前言
前陣子有同學(xué)反饋Flutter中的http請(qǐng)求無法通過fiddler抓包，作者喜歡使用Charles抓包工具，于是抽時(shí)間寫了個(gè)小demo測試了一下，結(jié)論是在手機(jī)上設(shè)置代理，Charles確實(shí)抓不到請(qǐng)求數(shù)據(jù)包。于是對(duì)該問題進(jìn)行了分析：
http請(qǐng)求源碼跟蹤
http.dart中的HttpClient是一個(gè)抽象類，成員方法的具體實(shí)現(xiàn)在http_impl.dart中，http的get請(qǐng)求實(shí)現(xiàn)如下：
Future<HttpClientRequest> getUrl(Uri url) => _openUrl("get", url);Future<_HttpClientRequest> _openUrl(String method, Uri uri) { . . . // Check to see if a proxy server should be used for this connection. var proxyConf = const _ProxyConfiguration.direct(); if (_findProxy != null) { // TODO(sgjesse): Keep a map of these as normally only a few // configuration strings will be used. try { proxyConf = new _ProxyConfiguration(_findProxy(uri)); } catch (error, stackTrace) { return new Future.error(error, stackTrace); } } return _getConnection(uri.host, port, proxyConf, isSecure) .then((_ConnectionInfo info) { . . . });}首先，我們可以發(fā)現(xiàn)方法中有一行注釋// Check to see if a proxy server should be used for this connection.，意思是“檢查是否應(yīng)該使用代理服務(wù)器進(jìn)行此連接”；
然后，有一個(gè)proxyConf對(duì)象初始化和根據(jù)_findProxy來創(chuàng)建新的proxyConf對(duì)象的語句，然后通過_getConnection(uri.host, port, proxyConf, isSecure)來創(chuàng)建連接，_getConnection的源碼如下：
Future<_ConnectionInfo> _getConnection(String uriHost, int uriPort, _ProxyConfiguration proxyConf, bool isSecure) { Iterator<_Proxy> proxies = proxyConf.proxies.iterator; Future<_ConnectionInfo> connect(error) { if (!proxies.moveNext()) return new Future.error(error); _Proxy proxy = proxies.current; String host = proxy.isDirect ? uriHost : proxy.host; int port = proxy.isDirect ? uriPort : proxy.port; return _getConnectionTarget(host, port, isSecure) .connect(uriHost, uriPort, proxy, this) // On error, continue with next proxy. .catchError(connect); } return connect(new HttpException("No proxies given"));}從代碼中我們可以看到根據(jù)代理配置信息來將請(qǐng)求的host和port進(jìn)行重置，然后創(chuàng)建真實(shí)的連接。
跟蹤以上源碼我們發(fā)現(xiàn)dart中http請(qǐng)求是否走代理是需要配置的，而_findProxy變量和配置的代理信息有關(guān)。
http__impl.dart文件中的_HttpClient類中定義了_findProxy的默認(rèn)值
Function _findProxy = HttpClient.findProxyFromEnvironment;
HttpClient類中findProxyFromEnvironment方法的實(shí)現(xiàn)
static String findProxyFromEnvironment(Uri url, {Map<String, String> environment}) { HttpOverrides overrides = HttpOverrides.current; if (overrides == null) { return _HttpClient._findProxyFromEnvironment(url, environment); } return overrides.findProxyFromEnvironment(url, environment);}_HttpClient類中_findProxyFromEnvironment方法的實(shí)現(xiàn)
static String _findProxyFromEnvironment( Uri url, Map<String, String> environment) { checkNoProxy(String option) { if (option == null) return null; Iterator<String> names = option.split(",").map((s) => s.trim()).iterator; while (names.moveNext()) { var name = names.current; if ((name.startsWith("[") && name.endsWith("]") && "[${url.host}]" == name) || (name.isNotEmpty && url.host.endsWith(name))) { return "DIRECT"; } } return null; } checkProxy(String option) { if (option == null) return null; option = option.trim(); if (option.isEmpty) return null; int pos = option.indexOf("://"); if (pos >= 0) { option = option.substring(pos + 3); } pos = option.indexOf("/"); if (pos >= 0) { option = option.substring(0, pos); } // Add default port if no port configured. if (option.indexOf("[") == 0) { var pos = option.lastIndexOf(":"); if (option.indexOf("]") > pos) option = "$option:1080"; } else { if (option.indexOf(":") == -1) option = "$option:1080"; } return "PROXY $option"; } // Default to using the process current environment. if (environment == null) environment = _platformEnvironmentCache; String proxyCfg; String noProxy = environment["no_proxy"]; if (noProxy == null) noProxy = environment["NO_PROXY"]; if ((proxyCfg = checkNoProxy(noProxy)) != null) { return proxyCfg; } if (url.scheme == "http") { String proxy = environment["http_proxy"]; if (proxy == null) proxy = environment["HTTP_PROXY"]; if ((proxyCfg = checkProxy(proxy)) != null) { return proxyCfg; } } else if (url.scheme == "https") { String proxy = environment["https_proxy"]; if (proxy == null) proxy = environment["HTTPS_PROXY"]; if ((proxyCfg = checkProxy(proxy)) != null) { return proxyCfg; } } return "DIRECT";} 從以上代碼中可以發(fā)現(xiàn)代理配置從environment中讀取，設(shè)置代理時(shí)必須指定http_proxy或https_proxy等。而從_openUrl方法實(shí)現(xiàn)中proxyConf = new _ProxyConfiguration(_findProxy(uri));得出默認(rèn)情況下environment是為空的，所以要想在Flutter的http請(qǐng)求中使用代理，則要指定相應(yīng)的代理配置，即設(shè)置httpClient.findProxy的值。
示例代碼：
_getHttpData() async { var httpClient = new HttpClient(); httpClient.findProxy = (url) { return HttpClient.findProxyFromEnvironment(url, environment: {"http_proxy": 'http://192.168.124.7:8888',}); }; var uri = new Uri.http('t.weather.sojson.com', '/api/weather/city/101210101'); var request = await httpClient.getUrl(uri); var response = await request.close(); if (response.statusCode == 200) { print('請(qǐng)求成功'); var responseBody = await response.transform(Utf8Decoder()).join(); print('responseBody = $responseBody'); } else { print('請(qǐng)求失敗'); }}以上代碼設(shè)置后即可使用Fiddler或Charles抓包了。
注：
第二種抓包解決方案
如果使用Flutter寫的APP不手動(dòng)設(shè)置代理，則可以使用另一種方案來抓包。
通過電腦設(shè)置熱點(diǎn) -> 使用手機(jī)連接電腦熱點(diǎn)上網(wǎng) -> 在電腦上使用Wireshark抓數(shù)據(jù)包。
具體步驟如下（macOS系統(tǒng)下）：
1. 打開系統(tǒng)偏好設(shè)置，找到“共享”
2. 打開“共享”，顯示以下窗口，并選擇共享以下來源的連接為指定的有線網(wǎng)絡(luò)，用以下端口共享給電腦選擇為Wi-Fi
3. 點(diǎn)擊右下角Wi-Fi選項(xiàng)按鈕，顯示如下，填寫對(duì)應(yīng)信息后點(diǎn)擊“好”保存
4. 回到剛才的“共享”窗口，打開左側(cè)窗口中的服務(wù)“互聯(lián)網(wǎng)共享”
5. 然后打開Wireshark軟件界面，首頁選擇對(duì)應(yīng)開熱點(diǎn)的網(wǎng)絡(luò)雙擊
6. 請(qǐng)求接口域名t.weather.sojson.com對(duì)應(yīng)的IP為 58.222.18.24，則在上面輸入框中輸入請(qǐng)求過濾條件 "ip.dst == 58.222.18.24"，然后通過手機(jī)APP發(fā)起網(wǎng)絡(luò)請(qǐng)求
查看接口的IP地址
$ ping t.weather.sojson.comPING nm.ctn.aicdn.com (58.222.18.24): 56 data bytes64 bytes from 58.222.18.24: icmp_seq=0 ttl=54 time=16.792 ms64 bytes from 58.222.18.24: icmp_seq=1 ttl=54 time=16.926 ms64 bytes from 58.222.18.24: icmp_seq=2 ttl=54 time=15.804 ms
7. 選擇對(duì)應(yīng)的http請(qǐng)求，箭頭指定行，右鍵點(diǎn)擊，選擇Follow->HTTP Stream選項(xiàng)
8. 彈出具體網(wǎng)絡(luò)請(qǐng)求信息窗口如下
寫在最后
本篇分享了兩種Flutter中http數(shù)據(jù)包的抓包解決方案，大家可以根據(jù)實(shí)際情況來選擇使用。
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