yhirose
9bfd2ddf1c
Bring the READMEs and the docs pages (en and ja) in line with the current header: - Fix the client sample that does not compile, the Transfer-Encoding statement for default headers, the verifier callback comment, the thread pool spawn rule, the sanitize_filename description, and the inverted Accept-Encoding sentence. - Describe recent behaviour: TLS errors behind Read/Write failures, Host validation, Connection: close for a body without length, content_reader rules, refused CONNECT, WebSocketClient proxies, CPPHTTPLIB_INTERIM_RESPONSE_MAX_COUNT, the SSE event size limit, and the payload limit of the Stream API. - Complete the API references of WebSocket, WebSocketClient and the stream:: helpers, and the SSE reconnect rules. - Fix cookbook pages: keychain loading on every backend, received Close status, a multipart sample that trusted the client's file name, an echo sample that sent binary as text, SNI, pre-request handler scope, stop() with WebSocket handlers, and the thread pool notes. - Restore the mutex in the LLM app's Chapter 5 code.
4.0 KiB
title, order, status
| title | order | status |
|---|---|---|
| S07. Receive Multipart Data as a Stream | 26 | draft |
A naive upload handler puts the whole request into req.body, which blows up memory for large files. Use HandlerWithContentReader to receive the body chunk by chunk.
Basic usage
svr.Post("/upload",
[](const httplib::Request &req, httplib::Response &res,
const httplib::ContentReader &content_reader) {
if (req.is_multipart_form_data()) {
content_reader(
// headers of each part
[&](const httplib::FormData &file) {
std::cout << "name: " << file.name
<< ", filename: " << file.filename << std::endl;
return true;
},
// body of each part (called multiple times)
[&](const char *data, size_t len) {
// write to disk here, for example
return true;
});
} else {
// plain request body
content_reader([&](const char *data, size_t len) {
return true;
});
}
res.set_content("ok", "text/plain");
});
The content_reader has two call shapes. For multipart data, pass two callbacks (one for headers, one for body). For plain bodies, pass just one.
Write directly to disk
Here's how to stream an uploaded file to disk.
svr.Post("/upload",
[](const httplib::Request &req, httplib::Response &res,
const httplib::ContentReader &content_reader) {
std::ofstream ofs;
auto ok = content_reader(
[&](const httplib::FormData &file) {
if (ofs.is_open()) { ofs.close(); } // done with the previous file
if (file.filename.empty()) { return true; } // a plain field, skip it
auto name = httplib::sanitize_filename(file.filename);
if (name.empty()) { return false; } // reject an unsafe name
ofs.open("uploads/" + name, std::ios::binary);
return ofs.is_open();
},
[&](const char *data, size_t len) {
if (!ofs.is_open()) { return true; } // not part of a file
ofs.write(data, len);
return static_cast<bool>(ofs);
});
if (!ok) { return; } // the status is already set
res.set_content("uploaded", "text/plain");
});
The header callback runs at the start of every part, so it closes the previous file before opening the next one. file.filename is whatever the client sent, so always pass it through httplib::sanitize_filename(). An empty result means the name is unsafe.
Only a small chunk sits in memory at any moment, so gigabyte-scale files are no problem.
Count the parts yourself
There is a cap on the number of parts, CPPHTTPLIB_MULTIPART_FORM_DATA_FILE_MAX_COUNT (1024 by default), but it only applies to the buffered path, where every part is accumulated into req.form. The ContentReader keeps nothing on the library side, so the cap does not apply here.
If you want an upper bound, count the parts yourself and return false from the header callback. The parser stops right there.
svr.Post("/upload",
[](const httplib::Request &req, httplib::Response &res,
const httplib::ContentReader &content_reader) {
size_t count = 0;
auto ok = content_reader(
[&](const httplib::FormData &file) {
if (++count > 100) { return false; } // stop here
return true;
},
[&](const char *data, size_t len) {
return true;
});
if (!ok) {
res.status = httplib::StatusCode::BadRequest_400;
return;
}
res.set_content("ok", "text/plain");
});
When content_reader returns false, the response status becomes 400 (413 if the body exceeded the size limit). Set it yourself if you want a different one. The rest of the body is left unread and the connection is closed, so a client that is still sending sees the connection drop.
Warning: When you use
HandlerWithContentReader,req.bodystays empty. Handle the body yourself inside the callbacks.
For the client side of multipart uploads, see C07. Upload a file as multipart form data.