android DNS检测
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前段时间心血来潮，突然想研究一下dns检测是什么实现的，于是拿wifi管家开刀了，下面是分析结果：
首先入口函数：
protected boolean arQ() { String v0_2; String v4_1; int v12 = 2; int v11 = 3; int v4 = ((int)(this.fNS / 2)); int v5 = new n(ai.fNh).a("DnsLocalDetecter", PiSessionManagerUD.amB().kH()); boolean v0 = v5 == 0 ? true : false; boolean v3 = this.mCurrentSessionItem == null || this.mCurrentSessionItem.fOA == 4098 || this.mCurrentSessionItem.fOA == 4100 ? false : true; if((v0) && (v3)) { String v5_1 = "http://tools.3g.qq.com/wifi/ssl"; String v6 = "baidu.com"; String v3_1 = "http://m.taobao.com"; String v7 = "https://m.taobao.com"; a v8 = this.av(v5_1, v4); a v9 = this.av(v3_1, v4); try { v4_1 = URLEncoder.encode(v5_1, "UTF-8"); v0_2 = URLEncoder.encode(v3_1, "UTF-8"); } catch(Exception v0_1) { v0_2 = v3_1; v4_1 = v5_1; } if((TextUtils.isEmpty(((CharSequence)v4_1))) || (TextUtils.isEmpty(v4_1.toLowerCase()))) { v4_1 = v5_1; } if((TextUtils.isEmpty(((CharSequence)v0_2))) || (TextUtils.isEmpty(v0_2.toLowerCase()))) { v0_2 = v3_1; } if(!v8.fNY && !TextUtils.isEmpty(v8.bVW) && ((v8.bVW.toLowerCase().contains(v4_1.toLowerCase())) || (v8.bVW.toLowerCase().contains(((CharSequence)v5_1))))) { this.fNV = "Redirect baidu RedirectUrl = " + v8.bVW + ", taobao RedirectUrl = " + v9.bVW; this.bc(v12, 0); return 1; } if(!v8.fNY && !TextUtils.isEmpty(v8.bVW) && !v8.bVW.toLowerCase().contains(((CharSequence)v6))) { this.fNV = "baidu: " + v8.bVW; this.bc(v11, v11); return 1; } if(!v9.fNY && !TextUtils.isEmpty(v9.bVW) && ((v9.bVW.toLowerCase().contains(v0_2.toLowerCase())) || (v9.bVW.toLowerCase().contains(((CharSequence)v3_1))))) { this.fNV = "Redirect baidu RedirectUrl = " + v8.bVW + ", taobao RedirectUrl = " + v9.bVW; this.bc(v12, 0); return 1; } if(!v9.fNY && !TextUtils.isEmpty(v9.bVW) && !v9.bVW.toLowerCase().startsWith(v3_1) && !v9.bVW.toLowerCase().startsWith(v7)) { this.fNV = "taobao: " + v9.bVW; this.bc(v11, v11); return 1; } if(!v8.fNY && !v9.fNY && !TextUtils.isEmpty(v8.bVW) && !TextUtils.isEmpty(v9.bVW) && (TextUtils.equals(v8.bVW.toLowerCase(), v9.bVW.toLowerCase()))) { this.fNV = "baidu and taobao has the same redirectUrl, url = " + v9.bVW; this.bc(v11, v11); return 1; } this.fNV = "safe"; this.bc(v12, 0); } else { this.fNV = "isNetAvalible = " + v0 + ", isConnected = " + v3 + ", retCode = " + v5; this.bc(v12, 0); } return 1;}可以大概看到主要拿了两个网址作为检测的依据，第一个是http://tools.3g.qq.com/wifi/ssl，这个网址是腾讯自己的，会返回301响应，而且会重定向到baidu.com，另一个是https://m.taobao.com，这个会返回200的响应，然后就拿这两个Url分别进行请求，主要函数是this.av，下面看一下这个函数：
private a av(String arg7, int arg8) { HttpURLConnection v2_4; HttpURLConnection v3; String v1 = null; a v0 = new a(this); v0.fNX = arg7; v0.bVW = v1; InputStream v2 = null; try { v3 = this.aw(arg7, arg8); if(v3 != null) { goto label_15; } } catch(Throwable v0_1) { v2 = ((InputStream)v1); v3 = ((HttpURLConnection)v1); goto label_85; } catch(Exception v2_1) { v2 = ((InputStream)v1); v3 = ((HttpURLConnection)v1); goto label_74; } catch(IOException v2_2) { v2 = ((InputStream)v1); v3 = ((HttpURLConnection)v1); goto label_62; } catch(SocketTimeoutException v2_3) { v2_4 = ((HttpURLConnection)v1); goto label_50; } try { v0.fNY = true; if(0 != 0) { goto label_11; } goto label_12; } catch(Exception v2_1) { goto label_102; } catch(IOException v2_2) { goto label_107; } catch(SocketTimeoutException v2_3) { goto label_115; } catch(Throwable v0_1) { goto label_93; } try { label_11: v2.close(); label_12: if(v3 == null) { return v0; } v3.disconnect(); } catch(IOException v1_1) { } return v0; try { label_15: int v4 = v3.getResponseCode(); v2 = v3.getInputStream(); if(v4 != 200) { goto label_27; } } catch(Throwable v0_1) { label_93: v2 = ((InputStream)v1); goto label_85; } catch(Exception v2_1) { label_102: v2 = ((InputStream)v1); goto label_74; } catch(IOException v2_2) { label_107: v2 = ((InputStream)v1); goto label_62; } catch(SocketTimeoutException v2_3) { label_115: v2_4 = v3; goto label_50; } try { v0.bVW = arg7; if(v2 != null) { goto label_21; } goto label_22; } catch(Exception v1_2) { goto label_105; } catch(IOException v1_1) { goto label_110; } catch(SocketTimeoutException v1_3) { goto label_47; } catch(Throwable v0_1) { goto label_96; } try { label_21: v2.close(); label_22: if(v3 == null) { return v0; } v3.disconnect(); } catch(IOException v1_1) { } return v0; label_27: if(v4 == 301 || v4 == 302) { if(v2 != null) { int v1_4 = -1; try { v1 = n.a(v2, v1_4); label_34: v0.bVW = this.a(v3, arg7, v1); goto label_36; }... private HttpURLConnection aw(String arg4, int arg5) { HttpURLConnection v0_2; int v1_2; URLConnection v0_1; HttpURLConnection v1 = null; try { v0_1 = new URL(arg4).openConnection(); } catch(Exception v0) { goto label_26; } try { v1_2 = uc.KF(); goto label_5; } catch(Exception v1_1) { } catch(Exception v0) { label_26: v0_2 = ((HttpURLConnection)v1_2); return v0_2; try { label_5: if(v1_2 < 8) { System.setProperty("http.keepAlive", "false"); } ((HttpURLConnection)v0_1).setUseCaches(false); ((HttpURLConnection)v0_1).setRequestProperty("Pragma", "no-cache"); ((HttpURLConnection)v0_1).setRequestProperty("Cache-Control", "no-cache"); ((HttpURLConnection)v0_1).setInstanceFollowRedirects(false); ((HttpURLConnection)v0_1).setRequestMethod("GET"); ((HttpURLConnection)v0_1).setReadTimeout(arg5); ((HttpURLConnection)v0_1).setConnectTimeout(arg5); } catch(Exception v1_1) { } } return v0_2; }通过上面可以看到，主要是发送一个http请求，然后根据返回码进行处理，如果是200，那么bVW就是当前的url（bVW是redirec url,后面会根据这个判断，很重要），如果是301或302,那么说明发生了重定向，这种情况下就要获取重定向的url，有下面三种情况：
1. 如果response的header里面有Location这个字段，那么重定向url就是它里面的内容
2. 如果response的header里面有Refresh这个字段，那么重定向url就是它里面的部分内容
3. 如果response的url为空，那么查找body里面是否有location.href这个字段，有的话重定向url就是它指向的内容
具体代码如下：
private String a(HttpURLConnection arg5, String arg6, String arg7) { String v1_3; String v0 = ""; try { if(TextUtils.isEmpty(((CharSequence)v0))) { v0 = arg5.getHeaderField("Location"); } if(!TextUtils.isEmpty(((CharSequence)v0))) { goto label_18; } try { String[] v1_2 = arg5.getHeaderField("Refresh").split(";"); if(v1_2 == null) { goto label_18; } if(v1_2.length != 2) { goto label_18; } v0 = v1_2[1].trim(); goto label_18; } catch(Exception v1_1) { try { v1_1.printStackTrace(); label_18: if(TextUtils.isEmpty(((CharSequence)v0))) { String v2 = arg6 != null ? new URL(arg6).getHost() : ""; v1_3 = arg5.getURL() != null ? arg5.getURL().getHost() : ""; if(!TextUtils.isEmpty(((CharSequence)v0))) { goto label_58; } if(v2.compareTo(v1_3) == 0) { goto label_58; } v0 = arg5.getURL().toExternalForm(); v1_3 = v0; goto label_36; return v0; } else { } } catch(Throwable v1) { return v0; } } } catch(Throwable v1) { return v0; } label_58: v1_3 = v0; try { label_36: if((TextUtils.isEmpty(((CharSequence)v1_3))) && !TextUtils.isEmpty(((CharSequence)arg7))) { v0 = n.pN(arg7); if(v0 == null) { return v1_3; } return v0; } } catch(Throwable v0_1) { return v1_3; } return v1_3;}public static String pN(String arg3) { int v2; String v0 = ""; if(v0 != null) { int v1 = arg3.indexOf("location.href=\""); if(v1 > 0) { v1 += "location.href=\"".length(); v2 = arg3.indexOf("\"", v1); if(v2 > v1 && v2 > 0) { v0 = arg3.substring(v1, v2); if(v0 != null && !v0.trim().toLowerCase().startsWith("http")) { v0 = ""; } } } if(!TextUtils.isEmpty(((CharSequence)v0))) { return v0; } v1 = arg3.indexOf("location.href=\'"); if(v1 <= 0) { return v0; } v1 += "location.href=\'".length(); v2 = arg3.indexOf("\'", v1); if(v2 <= v1) { return v0; } if(v2 <= 0) { return v0; } v0 = arg3.substring(v1, v2); if(v0 == null) { return v0; } if(v0.trim().toLowerCase().startsWith("http")) { return v0; } v0 = ""; } return v0; }获取到重定向的url，接下来返回入口函数，对这个重定向url进行处理，下面是处理代码：
if((TextUtils.isEmpty(((CharSequence)v4_1))) || (TextUtils.isEmpty(v4_1.toLowerCase()))) { v4_1 = v5_1; } if((TextUtils.isEmpty(((CharSequence)v0_2))) || (TextUtils.isEmpty(v0_2.toLowerCase()))) { v0_2 = v3_1; } if(!v8.fNY && !TextUtils.isEmpty(v8.bVW) && ((v8.bVW.toLowerCase().contains(v4_1.toLowerCase())) || (v8.bVW.toLowerCase().contains(((CharSequence)v5_1))))) { this.fNV = "Redirect baidu RedirectUrl = " + v8.bVW + ", taobao RedirectUrl = " + v9.bVW; this.bc(v12, 0); return 1; } if(!v8.fNY && !TextUtils.isEmpty(v8.bVW) && !v8.bVW.toLowerCase().contains(((CharSequence)v6))) { this.fNV = "baidu: " + v8.bVW; this.bc(v11, v11); return 1; } if(!v9.fNY && !TextUtils.isEmpty(v9.bVW) && ((v9.bVW.toLowerCase().contains(v0_2.toLowerCase())) || (v9.bVW.toLowerCase().contains(((CharSequence)v3_1))))) { this.fNV = "Redirect baidu RedirectUrl = " + v8.bVW + ", taobao RedirectUrl = " + v9.bVW; this.bc(v12, 0); return 1; } if(!v9.fNY && !TextUtils.isEmpty(v9.bVW) && !v9.bVW.toLowerCase().startsWith(v3_1) && !v9.bVW.toLowerCase().startsWith(v7)) { this.fNV = "taobao: " + v9.bVW; this.bc(v11, v11); return 1; } if(!v8.fNY && !v9.fNY && !TextUtils.isEmpty(v8.bVW) && !TextUtils.isEmpty(v9.bVW) && (TextUtils.equals(v8.bVW.toLowerCase(), v9.bVW.toLowerCase()))) { this.fNV = "baidu and taobao has the same redirectUrl, url = " + v9.bVW; this.bc(v11, v11); return 1; }首先解释一下相关变量的意义，fNY是一个boolean值，代表的是响应是否是301、302这两个里面的一个，如果不是，那就是没有重定向，默认是safe.然后是bVW这个变量，这个就是之前获取到的重定向的url，最后是v11和v12这两个变量代表检测结果，v11代表有危险，v12代表安全，所以看到返回v11的就是不安全的几种情况，比如http://tools.3g.qq.com/wifi/ssl本来应该重定向到baidu.com，如果重定向结果不是这个说明dns遭到篡改了，还有就是淘宝的那个url本来不应该重定向的，如果发生了重定向也说明dns有问题，列出了所有情况，检测就结束了
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