Azure functions messing up gzipped POST data - node.js

Question

Currently i'm implementing a webhook which states that the request sent to the configured endpoint will be gzipped, and i'm experiencing a weird bug with that.
I created a middleware to handle de gunzip of the request data:
const buffer: Buffer[] = [];
request
.on("data", (chunk) => {
buffer.push(Buffer.from(chunk));
})
.on("end", () => {
const concatBuff: Buffer = Buffer.concat(buffer);
zlib.gunzip(concatBuff, (err, buff) => {
if (err) {
console.log("gunzip err", err);
return next(err);
}
request.body = buff.toString();
next();
});
});
I added this middleware before all the other body parser middlewares to avoid any incompatibility with that.
So i'm testing it with this curl command:
cat webhook.txt | gzip | curl -v -i --data-binary #- -H "Content-Encoding: gzip" http://localhost:3334
In this server, which uses azure-function-express, i'm getting this error:
[1/9/2020 22:36:21] gunzip err Error: incorrect header check
[1/9/2020 22:36:21] at Zlib.zlibOnError [as onerror] (zlib.js:170:17) {
[1/9/2020 22:36:21] errno: -3,
[1/9/2020 22:36:21] code: 'Z_DATA_ERROR'
[1/9/2020 22:36:21] }
[1/9/2020 22:36:21]
it seems that the error is caused because the header is not the "magical number" of a gzip file:
<Buffer 1f ef bf bd 08 00 ef bf bd ef bf bd 4e 5f 00 03 ef bf bd 5d 6d 73 db b8 11 ef bf bd ef b
f bd 5f ef bf bd e1 97 bb 6b 7d 16 ef bf bd 77 ef bf bd 73 ef ... 4589 more bytes>
But here is the weird thing, i created a new express application to test this using the exactly same curl, and it works perfectly in there, so it seems that there is some problem with the createAzureFunctionHandler, or i'm missing out something.
Have you guys experienced any of those problems using Azure functions??
Any idea of what is Azure messing up with the gzip data??

Answer 1

I just got an answer from the Azure team, they recommend me to set a proxy inside proxies.json as a workaround, so if anyone is having the same issue you can just set a new proxy to override the Content-Type.
In my case i was always expecting a gzipped json, so maybe if you don't know beforehand which type is this wouldn't work for you.
{
"$schema": "http://json.schemastore.org/proxies",
"proxies": {
"RequireContentType": {
"matchCondition": {
"route": "/api/HttpTrigger"
},
"backendUri": "https://proxy-example.azurewebsites.net/api/HttpTrigger",
"requestOverrides": {
"backend.request.headers.content-type": "application/octet-stream",
"backend.request.headers.request-content-type": "'{request.headers.content-type}'"
}
}
}
}