fix string termination with 0

Author: ktoso

Sources/MetricsTestUtils/TestMetrics.swift

@@ -143,6 +143,7 @@ extension TestMetrics.FullKey: Hashable {
 
 extension TestMetrics {
     // ==== ------------------------------------------------------------------------------------------------------------
+
     // MARK: Counter
 
     /// Assert that the passed in `metric` is a ``TestCounter`` and return it for further executing assertions.
@@ -174,12 +175,14 @@ extension TestMetrics {
     }
 
     // ==== ------------------------------------------------------------------------------------------------------------
+
     // MARK: Gauge
 
     /// Assert that the passed in `metric` is a ``TestRecorder`` and return it for further executing assertions.
     public func expectGauge(_ metric: Gauge) throws -> TestRecorder {
         return try self.expectRecorder(metric)
     }
+
     /// Locate a ``TestRecorder`` created by the ``TestMetrics`` factory identified by the passed in ``label`` and ``dimensions``, and return it for further executing assertions.
     ///
     /// - Parameters:
@@ -192,6 +195,7 @@ extension TestMetrics {
     }
 
     // ==== ------------------------------------------------------------------------------------------------------------
+
     // MARK: Recorder
 
     /// Assert that the passed in `metric` is a ``TestRecorder`` and return it for further executing assertions.
@@ -223,6 +227,7 @@ extension TestMetrics {
     }
 
     // ==== ------------------------------------------------------------------------------------------------------------
+
     // MARK: Timer
 
     /// Assert that the passed in `metric` is a ``TestTimer`` and return it for further executing assertions.

Sources/SystemMetrics/SystemMetrics.swift

@@ -188,7 +188,9 @@ public enum SystemMetrics {
 
     #if os(Linux)
     internal static func linuxSystemMetrics() -> SystemMetrics.Data? {
-        class CFile {
+        /// Minimal file reading implementation so we don't have to depend on Foundation.
+        /// Designed only for the narrow use case of this library, reading `/proc/self/stat`.
+        final class CFile {
             let path: String
 
             private var file: UnsafeMutablePointer<FILE>?
@@ -221,7 +223,7 @@ public enum SystemMetrics {
                     return nil
                 }
                 #if compiler(>=5.1)
-                let buff: [CChar] = Array(unsafeUninitializedCapacity: 1024) { ptr, size in
+                var buff: [CChar] = Array(unsafeUninitializedCapacity: 1024) { ptr, size in
                     guard fgets(ptr.baseAddress, Int32(ptr.count), f) != nil else {
                         if feof(f) != 0 {
                             size = 0
@@ -230,9 +232,10 @@ public enum SystemMetrics {
                             preconditionFailure("Error reading line")
                         }
                     }
-                    size = strlen(ptr.baseAddress!)
+                    size = strlen(ptr.baseAddress!) + 1 // the string + NULL to terminate it
                 }
                 if buff.isEmpty { return nil }
+                buff[buff.index(before: buff.endIndex)] = 0 // ensure the string is null-terminated
                 return String(cString: buff)
                 #else
                 var buff = [CChar](repeating: 0, count: 1024)