Go 中的“http：写入超过声明的 Content-Length”错误

PHP小编新一今天将为大家介绍一种常见的错误，即在Go语言中出现的“Http：写入超过声明的Content-Length”错误。当我们在使用Go语言编写HTTP请求时，有时会遇到这个错误。这个错误的原因是我们在请求头中声明的Content-Length与实际发送的请求体长度不一致。接下来，我们将详细解释这个错误的产生原因以及如何解决它。

问题内容

我正在尝试 Go 并编写了一个应用程序来管理由工作协程处理的 HTTP 请求队列。

并发的东西似乎工作正常，但在发送回 http 响应时出现此错误：写入的内容超过声明的 Content-Length。

完整代码如下：

package main

import (
    "log"
    "net/http"
    "sync"
)

// Job represents a unit of work to be processed by a worker.
type Job struct {
    r *http.Request       // HTTP request to be processed
    w http.ResponseWriter // Response writer to send the result
}

// Queue manages a list of jobs to be processed by workers.
type Queue struct {
    jobs []*Job     // List of jobs in the queue
    mu   sync.Mutex // Mutex to synchronize access to the queue
    cond *sync.Cond // Condition variable for signaling
}

var q Queue // Global instance of the queue
var WORKER_POOL_SIZE = 4 // Number of workers

// Push adds a job to the queue.
func (q *Queue) Push(j *Job) {
    q.mu.Lock()
    defer q.mu.Unlock()
    q.jobs = append(q.jobs, j)
    q.cond.Signal() // Signal a waiting worker that a job is available
    log.Println("Job added to queue")
}

// Pop retrieves and removes a job from the queue.
func (q *Queue) Pop() (*Job, bool) {
    q.mu.Lock()
    defer q.mu.Unlock()
    if len(q.jobs) == 0 {
        q.cond.Wait() // If the queue is empty, wait for a signal
    }
    job := q.jobs[0]
    q.jobs = q.jobs[1:]
    log.Println("Job removed from queue")
    return job, true
}

// handler adds a job to the queue.
func handler(w http.ResponseWriter, r *http.Request) {
    // Create a job with the request and response.
    job := &Job{r, w}

    // Push the job onto the queue.
    q.Push(job)
    log.Println("Received request and added job to queue")
}

// init initializes the condition variable and starts worker goroutines.
func init() {
    q.cond = sync.NewCond(&q.mu)
    for i := 0; i < WORKER_POOL_SIZE; i++ {
        go worker()
    }
}

// worker processes jobs from the queue.
func worker() {
    for {
        job, ok := q.Pop()
        if ok {
            log.Println("Worker processing job")
            doWork(job)
        }
    }
}

// doWork simulates processing a job and sends a response.
func doWork(job *Job) {
    // Extract the "Name" parameter from the request query.
    name := job.r.URL.Query().Get("Name")

    // Check if the name is not empty.
    if name != "" {
        // Send the name as the response.
        _, err := job.w.Write([]byte("Hello, " + name))
        if err != nil {
            log.Println("Error writing response:", err)
        }
        log.Println("Response sent: Hello,", name)
    } else {
        // If the "Name" parameter is missing or empty, send an error response.
        http.Error(job.w, "Name parameter is missing or empty", http.StatusBadRequest)
        log.Println("Error: Name parameter is missing or empty")
    }
}

func main() {
    http.HandleFunc("/addJob", handler)
    log.Println("Server started and listening on :8080")
    err := http.ListenAndServe(":8080", nil)
    if err != nil {
        log.Fatal("Error starting server:", err)
    }
}

知道如何解决这个问题吗？另外，由于我对 go 中的并发性很陌生，你认为它可以改进吗？谢谢！

解决方法

根据 http.Handler 文档：

您的 handler 正在将请求/编写器推送到队列中，然后返回。这意味着您在处理程序返回后尝试写入 ResponseWriter ，违反了上述规定（由于没有同步，写入也可能实际发生在 return 之前或同时发生）。

有很多方法可以解决这个问题；一种技术是：

// Job represents a unit of work to be processed by a worker.
type Job struct {
    r    *http.Request       // HTTP request to be processed
    w    http.ResponseWriter // Response writer to send the result
    done chan struct{}       // Closed when write competed
}

...

func handler(w http.ResponseWriter, r *http.Request) {
    // Create a job with the request and response.
    job := &Job{r, w, make(chan struct{})}

    // Push the job onto the queue.
    q.Push(job)
    log.Println("Received request and added job to queue")
    <-job.done // Wait until job has been processed
}

...

// worker processes jobs from the queue.
func worker() {
    for {
        job, ok := q.Pop()
        if ok {
            log.Println("Worker processing job")
            doWork(job)
            close(job.done) // Notify requester that we are done
        }
    }
}

这实际上取决于要求。一个常见的解决方案是仅使用通道（处理程序将请求发送到通道，多个工作人员从同一通道接收）。

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