Limit lyng.io HTTP redirect chains

docs/lyng.io.http.md

@@ -42,6 +42,21 @@ suspend fun bootstrapHttp() {
 }
 ```
 
+Redirects are followed transparently, up to 10 hops by default. Hosts can set a different
+limit when installing the module:
+
+```kotlin
+createHttpModule(
+    PermitAllHttpAccessPolicy,
+    scope,
+    LyngHttpConfig(maxRedirects = 5),
+)
+```
+
+Exceeding the limit raises an `HTTP_REDIRECT_LIMIT_EXCEEDED` error containing the configured
+limit, initial URL, and last redirect target. HTTPS-to-HTTP redirects remain disabled, and the
+`Authorization` header is removed when a redirect changes authority.
+
 ---
 
 ## Using from Lyng scripts

lyngio/src/androidMain/kotlin/net/sergeych/lyngio/http/PlatformAndroid.kt

@@ -2,4 +2,4 @@ package net.sergeych.lyngio.http
 
 import io.ktor.client.engine.cio.CIO
 
-actual fun getSystemHttpEngine(): LyngHttpEngine = createKtorHttpEngine(CIO)
+actual fun getSystemHttpEngine(config: LyngHttpConfig): LyngHttpEngine = createKtorHttpEngine(CIO, config)

lyngio/src/commonMain/kotlin/net/sergeych/lyng/io/http/LyngHttpModule.kt

@@ -41,6 +41,7 @@ import net.sergeych.lyng.requireNoArgs
 import net.sergeych.lyng.requireScope
 import net.sergeych.lyngio.http.LyngHttpRequest
 import net.sergeych.lyngio.http.LyngHttpResponse
+import net.sergeych.lyngio.http.LyngHttpConfig
 import net.sergeych.lyngio.http.getSystemHttpEngine
 import net.sergeych.lyngio.http.security.HttpAccessDeniedException
 import net.sergeych.lyngio.http.security.HttpAccessOp
@@ -51,21 +52,36 @@ import net.sergeych.lyngio.stdlib_included.http_typesLyng
 private const val HTTP_MODULE_NAME = "lyng.io.http"
 internal const val HTTP_TYPES_MODULE_NAME = "lyng.io.http.types"
 
-fun createHttpModule(policy: HttpAccessPolicy, scope: Scope): Boolean =
-    createHttpModule(policy, scope.importManager)
+fun createHttpModule(
+    policy: HttpAccessPolicy,
+    scope: Scope,
+    config: LyngHttpConfig = LyngHttpConfig(),
+): Boolean = createHttpModule(policy, scope.importManager, config)
 
-fun createHttp(policy: HttpAccessPolicy, scope: Scope): Boolean = createHttpModule(policy, scope)
+fun createHttp(
+    policy: HttpAccessPolicy,
+    scope: Scope,
+    config: LyngHttpConfig = LyngHttpConfig(),
+): Boolean = createHttpModule(policy, scope, config)
 
-fun createHttpModule(policy: HttpAccessPolicy, manager: ImportManager): Boolean {
+fun createHttpModule(
+    policy: HttpAccessPolicy,
+    manager: ImportManager,
+    config: LyngHttpConfig = LyngHttpConfig(),
+): Boolean {
     createHttpTypesModule(manager)
     if (manager.packageNames.contains(HTTP_MODULE_NAME)) return false
     manager.addPackage(HTTP_MODULE_NAME) { module ->
-        buildHttpModule(module, policy)
+        buildHttpModule(module, policy, config)
     }
     return true
 }
 
-fun createHttp(policy: HttpAccessPolicy, manager: ImportManager): Boolean = createHttpModule(policy, manager)
+fun createHttp(
+    policy: HttpAccessPolicy,
+    manager: ImportManager,
+    config: LyngHttpConfig = LyngHttpConfig(),
+): Boolean = createHttpModule(policy, manager, config)
 
 internal fun createHttpTypesModule(manager: ImportManager): Boolean {
     if (manager.packageNames.contains(HTTP_TYPES_MODULE_NAME)) return false
@@ -80,9 +96,9 @@ private suspend fun buildHttpTypesModule(module: ModuleScope) {
     module.addConst("HttpHeaders", ObjHttpHeaders.type)
 }
 
-private suspend fun buildHttpModule(module: ModuleScope, policy: HttpAccessPolicy) {
+private suspend fun buildHttpModule(module: ModuleScope, policy: HttpAccessPolicy, config: LyngHttpConfig) {
     module.eval(Source(HTTP_MODULE_NAME, httpLyng))
-    val engine = getSystemHttpEngine()
+    val engine = getSystemHttpEngine(config)
 
     val headersType = ObjHttpHeaders.type
     val requestType = ObjHttpRequest.type

lyngio/src/commonMain/kotlin/net/sergeych/lyngio/http/CappedHttpRedirect.kt

@@ -0,0 +1,100 @@
+@file:OptIn(io.ktor.utils.io.InternalAPI::class)
+
+package net.sergeych.lyngio.http
+
+import io.ktor.client.HttpClient
+import io.ktor.client.call.HttpClientCall
+import io.ktor.client.plugins.HttpResponseRedirectEvent
+import io.ktor.client.plugins.api.ClientPlugin
+import io.ktor.client.plugins.api.Send
+import io.ktor.client.plugins.api.createClientPlugin
+import io.ktor.client.request.HttpRequestBuilder
+import io.ktor.http.HttpHeaders
+import io.ktor.http.HttpMethod
+import io.ktor.http.HttpStatusCode
+import io.ktor.http.authority
+import io.ktor.http.isSecure
+import io.ktor.http.takeFrom
+
+private val redirectMethods = setOf(HttpMethod.Get, HttpMethod.Head)
+
+internal class HttpRedirectLimitExceededException(
+    val limit: Int,
+    val initialUrl: String,
+    val lastUrl: String,
+) : IllegalStateException(
+    "HTTP_REDIRECT_LIMIT_EXCEEDED: limit=$limit, initialUrl=$initialUrl, lastUrl=$lastUrl"
+)
+
+internal class CappedHttpRedirectConfig {
+    var maxRedirects: Int = LyngHttpConfig.DEFAULT_MAX_REDIRECTS
+    var checkHttpMethod: Boolean = true
+    var allowHttpsDowngrade: Boolean = false
+}
+
+internal val CappedHttpRedirect: ClientPlugin<CappedHttpRedirectConfig> = createClientPlugin(
+    "CappedHttpRedirect",
+    ::CappedHttpRedirectConfig,
+) {
+    val maxRedirects = pluginConfig.maxRedirects.also {
+        require(it >= 0) { "maxRedirects must not be negative" }
+    }
+    val checkHttpMethod = pluginConfig.checkHttpMethod
+    val allowHttpsDowngrade = pluginConfig.allowHttpsDowngrade
+
+    suspend fun Send.Sender.followRedirects(
+        context: HttpRequestBuilder,
+        origin: HttpClientCall,
+        client: HttpClient,
+    ): HttpClientCall {
+        var call = origin
+        var requestBuilder = context
+        val initialUrl = origin.request.url.toString()
+        var redirectCount = 0
+
+        while (call.response.status.isRedirectStatus()) {
+            val location = call.response.headers[HttpHeaders.Location] ?: return call
+            val previousProtocol = call.request.url.protocol
+            val previousAuthority = call.request.url.authority
+            requestBuilder = HttpRequestBuilder().apply {
+                takeFrom(requestBuilder)
+                url.parameters.clear()
+                url.takeFrom(location)
+                if (!allowHttpsDowngrade && previousProtocol.isSecure() && !url.protocol.isSecure()) {
+                    return call
+                }
+                if (previousAuthority != url.authority) {
+                    headers.remove(HttpHeaders.Authorization)
+                }
+            }
+            if (redirectCount >= maxRedirects) {
+                throw HttpRedirectLimitExceededException(
+                    maxRedirects,
+                    initialUrl,
+                    requestBuilder.url.buildString(),
+                )
+            }
+            redirectCount += 1
+            client.monitor.raise(HttpResponseRedirectEvent, call.response)
+            call = proceed(requestBuilder)
+        }
+        return call
+    }
+
+    on(Send) { request ->
+        val origin = proceed(request)
+        if (checkHttpMethod && origin.request.method !in redirectMethods) {
+            return@on origin
+        }
+        followRedirects(request, origin, client)
+    }
+}
+
+private fun HttpStatusCode.isRedirectStatus(): Boolean = when (value) {
+    HttpStatusCode.MovedPermanently.value,
+    HttpStatusCode.Found.value,
+    HttpStatusCode.TemporaryRedirect.value,
+    HttpStatusCode.PermanentRedirect.value,
+    HttpStatusCode.SeeOther.value -> true
+    else -> false
+}

lyngio/src/commonMain/kotlin/net/sergeych/lyngio/http/KtorHttpEngine.kt

@@ -14,14 +14,20 @@ import io.ktor.http.takeFrom
 
 internal fun createKtorHttpEngine(
     engineFactory: HttpClientEngineFactory<HttpClientEngineConfig>,
-): LyngHttpEngine = KtorLyngHttpEngine(engineFactory)
+    config: LyngHttpConfig,
+): LyngHttpEngine = KtorLyngHttpEngine(engineFactory, config)
 
 private class KtorLyngHttpEngine(
     engineFactory: HttpClientEngineFactory<HttpClientEngineConfig>,
+    config: LyngHttpConfig,
 ) : LyngHttpEngine {
     private val clientResult = runCatching {
         HttpClient(engineFactory) {
             expectSuccess = false
+            followRedirects = false
+            install(CappedHttpRedirect) {
+                maxRedirects = config.maxRedirects
+            }
         }
     }
 

lyngio/src/commonMain/kotlin/net/sergeych/lyngio/http/LyngHttp.kt

@@ -33,6 +33,18 @@ data class LyngHttpResponse(
     val bodyBytes: ByteArray,
 )
 
+data class LyngHttpConfig(
+    val maxRedirects: Int = DEFAULT_MAX_REDIRECTS,
+) {
+    init {
+        require(maxRedirects >= 0) { "maxRedirects must not be negative" }
+    }
+
+    companion object {
+        const val DEFAULT_MAX_REDIRECTS: Int = 10
+    }
+}
+
 interface LyngHttpEngine {
     val isSupported: Boolean
     suspend fun request(request: LyngHttpRequest): LyngHttpResponse
@@ -46,4 +58,4 @@ internal object UnsupportedHttpEngine : LyngHttpEngine {
     }
 }
 
-expect fun getSystemHttpEngine(): LyngHttpEngine
+expect fun getSystemHttpEngine(config: LyngHttpConfig = LyngHttpConfig()): LyngHttpEngine

lyngio/src/darwinMain/kotlin/net/sergeych/lyngio/http/PlatformDarwin.kt

@@ -2,4 +2,4 @@ package net.sergeych.lyngio.http
 
 import io.ktor.client.engine.darwin.Darwin
 
-actual fun getSystemHttpEngine(): LyngHttpEngine = createKtorHttpEngine(Darwin)
+actual fun getSystemHttpEngine(config: LyngHttpConfig): LyngHttpEngine = createKtorHttpEngine(Darwin, config)

lyngio/src/jsMain/kotlin/net/sergeych/lyngio/http/PlatformJs.kt

@@ -2,4 +2,4 @@ package net.sergeych.lyngio.http
 
 import io.ktor.client.engine.js.Js
 
-actual fun getSystemHttpEngine(): LyngHttpEngine = createKtorHttpEngine(Js)
+actual fun getSystemHttpEngine(config: LyngHttpConfig): LyngHttpEngine = createKtorHttpEngine(Js, config)

lyngio/src/jvmMain/kotlin/net/sergeych/lyngio/http/PlatformJvm.kt

@@ -2,4 +2,4 @@ package net.sergeych.lyngio.http
 
 import io.ktor.client.engine.cio.CIO
 
-actual fun getSystemHttpEngine(): LyngHttpEngine = createKtorHttpEngine(CIO)
+actual fun getSystemHttpEngine(config: LyngHttpConfig): LyngHttpEngine = createKtorHttpEngine(CIO, config)

lyngio/src/jvmTest/kotlin/net/sergeych/lyngio/http/KtorHttpRedirectTest.kt

@@ -0,0 +1,73 @@
+package net.sergeych.lyngio.http
+
+import com.sun.net.httpserver.HttpExchange
+import com.sun.net.httpserver.HttpServer
+import io.ktor.client.engine.cio.CIO
+import kotlinx.coroutines.runBlocking
+import java.net.InetSocketAddress
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertTrue
+
+class KtorHttpRedirectTest {
+    @Test
+    fun redirectsWithinLimitRemainTransparent() = runBlocking {
+        val server = newServer { exchange ->
+            when (exchange.requestURI.path) {
+                "/start" -> redirect(exchange, "/middle")
+                "/middle" -> redirect(exchange, "/result")
+                else -> writeResponse(exchange, 200, "redirected")
+            }
+        }
+        try {
+            val engine = createKtorHttpEngine(CIO, LyngHttpConfig(maxRedirects = 2))
+            val response = engine.request(LyngHttpRequest("GET", url(server, "/start")))
+            assertEquals(200, response.status)
+            assertEquals("redirected", response.bodyBytes.decodeToString())
+        } finally {
+            server.stop(0)
+        }
+    }
+
+    @Test
+    fun redirectLimitProducesDiagnosticError() = runBlocking {
+        val server = newServer { exchange ->
+            val next = exchange.requestURI.path.removePrefix("/").toIntOrNull()?.plus(1) ?: 1
+            redirect(exchange, "/$next")
+        }
+        try {
+            val engine = createKtorHttpEngine(CIO, LyngHttpConfig(maxRedirects = 2))
+            val error = assertFailsWith<HttpRedirectLimitExceededException> {
+                engine.request(LyngHttpRequest("GET", url(server, "/0")))
+            }
+            assertEquals(2, error.limit)
+            assertTrue(error.initialUrl.endsWith("/0"), error.initialUrl)
+            assertTrue(error.lastUrl.endsWith("/3"), error.lastUrl)
+            assertTrue(error.message.orEmpty().startsWith("HTTP_REDIRECT_LIMIT_EXCEEDED:"), error.message)
+        } finally {
+            server.stop(0)
+        }
+    }
+
+    private fun newServer(handler: (HttpExchange) -> Unit): HttpServer =
+        HttpServer.create(InetSocketAddress("127.0.0.1", 0), 0).apply {
+            createContext("/") { exchange -> handler(exchange) }
+            start()
+        }
+
+    private fun url(server: HttpServer, path: String) =
+        "http://127.0.0.1:${server.address.port}$path"
+
+    private fun redirect(exchange: HttpExchange, location: String) {
+        exchange.responseHeaders.add("Location", location)
+        exchange.sendResponseHeaders(302, -1)
+        exchange.close()
+    }
+
+    private fun writeResponse(exchange: HttpExchange, status: Int, body: String) {
+        val bytes = body.encodeToByteArray()
+        exchange.sendResponseHeaders(status, bytes.size.toLong())
+        exchange.responseBody.use { it.write(bytes) }
+    }
+}

lyngio/src/linuxMain/kotlin/net/sergeych/lyngio/http/PlatformLinux.kt

@@ -2,4 +2,4 @@ package net.sergeych.lyngio.http
 
 import io.ktor.client.engine.curl.Curl
 
-actual fun getSystemHttpEngine(): LyngHttpEngine = createKtorHttpEngine(Curl)
+actual fun getSystemHttpEngine(config: LyngHttpConfig): LyngHttpEngine = createKtorHttpEngine(Curl, config)

lyngio/src/mingwMain/kotlin/net/sergeych/lyngio/http/PlatformMingw.kt

@@ -2,4 +2,4 @@ package net.sergeych.lyngio.http
 
 import io.ktor.client.engine.winhttp.WinHttp
 
-actual fun getSystemHttpEngine(): LyngHttpEngine = createKtorHttpEngine(WinHttp)
+actual fun getSystemHttpEngine(config: LyngHttpConfig): LyngHttpEngine = createKtorHttpEngine(WinHttp, config)