How is a PDF supposed to be encoded? - pdf

Question

I'm trying to set up an API that generate PDF from web page (provided as URL). The API is gotenberg from thecodingmachine. I have it on Docker, it works just fine, I can't generate PDF through http request send with curl (for now I'm just trying to make it work, so I use the request provided as example in the documentation)
Now I am trying to make it work with my groovy/grails app. So I'm using the java tools to make the request.
Now here is my problem : the PDF file I get is blank (my app opend directly in my browser). It do has the right content, if I open it with the text editor, it's not empty, and it has almost the same content as the one I make using the curl request (which isn't blank).
I am 99% sure the problem come from the encoding. I tried changing the InputStreamReader encoding parameter, but it doesn't change anything. Here I put "X-MACROMAN" because that the encoding inside the pdf file that isn't blank, but it still doesn't change.
Here is my code :
static def execute(def apiURL)
{
def httpClient = HttpClients.createDefault()
// Request parameters and other properties.
def request = new HttpPost(apiURL)
MultipartEntityBuilder builder = MultipartEntityBuilder.create()
builder.addTextBody("remoteURL", 'https://google.com')
builder.addTextBody("marginTop", '0')
builder.addTextBody("marginBottom", '0')
builder.addTextBody("marginLeft", '0')
builder.addTextBody("marginRight", '0')
HttpEntity multipart = builder.build()
request.setEntity(multipart)
def response = httpClient.execute(request)
BufferedReader rd = new BufferedReader(
new InputStreamReader(response.getEntity().getContent(), "X-MACROMAN"))
StringBuffer result = new StringBuffer()
String line = ""
Boolean a = Boolean.FALSE
while ((line = rd.readLine()) != null) {
if(!a){
a = Boolean.TRUE
}
else {
result.append("\n")
}
result.append(line)
}
return result
I am 99% sure the problem come from the encoding. I tried changing the InputStreamReader encoding parameter, but it doesn't change anything. Here I put "X-MACROMAN" because that the encoding inside the pdf file that isn't blank, but it still doesn't change.
Did I made myself clear ? And does those who understands has any ideas why my PDFs are blank ?