Implement custom DoH

app/src/main/java/com/hippo/ehviewer/client/EhDns.kt

@@ -2,6 +2,7 @@ package com.hippo.ehviewer.client
 
 import android.os.Build
 import com.hippo.ehviewer.Settings
+import com.hippo.ehviewer.preference.EhDoH
 import okhttp3.AsyncDns
 import okhttp3.Dns
 import okhttp3.android.AndroidAsyncDns
@@ -23,10 +24,10 @@ private fun HostsMap.hosts(vararg hosts: String, builder: HostMapBuilder.() -> U
     }
 }
 
-private val dnsSystem = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) AsyncDns.toDns(AndroidAsyncDns.IPv4, AndroidAsyncDns.IPv6) else Dns.SYSTEM
+val systemDns = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) AsyncDns.toDns(AndroidAsyncDns.IPv4, AndroidAsyncDns.IPv6) else Dns.SYSTEM
 
 object EhDns : Dns {
-    override fun lookup(hostname: String): List<InetAddress> = builtInHosts[hostname].takeIf { Settings.builtInHosts } ?: dnsSystem.lookup(hostname)
+    override fun lookup(hostname: String): List<InetAddress> = builtInHosts[hostname].takeIf { Settings.builtInHosts } ?: EhDoH.lookup(hostname) ?: systemDns.lookup(hostname)
 
     operator fun contains(hostname: String) = builtInHosts.contains(hostname) && Settings.builtInHosts
 }

app/src/main/java/com/hippo/ehviewer/preference/DohPreference.kt

@@ -1,11 +1,17 @@
 package com.hippo.ehviewer.preference
 
 import android.content.Context
+import android.content.DialogInterface
 import android.util.AttributeSet
 import androidx.preference.Preference
+import com.hippo.ehviewer.EhApplication
 import com.hippo.ehviewer.R
 import com.hippo.ehviewer.Settings
+import com.hippo.ehviewer.client.systemDns
 import com.hippo.ehviewer.ui.legacy.EditTextDialogBuilder
+import okhttp3.HttpUrl.Companion.toHttpUrl
+import okhttp3.dnsoverhttps.DnsOverHttps
+import java.net.InetAddress
 
 class DohPreference @JvmOverloads constructor(
     context: Context,
@@ -14,6 +20,34 @@ class DohPreference @JvmOverloads constructor(
     override fun onClick() {
         val builder = EditTextDialogBuilder(context, Settings.dohUrl, context.getString(R.string.settings_advanced_dns_over_http_hint))
         builder.setTitle(R.string.settings_advanced_dns_over_http_title)
-        builder.setPositiveButton(android.R.string.ok) { _, _ -> Settings.putDohUrl(builder.text.trim()) }.show()
+        builder.setPositiveButton(android.R.string.ok, null)
+        val dialog = builder.create()
+        dialog.show()
+        dialog.getButton(DialogInterface.BUTTON_POSITIVE).setOnClickListener {
+            val text = builder.text.trim()
+            runCatching {
+                if (text.isNotBlank()) text.toHttpUrl()
+            }.onFailure {
+                builder.setError("Invalid URL!")
+            }.onSuccess {
+                Settings.putDohUrl(text)
+                dialog.dismiss()
+            }
+        }
     }
 }
+
+private fun buildDoHDNS(url: String): DnsOverHttps {
+    return DnsOverHttps.Builder().apply {
+        client(EhApplication.okHttpClient)
+        url(url.toHttpUrl())
+        post(true)
+        systemDns(systemDns)
+    }.build()
+}
+
+private var doh: DnsOverHttps? = Settings.dohUrl.runCatching { buildDoHDNS(this) }.getOrNull()
+
+object EhDoH {
+    fun lookup(hostname: String): List<InetAddress>? = doh?.runCatching { lookup(hostname).takeIf { it.isNotEmpty() } }?.getOrNull()
+}