Added types for recording and storing performance metrics. (#567)

* Added types for recording and storing performance metrics.

This adds SNTMetricSet and various gauge and counter types to allow for
exporting metrics such as CPU,Memory usage and other properties that are useful
for tracking reliability and debugging.

This is the first commit of a series to add support for monitoring systems.

Co-authored-by: Kent Ma <tnek@google.com>

Source/common/BUILD

@@ -188,6 +188,12 @@ objc_library(
     ],
 )
 
+objc_library(
+    name = "SNTMetricSet",
+    srcs = ["SNTMetricSet.m"],
+    hdrs = ["SNTMetricSet.h"],
+)
+
 objc_library(
     name = "SNTXPCSyncdInterface",
     srcs = ["SNTXPCSyncdInterface.m"],
@@ -241,5 +247,11 @@ santa_unit_test(
 santa_unit_test(
     name = "SNTPrefixTreeTest",
     srcs = ["SNTPrefixTreeTest.mm"],
-    deps = ["SNTPrefixTree"],
+    deps = [":SNTPrefixTree"],
+)
+
+santa_unit_test(
+    name = "SNTMetricSetTest",
+    srcs = ["SNTMetricSetTest.m"],
+    deps = [":SNTMetricSet"],
 )

Source/common/SNTMetricSet.h

@@ -0,0 +1,173 @@
+/// Copyright 2021 Google Inc. All rights reserved.
+///
+/// Licensed under the Apache License, Version 2.0 (the "License");
+/// you may not use this file except in compliance with the License.
+/// You may obtain a copy of the License at
+///
+///    http://www.apache.org/licenses/LICENSE-2.0
+///
+///    Unless required by applicable law or agreed to in writing, software
+///    distributed under the License is distributed on an "AS IS" BASIS,
+///    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+///    See the License for the specific language governing permissions and
+///    limitations under the License.
+
+#import <Foundation/Foundation.h>
+
+/**
+ * Provides an abstraction for various metric systems that will be exported to
+ * monitoring systems via the MetricService. This is used to store internal
+ * counters and metrics that can be exported to an external monitoring system.
+ *
+ * `SNTMetricSet` for storing and creating metrics and counters. This is
+ *   the externally visible interface
+ *   class.
+ *
+ *  Metric classes:
+ *   * `SNTMetric` to store metric values broken down by "field" dimensions.
+ *   * subclasses of `SNTMetric` with suitable setters:
+ *     * `SNTMetricCounter`
+ *     * `SNTMetricGaugeInt64`
+ *     * `SNTMetricGaugeDouble`
+ *     * `SNTMetricString`
+ *     * `SNTMetricBool`
+ */
+
+NS_ASSUME_NONNULL_BEGIN
+
+typedef NS_ENUM(NSInteger, SNTMetricType) {
+  SNTMetricTypeUnknown = 0,
+  SNTMetricTypeConstantBool = 1,
+  SNTMetricTypeConstantString = 2,
+  SNTMetricTypeConstantInt64 = 3,
+  SNTMetricTypeConstantDouble = 4,
+  SNTMetricTypeGaugeBool = 5,
+  SNTMetricTypeGaugeString = 6,
+  SNTMetricTypeGaugeInt64 = 7,
+  SNTMetricTypeGaugeDouble = 8,
+  SNTMetricTypeCounter = 9,
+};
+
+@interface SNTMetric : NSObject
+- (NSDictionary *)export;
+@end
+
+@interface SNTMetricCounter : SNTMetric
+- (void)incrementBy:(long long)step forFieldValues:(NSArray<NSString *> *)fieldValues;
+- (void)incrementForFieldValues:(NSArray<NSString *> *)fieldValues;
+- (long long)getCountForFieldValues:(NSArray<NSString *> *)fieldValues;
+@end
+
+@interface SNTMetricInt64Gauge : SNTMetric
+- (void)set:(long long)value forFieldValues:(NSArray<NSString *> *)fieldValues;
+- (long long)getGaugeValueForFieldValues:(NSArray<NSString *> *)fieldValues;
+@end
+
+@interface SNTMetricDoubleGauge : SNTMetric
+- (void)set:(double)value forFieldValues:(NSArray<NSString *> *)fieldValues;
+- (double)getGaugeValueForFieldValues:(NSArray<NSString *> *)fieldValues;
+@end
+
+@interface SNTMetricStringGauge : SNTMetric
+- (void)set:(NSString *)value forFieldValues:(NSArray<NSString *> *)fieldValues;
+- (NSString *)getStringValueForFieldValues:(NSArray<NSString *> *)fieldValues;
+@end
+
+@interface SNTMetricBooleanGauge : SNTMetric
+- (void)set:(BOOL)value forFieldValues:(NSArray<NSString *> *)fieldValues;
+- (BOOL)getBoolValueForFieldValues:(NSArray<NSString *> *)fieldValues;
+@end
+
+/**
+ * A registry of metrics with associated fields.
+ */
+@interface SNTMetricSet : NSObject
+- (instancetype)initWithHostname:(NSString *)hostname username:(NSString *)username;
+
+/* Returns a counter with the given name, field names and help
+ *  text, registered with the MetricSet.
+ *
+ * @param name The counter name, for example @"/proc/cpu".
+ * @param fieldNames The counter's field names, for example @[@"result"].
+ * @param helpText The counter's help description.
+ * @return A counter with the given specification registered with this root.
+ *   The returned counter might have been created earlier with the same
+ *   specification.
+ * @throw NSInternalInconsistencyException When trying to register a second
+ *   counter with the same name but a different schema as an existing one
+ */
+- (SNTMetricCounter *)counterWithName:(NSString *)name
+                           fieldNames:(NSArray<NSString *> *)fieldNames
+                             helpText:(NSString *)text;
+
+- (void)addRootLabel:(NSString *)label value:(NSString *)value;
+
+/**
+ * Returns a int64 gauge metric with the given Streamz name and help text,
+ * registered with this MetricSet.
+ *
+ * @param name The metric name, for example @"/memory/free".
+ * @param fieldNames The metric's field names, for example @[@"type"].
+ * @param helpText The metric's help description.
+ */
+- (SNTMetricInt64Gauge *)int64GaugeWithName:(NSString *)name
+                                 fieldNames:(NSArray<NSString *> *)fieldNames
+                                   helpText:(NSString *)helpText;
+
+/**
+ * Returns a double gauge metric with the given name and help text,
+ * registered with this root.
+ *
+ * @param name The metric name, for example @"/memory/free".
+ * @param fieldNames The metric's field names, for example @[@"type"].
+ * @param helpText The metric's help description.
+ */
+- (SNTMetricDoubleGauge *)doubleGaugeWithName:(NSString *)name
+                                   fieldNames:(NSArray<NSString *> *)fieldNames
+                                     helpText:(NSString *)helpText;
+
+/**
+ * Returns a string gauge metric with the given name and help text,
+ * registered with this metric set.
+ *
+ * @param name The metric name, for example @"/santa/mode".
+ * @param fieldNames The metric's field names, for example @[@"type"].
+ * @param helpText The metric's help description.
+ */
+- (SNTMetricStringGauge *)stringGaugeWithName:(NSString *)name
+                                   fieldNames:(NSArray<NSString *> *)fieldNames
+                                     helpText:(NSString *)helpText;
+
+/**
+ * Returns a boolean gauge metric with the given name and help text,
+ * registered with this metric set.
+ *
+ * @param name The metric name, for example @"/memory/free".
+ * @param fieldNames The metric's field names, for example @[@"type"].
+ * @param helpText The metric's help description.
+ */
+- (SNTMetricBooleanGauge *)booleanGaugeWithName:(NSString *)name
+                                     fieldNames:(NSArray<NSString *> *)fieldNames
+                                       helpText:(NSString *)helpText;
+
+/** Creates a constant metric with a string value and no fields. */
+- (void)addConstantStringWithName:(NSString *)name
+                         helpText:(NSString *)helpText
+                            value:(NSString *)value;
+
+/** Creates a constant metric with an integer value and no fields. */
+- (void)addConstantIntegerWithName:(NSString *)name
+                          helpText:(NSString *)helpText
+                             value:(long long)value;
+
+/** Creates a constant metric with an integer value and no fields. */
+- (void)addConstantBooleanWithName:(NSString *)name helpText:(NSString *)helpText value:(BOOL)value;
+
+/** Register a callback to get executed just before each export. */
+- (void)registerCallback:(void (^)(void))callback;
+
+/** Export creates an NSDictionary of the state of the metrics */
+- (NSDictionary *)export;
+@end
+
+NS_ASSUME_NONNULL_END