我正在攻击node.js程序,该程序捕获SMTP邮件并对邮件数据执行操作。 'smtp-protocol'节点库以流形式提供邮件数据,作为node.js新手,我不知道如何将该流写入字符串变量。我目前使用以下行写入stdout:
stream.pipe(process.stdout, { end : false });
正如我所说,我需要将此流数据写入字符串变量,然后在流结束后我将使用它。
非常感谢!
答案 0 :(得分:51)
希望这比上面的答案(现在有一个断开的链接)更有用。
另请注意,字符串连接不是收集字符串部分的有效方法,但它是为了简单起见而使用(也许您的代码不关心效率)
var string = ''
stream.on('readable',function(buffer){
var part = buffer.read().toString();
string += part;
console.log('stream data ' + part);
});
stream.on('end',function(){
console.log('final output ' + string);
});
答案 1 :(得分:46)
以上都不适合我。我需要使用Buffer对象:
const chunks = [];
readStream.on("data", function (chunk) {
chunks.push(chunk);
});
// Send the buffer or you can put it into a var
readStream.on("end", function () {
res.send(Buffer.concat(chunks));
});
答案 2 :(得分:30)
另一种方法是将流转换为promise(请参阅下面的示例)并使用then
(或await
)将已解析的值分配给变量。
function streamToString (stream) {
const chunks = []
return new Promise((resolve, reject) => {
stream.on('data', chunk => chunks.push(chunk))
stream.on('error', reject)
stream.on('end', () => resolve(Buffer.concat(chunks).toString('utf8')))
})
}
const result = await streamToString(stream)
答案 3 :(得分:28)
关键是要使用这两个Stream events:
对于stream.on('data', ...)
,您应该将数据数据收集到缓冲区(如果是二进制)或字符串中。
对于on('end', ...)
,您应该使用已完成的缓冲区调用回调,或者如果您可以内联它并使用Promises库返回。
答案 4 :(得分:17)
我通常使用这个简单的函数将流转换为字符串:
function streamToString(stream, cb) {
const chunks = [];
stream.on('data', (chunk) => {
chunks.push(chunk.toString());
});
stream.on('end', () => {
cb(chunks.join(''));
});
}
用法示例:
let stream = fs.createReadStream('./myFile.foo');
streamToString(stream, (data) => {
console.log(data); // data is now my string variable
});
答案 5 :(得分:9)
您对此有何看法?
import random
import sys
from PyQt5 import QtCore, QtGui, QtWidgets, QtSerialPort
from matplotlib.figure import Figure
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg
class MainWindowm(QtWidgets.QMainWindow):
def __init__(self, *args, **kwargs):
super(MainWindowm, self).__init__(*args, **kwargs)
self.canvas = FigureCanvasQTAgg(Figure(figsize=(5, 4), dpi=100))
self.setCentralWidget(self.canvas)
self.axes = self.canvas.figure.subplots()
n_data = 50
self.xdata = list(range(n_data))
self.ydata = [random.randint(0, 10) for i in range(n_data)]
self.serial_port = QtSerialPort.QSerialPort("COM3")
self.serial_port.setBaudRate(QtSerialPort.QSerialPort.Baud9600)
self.serial_port.errorOccurred.connect(self.handle_error)
self.serial_port.readyRead.connect(self.handle_ready_read)
self.serial_port.open(QtCore.QIODevice.ReadWrite)
def handle_ready_read(self):
while self.serial_port.canReadLine():
codec = QtCore.QTextCodec.codecForName("UTF-8")
line = codec.toUnicode(self.serial_port.readLine()).strip().strip('\x00')
try:
print(line)
value = float(line)
except ValueError as e:
print("error", e)
else:
self.update_plot(value)
def handle_error(self, error):
if error == QtSerialPort.QSerialPort.NoError:
return
print(error, self.serial_port.errorString())
def update_plot(self, value):
self.ydata = self.ydata[1:] + [value]
self.axes.cla()
self.axes.plot(self.xdata, self.ydata, "r")
self.canvas.draw()
if __name__ == "__main__":
app = QtWidgets.QApplication(sys.argv)
w = MainWindowm()
w.show()
sys.exit(app.exec_())
答案 6 :(得分:7)
从nodejs documentation你应该这样做 - 总是记住一个字符串而不知道编码只是一堆字节:
var readable = getReadableStreamSomehow();
readable.setEncoding('utf8');
readable.on('data', function(chunk) {
assert.equal(typeof chunk, 'string');
console.log('got %d characters of string data', chunk.length);
})
答案 7 :(得分:6)
Streams没有简单的.toString()
函数(我理解),也没有.toStringAsync(cb)
函数(我不明白)。
所以我创建了自己的辅助函数:
var streamToString = function(stream, callback) {
var str = '';
stream.on('data', function(chunk) {
str += chunk;
});
stream.on('end', function() {
callback(str);
});
}
// how to use:
streamToString(myStream, function(myStr) {
console.log(myStr);
});
答案 8 :(得分:4)
轻松使用流行的(每周下载量超过500万)和轻量级的获取流库:
https://www.npmjs.com/package/get-stream
const fs = require('fs');
const getStream = require('get-stream');
(async () => {
const stream = fs.createReadStream('unicorn.txt');
console.log(await getStream(stream)); //output is string
})();
答案 9 :(得分:3)
我有这样的运气:
template<template<class, size_t> class P, class T, size_t i>
P<T, i - 1> my_func(const P<T, i> & my_P);
int main()
{
A<int, 10> a;
B<char, 3> b;
C<double, 7> c;
auto smaller_a = my_func(a); // is a A<int, 9>
auto smaller_b = my_func(b); // is a B<char, 2>
auto smaller_c = my_func(c); // is a C<double, 6>
}
我使用节点let string = '';
readstream
.on('data', (buf) => string += buf.toString())
.on('end', () => console.log(string));
,v9.11.1
是来自readstream
回调的响应。
答案 10 :(得分:3)
还有一个使用promise的字符串:
function getStream(stream) {
return new Promise(resolve => {
const chunks = [];
stream.on("data", chunk => chunks.push(chunk));
stream.on("end", () => resolve(Buffer.concat(chunks).toString()));
});
}
用法:
const stream = fs.createReadStream(__filename);
getStream(stream).then(r=>console.log(r));
如有必要,删除.toString()
以用于二进制数据。
答案 11 :(得分:2)
像流减速器这样的东西呢?
以下是使用ES6类的示例如何使用。
var stream = require('stream')
class StreamReducer extends stream.Writable {
constructor(chunkReducer, initialvalue, cb) {
super();
this.reducer = chunkReducer;
this.accumulator = initialvalue;
this.cb = cb;
}
_write(chunk, enc, next) {
this.accumulator = this.reducer(this.accumulator, chunk);
next();
}
end() {
this.cb(null, this.accumulator)
}
}
// just a test stream
class EmitterStream extends stream.Readable {
constructor(chunks) {
super();
this.chunks = chunks;
}
_read() {
this.chunks.forEach(function (chunk) {
this.push(chunk);
}.bind(this));
this.push(null);
}
}
// just transform the strings into buffer as we would get from fs stream or http request stream
(new EmitterStream(
["hello ", "world !"]
.map(function(str) {
return Buffer.from(str, 'utf8');
})
)).pipe(new StreamReducer(
function (acc, v) {
acc.push(v);
return acc;
},
[],
function(err, chunks) {
console.log(Buffer.concat(chunks).toString('utf8'));
})
);
答案 12 :(得分:2)
最干净的解决方案可能是使用&#34; string-stream&#34; package,它将流转换为带有promise的字符串。
const streamString = require('stream-string')
streamString(myStream).then(string_variable => {
// myStream was converted to a string, and that string is stored in string_variable
console.log(string_variable)
}).catch(err => {
// myStream emitted an error event (err), so the promise from stream-string was rejected
throw err
})
答案 13 :(得分:1)
列出的所有答案似乎都是在流动模式下打开“可读流”,这不是NodeJS的默认设置,并且由于缺少NodeJS在“暂停的可读流”模式下提供的反压支持,因此存在局限性。 这是使用Just Buffer,本机流和本机流转换的实现,并支持对象模式
import {Transform} from 'stream';
let buffer =null;
function objectifyStream() {
return new Transform({
objectMode: true,
transform: function(chunk, encoding, next) {
if (!buffer) {
buffer = Buffer.from([...chunk]);
} else {
buffer = Buffer.from([...buffer, ...chunk]);
}
next(null, buffer);
}
});
}
process.stdin.pipe(objectifyStream()).process.stdout
答案 14 :(得分:0)
这对我有用,并且基于Node v6.7.0 docs:
let output = '';
stream.on('readable', function() {
let read = stream.read();
if (read !== null) {
// New stream data is available
output += read.toString();
} else {
// Stream is now finished when read is null.
// You can callback here e.g.:
callback(null, output);
}
});
stream.on('error', function(err) {
callback(err, null);
})
答案 15 :(得分:0)
使用您可能已经在项目依赖项中使用的quite popular stream-buffers
package,这非常简单:
// imports
const { WritableStreamBuffer } = require('stream-buffers');
const { promisify } = require('util');
const { createReadStream } = require('fs');
const pipeline = promisify(require('stream').pipeline);
// sample stream
let stream = createReadStream('/etc/hosts');
// pipeline the stream into a buffer, and print the contents when done
let buf = new WritableStreamBuffer();
pipeline(stream, buf).then(() => console.log(buf.getContents().toString()));
答案 16 :(得分:0)
上面的塞巴斯蒂安·J做得很好。
我遇到了带有一些测试代码的“缓冲区问题”,并添加了编码信息并解决了该问题,请参见下文。
软件
// process.stdin.setEncoding('utf8');
process.stdin.on('data', (data) => {
console.log(typeof(data), data);
});
输入
hello world
输出
object <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64 0d 0a>
软件
process.stdin.setEncoding('utf8'); // <- Activate!
process.stdin.on('data', (data) => {
console.log(typeof(data), data);
});
输入
hello world
输出
string hello world
答案 17 :(得分:0)
就我而言,内容类型响应标头为 Content-Type:文本/纯文本。因此,我已经从Buffer中读取了数据,例如:
let data = [];
stream.on('data', (chunk) => {
console.log(Buffer.from(chunk).toString())
data.push(Buffer.from(chunk).toString())
});