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65 lines
2.0 KiB
Markdown
65 lines
2.0 KiB
Markdown
---
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title: "S22. Talk Over a Unix Domain Socket"
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order: 41
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status: "draft"
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---
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When you want to talk only to other processes on the same host, a Unix domain socket is a nice fit. It avoids TCP overhead and uses filesystem permissions for access control. Local IPC and services sitting behind a reverse proxy are classic use cases.
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## Server side
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```cpp
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httplib::Server svr;
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svr.set_address_family(AF_UNIX);
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svr.Get("/", [](const auto &, auto &res) {
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res.set_content("hello from unix socket", "text/plain");
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});
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svr.listen("/tmp/httplib.sock", 80);
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```
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Call `set_address_family(AF_UNIX)` first, then pass the socket file path as the first argument to `listen()`. The port number is unused but required by the signature — pass any value.
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## Client side
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```cpp
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httplib::Client cli("/tmp/httplib.sock");
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cli.set_address_family(AF_UNIX);
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auto res = cli.Get("/");
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if (res) {
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std::cout << res->body << std::endl;
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}
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```
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Pass the socket file path to the `Client` constructor and call `set_address_family(AF_UNIX)`. Everything else works like a normal HTTP request.
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## When to use it
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- **Behind a reverse proxy**: An nginx-to-backend setup over a Unix socket is faster than TCP and sidesteps port management
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- **Local-only APIs**: IPC between tools that shouldn't be reachable from outside
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- **In-container IPC**: Process-to-process communication within the same pod or container
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- **Dev environments**: No more worrying about port conflicts
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## Clean up the socket file
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A Unix domain socket creates a real file in the filesystem. It doesn't get removed on shutdown, so delete it before starting if needed.
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```cpp
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std::remove("/tmp/httplib.sock");
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svr.listen("/tmp/httplib.sock", 80);
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```
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## Permissions
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You control who can connect via the socket file's permissions.
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```cpp
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svr.listen("/tmp/httplib.sock", 80);
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// from another process or thread
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chmod("/tmp/httplib.sock", 0660); // owner and group only
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```
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> **Warning:** Some Windows versions support AF_UNIX, but the implementation and behavior differ by platform. Test thoroughly before running cross-platform in production.
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