How to Fix the Django Error Using cURL Download with CURLOPT_RESUME_FROM_LARGE

I ran into a strange issue while building a file download service using Django as the server and cURL on the client side. Everything was working great until I added resume functionality using CURLOPT_RESUME_FROM_LARGE. Then, out of nowhere, I started getting this annoying error:

error: [Errno 32] Broken pipe

At first, I wasn’t sure if the error was coming from Django or my client code. After hours of digging, testing, and trial and error debugging, I found the culprit. It was a simple but sneaky mistake on the client side. In this post, I’ll walk you through what happened, what I learned, and how I fixed it.

Problem Setup

I’m using Django 1.4 (yes, it’s old but still kicking in this project) to serve files, and I wrote a client in C++ that uses libcurl to download the files. I wanted the download to support resuming if it ever got interrupted.

Here’s the original client code:

FILE* ptmpfile = fopen((m_download_filepath_pre + tmpfilename).c_str(), "ab+");
fseek(ptmpfile, 0L, SEEK_END);
int currentsize = ftell(ptmpfile);

curl_easy_setopt(curl, CURLOPT_FILE, ptmpfile);
curl_easy_setopt(curl, CURLOPT_HEADER, 0);
curl_easy_setopt(curl, CURLOPT_NOBODY, 0);
curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 60);
curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0);
curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, my_progress_func);
curl_easy_setopt(curl, CURLOPT_PROGRESSDATA, sDownload);
curl_easy_setopt(curl, CURLOPT_RESUME_FROM_LARGE, currentsize);  // 🔴 ERROR LINE

What I Saw on the Server

On the Django side, I saw this traceback in the terminal:

 happened during processing of request from ('127.0.0.1', 50232)
...
error: [Errno 32] Broken pipe

I was confused. My server wasn’t even doing anything fancy it was just serving a file. So why was the pipe breaking?

Root Cause of the Error

After inspecting and experimenting, I realized this wasn’t Django’s fault. It was a client-side error.

The problem was in this line:

curl_easy_setopt(curl, CURLOPT_RESUME_FROM_LARGE, currentsize);

CURLOPT_RESUME_FROM_LARGE expects a value of type curl_off_t. But currentsize was declared as an int. On most modern systems, curl_off_t is a 64-bit type, while int is 32-bit. This mismatch silently causes issues.

That incorrect type causes cURL to send the wrong byte range in the Range header. Django, not expecting such a value, closes the connection thus the “broken pipe.”

The Fix

Here’s the corrected line:

curl_easy_setopt(curl, CURLOPT_RESUME_FROM_LARGE, (curl_off_t)currentsize);

If you’re only working with small files (<2 GB), you can also use:

curl_easy_setopt(curl, CURLOPT_RESUME_FROM, currentsize);

CURLOPT_RESUME_FROM vs CURLOPT_RESUME_FROM_LARGE

I now always use CURLOPT_RESUME_FROM_LARGE for safer and future-proof code.

Enhance Practice Version

To really learn from this, I created a better version of the client download code. This one has:

• Automatic retries
• Logging
• Correct resume support

#include <iostream>
#include <fstream>
#include <curl/curl.h>

size_t write_data(void* ptr, size_t size, size_t nmemb, FILE* stream) {
    return fwrite(ptr, size, nmemb, stream);
}

void download_with_resume(const std::string& url, const std::string& filepath) {
    CURL* curl = curl_easy_init();
    if (!curl) {
        std::cerr << "Failed to initialize CURL.\n";
        return;
    }

    // Get current file size
    FILE* file = fopen(filepath.c_str(), "ab+");
    fseek(file, 0L, SEEK_END);
    curl_off_t existing_size = ftell(file);
    fclose(file);

    // Reopen for writing
    file = fopen(filepath.c_str(), "ab+");

    // Set curl options
    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, file);
    curl_easy_setopt(curl, CURLOPT_RESUME_FROM_LARGE, existing_size);
    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0);
    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);  // Log to console

    // Retry logic
    CURLcode res;
    int retries = 3;
    do {
        res = curl_easy_perform(curl);
        if (res != CURLE_OK) {
            std::cerr << "Download failed: " << curl_easy_strerror(res) << "\n";
            retries--;
        } else {
            break;
        }
    } while (retries > 0);

    fclose(file);
    curl_easy_cleanup(curl);
}

Tips for Django Server

If you’re using Django to serve files and want to support cURL resume downloads, keep these in mind:

• Django by default does not support Range requests (used by resume).
• You can:
  • Use a plugin like django-range-file
  • Serve files with Nginx or Apache (which handle range requests perfectly)
  • Write a custom Django view that reads the Range header and serves partial content

Final Thoughts

The error wasn’t Django’s fault it was a simple misuse of the cURL API on my part. A type mismatch in one line caused hours of unnecessary debugging. The key takeaways? Always use the correct data types like curl_off_t for large file resumes, add retry and logging to your download logic, and make sure your server supports HTTP Range headers. After fixing these, my file download works smoothly even after interruptions. I hope this helps you avoid the same mistake.