app: net.captive_portal probe — reproduce Android's internet/portal checks
Mirrors NetworkMonitor: per active network, fetch the AOSP default generate_204 endpoints and check for HTTP 204 No Content. - HTTPS https://www.google.com/generate_204 == 204 -> validated internet - HTTP http://connectivitycheck.gstatic.com/generate_204: 204 -> clean; an unfollowed 3xx or a 200-with-body -> captive portal (Location captured) - both fail -> no_internet Per-network verdicts (bound via Network.openConnection), redirects not followed (the 3xx IS the evidence). Findings: captive_portal (medium) and no_internet (high). New test type net.captive_portal (net family -> connectivity category). App gains usesCleartextTraffic (a network diagnostic that intentionally probes plain HTTP). Builds; measurement verdict tests still green. On-device verification deferred with the rest (flaky test devices). Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
mrambossek
co-authored by
Claude Opus 5
Claude Opus 5
parent
aaed22dd3f
commit
6e269d424b
@@ -15,6 +15,7 @@
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android:allowBackup="false"
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android:label="Echolot"
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android:supportsRtl="true"
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android:usesCleartextTraffic="true"
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android:theme="@style/Theme.Echolot">
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<activity
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@@ -11,6 +11,7 @@ import androidx.compose.runtime.setValue
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import androidx.lifecycle.AndroidViewModel
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import androidx.lifecycle.viewModelScope
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import app.echo_lot.measurement.*
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import app.echo_lot.probe.CaptivePortalProbe
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import app.echo_lot.probe.IcmpProbe
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import app.echo_lot.probe.LinkSnapshotProbe
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import app.echo_lot.probe.NetworkInventory
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@@ -69,6 +70,7 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
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LinkSnapshotProbe(entries),
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IcmpProbe(entries, v6 = false),
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IcmpProbe(entries, v6 = true),
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CaptivePortalProbe(entries),
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)
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val tests = ArrayList<Test>()
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@@ -132,6 +134,29 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
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val out = ArrayList<Finding>()
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val ids = RunIds()
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for (t in tests) {
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if (t.type == TestType.NET_CAPTIVE_PORTAL) {
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val ev = t.evidence?.toString() ?: ""
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when {
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ev.contains("\"captive_portal\"") -> out.add(
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Finding(
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id = ids.uuid(), code = "connectivity.captive_portal", category = Category.CONNECTIVITY,
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severity = Severity.MEDIUM, confidence = Confidence.HIGH,
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title = "Captive portal intercepting connections",
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description = "The generate_204 check returned a redirect or a page instead of HTTP 204 — a captive portal (login/splash page) is intercepting traffic on this network.",
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evidenceRefs = listOf(EvidenceRef(t.id)),
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)
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)
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t.status == TestStatus.FAILED -> out.add(
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Finding(
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id = ids.uuid(), code = "connectivity.no_internet", category = Category.CONNECTIVITY,
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severity = Severity.HIGH, confidence = Confidence.HIGH,
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title = "No working internet on any network",
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description = "Android's own generate_204 connectivity checks failed on every active network (no HTTP 204) — this device has no validated internet path.",
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evidenceRefs = listOf(EvidenceRef(t.id)),
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)
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)
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}
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}
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if (t.type == TestType.ICMP_PING6 && t.status == TestStatus.FAILED) {
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out.add(
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Finding(
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@@ -55,6 +55,8 @@ object TestType {
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const val LINK_SNAPSHOT = "link.snapshot"
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const val LINK_DHCP_RENEWAL_WATCH = "link.dhcp_renewal_watch"
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const val LINK_IP_MONITOR = "link.ip_monitor"
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// net — connectivity validation (reproduces Android's NetworkMonitor generate_204 checks)
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const val NET_CAPTIVE_PORTAL = "net.captive_portal"
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// icmp
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const val ICMP_PING4 = "icmp.ping4"
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const val ICMP_PING6 = "icmp.ping6"
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@@ -131,7 +133,7 @@ object TestType {
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/** Maps a dotted test type to its §7.2 category for verdict rollup. */
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fun category(type: String): Category = when (type.substringBefore('.')) {
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"link", "icmp", "trace", "traceroute", "train", "port", "time" -> Category.CONNECTIVITY
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"link", "icmp", "trace", "traceroute", "train", "port", "time", "net" -> Category.CONNECTIVITY
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"dns" -> Category.DNS
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"nat" -> Category.NAT
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"mtu" -> Category.MTU
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@@ -0,0 +1,118 @@
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// SPDX-FileCopyrightText: 2026 Echolot contributors
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// SPDX-License-Identifier: GPL-3.0-or-later
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package app.echo_lot.probe
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import android.content.Context
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import android.net.Network
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import app.echo_lot.measurement.Test
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import app.echo_lot.measurement.TestStatus
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import app.echo_lot.measurement.TestType
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import app.echo_lot.measurement.Tier
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import kotlinx.coroutines.Dispatchers
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import kotlinx.coroutines.withContext
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import kotlinx.serialization.json.JsonObject
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import kotlinx.serialization.json.buildJsonObject
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import kotlinx.serialization.json.put
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import kotlinx.serialization.json.putJsonObject
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import java.io.IOException
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import java.net.HttpURLConnection
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import java.net.URL
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/**
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* Reproduces Android's own "do I have internet / is there a captive portal?" logic
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* (NetworkMonitor): it fetches `generate_204` endpoints and checks for **HTTP 204 No Content**.
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*
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* Per active network (bound via Network.openConnection):
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* - **HTTPS 204** (`https://www.google.com/generate_204`) → real validated internet.
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* - **HTTP 204** (`http://connectivitycheck.gstatic.com/generate_204`) → a plain-HTTP path with
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* no interference. A 3xx redirect or a 200-with-body instead of 204 is the classic **captive
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* portal** signature (the portal's login page); the redirect Location is captured.
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* - timeout/IO error on both → no working internet on that network.
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*
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* These are the AOSP default probe URLs (Settings.Global CAPTIVE_PORTAL_HTTPS_URL /
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* CAPTIVE_PORTAL_HTTP_URL). Redirects are NOT followed — an unfollowed 3xx is the evidence.
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*/
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class CaptivePortalProbe(private val entries: List<NetworkInventory.Entry>) : Probe {
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override val type = TestType.NET_CAPTIVE_PORTAL
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override val tier = Tier.APP
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private val httpsUrl = "https://www.google.com/generate_204"
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private val httpUrl = "http://connectivitycheck.gstatic.com/generate_204"
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override suspend fun run(ctx: Context, ids: ProbeIds): Test = withContext(Dispatchers.IO) {
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val b = TestBuilder(type, tier, ids)
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val perNet = LinkedHashMap<String, ProbeResult>()
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// Default network first, then each active network explicitly.
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perNet["default"] = validate(null)
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for (e in entries) {
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perNet["${e.model.transport.name.lowercase()}:${e.model.id}"] = validate(e.handle)
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}
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val evidence: JsonObject = buildJsonObject {
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put("https_url", httpsUrl); put("http_url", httpUrl)
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for ((label, r) in perNet) putJsonObject(label) {
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put("https_code", r.httpsCode); put("http_code", r.httpCode)
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r.portalLocation?.let { put("portal_location", it) }
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put("verdict", r.verdict)
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}
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}
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// Best verdict across networks: validated > portal > none.
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val anyValidated = perNet.values.any { it.verdict == "validated" }
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val anyPortal = perNet.values.any { it.verdict == "captive_portal" }
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val status = when {
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anyValidated -> TestStatus.OK
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anyPortal -> TestStatus.PARTIAL // reachable but intercepted
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else -> TestStatus.FAILED // no working internet anywhere
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}
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b.build(status, evidence = evidence)
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}
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private data class ProbeResult(
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val httpsCode: Int, val httpCode: Int, val portalLocation: String?, val verdict: String,
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)
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private fun validate(network: Network?): ProbeResult {
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val https = probe(network, httpsUrl)
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val http = probe(network, httpUrl)
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val portalLoc = http.location.takeIf { http.code in 300..399 }
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val verdict = when {
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https.code == 204 -> "validated" // real internet
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http.code == 204 -> "validated_http_only" // HTTP clean, HTTPS blocked
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http.code in 300..399 || (http.code == 200 && http.hadBody) -> "captive_portal"
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https.code < 0 && http.code < 0 -> "no_internet"
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else -> "inconclusive"
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}
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return ProbeResult(https.code, http.code, portalLoc, verdict)
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}
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private data class Resp(val code: Int, val location: String?, val hadBody: Boolean)
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/** One probe: code (-1 on failure), Location header, and whether a body was present (204 has none). */
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private fun probe(network: Network?, urlStr: String): Resp {
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var conn: HttpURLConnection? = null
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return try {
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val url = URL(urlStr)
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conn = (network?.openConnection(url) ?: url.openConnection()) as HttpURLConnection
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conn.instanceFollowRedirects = false // an unfollowed 3xx is the portal signal
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conn.connectTimeout = 4000
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conn.readTimeout = 4000
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conn.requestMethod = "GET"
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conn.setRequestProperty("User-Agent", "Echolot")
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conn.setRequestProperty("Connection", "close")
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val code = conn.responseCode
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val loc = conn.getHeaderField("Location")
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val body = runCatching {
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(conn.inputStream ?: conn.errorStream)?.use { it.read() != -1 }
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}.getOrNull() ?: false
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Resp(code, loc, body)
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} catch (e: IOException) {
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Resp(-1, null, false)
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} catch (e: Throwable) {
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Resp(-1, null, false)
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} finally {
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conn?.disconnect()
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}
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}
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}
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