Add JSONMessageStreamingParser to help parse swiftc & xcbuild

Sources/TSCUtility/CMakeLists.txt

@@ -13,12 +13,15 @@ add_library(TSCUtility
   BuildFlags.swift
   CollectionExtensions.swift
   Diagnostics.swift
+  dlopen.swift
   Downloader.swift
-  FSWatch.swift
   FloatingPointExtensions.swift
+  FSWatch.swift
   Git.swift
   IndexStore.swift
   InterruptHandler.swift
+  JSONMessageStreamingParser.swift
+  misc.swift
   OSLog.swift
   PkgConfig.swift
   Platform.swift
@@ -30,8 +33,7 @@ add_library(TSCUtility
   Verbosity.swift
   Version.swift
   Versioning.swift
-  dlopen.swift
-  misc.swift)
+)
 target_link_libraries(TSCUtility PUBLIC
   TSCBasic)
 # NOTE(compnerd) workaround for CMake not setting up include flags yet

Sources/TSCUtility/JSONMessageStreamingParser.swift

@@ -0,0 +1,167 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2020 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See http://swift.org/LICENSE.txt for license information
+ See http://swift.org/CONTRIBUTORS.txt for Swift project authors
+ */
+
+import Foundation
+
+/// Protocol for the parser delegate to get notified of parsing events.
+public protocol JSONMessageStreamingParserDelegate: class {
+
+    /// A decodable type representing the JSON messages being parsed.
+    associatedtype Message: Decodable
+
+    /// Called for each message parsed.
+    func jsonMessageStreamingParser(_ parser: JSONMessageStreamingParser<Self>, didParse message: Message)
+
+    /// Called when parsing raw text instead of message size.
+    func jsonMessageStreamingParser(_ parser: JSONMessageStreamingParser<Self>, didParseRawText text: String)
+
+    /// Called on an un-expected parsing error. No more events will be received after that.
+    func jsonMessageStreamingParser(_ parser: JSONMessageStreamingParser<Self>, didFailWith error: Error)
+}
+
+/// Streaming parser for JSON messages seperated by integers to represent size of message. Used by the Swift compiler
+/// and XCBuild to share progess information: https://github.com/apple/swift/blob/master/docs/DriverParseableOutput.rst.
+public final class JSONMessageStreamingParser<Delegate: JSONMessageStreamingParserDelegate> {
+
+    /// The object representing the JSON message being parsed.
+    public typealias Message = Delegate.Message
+
+    /// State of the parser state machine.
+    private enum State {
+        case parsingMessageSize
+        case parsingMessage(size: Int)
+        case parsingNewlineAfterMessage
+        case failed
+    }
+
+    /// Delegate to notify of parsing events.
+    public weak var delegate: Delegate?
+
+    /// Buffer containing the bytes until a full message can be parsed.
+    private var buffer: [UInt8] = []
+
+    /// The parser's state machine current state.
+    private var state: State = .parsingMessageSize
+
+    /// The JSON decoder to parse messages.
+    private let decoder: JSONDecoder
+
+    /// Initializes the parser.
+    /// - Parameters:
+    ///   - delegate: The `JSONMessageStreamingParserDelegate` that will receive parsing event callbacks.
+    ///   - decoder: The `JSONDecoder` to use for decoding JSON messages.
+    public init(delegate: Delegate, decoder: JSONDecoder = JSONDecoder())
+    {
+        self.delegate = delegate
+        self.decoder = decoder
+    }
+
+    /// Parse the next bytes of the stream.
+    /// - Note: If a parsing error is encountered, the delegate will be notified and the parser won't accept any further
+    ///   input.
+    public func parse<C>(bytes: C) where C: Collection, C.Element == UInt8 {
+        if case .failed = state { return }
+
+        do {
+            try parseImpl(bytes: bytes)
+        } catch {
+            state = .failed
+            delegate?.jsonMessageStreamingParser(self, didFailWith: error)
+        }
+    }
+}
+
+private extension JSONMessageStreamingParser {
+
+    /// Error corresponding to invalid Swift compiler output.
+    struct ParsingError: LocalizedError {
+
+        /// Text describing the specific reason for the parsing failure.
+        let reason: String
+
+        /// The underlying error, if there is one.
+        let underlyingError: Error?
+
+        var errorDescription: String? {
+            if let error = underlyingError {
+                return "\(reason): \(error)"
+            } else {
+                return reason
+            }
+        }
+    }
+
+    /// Throwing implementation of the parse function.
+    func parseImpl<C>(bytes: C) throws where C: Collection, C.Element == UInt8 {
+        switch state {
+        case .parsingMessageSize:
+            if let newlineIndex = bytes.firstIndex(of: newline) {
+                buffer.append(contentsOf: bytes[..<newlineIndex])
+                try parseMessageSize()
+
+                let nextIndex = bytes.index(after: newlineIndex)
+                try parseImpl(bytes: bytes[nextIndex...])
+            } else {
+                buffer.append(contentsOf: bytes)
+            }
+        case .parsingMessage(size: let size):
+            let remainingBytes = size - buffer.count
+            if remainingBytes <= bytes.count {
+                buffer.append(contentsOf: bytes.prefix(remainingBytes))
+
+                let message = try parseMessage()
+                delegate?.jsonMessageStreamingParser(self, didParse: message)
+
+                try parseImpl(bytes: bytes.dropFirst(remainingBytes))
+            } else {
+                buffer.append(contentsOf: bytes)
+            }
+        case .parsingNewlineAfterMessage:
+            if let firstByte = bytes.first {
+                precondition(firstByte == newline)
+                state = .parsingMessageSize
+                try parseImpl(bytes: bytes.dropFirst())
+            }
+        case .failed:
+            return
+        }
+    }
+
+    /// Parse the next message size from the buffer and update the state machine.
+    func parseMessageSize() throws {
+        guard let string = String(bytes: buffer, encoding: .utf8) else {
+            throw ParsingError(reason: "invalid UTF8 bytes", underlyingError: nil)
+        }
+
+        guard let messageSize = Int(string) else {
+            delegate?.jsonMessageStreamingParser(self, didParseRawText: string)
+            buffer.removeAll()
+            return
+        }
+
+        buffer.removeAll()
+        state = .parsingMessage(size: messageSize)
+    }
+
+    /// Parse the message in the buffer and update the state machine.
+    func parseMessage() throws -> Message {
+        let data = Data(buffer)
+        buffer.removeAll()
+        state = .parsingNewlineAfterMessage
+
+        do {
+            return try decoder.decode(Message.self, from: data)
+        } catch {
+            throw ParsingError(reason: "unexpected JSON message", underlyingError: error)
+        }
+    }
+}
+
+private let newline = UInt8(ascii: "\n")