Golang http写响应而无需等待完成

Question

I'm building an application that builds a pdf file and returns it to the client whenever it receives a request.

Since some of these pdf files might take some time to generate, I would like to periodically send some sort of status update back to client while it is running.

When it's finished building the pdf file, it should be returned to the client as well.

Something akin to:

func buildReport(writer http.ResponseWriter, request *http.Request){
    //build pdf build pdf file
    for { //for example purposes only
        writer.Write([]byte("building. Please wait."))
    }
    pdf.OutputFileAndClose("report.pdf")
    //set header to pdf so that the client knows it's a PDF
    writer.Header().Set("Content-Type", "application/pdf")
    http.ServeFile(writer, request, "report.pdf")
}

func main() {
    http.HandleFunc("/", buildReport)
    http.ListenAndServe(":8081", nil)
}

Setting the header might not work, as the writer can only have one header.

Answer 1

TL;DR is that it cannot be implemented that way. You need to

1. An API that requests the PDF creation. That queues PDF creation job in a task queue (so that too many PDF creation requests won't blow the HTTP server worker pool)
2. Provide an API that allows you to check where are you with the PDF rendering (I am assuming that the job can provide interim stats). This is going to be polled by the client on a regular basis.
3. An API to pull the PDF once it is ready.

Hope this helps and best of luck with your project.