本地Tcl Socket服务器如何同时处理HTTP音频传输与WebSocket请求？

问题场景 #

我用Tcl搭建了本地服务器，支持多浏览器/多标签页同时连接，通过WebSocket处理短时长SQLite查询请求。现在需要实现用户播放音频（讲座）的同时仍能发起数据库查询，但测试中遇到以下问题：

• 单个标签页通过WebSocket请求数据正常
• 打开第二个标签页通过HTTP请求音频后，服务器不再响应任何请求，关闭音频标签后恢复正常

初始发送音频代码 #

proc ::HTTP::REQ::SendFile {sock filename type} {
  set fp [open $filename rb];  # NB: rb — b is for BINARY; this is important.
  set size [file size $filename]
  # HTTP spec says headers are ISO 8859-1 and CRLF-separated
  # chan configure $sock -encoding iso8859-1 -blocking 0 -translation crlf -buffering full
  chan puts $sock "HTTP/1.1 200 OK"
  chan puts $sock "Content-Type: $type; charset=utf-8"
  chan puts $sock "Content-Length: $size"
  chan puts $sock "Connection: Keep-Alive"
  chan puts $sock ""
  chan flush $sock

  # Ship the data in binary mode; fcopy is VERY efficient.
  chan configure $sock -translation binary
  chan copy $fp $sock -size $size
  close $fp
}

报错信息 #

关闭音频标签时出现如下错误：

error writing "sock5605cc3a4720": connection reset by peer
    while executing
"chan copy $fp $sock -size $size"

推测音频未一次性发送完成，拖动进度条至2/3时WebSocket恢复正常，关闭标签也无报错。

核心疑问1 #

Tcl服务器是否支持同时处理HTTP音频传输与WebSocket请求？若支持，我哪里操作导致了阻塞？

解决方案（编辑补充） #

我发现通过chan copy（即fcopy）的-command选项可解决问题，修改后的代码如下，现在能同时播放音频和处理WebSocket请求：

proc ::HTTP::REQ::SendFile {sock filename type} {
  set fp [open $filename rb];   # NB: rb — b is for BINARY; this is important.
  set size [file size $filename]
  # HTTP spec says headers are ISO 8859-1 and CRLF-separated
  # chan configure $sock -encoding iso8859-1 -blocking 0 -translation crlf -buffering full
  chan puts $sock "HTTP/1.1 200 OK"
  chan puts $sock "Content-Type: $type; charset=utf-8"
  chan puts $sock "Content-Length: $size"
  chan puts $sock "Connection: Keep-Alive"
  chan puts $sock ""
  chan flush $sock

  # Ship the data in binary mode; fcopy is VERY efficient
  chan configure $sock -translation binary
  chan copy $fp $sock -size $size -command [list ::HTTP::REQ::ChanCopyCleanup $fp $sock]
  chan puts "chan copy a.k.a. fcopy is not blocking"
  # close $fp
}

proc ::HTTP::REQ::ChanCopyCleanup {fp sock bytes {error {}} } {
  close $fp
  ::HTTP::ResetSock $sock
  chan puts stdout "Closed the file"
}

核心疑问2 #

想了解：

• Tcl与浏览器间的传输机制是怎样的？
• 是否无需手动分块，Tcl会按需发送音频数据？
• 大文件传输完成耗时久是否正常？

进一步测试与优化 #

测试发现浏览器会忽略preload请求，仅缓冲部分音频，无-command选项时chan copy会阻塞。我的目标是实现跳转至指定时间播放音频，通过Object URL实现了本地快速传输40MB音频并跳转至30分钟位置，前端代码如下：

let d = Date.now();
let iObj = { method: 'GET' };
fetch( "http://127.0.0.11:8000/audio.mp3", iObj )
.then( response => {
    console.log("Got a response.");
    if ( !response.ok ) {
      console.log( 'Network response was not ok.' );
    } else {
      const contentType = response.headers.get('content-type');
      if (!contentType || !contentType.includes('audio/mpeg')) {
        throw new TypeError("Oops, we haven't got an audio file!");
      }
    }
    return response.blob();
  })
.then( result => {
  let objectURL = URL.createObjectURL( result );
  let a = document.createElement("AUDIO");
  // a.preload="auto";
  a.src = objectURL;
  a.controls = true;
  a.style.width="100%";
  document.body.appendChild(a);
  /*
    Perhaps, it just needs time to load the source and then
    object url can be revoked and memory released.
  */
  a.oncanplaythrough = () => {
     URL.revokeObjectURL( objectURL );
     a.currentTime = 1800;
     console.log( Date.now() - d);
     /*
       WARNING This event fires every time the user clicks
       on the timeline UI element. Thus, once revoke the
       object url, reset this to nothing.
     */
     a.oncanplaythrough = null;
  };
 })
.catch( e => {
  console.log( "Error in fetch." );
  console.log( e )
 })
 ;

内容的提问来源于stack exchange，提问作者Gary