }

    return JsonConvert.SerializeObject(strippedFiles);
}

[HttpPost]
public string Post([FromForm] string communityName, [FromForm] string files) //FileContentResult
{
    var removedInvalidCharsFromFileName = removeInvalidCharsFromFileName(files);
    var tFiles = removedInvalidCharsFromFileName.Split(',');
    string rootPath = Configuration.GetValue<string>("ROOT_PATH");
    string communityPath = rootPath + "\\" + communityName;

    byte[] theZipFile = null;

    using (MemoryStream zipStream = new MemoryStream())
    {
        using (ZipArchive zip = new ZipArchive(zipStream, ZipArchiveMode.Create, true))
        {
            foreach (string attachment in tFiles)
            {
                var zipEntry = zip.CreateEntry(attachment);

                using (FileStream fileStream = new FileStream(communityPath + "\\" + attachment, FileMode.Open))
                using (Stream entryStream = zipEntry.Open())
                {
                    fileStream.CopyTo(entryStream);
                }
            }
        }

        theZipFile = zipStream.ToArray();
    }

    ////return File(theZipFile, "application/zip", communityName + ".zip");

    string tempFilesPath = Configuration.GetValue<string>("Temp_Files_Path");

    if (!System.IO.Directory.Exists(tempFilesPath))
        System.IO.Directory.CreateDirectory(tempFilesPath);

    System.IO.File.WriteAllBytes($"{tempFilesPath}\\{communityName}.zip", theZipFile);

    //return System.IO.File.ReadAllBytes($"{tempFilesPath}\\Test.zip");

    //return $"{tempFilesPath}\\{communityName}.zip";
    return $"{communityName}.zip";
}

Access to fetch at 'https://localhost:44368/api/communities' from origin 'http://localhost:3000' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

[HttpPost]
        public FileContentResult Post([FromForm] string communityName, [FromForm] string files)
        {
           
            var removedInvalidCharsFromFileName = removeInvalidCharsFromFileName(files);
               
            var tFiles = removedInvalidCharsFromFileName.Split(',');
            string rootPath = Configuration.GetValue<string>("ROOT_PATH");
            string communityPath = rootPath + "\\" + communityName;

            byte[] theZipFile = null;

            using (MemoryStream zipStream = new MemoryStream())
            {
                using (ZipArchive zip = new ZipArchive(zipStream, ZipArchiveMode.Create, true))
                {
                    foreach (string attachment in tFiles)
                    {
                        var zipEntry = zip.CreateEntry(attachment);

                        using (FileStream fileStream = new FileStream(communityPath + "\\" + attachment, FileMode.Open))
                        using (Stream entryStream = zipEntry.Open())
                        {
                            fileStream.CopyTo(entryStream);
                        }
                    }
                }
                theZipFile = zipStream.ToArray();
            }

            return File(theZipFile, "application/zip", communityName + ".zip");
        }

handleDownload = (e) => {
        e.preventDefault();

        var formData = new FormData();
        formData.append('communityname', this.state.selectedCommunity);
        formData.append('files', JSON.stringify(this.state['checkedFiles']));        
     
        let url = clientConfiguration['filesApi.local'];

        axios({
            method: 'post',
            url: url,
            data:  formData
        });

        window.open(url, '_blank');
    }