The http.TimeoutHandler
function in Golang is part of the net/http
package and is used to wrap an existing HTTP handler with a timeout. This ensures that if the wrapped handler takes longer than a specified duration to process a request, the client will receive a timeout response. This is particularly useful in preventing long-running requests from holding up server resources and providing a better user experience by ensuring timely responses.
Table of Contents
- Introduction
http.TimeoutHandler
Function Syntax- Examples
- Basic Usage
- Custom Timeout Message
- Using
http.TimeoutHandler
with Different Handlers
- Real-World Use Case
- Conclusion
Introduction
The http.TimeoutHandler
function allows you to enforce a maximum duration for handling HTTP requests. If the underlying handler does not complete the request within the specified time limit, the TimeoutHandler
automatically sends a timeout response to the client. This is useful for ensuring that your server remains responsive even under heavy load or when dealing with potentially slow external services.
http.TimeoutHandler Function Syntax
The syntax for the http.TimeoutHandler
function is as follows:
func TimeoutHandler(h http.Handler, dt time.Duration, msg string) http.Handler
Parameters:
h
: Thehttp.Handler
to wrap with a timeout. This is the handler that processes the actual request.dt
: The maximum time allowed to process the request. This is specified as atime.Duration
.msg
: A string containing the message to be sent to the client if the timeout is reached.
Returns:
http.Handler
: The function returns anhttp.Handler
that enforces the specified timeout when handling requests.
Examples
Basic Usage
This example demonstrates how to use the http.TimeoutHandler
function to enforce a timeout on a long-running handler.
Example
package main
import (
"net/http"
"time"
)
func main() {
// Define a handler that simulates a long-running process
longRunningHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
time.Sleep(5 * time.Second) // Simulate a long process
w.Write([]byte("Request completed"))
})
// Wrap the handler with a timeout of 2 seconds
timeoutHandler := http.TimeoutHandler(longRunningHandler, 2*time.Second, "Request timed out")
// Register the handler
http.Handle("/long", timeoutHandler)
// Start the server on port 8080
http.ListenAndServe(":8080", nil)
}
Explanation:
- The server listens on port 8080.
- The
longRunningHandler
simulates a long-running process by sleeping for 5 seconds. - The handler is wrapped with
http.TimeoutHandler
, enforcing a timeout of 2 seconds. - If the request takes longer than 2 seconds, the client will receive a "Request timed out" message.
Example Request:
http://localhost:8080/long
Response:
If the request takes longer than 2 seconds, the client will see:
Request timed out
Custom Timeout Message
This example shows how to customize the timeout message sent to the client.
Example
package main
import (
"net/http"
"time"
)
func main() {
// Define a handler that simulates a long-running process
slowHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
time.Sleep(3 * time.Second) // Simulate a delay
w.Write([]byte("Slow request completed"))
})
// Wrap the handler with a timeout and a custom message
timeoutHandler := http.TimeoutHandler(slowHandler, 1*time.Second, "Custom Timeout: Request took too long")
// Register the handler
http.Handle("/slow", timeoutHandler)
// Start the server on port 8080
http.ListenAndServe(":8080", nil)
}
Explanation:
- The
slowHandler
simulates a delay of 3 seconds. - The handler is wrapped with
http.TimeoutHandler
, enforcing a timeout of 1 second and a custom timeout message. - If the request takes longer than 1 second, the client will receive the custom timeout message.
Example Request:
http://localhost:8080/slow
Response:
If the request takes longer than 1 second, the client will see:
Custom Timeout: Request took too long
Using http.TimeoutHandler with Different Handlers
This example demonstrates how to apply http.TimeoutHandler
to different routes in a web server.
Example
package main
import (
"net/http"
"time"
)
func main() {
// Fast handler with no timeout
http.HandleFunc("/fast", func(w http.ResponseWriter, r *http.Request) {
w.Write([]byte("Fast request completed"))
})
// Slow handler with a timeout of 2 seconds
slowHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
time.Sleep(5 * time.Second) // Simulate a delay
w.Write([]byte("Slow request completed"))
})
http.Handle("/slow", http.TimeoutHandler(slowHandler, 2*time.Second, "Request timed out"))
// Start the server on port 8080
http.ListenAndServe(":8080", nil)
}
Explanation:
- The
/fast
route processes requests without a timeout. - The
/slow
route is wrapped withhttp.TimeoutHandler
, enforcing a timeout of 2 seconds. - Different routes can have different timeout settings based on their expected processing times.
Example Requests:
/fast
: This request will complete quickly without any timeout./slow
: If this request takes longer than 2 seconds, it will time out and return a timeout message.
Real-World Use Case
Preventing Slow Requests from Blocking the Server
In a real-world application, http.TimeoutHandler
can be used to prevent slow-running requests from consuming server resources and blocking other requests. For example, if you have a web service that performs complex calculations or interacts with slow external APIs, wrapping the handler with http.TimeoutHandler
ensures that these operations do not degrade the overall server performance.
Example: Protecting Against Slow External API Calls
package main
import (
"net/http"
"time"
)
func main() {
// Simulate an external API call that could be slow
externalAPICall := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// Simulate a delay
time.Sleep(4 * time.Second)
w.Write([]byte("External API response"))
})
// Wrap the handler with a timeout of 2 seconds
http.Handle("/api", http.TimeoutHandler(externalAPICall, 2*time.Second, "API request timed out"))
// Start the server on port 8080
http.ListenAndServe(":8080", nil)
}
Explanation:
- The server handles requests to
/api
by simulating an external API call that may take time to respond. - To protect against long response times, the handler is wrapped with
http.TimeoutHandler
with a 2-second timeout. - If the external API takes too long, the client receives a timeout message, preventing the request from hanging indefinitely.
Conclusion
The http.TimeoutHandler
function in Go is used for managing long-running HTTP requests, ensuring that your server remains responsive even under challenging conditions. By setting appropriate timeouts, you can protect your server from slow requests, enhance user experience by providing timely responses, and maintain overall performance. Whether you're dealing with slow external services or complex internal processing, http.TimeoutHandler
provides a simple and effective way to enforce time limits on HTTP requests.
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