Add OTelLogHandler that sends OTelLogEntry to an OTelLogEntryProcessor

Sources/OTel/Logging/OTLPLogEntryDataModel.swift

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+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift OTel open source project
+//
+// Copyright (c) 2024 Moritz Lang and the Swift OTel project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Logging
+
+@_spi(Logging)
+public struct OTelLogEntry: Equatable, Sendable {
+    public let body: String
+    public let level: Logger.Level
+    public let metadata: Logger.Metadata?
+    public let timeNanosecondsSinceEpoch: UInt64
+}

Sources/OTel/Logging/OTelLogHandler.swift

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+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift OTel open source project
+//
+// Copyright (c) 2024 Moritz Lang and the Swift OTel project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import AsyncAlgorithms
+import Logging
+import NIOConcurrencyHelpers
+import ServiceLifecycle
+import Logging
+import Tracing
+
+@_spi(Logging)
+public struct OTelLogHandler: Sendable, LogHandler {
+    public var metadata: Logging.Logger.Metadata
+    public var logLevel: Logging.Logger.Level
+    private let processor: any OTelLogEntryProcessor
+
+    public init(
+        processor: any OTelLogEntryProcessor,
+        logLevel: Logger.Level,
+        metadata: Logger.Metadata = [:]
+    ) {
+        self.processor = processor
+        self.logLevel = logLevel
+        self.metadata = metadata
+    }
+
+    public subscript(metadataKey key: String) -> Logging.Logger.Metadata.Value? {
+        get { metadata[key] }
+        set { metadata[key] = newValue }
+    }
+
+    public func log(
+        level: Logger.Level,
+        message: Logger.Message,
+        metadata: Logger.Metadata?,
+        source: String,
+        file: String,
+        function: String,
+        line: UInt
+    ) {
+        let instant = DefaultTracerClock().now
+
+        let message = OTelLogEntry(
+            body: message.description,
+            level: level,
+            metadata: metadata,
+            timeNanosecondsSinceEpoch: instant.nanosecondsSinceEpoch
+        )
+
+        processor.onLog(message)
+    }
+}

Sources/OTel/Logging/Processing/OTelLogEntryProcessor.swift

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+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift OTel open source project
+//
+// Copyright (c) 2024 Moritz Lang and the Swift OTel project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import ServiceLifecycle
+import ServiceContextModule
+
+/// Log processors allow for processing logs throughout their lifetime via ``onStart(_:parentContext:)`` and ``onEnd(_:)`` calls.
+/// Usually, log processors will forward logs to a configurable ``OTelLogEntryExporter``.
+///
+/// [OpenTelemetry specification: LogRecord processor](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.20.0/specification/logs/sdk.md#logrecordprocessor)
+///
+/// ### Implementation Notes
+///
+/// On shutdown, processors forwarding logs to an ``OTelLogEntryExporter`` MUST shutdown that exporter.
+@_spi(Logging)
+public protocol OTelLogEntryProcessor: Service & Sendable {
+    func onLog(_ log: OTelLogEntry)
+
+    /// Force log processors that batch logs to flush immediately.
+    func forceFlush() async throws
+}

Sources/OTel/Logging/Processing/OTelNoOpLogEntryProcessor.swift

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+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift OTel open source project
+//
+// Copyright (c) 2024 Moritz Lang and the Swift OTel project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import ServiceContextModule
+
+/// A log entry processor that ignores all operations, used when no logs should be processed.
+@_spi(Logging)
+public struct OTelNoOpLogEntryProcessor: OTelLogEntryProcessor, CustomStringConvertible {
+    public let description = "OTelNoOpLogEntryProcessor"
+
+    private let stream: AsyncStream<Void>
+    private let continuation: AsyncStream<Void>.Continuation
+
+    /// Initialize a no-op log entry processor.
+    public init() {
+        (stream, continuation) = AsyncStream.makeStream()
+    }
+
+    public func run() async {
+        for await _ in stream.cancelOnGracefulShutdown() {}
+    }
+
+    public func onLog(_ log: OTelLogEntry) {
+        // no-op
+    }
+
+    public func forceFlush() async throws {
+        // no-op
+    }
+}