How to post an image using multipart/form-data with hyper?

Question

I'm trying to post an image file using hyper like cURL does:

curl -F smfile=@11.jpg https://httpbin.org/post --trace-ascii -

The result is:

{
  "args": {},
  "data": "",
  "files": {
    "smfile": "data:image/jpeg;base64,..."
  },
  "form": {},
  "headers": {
    "Accept": "/",
    "Connection": "close",
    "Content-Length": "1709",
    "Content-Type": "multipart/form-data; boundary=------------------------58370e136081470e",
    "Expect": "100-continue",
    "Host": "httpbin.org",
    "User-Agent": "curl/7.59.0"
  },
  "json": null,
  "origin": "myip",
  "url": "https://httpbin.org/post"
}

I learned that Content-Type should be set to multipart/form-data with a boundary mark. Here's my code:

extern crate futures;
extern crate hyper;
extern crate hyper_tls;
extern crate tokio;

use futures::{future, Future};
use hyper::header::CONTENT_TYPE;
use hyper::rt::Stream;
use hyper::{Body, Client, Method, Request};
use hyper_tls::HttpsConnector;
use std::fs::File;
use std::io::prelude::*;
use std::io::{self, Write};

const BOUNDARY: &'static str = "------------------------ea3bbcf87c101592";

fn main() {
    tokio::run(future::lazy(|| {
        let https = HttpsConnector::new(4).unwrap();
        let client = Client::builder().build::<_, hyper::Body>(https);

        let mut req = Request::new(Body::from(image_data()));

        req.headers_mut().insert(
            CONTENT_TYPE,
            format!("multipart/form-data; boundary={}", BOUNDARY)
                .parse()
                .unwrap(),
        );
        *req.method_mut() = Method::POST;
        *req.uri_mut() = "https://httpbin.org/post".parse().unwrap();

        client
            .request(req)
            .and_then(|res| {
                println!("status: {}", res.status());

                res.into_body().for_each(|chunk| {
                    io::stdout()
                        .write_all(&chunk)
                        .map_err(|e| panic!("stdout error: {}", e))
                })
            })
            .map_err(|e| println!("request error: {}", e))
    }));
}

fn image_data() -> Vec<u8> {
    let mut result: Vec<u8> = Vec::new();
    result.extend_from_slice(format!("--{}\r\n", BOUNDARY).as_bytes());
    result
        .extend_from_slice(format!("Content-Disposition: form-data; name=\"text\"\r\n").as_bytes());
    result.extend_from_slice("title\r\n".as_bytes());
    result.extend_from_slice(format!("--{}\r\n", BOUNDARY).as_bytes());
    result.extend_from_slice(
        format!("Content-Disposition: form-data; name=\"smfile\"; filename=\"11.jpg\"\r\n")
            .as_bytes(),
    );
    result.extend_from_slice("Content-Type: image/jpeg\r\n\r\n".as_bytes());

    let mut f = File::open("11.jpg").unwrap();
    let mut file_data = Vec::new();
    f.read_to_end(&mut file_data).unwrap();

    result.append(&mut file_data);

    result.extend_from_slice(format!("--{}--\r\n", BOUNDARY).as_bytes());
    result
}

(complete code)

Note that a JPEG file named 11.jpg is needed to run this code. This can be any JPEG file.

httpbin shows that I posted nothing:

{
  "args": {},
  "data": "",
  "files": {},
  "form": {},
  "headers": {
    "Connection": "close",
    "Content-Length": "1803",
    "Content-Type": "multipart/form-data; boundary=------------------------ea3bbcf87c101592",
    "Host": "httpbin.org"
  },
  "json": null,
  "origin": "myip",
  "url": "https://httpbin.org/post"
}

I have no idea how to fix this.

Answer 1

You aren't correctly placing a newline/carriage return pair before your final boundary.

Here's how I'd write your body generation code, requiring less allocation:

fn image_data() -> io::Result<Vec<u8>> {
    let mut data = Vec::new();
    write!(data, "--{}\r\n", BOUNDARY)?;
    write!(data, "Content-Disposition: form-data; name=\"smfile\"; filename=\"11.jpg\"\r\n")?;
    write!(data, "Content-Type: image/jpeg\r\n")?;
    write!(data, "\r\n")?;

    let mut f = File::open("11.jpg")?;
    f.read_to_end(&mut data)?;

    write!(data, "\r\n")?; // The key thing you are missing
    write!(data, "--{}--\r\n", BOUNDARY)?;

    Ok(data)
}

Calling this code can also be simplified:

fn main() {
    let https = HttpsConnector::new(4).unwrap();
    let client = Client::builder().build::<_, hyper::Body>(https);

    let data = image_data().unwrap();
    let req = Request::post("https://httpbin.org/post")
        .header(CONTENT_TYPE, &*format!("multipart/form-data; boundary={}", BOUNDARY))
        .body(data.into())
        .unwrap();

    tokio::run(future::lazy(move || {
        client
            .request(req)
            .and_then(|res| {
                println!("status: {}", res.status());

                res.into_body().for_each(|chunk| {
                    io::stdout()
                        .write_all(&chunk)
                        .map_err(|e| panic!("stdout error: {}", e))
                })
            })
            .map_err(|e| println!("request error: {}", e))
    }));
}