consistent use of /proc

Author: andrurogerz

tools/swift-inspect/Sources/SwiftInspectLinux/AuxVec.swift

@@ -16,11 +16,7 @@ import LinuxSystemHeaders
 internal class AuxVec {
   // loads the auxiliary vector for a process
   public static func load(for process: Process) -> [Int32 : UInt64]? {
-    let filePath = "/proc/\(process.pid)/auxv"
-    guard let fileHandle = FileHandle(forReadingAtPath: filePath) else { return nil }
-    defer { fileHandle.closeFile() }
-
-    guard let data = try? fileHandle.readToEnd(), data.count > 0 else { return nil }
+    guard let data = ProcFS.loadFile(for: process.pid, "auxv") else { return nil }
 
     func fromData<T: UnsignedInteger>(_ data: Data) -> [(T, T)] {
       return data.withUnsafeBytes {

tools/swift-inspect/Sources/SwiftInspectLinux/MemoryMap.swift

@@ -14,7 +14,7 @@ import Foundation
 
 public class MemoryMap {
   public enum Error: Swift.Error {
-    case InvalidProcMapsFile(_ filePath: String)
+    case InvalidProcMapsFile
   }
 
   public struct Entry {
@@ -30,12 +30,8 @@ public class MemoryMap {
   public let entries: [Entry]
 
   public init(for pid: pid_t) throws {
-    let filePath = "/proc/\(pid)/maps"
-    let file = try FileHandle(forReadingFrom: URL(fileURLWithPath: filePath))
-    defer { file.closeFile() }
-
-    guard let content = String(data: file.readDataToEndOfFile(), encoding: .ascii) else {
-      throw Error.InvalidProcMapsFile(filePath)
+    guard let content = ProcFS.loadFileAsString(for: pid, "maps") else {
+      throw Error.InvalidProcMapsFile
     }
 
     var entries: [Entry] = []

tools/swift-inspect/Sources/SwiftInspectLinux/ProcFS.swift

@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import LinuxSystemHeaders
+
+public class ProcFS {
+  public static func loadFile(for pid: pid_t, _ fileName: String) -> Data? {
+    let filePath = "/proc/\(pid)/\(fileName)"
+    // Loading contents of files under /proc may not work correctly using
+    // Data(contentsOf:) or String(contentsOfFile:) because the files may
+    // appear empty from stat(2) and may not be seekable. FileHandle.readToEnd
+    // handles these cases.
+    guard let fileHandle = FileHandle(forReadingAtPath: filePath) else { return nil }
+    defer { fileHandle.closeFile() }
+    guard let data = try? fileHandle.readToEnd() else { return nil }
+    return data
+  }
+
+  public static func loadFileAsString(
+    for pid: pid_t, _ fileName: String, encoding: String.Encoding = .utf8
+  ) -> String? {
+    guard let data = Self.loadFile(for: pid, fileName) else { return nil }
+    return String(data: data, encoding: encoding)
+  }
+}

tools/swift-inspect/Sources/swift-inspect/LinuxRemoteProcess.swift

@@ -102,9 +102,12 @@
 
     init?(processId: ProcessIdentifier) {
       self.processIdentifier = processId
+
+      if let processName = SwiftInspectLinux.ProcFS.loadFileAsString(for: processId, "cmdline") {
+        self.processName = processName
+      }
+
       do {
-        let path = "/proc/\(processId)/cmdline"
-        self.processName = try String(contentsOfFile: path, encoding: .ascii)
         self.process = try SwiftInspectLinux.Process(processId)
         self.symbolCache = try SwiftInspectLinux.SymbolCache(for: process)
         self.memoryMap = try SwiftInspectLinux.MemoryMap(for: processId)