How to use context to implement request log filtering control in Go

How to use context to implement request log filtering control in Go

Introduction:
In a large web application, logs are very important, it can help us understand the operation of the application , and it is also an important basis for troubleshooting and monitoring. However, for some large applications, the amount of logs may be very huge. If a log is recorded for each request, the log file will be very large and it will be difficult to directly locate the information we want to view. Therefore, this article will introduce how to use Go's context package to implement filtering control of request logs in order to reduce log redundancy and improve log readability.

1. What is context
Before we start, let’s first understand the context package in Go language. Context is a standard library provided by the Go language, which is used to transfer request-related data. It is mainly used for context transfer across Goroutine requests. In a request, context can be used to pass request-related information, such as user authentication, requested ID, etc. In Go language, using context can avoid the trouble of passing context in the function call stack.

2. Use context to implement request log filtering
In a web application, requests will pass through multiple middleware and processing functions, and each middleware and processing function may record request-related logs. . In order to implement filtering control, we can add a flag bit in the request to determine whether logging needs to be recorded. The following is a simple example:

package main

import (
    "fmt"
    "log"
    "net/http"
    "context"
)

type key int

const (
    loggerKey key = iota
)

func main() {
    http.HandleFunc("/", withLogging(handleRequest))
    log.Fatal(http.ListenAndServe(":8080", nil))
}

func withLogging(next http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        logger := log.New(w, "", log.LstdFlags)
        ctx := context.WithValue(r.Context(), loggerKey, logger)
        next(w, r.WithContext(ctx))
    }
}

func handleRequest(w http.ResponseWriter, r *http.Request) {
    logger := r.Context().Value(loggerKey).(*log.Logger)
    logger.Printf("Received request from %s", r.RemoteAddr)
    fmt.Fprintf(w, "Hello, World!
")
}

In the above example, we use the WithValue function in context to save the log output object logger as a value in the context of the request. In the withLogging middleware, we create a logger object and set it to the request's context. In the handleRequest processing function, we obtain the logger object from the request context through the context's Value method and use this object to record logs.

3. Implement log filtering
In order to implement log filtering, we can obtain the URL or other information in the request in the withLogging middleware, and use this information to determine whether logs need to be recorded. The following is a simple example where we only record request logs for accessing a specific path:

func withLogging(next http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        logger := log.New(w, "", log.LstdFlags)
        
        // 检查请求是否需要记录日志
        if shouldLog(r) {
            ctx := context.WithValue(r.Context(), loggerKey, logger)
            next(w, r.WithContext(ctx))
        } else {
            next(w, r)
        }
    }
}

func shouldLog(r *http.Request) bool {
    if r.URL.Path == "/logs" {
        return true
    }
    return false
}

In the above example, we defined a shouldLog function to determine whether the request needs to be logged. If the requested URL is /logs, then return true, indicating that logging is required; otherwise, return false, indicating that logging is not required. In the withLogging middleware, we first check whether the request needs to be logged, and if so, continue processing. If not, we directly call the next function.

4. Summary
This article introduces how to use Go's context package to implement filtering control of request logs. By adding a flag bit to each request and judging the value of the flag bit in the middleware to decide whether to record the log, the redundancy of the log can be effectively reduced and the readability of the log can be improved. I hope this article can help you implement log filtering control in Go.

Reference materials:
https://golang.org/pkg/context/
https://blog.golang.org/context
https://www.alexedwards.net /blog/working-with-go-via-requests-context

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