Support UNIX Domain Sockets (#151)

Adds support for UNIX Domain Socket requests.

Usage:

```
let httpClient = HTTPClient(eventLoopGroupProvider: .createNew)
let socketURL = URL(string: "unix:///var/run/docker.sock")!
let req = try HTTPClient.Request(url: URL(string: "/users/list", relativeTo: socketURL)!, method: .GET)
let response = try httpClient.execute(request: req).wait()
```

Author: krzyzanowskim

Sources/AsyncHTTPClient/HTTPClient.swift

@@ -281,15 +281,22 @@ public class HTTPClient {
             bootstrap = bootstrap.connectTimeout(timeout)
         }
 
-        let address = self.resolveAddress(request: request, proxy: self.configuration.proxy)
-        bootstrap.connect(host: address.host, port: address.port)
-            .map { channel in
-                task.setChannel(channel)
-            }
-            .flatMap { channel in
-                channel.writeAndFlush(request)
-            }
-            .cascadeFailure(to: task.promise)
+        let eventLoopChannel: EventLoopFuture<Channel>
+        if request.kind == .unixSocket, let baseURL = request.url.baseURL {
+            eventLoopChannel = bootstrap.connect(unixDomainSocketPath: baseURL.path)
+        } else {
+            let address = self.resolveAddress(request: request, proxy: self.configuration.proxy)
+            eventLoopChannel = bootstrap.connect(host: address.host, port: address.port)
+        }
+
+        eventLoopChannel.map { channel in
+            task.setChannel(channel)
+        }
+        .flatMap { channel in
+            channel.writeAndFlush(request)
+        }
+        .cascadeFailure(to: task.promise)
+
         return task
     }
 
@@ -481,12 +488,12 @@ private extension ChannelPipeline {
     func addProxyHandler(for request: HTTPClient.Request, decoder: ByteToMessageHandler<HTTPResponseDecoder>, encoder: HTTPRequestEncoder, tlsConfiguration: TLSConfiguration?, proxy: HTTPClient.Configuration.Proxy?) -> EventLoopFuture<Void> {
         let handler = HTTPClientProxyHandler(host: request.host, port: request.port, authorization: proxy?.authorization, onConnect: { channel in
             channel.pipeline.removeHandler(decoder).flatMap {
-                return channel.pipeline.addHandler(
+                channel.pipeline.addHandler(
                     ByteToMessageHandler(HTTPResponseDecoder(leftOverBytesStrategy: .forwardBytes)),
                     position: .after(encoder)
                 )
             }.flatMap {
-                return channel.pipeline.addSSLHandlerIfNeeded(for: request, tlsConfiguration: tlsConfiguration)
+                channel.pipeline.addSSLHandlerIfNeeded(for: request, tlsConfiguration: tlsConfiguration)
             }
         })
         return self.addHandler(handler)

Sources/AsyncHTTPClient/HTTPHandler.swift

@@ -88,12 +88,54 @@ extension HTTPClient {
 
     /// Represent HTTP request.
     public struct Request {
+        /// Represent kind of Request
+        enum Kind {
+            /// Remote host request.
+            case host
+            /// UNIX Domain Socket HTTP request.
+            case unixSocket
+
+            private static var hostSchemes = ["http", "https"]
+            private static var unixSchemes = ["unix"]
+
+            init(forScheme scheme: String) throws {
+                if Kind.host.supports(scheme: scheme) {
+                    self = .host
+                } else if Kind.unixSocket.supports(scheme: scheme) {
+                    self = .unixSocket
+                } else {
+                    throw HTTPClientError.unsupportedScheme(scheme)
+                }
+            }
+
+            func hostFromURL(_ url: URL) throws -> String {
+                switch self {
+                case .host:
+                    guard let host = url.host else {
+                        throw HTTPClientError.emptyHost
+                    }
+                    return host
+                case .unixSocket:
+                    return ""
+                }
+            }
+
+            func supports(scheme: String) -> Bool {
+                switch self {
+                case .host:
+                    return Kind.hostSchemes.contains(scheme)
+                case .unixSocket:
+                    return Kind.unixSchemes.contains(scheme)
+                }
+            }
+        }
+
         /// Request HTTP method, defaults to `GET`.
-        public let method: HTTPMethod
+        public var method: HTTPMethod
         /// Remote URL.
-        public let url: URL
+        public var url: URL
         /// Remote HTTP scheme, resolved from `URL`.
-        public let scheme: String
+        public var scheme: String
         /// Remote host, resolved from `URL`.
         public let host: String
         /// Request custom HTTP Headers, defaults to no headers.
@@ -107,6 +149,7 @@ extension HTTPClient {
         }
 
         var redirectState: RedirectState?
+        let kind: Kind
 
         /// Create HTTP request.
         ///
@@ -133,7 +176,6 @@ extension HTTPClient {
         ///
         /// - parameters:
         ///     - url: Remote `URL`.
-        ///     - version: HTTP version.
         ///     - method: HTTP method.
         ///     - headers: Custom HTTP headers.
         ///     - body: Request body.
@@ -146,22 +188,15 @@ extension HTTPClient {
                 throw HTTPClientError.emptyScheme
             }
 
-            guard Request.isSchemeSupported(scheme: scheme) else {
-                throw HTTPClientError.unsupportedScheme(scheme)
-            }
-
-            guard let host = url.host else {
-                throw HTTPClientError.emptyHost
-            }
+            self.kind = try Kind(forScheme: scheme)
+            self.host = try self.kind.hostFromURL(url)
 
-            self.method = method
+            self.redirectState = nil
             self.url = url
+            self.method = method
             self.scheme = scheme
-            self.host = host
             self.headers = headers
             self.body = body
-
-            self.redirectState = nil
         }
 
         /// Whether request will be executed using secure socket.
@@ -173,10 +208,6 @@ extension HTTPClient {
         public var port: Int {
             return self.url.port ?? (self.useTLS ? 443 : 80)
         }
-
-        static func isSchemeSupported(scheme: String) -> Bool {
-            return scheme == "http" || scheme == "https"
-        }
     }
 
     /// Represent HTTP response.
@@ -812,7 +843,7 @@ internal struct RedirectHandler<ResponseType> {
             return nil
         }
 
-        guard HTTPClient.Request.isSchemeSupported(scheme: self.request.scheme) else {
+        guard self.request.kind.supports(scheme: self.request.scheme) else {
             return nil
         }
 

Tests/AsyncHTTPClientTests/HTTPClientTests.swift

@@ -47,14 +47,21 @@ class HTTPClientTests: XCTestCase {
 
         let request2 = try Request(url: "https://someserver.com")
         XCTAssertEqual(request2.url.path, "")
+
+        let request3 = try Request(url: "unix:///tmp/file")
+        XCTAssertNil(request3.url.host)
+        XCTAssertEqual(request3.host, "")
+        XCTAssertEqual(request3.url.path, "/tmp/file")
+        XCTAssertEqual(request3.port, 80)
+        XCTAssertFalse(request3.useTLS)
     }
 
     func testBadRequestURI() throws {
         XCTAssertThrowsError(try Request(url: "some/path"), "should throw") { error in
             XCTAssertEqual(error as! HTTPClientError, HTTPClientError.emptyScheme)
         }
-        XCTAssertThrowsError(try Request(url: "file://somewhere/some/path?foo=bar"), "should throw") { error in
-            XCTAssertEqual(error as! HTTPClientError, HTTPClientError.unsupportedScheme("file"))
+        XCTAssertThrowsError(try Request(url: "app://somewhere/some/path?foo=bar"), "should throw") { error in
+            XCTAssertEqual(error as! HTTPClientError, HTTPClientError.unsupportedScheme("app"))
         }
         XCTAssertThrowsError(try Request(url: "https:/foo"), "should throw") { error in
             XCTAssertEqual(error as! HTTPClientError, HTTPClientError.emptyHost)
@@ -63,6 +70,7 @@ class HTTPClientTests: XCTestCase {
 
     func testSchemaCasing() throws {
         XCTAssertNoThrow(try Request(url: "hTTpS://someserver.com:8888/some/path?foo=bar"))
+        XCTAssertNoThrow(try Request(url: "uNIx:///some/path"))
     }
 
     func testGet() throws {