I am building a web server from an ESP8266 that will send environmental data to any web client as a web page. I'm using the Arduino IDE.
The problem is that the data can get rather large at times, and all of the examples I can find show assembling a web page in memory and sending it all at once to the client via ESP8266WebServer.send(). This is ok for small web pages, but won't work with the amount of data I need to send.
What I want to do is send the first part of the web page, then send the data out directly as I gather it, then send the closing parts of the web page. Is this even possible? I've looked unsuccessfully for documentation and there doesn't seem to be any examples anywhere.
For future reference, I think I figured out how to do it, with help from this page: https://gist.github.com/spacehuhn/6c89594ad0edbdb0aad60541b72b2388
The gist of it is that you still use ESP8266WebServer.send(), but you first send an empty string with the Content-Length header set to the size of your data, like this:
server.sendHeader("Content-Length", (String)fileSize);
server.send(200, "text/html", "");
Then you send buffers of data using ESP8266WebServer.sendContent() repeatedly until all of the data is sent.
Hope this helps someone else.
I was having a big issue and a headache in serving big strings concatenating together with other strings variables to the ESP32 Ardunio webserver with
server.send(200, "text/html", BIG_WEBPAGE);
and often resulted in a blank page as I reported in my initial error.
What was happening was this error
E (369637) uart: uart_write_bytes(1159): buffer null
I don't reccommend to use the above server.send() function
After quite a lot of reaserch I found this piece of code that simply works like a charm. I just chunked my webpage in 5 pieces like you see below.
server.sendHeader("Cache-Control", "no-cache, no-store, must-revalidate");
server.sendHeader("Pragma", "no-cache");
server.sendHeader("Expires", "-1");
server.setContentLength(CONTENT_LENGTH_UNKNOWN);
// here begin chunked transfer
server.send(200, "text/html", "");
server.sendContent(WEBPAGE_BIG_0);
server.sendContent(WEBPAGE_BIG_1);
server.sendContent(WEBPAGE_BIG_2);
server.sendContent(WEBPAGE_BIG_3);
server.sendContent(WEBPAGE_BIG_4);
server.sendContent(WEBPAGE_BIG_5);
server.client().stop();
I really own much to this post. Hope the answer hepls someone else.
After some more experiments I realized it is faster and more efficient the code if you do not feed the string variable into the server.sendContent function. Instead you just paste there the actual string value.
server.sendContent("<html><head>my great page</head><body>");
server.sendContent("my long body</body></html>");
It is very important the when you chunk the webpage you don't chunk html tags and you don't chunk an expression of a javascript code (like cutting in half a while or an if), while chunking scripts just chunk after the semicolon or better between two function declarations.
Chunked transfer encoding is probably what you want, and it's helpful in the situation where the web page you are sending is being dynamically created on-the-fly and is also too large to fit into memory. In this situation, you have two problems. One, you can't send it all at once, and two, you don't know ahead of time how big the result is going to be. Both problems can be fixed like this:
String webPageChunk = "some html";
server.setContentLength(CONTENT_LENGTH_UNKNOWN);
server.send ( 200, "text/html", webPageChunk);
while (<page is being generated>) {
webPageChunk = "some more html";
server.sendContent(webPageChunk);
}
server.sendContent("");
Sending a blank line will tell the client to terminate the session. Be careful not to send one in your loop before you're done generating the whole page.
ES6 modules allows us to create a single point of entry like so:
// main.js
import foo from 'foo';
foo()
<script src="scripts/main.js" type="module"></script>
foo.js will be stored in the browser cache. This is desirable until I push a new version of foo.js to production.
It is common practice to add a query string param with a unique id to force the browser to fetch a new version of a js file (foo.js?cb=1234)
How can this be achieved using the es6 module pattern?
There is one solution for all of this that doesn't involve query string. let's say your module files are in /modules/. Use relative module resolution ./ or ../ when importing modules and then rewrite your paths in server side to include version number. Use something like /modules/x.x.x/ then rewrite path to /modules/. Now you can just have global version number for modules by including your first module with
<script type="module" src="/modules/1.1.2/foo.mjs"></script>
Or if you can't rewrite paths, then just put files into folder /modules/version/ during development and rename version folder to version number and update path in script tag when you publish.
HTTP headers to the rescue. Serve your files with an ETag that is the checksum of the file. S3 does that by default at example.
When you try to import the file again, the browser will request the file, this time attaching the ETag to a "if-none-match" header: the server will verify if the ETag matches the current file and send back either a 304 Not Modified, saving bandwith and time, or the new content of the file (with its new ETag).
This way if you change a single file in your project the user will not have to download the full content of every other module. It would be wise to add a short max-age header too, so that if the same module is requested twice in a short time there won't be additional requests.
If you add cache busting (e.g. appending ?x={randomNumber} through a bundler, or adding the checksum to every file name) you will force the user to download the full content of every necessary file at every new project version.
In both scenario you are going to do a request for each file anyway (the imported files on cascade will produce new requests, which at least may end in small 304 if you use etags). To avoid that you can use dynamic imports e.g if (userClickedOnSomethingAndINeedToLoadSomeMoreStuff) { import('./someModule').then('...') }
From my point of view dynamic imports could be a solution here.
Step 1)
Create a manifest file with gulp or webpack. There you have an mapping like this:
export default {
"/vendor/lib-a.mjs": "/vendor/lib-a-1234.mjs",
"/vendor/lib-b.mjs": "/vendor/lib-b-1234.mjs"
};
Step 2)
Create a file function to resolve your paths
import manifest from './manifest.js';
const busted (file) => {
return manifest[file];
};
export default busted;
Step 3)
Use dynamic import
import busted from '../busted.js';
import(busted('/vendor/lib-b.mjs'))
.then((module) => {
module.default();
});
I give it a short try in Chrome and it works. Handling relative paths is tricky part here.
I've created a Babel plugin which adds a content hash to each module name (static and dynamic imports).
import foo from './js/foo.js';
import('./bar.js').then(bar => bar());
becomes
import foo from './js/foo.abcd1234.js';
import('./bar.1234abcd.js').then(bar => bar());
You can then use Cache-control: immutable to let UAs (browsers, proxies, etc) cache these versioned URLs indefinitely. Some max-age is probably more reasonable, depending on your setup.
You can use the raw source files during development (and testing), and then transform and minify the files for production.
what i did was handle the cache busting in webserver (nginx in my instance)
instead of serving
<script src="scripts/main.js" type="module"></script>
serve it like this where 123456 is your cache busting key
<script src="scripts/123456/main.js" type="module"></script>
and include a location in nginx like
location ~ (.+)\/(?:\d+)\/(.+)\.(js|css)$ {
try_files $1/$2.min.$3 $uri;
}
requesting scripts/123456/main.js will serve scripts/main.min.js and an update to the key will result in a new file being served, this solution works well for cdns too.
Just a thought at the moment but you should be able to get Webpack to put a content hash in all the split bundles and write that hash into your import statements for you. I believe it does the second by default.
You can use an importmap for this purpose. I've tested it at least in Edge. It's just a twist on the old trick of appending a version number or hash to the querystring. import doesn't send the querystring onto the server but if you use an importmap it will.
<script type="importmap">
{
"imports": {
"/js/mylib.js": "/js/mylib.js?v=1",
"/js/myOtherLib.js": "/js/myOtherLib.js?v=1"
}
}
</script>
Then in your calling code:
import myThing from '/js/mylib.js';
import * as lib from '/js/myOtherLib.js';
You can use ETags, as pointed out by a previous answer, or alternatively use Last-Modified in relation with If-Modified-Since.
Here is a possible scenario:
The browser first loads the resource. The server responds with Last-Modified: Sat, 28 Mar 2020 18:12:45 GMT and Cache-Control: max-age=60.
If the second time the request is initiated earlier than 60 seconds after the first one, the browser serves the file from cache and doesn't make an actual request to the server.
If a request is initiated after 60 seconds, the browser will consider cached file stale and send the request with If-Modified-Since: Sat, 28 Mar 2020 18:12:45 GMT header. The server will check this value and:
If the file was modified after said date, it will issue a 200 response with the new file in the body.
If the file was not modified after the date, the server will issue a304 "not modified" status with empty body.
I ended up with this set up for Apache server:
<IfModule headers_module>
<FilesMatch "\.(js|mjs)$">
Header set Cache-Control "public, must-revalidate, max-age=3600"
Header unset ETag
</FilesMatch>
</IfModule>
You can set max-age to your liking.
We have to unset ETag. Otherwise Apache keeps responding with 200 OK every time (it's a bug). Besides, you won't need it if you use caching based on modification date.
A solution that crossed my mind but I wont use because I don't like it LOL is
window.version = `1.0.0`;
let { default: fu } = await import( `./bar.js?v=${ window.version }` );
Using the import "method" allows you to pass in a template literal string. I also added it to window so that it can be easily accessible no matter how deep I'm importing js files. The reason I don't like it though is I have to use "await" which means it has to be wrapped in an async method.
If you are using Visual Studio 2022 and TypeScript to write your code, you can follow a convention of adding a version number to your script file names, e.g. MyScript.v1.ts. When you make changes and rename the file to MyScript.v2.ts Visual Studio shows the following dialog similar to the following:
If you click Yes it will go ahead and update all the files that were importing this module to refer to MyScript.v2.ts instead of MyScript.v1.ts. The browser will notice the name change too and download the new modules as expected.
It's not a perfect solution (e.g. if you rename a heavily used module, a lot of files can end up being updated) but it is a simple one!
this work for me
let url = '/module/foo.js'
url = URL.createObjectURL(await (await fetch(url)).blob())
let foo = await import(url)
I came to the conclusion that cache-busting should not be used with ES Module.
Actually, if you have the versioning in the URL, the version is acting like a cache-busting. For instance https://unpkg.com/react#18.2.0/umd/react.production.min.js
If you don't have versioning in the URL, use the following HTTP header Cache-Control: max-age=0, no-cache to force the browser to always check if a new version of the file is available.
no-cache tells the browser to cache the file but to always perform a check
no-store tells the browser to don't cache the file. Don't use it!
Another approach: redirection
unpkg.com solved this problem with HTTP redirection.
Therefore it is not an ideal solution because it involves 2 HTTP requests instead of 1.
The first request is to get redirected to the latest version of the file (not cached, or cached for a short period of time)
The second request is to get the JS file (cached)
=> All JS files include the versioning in the URL (and have an aggressive caching strategy)
For instance https://unpkg.com/react#18.2.0/umd/react.production.min.js
=> Removing the version in the URL, will lead to a HTTP 302 redirect pointing to the latest version of the file
For instance https://unpkg.com/react/umd/react.production.min.js
Make sure the redirection is not cached by the browser, or cached for a short period of time. (unpkg allows 600 seconds of caching, but it's up to you)
About multiple HTTP requests: Yes, if you import 100 modules, your browser will do 100 requests. But with HTTP2 / HTTP3, it is not a problem anymore because all requests will be multiplexed into 1 (it is transparent for you)
About recursion:
If the module you are importing also imports other modules, you will want to check about <link rel="modulepreload"> (source Chrome dev blog).
The modulepreload spec actually allows for optionally loading not just the requested module, but all of its dependency tree as well. Browsers don't have to do this, but they can.
If you are using this technic in production, I am deeply interested to get your feedback!
Append version to all ES6 imports with PHP
I didn't want to use a bundler only because of this, so I created a small function that modifies the import statements of all the JS files in the given directory so that the version is at the end of each file import path in the form of a query parameter. It will break the cache on version change.
This is far from an ideal solution, as all JS file contents are verified by the server on each request and on each version change the client reloads every JS file that has imports instead of just the changed ones.
But it is good enough for my project right now. I thought I'd share.
$assetsPath = '/public/assets'
$version = '0.7';
$rii = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($assetsPath, FilesystemIterator::SKIP_DOTS) );
foreach ($rii as $file) {
if (pathinfo($file->getPathname())['extension'] === 'js') {
$content = file_get_contents($file->getPathname());
$originalContent = $content;
// Matches lines that have 'import ' then any string then ' from ' and single or double quote opening then
// any string (path) then '.js' and optionally numeric v GET param '?v=234' and '";' at the end with single or double quotes
preg_match_all('/import (.*?) from ("|\')(.*?)\.js(\?v=\d*)?("|\');/', $content, $matches);
// $matches array contains the following:
// Key [0] entire matching string including the search pattern
// Key [1] string after the 'import ' word
// Key [2] single or double quotes of path opening after "from" word
// Key [3] string after the opening quotes -> path without extension
// Key [4] optional '?v=1' GET param and [5] closing quotes
// Loop over import paths
foreach ($matches[3] as $key => $importPath) {
$oldFullImport = $matches[0][$key];
// Remove query params if version is null
if ($version === null) {
$newImportPath = $importPath . '.js';
} else {
$newImportPath = $importPath . '.js?v=' . $version;
}
// Old import path potentially with GET param
$existingImportPath = $importPath . '.js' . $matches[4][$key];
// Search for old import path and replace with new one
$newFullImport = str_replace($existingImportPath, $newImportPath, $oldFullImport);
// Replace in file content
$content = str_replace($oldFullImport, $newFullImport, $content);
}
// Replace file contents with modified one
if ($originalContent !== $content) {
file_put_contents($file->getPathname(), $content);
}
}
}
$version === null removes all query parameters of the imports in the given directory.
This adds between 10 and 20ms per request on my application (approx. 100 JS files when content is unchanged and 30—50ms when content changes).
Use of relative path works for me:
import foo from './foo';
or
import foo from './../modules/foo';
instead of
import foo from '/js/modules/foo';
EDIT
Since this answer is down voted, I update it. The module is not always reloaded. The first time, you have to reload the module manually and then the browser (at least Chrome) will "understand" the file is modified and then reload the file every time it is updated.
I got feedback to preserve the modified date of downloaded file. I found a way to preserve it if I serve the file inside a zip, however got problem when I just serve the file as it is from my nodejs server.
Below is my current implementation :
try{
var stat = fs.statSync(fullpath);
self.response.writeHead(200, {
'Content-Type': mimeType,
'Last-Modified': stat.mtime // not working
});
var fileStream = fs.createReadStream(fullpath);
fileStream.pipe(self.response);
fileStream.on('end', function() {
console.log("complete")
});
}catch(e)
{ //to handle user cancel the download and bring down whole system
logger.error("streaming failed,because of:"+e.message);
}
Initially I thought that setting the header 'Last-Modified' should do the trick but apparently it is not. Need to be able to work in Chrome, but if it works across browser, it would be great.
Note : It is not because of the format because using "Tue, 15 Nov 1994 12:45:26 GMT" instead of stat.mtime is not working as well.
Update : Seems impossible for browser right now as per early 2017, as shown in this link, the only way to do this is curl, or wget.
Do you mean the modified date on a file when the browser has downloaded and saved it? You can't do that, as that would require operating system access on the remote computer. The modified date on a file is a function of the filesystem on the client computer.
I use Content Security Policy. I get genuinely useful warnings like this:
CSP violation!
{ 'csp-report':
{ 'document-uri': 'about:blank',
referrer: '',
'violated-directive': 'img-src \'self\' data: pbs.twimg.com syndication.twitter.com p.typekit.net',
'original-policy': 'longPolicyGoesHere',
'blocked-uri': 'https://platform.twitter.com',
'source-file': 'https://platform.twitter.com',
'line-number': 2 } }
Cool, I need to add 'platform.twitter.com' as an img-src
But sometimes I get blank CSP warnings like this:
CSP violation!
{}
Ie, there's been a POST, but the JSON is empty. What do I do?
I found the problem in my case; it might not be the problem for you.
Since the CSP reporter calls the report-uri file with the POST method, I assumed that the $_POST variable would contain the posted data. This turned out to be false, because the data was not sent from a form or file upload (see PHP "php://input" vs $_POST).
The following code works for me perfectly (thanks to inspiration by the slightly buggy code in https://mathiasbynens.be/notes/csp-reports):
<?php
// Receive and log Content-Security-Policy report
// (WriteLog function omitted here: it just writes text into a log file)
$data=file_get_contents('php://input');
if (!$data) // Data is usually non-empty
exit(0);
// Prettify the JSON-formatted data.
$val=json_decode($data);
$data = json_encode($val,JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES);
WriteLog($data);
?>
I am having a problem submitting a UTF8 encoded text file in a POST request using NodeJS "shred"
The text content I am trying to post looks fine on the client side, I know because I console.log it to the screen just before calling client.post, what the server gets is the content of the text file but the last 2 chars are always missing/chopped. This is not a problem with ANSI text files. If I convert the textfile from UTF8 to ANSI, it is complete when it reaches the server.
var Shred = require('shred');
var client = new Shred();
var textToPost = fs.readFileSync("myfile.txt", 'utf8');
console.log (textToPost);
client.post({
url: "http://www.example.com/readTextFile.php",
headers: { 'Content-Type': 'application/x-subrip'},
content: textToPost,
on: {
200: function (response) {
console.log("posted ok");
console.log(response.content.body);
},
500: function (response) {
asyncCb(new Error('bad response\n' + response.content.body));
}
}
What is recieved on the server (by readTextFile.php) is the contents of myfile.txt with the last 2 chars stripped out. I cannot understand why. This has big downstream implications so any patchy workarounds are not likely to help.
I also noticed that when the contents of textToPost are logged to the console, there is a "?" preceding the contents. This doesn't appear when the file is an ANSI encoded file.
Please help.. thank you
Ok, after the comments above (thanks rdrey and JohnnyHK), I decided to try stripping out the BOM from the file(s). So I used a hex editor, deleted the EF BB BF chars and saved, this time the file arrived at the server fully intact with no chars missing at the end. Now I'll modify my nodeJS to strip the chars out also. This doesn't completely answer my question (why is there an issue with the BOM). Perhaps shred has a problem posting text files with a BOM. Maybe it incorrectly reads it and decides the file is smaller than it actually is and as a result, chops the end off. I am not sure.