mirror of
https://github.com/yhirose/cpp-httplib.git
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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.
52 lines
1.7 KiB
Markdown
52 lines
1.7 KiB
Markdown
---
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title: "S13. Return a Custom Error Page"
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order: 32
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status: "draft"
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---
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To customize the response for 4xx or 5xx errors, use `set_error_handler()`. By default, an error response has an empty body; an error handler lets you fill it with your own HTML or JSON.
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## Basic usage
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```cpp
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svr.set_error_handler([](const httplib::Request &req, httplib::Response &res) {
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auto body = "<h1>Error " + std::to_string(res.status) + "</h1>";
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res.set_content(body, "text/html");
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});
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```
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The error handler runs right before an error response is sent — any time `res.status` is 4xx or 5xx. Replace the body with `res.set_content()` and every error response uses the same template.
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## Branch by status code
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```cpp
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svr.set_error_handler([](const httplib::Request &req, httplib::Response &res) {
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if (res.status == 404) {
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res.set_content("<h1>Not Found</h1><p>" + req.path + "</p>", "text/html");
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} else if (res.status >= 500) {
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res.set_content("<h1>Server Error</h1>", "text/html");
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}
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});
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```
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Checking `res.status` lets you show a custom message for 404s and a "contact support" link for 5xx errors.
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## JSON error responses
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For an API server, you probably want errors as JSON.
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```cpp
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svr.set_error_handler([](const httplib::Request &req, httplib::Response &res) {
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nlohmann::json j = {
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{"error", true},
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{"status", res.status},
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{"path", req.path},
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};
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res.set_content(j.dump(), "application/json");
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});
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```
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Now every error comes back in a consistent JSON shape.
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> **Note:** `set_error_handler()` also fires for 500 responses caused by exceptions thrown from a route handler. To get at the exception itself, combine it with `set_exception_handler()`. See [S14. Catch exceptions](../s14-exception-handler).
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