writable._write(chunk, encoding, callback)
chunk
<Buffer> | <string> | <any> 要写入的Buffer
,从string
转换为stream.write()
。 如果流的decodeStrings
选项是false
或者流在对象模式下运行,则块将不会被转换,而是传给stream.write()
的任何内容。encoding
<string> 如果块是字符串,则encoding
是该字符串的字符编码。 如果块是Buffer
,或者如果流在对象模式下运行,则可以忽略encoding
。callback
<Function> 当对提供的块的处理完成时调用此函数(可选地带有错误参数)。
所有 Writable
流实现都必须提供 writable._write()
和/或 writable._writev()
方法来将数据发送到底层资源。
Transform
流提供了它们自己的 writable._write()
实现。
此函数不得由应用程序代码直接调用。
它应该由子类实现,并且只能由内部 Writable
类方法调用。
callback
函数必须在 writable._write()
内部同步调用或异步调用(即不同的滴答),以表示写入成功完成或因错误而失败。
如果调用失败,则传给 callback
的第一个参数必须是 Error
对象,如果写入成功,则传入 null
对象。
在调用 writable._write()
和调用 callback
之间发生的对 writable.write()
的所有调用都将导致写入的数据被缓冲。
当调用 callback
时,流可能会触发 'drain'
事件。
如果流实现能够同时处理多个数据块,则应实现 writable._writev()
方法。
如果在构造函数选项中将 decodeStrings
属性显式设置为 false
,则 chunk
将保持传给 .write()
的相同对象,并且可能是字符串而不是 Buffer
。
这是为了支持对某些字符串数据编码进行优化处理的实现。
在这种情况下,encoding
参数将指示字符串的字符编码。
否则,可以安全地忽略 encoding
参数。
writable._write()
方法以下划线为前缀,因为它是定义它的类的内部方法,不应由用户程序直接调用。
chunk
<Buffer> | <string> | <any> TheBuffer
to be written, converted from thestring
passed tostream.write()
. If the stream'sdecodeStrings
option isfalse
or the stream is operating in object mode, the chunk will not be converted & will be whatever was passed tostream.write()
.encoding
<string> If the chunk is a string, thenencoding
is the character encoding of that string. If chunk is aBuffer
, or if the stream is operating in object mode,encoding
may be ignored.callback
<Function> Call this function (optionally with an error argument) when processing is complete for the supplied chunk.
All Writable
stream implementations must provide a
writable._write()
and/or
writable._writev()
method to send data to the underlying
resource.
Transform
streams provide their own implementation of the
writable._write()
.
This function MUST NOT be called by application code directly. It should be
implemented by child classes, and called by the internal Writable
class
methods only.
The callback
function must be called synchronously inside of
writable._write()
or asynchronously (i.e. different tick) to signal either
that the write completed successfully or failed with an error.
The first argument passed to the callback
must be the Error
object if the
call failed or null
if the write succeeded.
All calls to writable.write()
that occur between the time writable._write()
is called and the callback
is called will cause the written data to be
buffered. When the callback
is invoked, the stream might emit a 'drain'
event. If a stream implementation is capable of processing multiple chunks of
data at once, the writable._writev()
method should be implemented.
If the decodeStrings
property is explicitly set to false
in the constructor
options, then chunk
will remain the same object that is passed to .write()
,
and may be a string rather than a Buffer
. This is to support implementations
that have an optimized handling for certain string data encodings. In that case,
the encoding
argument will indicate the character encoding of the string.
Otherwise, the encoding
argument can be safely ignored.
The writable._write()
method is prefixed with an underscore because it is
internal to the class that defines it, and should never be called directly by
user programs.