mirror of
https://github.com/yhirose/cpp-httplib.git
synced 2026-10-08 12:23:47 +00:00
199d7ee248
read() collapsed every failure into Fail and marked the connection closed with it, so a read timeout could not be used to get control back and send on the same connection -- it killed the connection instead. The information was already there and thrown away: SocketStream::read records Error::Timeout, and read_websocket_frame flattened it into a bool. ReadResult gains Timeout, reported only when the timeout elapsed on a frame boundary with nothing consumed, which is the only case where the stream can be read again. Every multi-byte field now loops until it has its bytes, which also fixes a frame header straddling the read buffer's boundary failing the frame: Stream::read is allowed to return less than asked for, and only the payload was reading in a loop. ws::WebSocket::set_read_timeout() lets a server handler bound its own reads, and WebSocketClient::set_read_timeout() now reaches an already-open connection instead of only seeding the next connect(). The read timeout macro splits in two. A client waits forever by default -- a read timeout is the caller's tool for taking back control, not a liveness check, which is ping/pong's job -- while a server keeps the 300s that reclaims a worker from a peer gone quiet. Defining the old name still sets both. Also record a reason on the two WebSocketSSLStream::read failure paths that returned -1 without one, so get_error() cannot report a previous call's timeout, and make SocketStream's read timeout atomic now that it can be changed while a read is in flight.
89 lines
2.9 KiB
Markdown
89 lines
2.9 KiB
Markdown
---
|
|
title: "W04. Send and Receive Binary Frames"
|
|
order: 55
|
|
status: "draft"
|
|
---
|
|
|
|
WebSocket has two frame types: text and binary. JSON and plain text go in text frames; images and raw protocol bytes go in binary. In cpp-httplib, `send()` picks the right type via overload.
|
|
|
|
## How to pick a frame type
|
|
|
|
```cpp
|
|
ws.send(std::string("Hello")); // text
|
|
ws.send("Hello", 5); // binary
|
|
ws.send(binary_data, binary_data_size); // binary
|
|
```
|
|
|
|
The `std::string` overload sends as **text**. The `const char*` + size overload sends as **binary**. A bit subtle, but once you know it, it sticks.
|
|
|
|
If you have a `std::string` and want to send it as binary, pass `.data()` and `.size()` explicitly.
|
|
|
|
```cpp
|
|
std::string raw = build_binary_payload();
|
|
ws.send(raw.data(), raw.size()); // binary frame
|
|
```
|
|
|
|
## Detect frame type on receive
|
|
|
|
The return value of `ws.read()` tells you whether the received frame was text or binary.
|
|
|
|
```cpp
|
|
std::string msg;
|
|
auto result = ws.read(msg);
|
|
|
|
switch (result) {
|
|
case httplib::ws::ReadResult::Text:
|
|
std::cout << "text: " << msg << std::endl;
|
|
break;
|
|
case httplib::ws::ReadResult::Binary:
|
|
std::cout << "binary: " << msg.size() << " bytes" << std::endl;
|
|
handle_binary(msg.data(), msg.size());
|
|
break;
|
|
case httplib::ws::ReadResult::Fail:
|
|
// error or closed
|
|
break;
|
|
case httplib::ws::ReadResult::Timeout:
|
|
// read timeout elapsed; the connection is still open
|
|
break;
|
|
}
|
|
```
|
|
|
|
Binary frames still come back in a `std::string`, but treat its contents as raw bytes — use `msg.data()` and `msg.size()`.
|
|
|
|
## When binary is the right call
|
|
|
|
- **Images, video, audio**: No Base64 overhead
|
|
- **Custom protocols**: protobuf, MessagePack, or any structured binary format
|
|
- **Game networking**: When latency matters
|
|
- **Sensor data streams**: Push numeric arrays directly
|
|
|
|
## Ping is binary-ish, but hidden
|
|
|
|
WebSocket Ping/Pong frames are close cousins of binary frames at the opcode level, but cpp-httplib handles them automatically — you don't touch them. See [W02. Set a WebSocket heartbeat](../w02-websocket-ping).
|
|
|
|
## Example: send an image
|
|
|
|
```cpp
|
|
// Server: push an image
|
|
svr.WebSocket("/image", [](const auto &req, auto &ws) {
|
|
auto img = read_image_file("logo.png");
|
|
ws.send(img.data(), img.size());
|
|
});
|
|
```
|
|
|
|
```cpp
|
|
// Client: receive and save
|
|
httplib::ws::WebSocketClient cli("ws://localhost:8080/image");
|
|
cli.connect();
|
|
|
|
std::string buf;
|
|
if (cli.read(buf) == httplib::ws::ReadResult::Binary) {
|
|
std::ofstream ofs("received.png", std::ios::binary);
|
|
ofs.write(buf.data(), buf.size());
|
|
}
|
|
```
|
|
|
|
You can mix text and binary in the same connection. A common pattern: JSON for control messages, binary for the actual data — you get efficient handling of metadata and payload both.
|
|
|
|
> **Note:** WebSocket frames don't have an infinite size limit. For very large data, chunk it in your application code. cpp-httplib can handle a big frame in one shot, but it does load it all into memory at once.
|