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 http.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 handler ，违反了上述规定（由于没有同步，写入也可能实际发生在 ResponseWriter 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）。
