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yhirose
f29721c7d8
set_keep_alive_max_count(0) tripped an assert, a negative WebSocket ping interval sent pings in a tight loop, and the form length, multipart file count and range count macros rejected every request at 0. Make 0 mean no limit for those, and a ping interval of 0 or less turn pings off. The URI, header and line bounds cannot be lifted, so a static_assert keeps them positive.
58 lines
1.8 KiB
Markdown
58 lines
1.8 KiB
Markdown
---
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title: "S20. Tune Keep-Alive"
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order: 39
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status: "draft"
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---
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`httplib::Server` enables HTTP/1.1 Keep-Alive automatically. From the client's perspective, connections are reused — so they don't pay the TCP handshake cost on every request. When you need to tune the behavior, there are two setters.
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## What you can configure
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| API | Default | Meaning |
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| --- | --- | --- |
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| `set_keep_alive_max_count` | 100 | Max requests served over a single connection (0 for no limit) |
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| `set_keep_alive_timeout` | 5s | How long an idle connection is kept before closing |
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## Basic usage
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```cpp
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httplib::Server svr;
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svr.set_keep_alive_max_count(20);
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svr.set_keep_alive_timeout(10); // 10 seconds
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svr.listen("0.0.0.0", 8080);
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```
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`set_keep_alive_timeout()` also has a `std::chrono` overload.
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```cpp
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using namespace std::chrono_literals;
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svr.set_keep_alive_timeout(10s);
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```
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## Tuning ideas
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**Too many idle connections eating resources**
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Shorten the timeout so idle connections drop and release their worker threads.
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```cpp
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svr.set_keep_alive_timeout(2s);
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```
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**API is hammered and you want max reuse**
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Raising the per-connection request cap improves benchmark numbers.
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```cpp
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svr.set_keep_alive_max_count(1000);
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```
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**Never reuse connections**
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Set `set_keep_alive_max_count(1)` and every request gets its own connection. Mostly only useful for debugging or compatibility testing.
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## Relationship with the thread pool
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A Keep-Alive connection holds a worker thread for its entire lifetime. If `connections × concurrent requests` exceeds the thread pool size, new requests wait. For thread counts, see [S21. Configure the thread pool](../s21-thread-pool).
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> **Note:** For the client side, see [C14. Understand connection reuse and Keep-Alive behavior](../c14-keep-alive). Even when the server closes the connection on timeout, the client reconnects automatically.
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