Update attribute processor for stable metrics

Previously AttribtueProcessor is a class and not open. It can't be
customized externally. Now it's changed to procotol and its static
functions are moved into SimpleAttributeProcessor (now it's public).

Also duplicated NoopAttributesProcessor is removed and more tests are
added.

Sources/OpenTelemetrySdk/Metrics/Stable/View/AttributeProcessor.swift

@@ -6,87 +6,80 @@
 import Foundation
 import OpenTelemetryApi
 
-public protocol AttributeProcessorProtocol  {
+public protocol AttributeProcessor  {
     func process(incoming : [String: AttributeValue]) -> [String: AttributeValue]
 }
-public class AttributeProcessor : AttributeProcessorProtocol {
-    
-    public func then(other : AttributeProcessor) -> AttributeProcessor {
+
+public extension AttributeProcessor {
+    func then(other : AttributeProcessor) -> AttributeProcessor {
         if type(of: other) == NoopAttributeProcessor.self {
             return self
         }
         if type(of: self) == NoopAttributeProcessor.self {
             return other
         }
 
-        if type(of: other) == JoinedAttributeProcessor.self {
-            return (other as! JoinedAttributeProcessor).prepend(processor:self)
+        if let joined = self as? JoinedAttributeProcessor {
+            return joined.append(processor:other)
         }
+        if let joined = other as? JoinedAttributeProcessor {
+            return joined.prepend(processor:self)
+        }
+
         return JoinedAttributeProcessor([self, other])
     }
+}
+
+public class SimpleAttributeProcessor : AttributeProcessor {
+    let attributeProcessor : ([String: AttributeValue]) -> [String:AttributeValue]
 
+    init(attributeProcessor : @escaping ([String: AttributeValue]) -> [String: AttributeValue]) {
+        self.attributeProcessor = attributeProcessor
+    }
 
     public func process(incoming: [String : AttributeValue]) -> [String : AttributeValue] {
-        return incoming
+        return attributeProcessor(incoming)
     }
 
-    public static func filterByKeyName( nameFilter : @escaping (String) -> Bool) -> AttributeProcessor {
+    static func filterByKeyName( nameFilter : @escaping (String) -> Bool) -> AttributeProcessor {
         return SimpleAttributeProcessor { attributes in
             attributes.filter { key, value in
                 nameFilter(key)
             }
         }
     }
 
-    public static func append(attributes: [String : AttributeValue]) -> AttributeProcessor {
+    static func append(attributes: [String : AttributeValue]) -> AttributeProcessor {
         SimpleAttributeProcessor { incoming in
             incoming.merging(attributes) { a, b in
                 b
             }
         }
     }
-
-
-}
-
-internal class SimpleAttributeProcessor : AttributeProcessor {
-
-    let attributeProcessor : ([String: AttributeValue]) -> [String:AttributeValue]
-
-    init(attributeProcessor : @escaping ([String: AttributeValue]) -> [String: AttributeValue]) {
-        self.attributeProcessor = attributeProcessor
-
-    }
-
-    override func process(incoming: [String : OpenTelemetryApi.AttributeValue]) -> [String : OpenTelemetryApi.AttributeValue] {
-        return attributeProcessor(incoming)
-    }
-
-
 }
 
 
 public class JoinedAttributeProcessor : AttributeProcessor {
 
-    override public func process(incoming: [String : OpenTelemetryApi.AttributeValue]) -> [String : OpenTelemetryApi.AttributeValue] {
+    public func process(incoming: [String : AttributeValue]) -> [String : AttributeValue] {
         var result = incoming
         for processor in processors {
             result = processor.process(incoming: result)
         }
         return result
     }
 
-    override public func then(other: AttributeProcessor) -> AttributeProcessor {
+    public func append(processor: AttributeProcessor) -> JoinedAttributeProcessor {
         var newList = processors
-        if let otherJoined = other as? JoinedAttributeProcessor {
-            newList.append(contentsOf: otherJoined.processors)
+        if let joinedProcessor = processor as? JoinedAttributeProcessor {
+            newList.append(contentsOf: joinedProcessor.processors)
         } else {
-            newList.append(other)
+            newList.append(processor)
         }
         return JoinedAttributeProcessor(newList)
     }
 
-    public func prepend(processor: AttributeProcessor) -> AttributeProcessor {
+    public func prepend(processor: AttributeProcessor) -> JoinedAttributeProcessor {
         var newProcessors = [processor]
         newProcessors.append(contentsOf: processors)
         return JoinedAttributeProcessor(newProcessors)
@@ -101,8 +94,8 @@ public class JoinedAttributeProcessor : AttributeProcessor {
 
 public class NoopAttributeProcessor : AttributeProcessor {
     static let noop = NoopAttributeProcessor()
-    private override init() {}
-    override public func process(incoming: [String : AttributeValue]) -> [String : AttributeValue] {
+    private init() {}
+    public func process(incoming: [String : AttributeValue]) -> [String : AttributeValue] {
         return incoming
     }
 }

Sources/OpenTelemetrySdk/Metrics/Stable/View/ViewBuilder.swift

@@ -30,8 +30,13 @@ public class ViewBuilder {
         return self
     }
 
+    public func withAttributeProcessor(processor: AttributeProcessor) -> Self {
+        self.processor = processor
+        return self
+    }
+
     public func addAttributeFilter(keyFilter: @escaping (String) -> Bool) -> Self {
-        addAttributeProcessor(processor: AttributeProcessor.filterByKeyName(nameFilter: keyFilter))
+        addAttributeProcessor(processor: SimpleAttributeProcessor.filterByKeyName(nameFilter: keyFilter))
     }
 
     public func addAttributeProcessor(processor: AttributeProcessor) -> Self {

Tests/OpenTelemetrySdkTests/Metrics/StableMetrics/AttributeProcessorTests.swift

@@ -0,0 +1,44 @@
+//
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+// 
+
+import Foundation
+
+import OpenTelemetryApi
+@testable import OpenTelemetrySdk
+import XCTest
+
+class AttributeProcessorTests : XCTestCase {
+    func testStaticNoop() {
+        XCTAssertNotNil(NoopAttributeProcessor.noop)
+        XCTAssertEqual(NoopAttributeProcessor.noop.process(incoming: ["hello": AttributeValue.string("world")]), ["hello" : AttributeValue.string("world")])
+    }
+
+    func testSimpleProcessor() {
+        let incoming = ["hello": AttributeValue("world")]
+
+        var processor: AttributeProcessor = SimpleAttributeProcessor.append(attributes: ["foo" : .string("bar")])
+        XCTAssertEqual(processor.process(incoming: incoming), ["hello" : .string("world"), "foo": .string("bar")])
+
+        processor = processor.then(other: SimpleAttributeProcessor.filterByKeyName(nameFilter: { $0 == "foo" }))
+        XCTAssertEqual(processor.process(incoming: incoming), ["foo": .string("bar")])
+    }
+
+    func testJoinedProcessor() {
+        let incoming = ["hello": AttributeValue("world")]
+
+        let processor0 = SimpleAttributeProcessor.append(attributes: ["foo" : .string("bar0")])
+        let processor1 = SimpleAttributeProcessor.append(attributes: ["foo" : .string("bar1")])
+        let processor2 = SimpleAttributeProcessor.append(attributes: ["foo" : .string("bar2")])
+
+        var processor = JoinedAttributeProcessor([processor0])
+        XCTAssertEqual(processor.process(incoming: incoming), ["hello" : .string("world"), "foo": .string("bar0")])
+
+        processor = processor.prepend(processor: processor1)
+        XCTAssertEqual(processor.process(incoming: incoming), ["hello" : .string("world"), "foo": .string("bar0")])
+
+        processor = processor.append(processor: processor2)
+        XCTAssertEqual(processor.process(incoming: incoming), ["hello" : .string("world"), "foo": .string("bar2")])
+    }
+}