Convert curl to C

libcurl is the C library behind the curl command-line tool. It's the most portable and widely deployed HTTP client library in existence, supporting 25+ protocols. Used by thousands of applications and embedded systems. Add with your system package manager or link statically. curl2code generates libcurl C code using the easy interface.

The easy interface (curl_easy_*) is for single synchronous transfers — simple and straightforward. The multi interface (curl_multi_*) enables non-blocking concurrent transfers in a single thread. Use easy for scripts and simple tools, multi for high-performance applications. For a higher-level C-family language, see curl to Rust.

For Bearer: set a custom header with curl_slist_append(headers, "Authorization: Bearer token"). For Basic auth: curl_easy_setopt(curl, CURLOPT_USERPWD, "user:pass"). libcurl automatically encodes Basic auth credentials. curl2code converts -u and header flags to the correct C API calls.

Use the MIME API (libcurl 7.56+): curl_mime_init() to create a mime structure, curl_mime_addpart() for each field, curl_mime_name() and curl_mime_filedata() for file uploads. Set with CURLOPT_MIMEPOST. Free with curl_mime_free().

Every curl_easy_* function returns a CURLcode — check against CURLE_OK. Use curl_easy_strerror(code) for human-readable messages. Set CURLOPT_ERRORBUFFER for detailed error strings. Get the HTTP status with curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &code).

Always call curl_easy_cleanup() when done with a handle. Free header lists with curl_slist_free_all(). Free MIME structures with curl_mime_free(). For write callbacks, manage your own buffer allocation. Call curl_global_cleanup() once at program exit. Failing to free resources causes memory leaks.

Set CURLOPT_CONNECTTIMEOUT for connection timeout and CURLOPT_TIMEOUT for total transfer time (both in seconds). For millisecond precision, use CURLOPT_CONNECTTIMEOUT_MS and CURLOPT_TIMEOUT_MS. These are the exact same options curl CLI uses with --connect-timeout and --max-time.

Set CURLOPT_PROXY to the proxy URL: curl_easy_setopt(curl, CURLOPT_PROXY, "http://proxy:8080"). For SOCKS5: set CURLOPT_PROXYTYPE to CURLPROXY_SOCKS5. For proxy auth: CURLOPT_PROXYUSERPWD. libcurl also respects the http_proxy environment variable.

Convert a curl POST command like curl -X POST -H "Content-Type: application/json" -d "{"key":"value"}" URL to C using curl2code. The generated code uses curl_easy_setopt(curl, CURLOPT_POSTFIELDS, json_string). curl2code automatically detects -d/--data flags with JSON content and sets the appropriate Content-Type header in the libcurl code.

Pass curl -H "Authorization: Bearer YOUR_TOKEN" URL to curl2code and it generates libcurl code with the auth header: struct curl_slist *headers = curl_slist_append(NULL, "Authorization: Bearer TOKEN"). curl2code detects Bearer tokens from both -H "Authorization: Bearer ..." and --oauth2-bearer flags. For Basic auth, use -u user:pass.

curl2code converts curl -H "Content-Type: application/json" URL to libcurl code with the proper header: curl_slist_append(headers, "Content-Type: application/json"). For -d data, curl defaults to application/x-www-form-urlencoded; for -F form uploads, it uses multipart/form-data. curl2code maps each to the correct libcurl API.