本文介绍了Dart HTTP服务器和Futures的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我试图编写简单的HTTP服务器解析client.getUrl（）的结果。我有一切工作，但我不能写回http请求对象（打印到控制台工作正常）。
相关代码是：
main（）{
HttpServer.bind（InternetAddress.ANY_IP_V4，4040）
.then（（HttpServer server）{
print $ {server.port}'）;
server.listen（（HttpRequest request）{
Future loadedContent = loadUrl（furl）;
loadedContent.then（（content）=> print内容））;
// loadedContent.then（（content）=> request.response.write（content））;
request.response.close（）;
print（response closed）;
}）;
}）catchError（（e）=> print（e.toString（）））;
}
问题是主函数在从Future获得结果之前结束通过打印在结果之前出现第二的响应关闭）。是否有办法等待主函数中的结果？
编辑：它与
我将重写我的代码，但如果有一个方法等待getUrl未来在main函数中，我更喜欢它。
编辑：my loadUrl
未来的loadUrl url）
{
final c = new Completer（）;
HttpClient client = new HttpClient（）;
client.addCredentials（
Uri.parse（https：//*****.tpondemand.com/api），
tprealm，
new HttpClientBasicCredentials *****，*****））;
client.getUrl（Uri.parse（url））
.then（（HttpClientRequest request）{
//可选设置标头...
//可选写入请求对象...
//然后调用close。
return request.close（）;
}）
.then（（HttpClientResponse response）{
//处理响应
//print(response.reasonPhrase）;
response.transform（UTF8.decoder）.listen（（contents）{
// handle data
map parsedMap = JSON.decode（contents）;
c.complete（parsedMap）;
//req.response.write(parsedMap[\"Items\"][0]）;
}）;
}）;
return c.future;
}
上次编辑：这是工作代码
import'dart：io';
import'dart：async';
import'package：http_server / http_server.dart';
import'dart：convert';
final furl =https：//***.tpondemand.com;
未来的loadUrlBody（String url）{
final c = new Completer（）;
HttpClient client = new HttpClient（）;
client.addCredentials（Uri.parse（https：//***.tpondemand.com/api），tprealm，new HttpClientBasicCredentials（user，password））;
client.getUrl（Uri.parse（url））
.then（（HttpClientRequest response）=> response.close（））
.then（HttpBodyHandler.processResponse）
.then（（HttpClientResponseBody body）{
c.complete（body）;
}）;
return c.future;
}
main（）{
final filter =/api/v1/Userstories?format=json&where=(Team.Id+eq+111111)&include=[Name， CreateDate，ModifyDate，LastCommentDate]& take = 1000;
HttpServer.bind（InternetAddress.ANY_IP_V4，4040）.then（（HttpServer server）{
print（'listen on localhost，port $ {server.port}'）;
server.listen （（HttpRequest request）{
print（request.connectionInfo.remoteAddress）;
loadUrlBody（furl + filter）.then（（content）{
Map parsedMap = content.body;
// print（Map parsed）;
request.response.write（parsedMap [Items]）;
request.response.close（）;
// print响应关闭）;
}）。catchError（（e）=> print（e.toString（）））;
} > print（e.toString（）））;
}
解决方案
c> loadUrl（）返回未来（它可能应该），然后这应该工作
HttpServer.bind（InternetAddress.ANY_IP_V4，4040）
.then（（HttpServer服务器）{
打印'listen on localhost，port $ {server.port}'）;
server.listen（（HttpRequest request）{
loadUrl（furl）.then（（）{
// loadedContent。那么（（content）=> print（content））;
loadedContent.then（（content）=> request.response.write（content））;
request.response。 close（）;
print（response closed）;
}）;
}）;
}）catchError（（e）=> print（e.toString （）））;
}
更新
您需要修改 getData（）或 loadUrl（）方法
未来getData（HttpRequest请求）{//添加的返回类型Future（不必要）
return dao.findAll（）。then（（value）{// added'return'
print（value）;
}）;
}
更新2 b
未来的loadUrl（String url）
{
// final c = new Completer //< == commented out
HttpClient client = new HttpClient（）;
client.addCredentials（
Uri.parse（https：//*****.tpondemand.com/api），
tprealm，
new HttpClientBasicCredentials *****，*****））;
return client.getUrl（Uri.parse（url））//< == added return
.then（（HttpClientRequest request）{
//可选设置标题...
//可选地写入请求对象...
//然后调用close。
return request.close（）;
}）
。那么（（HttpClientResponse response）{
//处理响应
//print(response.reasonPhrase）;
return response.transform（UTF8.decoder）.listen（ //< == added return
// handle data
Map parsedMap = JSON.decode（contents）;
// c.complete（parsedMap）; //< == commented out
//req.response.write(parsedMap[\"Items\"][0]）;
}）。asFuture（）; //< == added` .asFuture（）`
}）;
// return c.future; //< == commented out
}
通常情况下， return 在每次调用返回Future的方法之前，您可以避免使用完成器。完成者只适用于更复杂的情况（例如，当您从一个方法返回completer.future，但从其他地方完成它，例如一个事件处理程序）。
I am trying to write simple HTTP server which parse result of client.getUrl(). I've got everything working except I am not able to write back to http request object (print to console works fine).
Relevant code is:
main() {
HttpServer.bind(InternetAddress.ANY_IP_V4, 4040)
.then((HttpServer server) {
print('listening on localhost, port ${server.port}');
server.listen((HttpRequest request) {
Future loadedContent = loadUrl(furl);
loadedContent.then((content) => print(content));
// loadedContent.then((content) => request.response.write(content));
request.response.close();
print ("response closed");
});
}).catchError((e) => print(e.toString()));
}
Problem is that main function ends before I get result from Future (figured that out by printing "response closed" which appears second before results). Is there way to wait for results in main function?
Edit: It is related to Dart HttpRequest return futureI will rewrite my code, but if there is a way to wait for getUrl Future in main function, I would prefer it.
Edit: my loadUrl
Future loadUrl(String url)
{
final c = new Completer();
HttpClient client = new HttpClient();
client.addCredentials(
Uri.parse("https://*****.tpondemand.com/api"),
"tprealm",
new HttpClientBasicCredentials("*****", "*****"));
client.getUrl(Uri.parse(url))
.then((HttpClientRequest request) {
// Optionally set up headers...
// Optionally write to the request object...
// Then call close.
return request.close();
})
.then((HttpClientResponse response) {
// Process the response.
//print(response.reasonPhrase);
response.transform(UTF8.decoder).listen((contents) {
// handle data
Map parsedMap = JSON.decode(contents);
c.complete(parsedMap);
//req.response.write(parsedMap["Items"][0]);
});
});
return c.future;
}
last edit: this is working code
import 'dart:io';
import 'dart:async';
import 'package:http_server/http_server.dart';
import 'dart:convert';
final furl = "https://***.tpondemand.com";
Future loadUrlBody(String url) {
final c = new Completer();
HttpClient client = new HttpClient();
client.addCredentials(Uri.parse("https://***.tpondemand.com/api"), "tprealm", new HttpClientBasicCredentials("user", "password"));
client.getUrl(Uri.parse(url))
.then((HttpClientRequest response) => response.close())
.then(HttpBodyHandler.processResponse)
.then((HttpClientResponseBody body) {
c.complete(body);
});
return c.future;
}
main() {
final filter = "/api/v1/Userstories?format=json&where=(Team.Id+eq+111111)&include=[Name,CreateDate,ModifyDate,LastCommentDate]&take=1000";
HttpServer.bind(InternetAddress.ANY_IP_V4, 4040).then((HttpServer server) {
print('listening on localhost, port ${server.port}');
server.listen((HttpRequest request) {
print(request.connectionInfo.remoteAddress);
loadUrlBody(furl + filter).then((content) {
Map parsedMap = content.body;
//print("Map parsed");
request.response.write(parsedMap["Items"]);
request.response.close();
//print("response closed");
}).catchError((e) => print(e.toString()));
});
}).catchError((e) => print(e.toString()));
}
解决方案
When your loadUrl() returns a Future (which it probably should) then this should work
main() {
HttpServer.bind(InternetAddress.ANY_IP_V4, 4040)
.then((HttpServer server) {
print('listening on localhost, port ${server.port}');
server.listen((HttpRequest request) {
loadUrl(furl).then(() {
// loadedContent.then((content) => print(content));
loadedContent.then((content) => request.response.write(content));
request.response.close();
print ("response closed");
});
});
}).catchError((e) => print(e.toString()));
}
update
You need to modify your getData() or loadUrl() method
Future getData(HttpRequest request) { // added return type 'Future' (not necessary)
return dao.findAll().then((value) { // added 'return'
print(value);
});
}
update 2
Future loadUrl(String url)
{
// final c = new Completer(); // <== commented out
HttpClient client = new HttpClient();
client.addCredentials(
Uri.parse("https://*****.tpondemand.com/api"),
"tprealm",
new HttpClientBasicCredentials("*****", "*****"));
return client.getUrl(Uri.parse(url)) // <== added return
.then((HttpClientRequest request) {
// Optionally set up headers...
// Optionally write to the request object...
// Then call close.
return request.close();
})
.then((HttpClientResponse response) {
// Process the response.
//print(response.reasonPhrase);
return response.transform(UTF8.decoder).listen((contents) { // <== added return
// handle data
Map parsedMap = JSON.decode(contents);
// c.complete(parsedMap); // <== commented out
//req.response.write(parsedMap["Items"][0]);
}).asFuture(); // <== added `.asFuture()`
});
// return c.future; // <== commented out
}
Normally it should be sufficient to prepend a return before each call to a method that returns a Future, then you can avoid using a completer. Completer are only for more complex situations (for example when you return the completer.future from one method but complete it from somewhere else, for example an event handler).
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