Go 为什么 nethttp 不遵守超过 30 秒的超时持续时间

使用Golang 1.20.1.

在Golang的net/http和上下文包中，我无法设置超过30秒的超时.设置较短的超时时间很好，例如

代码:

    log.Infof("Elasticsearch URL is %v", elasticsearchURL)
    client := &http.Client{Timeout: time.Duration(time.Second * 60)}
    req, err := http.NewRequest("GET", listBackupsURL, nil)
    if err != nil {
        internalError(w, fmt.Sprintf("error creating request: %v", err))
        return
    }
    req.SetBasicAuth(username, password)
    resp, err := client.Do(req)
    if err != nil {
        // handle error
        internalError(w, fmt.Sprintf("error accessing elasticsearch: %v", err))
        return
    }

日志(log):

I0503 23:01:55.973821       1 somecode.go:85] URL is http://elasticsearch.example.ingest:9200
E0503 23:02:25.976345       1 caller_handler.go:63] 500 Internal Server Error: error accessing elasticsearch: Get "http://elasticsearch.example.ingest:9200/_cat/snapshots/object-store-repo?v&s=id": dial tcp 1.2.3.4:9200: i/o timeout

超时时间是30秒，而不是60秒.

如果我使用http.NewRequestWithContext(...)并使用上下文设置相同的超时，我会得到相同的行为:

代码:

    log.Infof("Elasticsearch URL is %v", elasticsearchURL)
    ctx, cancel := context.WithTimeout(context.Background(), time.Duration(time.Second * 60)) 
    defer cancel()
    req, err := http.NewRequestWithContext(ctx, "GET", listBackupsURL, nil)
    if err != nil {
        internalError(w, fmt.Sprintf("error creating request: %v", err))
        return
    }
    req.SetBasicAuth(username, password)
    resp, err := client.Do(req)
    if err != nil {
        // handle error
        internalError(w, fmt.Sprintf("error accessing elasticsearch: %v", err))
        return
    }

日志(log):

I0503 23:31:10.941169       1 somecode.go:85] Elasticsearch URL is http://elasticsearch.example.ingest:9200
E0503 23:31:40.941642       1 caller_handler.go:63] 500 Internal Server Error: error accessing elasticsearch: Get "http://elasticsearch.example.ingest:9200/_cat/snapshots/object-store-repo?v&s=id": dial tcp 1.2.3.4:9200: i/o timeout

但是，如果我将超时更改为3秒(在任何一种方法中都是time.Duration(time.Second * 3))秒)，它将按预期工作:

I0503 23:44:17.622121       1 somecode.go:85] Elasticsearch URL is http://elasticsearch.example.ingest:9200
E0503 23:44:20.624795       1 caller_handler.go:63] 500 Internal Server Error: error accessing elasticsearch: Get "http://elasticsearch.example.ingest:9200/_cat/snapshots/object-store-repo?v&s=id": context deadline exceeded (Client.Timeout exceeded while awaiting headers)