React Native
REST Stream Multipart Body from File

Demonstrates how to send a multipart/form-data HTTP request, where one of the parts contains data streamed directly from a file. This is good for cases where the file to be uploaded is very large.
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import { Rest, Stream, StringBuilder } from '@chilkat/react-native'

async function chilkatExample() {
  // This example requires the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  const rest = new Rest();

  // Connect to the destination web server.
  const bTls = true;
  const port = 443;
  const bAutoReconnect = true;
  await rest.connectAsync('www.somewebserver.com', port, bTls, bAutoReconnect);

  // This example will send the following multipart/form-data request.
  // The Content-Length is automatically computed and added by Chilkat.

  // 	POST /some_path HTTP/1.1
  // 	Content-Type: multipart/form-data; boundary=---------------------------735323031399963166993862150
  // 	Content-Length: 834
  // 
  // 	-----------------------------735323031399963166993862150
  // 	Content-Disposition: form-data; name="text1"
  // 
  // 	text 123 abc
  // 	-----------------------------735323031399963166993862150
  // 	Content-Disposition: form-data; name="text2"
  // 
  // 	xyz
  // 	-----------------------------735323031399963166993862150
  // 	Content-Disposition: form-data; name="file1"; filename="a.txt"
  // 	Content-Type: text/plain
  // 
  // 	Content of a.txt.
  // 
  // 	-----------------------------735323031399963166993862150
  // 	Content-Disposition: form-data; name="file2"; filename="a.html"
  // 	Content-Type: text/html
  // 
  // 	<!DOCTYPE html><title>Content of a.html.</title>
  // 
  // 	-----------------------------735323031399963166993862150
  // 	Content-Disposition: form-data; name="file3"; filename="starfish.jpg"
  // 	Content-Type: image/jpeg
  // 
  // 	binary data goes here
  // 	-----------------------------735323031399963166993862150--

  // Set the Content-Type for the topmost MIME part.
  rest.addHeader('Content-Type', 'multipart/form-data');

  // Specify each part of the request.
  rest.partSelector = '1';
  rest.addHeader('Content-Disposition', 'form-data; name="text1"');
  rest.setMultipartBodyString('text 123 abc');

  rest.partSelector = '2';
  rest.addHeader('Content-Disposition', 'form-data; name="text2"');
  rest.setMultipartBodyString('xyz');

  rest.partSelector = '3';
  rest.addHeader('Content-Disposition', 'form-data; name="file1"; filename="a.txt"');
  rest.addHeader('Content-Type', 'text/plain');
  rest.setMultipartBodyString('Content of a.txt.');

  rest.partSelector = '4';
  rest.addHeader('Content-Disposition', 'form-data; name="file2"; filename="a.html"');
  rest.addHeader('Content-Type', 'text/html');
  const sbHtml = new StringBuilder();
  sbHtml.loadFile('qa_data/html/a.html', 'utf-8');
  rest.setMultipartBodySb(sbHtml);

  rest.partSelector = '5';
  rest.addHeader('Content-Disposition', 'form-data; name="file3"; filename="starfish.jpg"');
  rest.addHeader('Content-Type', 'image/jpeg');

  // When the request is sent, stream this part directly from the file.
  // This avoids having to load the entire file into memory.
  const fileStream = new Stream();
  fileStream.sourceFile = 'qa_data/jpg/starfish.jpg';
  rest.setMultipartBodyStream(fileStream);

  let responseBody: string;
  try {
    responseBody = await rest.fullRequestMultipartAsync('POST', '/some_path');
  } catch {
    console.log(rest.lastErrorText);
    return;
  }

  // ...
  // ...

  // Clear the REST object for any subsequent requests..
  rest.clearAllHeaders();
  rest.clearAllParts();
  rest.partSelector = '';
}