Improve error handling around various Win32 APIs

Audited the codebase for suspicious calls and improved the error handling.

Author: jakepetroules

Sources/SWBUtil/Library.swift

@@ -64,15 +64,18 @@ public enum Library: Sendable {
     }
 
     public static func locate<T>(_ pointer: T.Type) -> Path {
-        let outPointer: UnsafeMutablePointer<CInterop.PlatformChar>
         #if os(Windows)
         var handle: HMODULE?
-        GetModuleHandleExW(DWORD(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS | GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT), unsafeBitCast(pointer, to: LPCWSTR?.self), &handle)
-        let capacity = 260
-        outPointer = .allocate(capacity: capacity)
-        defer { outPointer.deallocate() }
-        GetModuleFileNameW(handle, outPointer, DWORD(capacity))
+        guard GetModuleHandleExW(DWORD(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS | GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT), unsafeBitCast(pointer, to: LPCWSTR?.self), &handle) else {
+            return Path("")
+        }
+        do {
+            return try Path(SWB_GetModuleFileNameW(handle))
+        } catch {
+            return Path("")
+        }
         #else
+        let outPointer: UnsafeMutablePointer<CInterop.PlatformChar>
         var info = Dl_info()
         #if os(Android)
         dladdr(unsafeBitCast(pointer, to: UnsafeMutableRawPointer.self), &info)
@@ -81,8 +84,8 @@ public enum Library: Sendable {
         dladdr(unsafeBitCast(pointer, to: UnsafeMutableRawPointer?.self), &info)
         outPointer = UnsafeMutablePointer(mutating: info.dli_fname)
         #endif
-        #endif
         return Path(platformString: outPointer)
+        #endif
     }
 }
 
@@ -114,3 +117,32 @@ public struct LibraryHandle: @unchecked Sendable {
         self.rawValue = rawValue
     }
 }
+
+#if os(Windows)
+@_spi(Testing) public func SWB_GetModuleFileNameW(_ hModule: HMODULE?) throws -> String {
+#if DEBUG
+    var bufferCount = Int(1) // force looping
+#else
+    var bufferCount = Int(MAX_PATH)
+#endif
+    while true {
+        if let result = try withUnsafeTemporaryAllocation(of: WCHAR.self, capacity: bufferCount, { buffer in
+            switch (GetModuleFileNameW(hModule, buffer.baseAddress!, DWORD(buffer.count)), GetLastError()) {
+            case (1..<DWORD(bufferCount), DWORD(ERROR_SUCCESS)):
+                guard let result = String.decodeCString(buffer.baseAddress!, as: UTF16.self)?.result else {
+                    throw Win32Error(DWORD(ERROR_ILLEGAL_CHARACTER))
+                }
+                return result
+            case (DWORD(bufferCount), DWORD(ERROR_INSUFFICIENT_BUFFER)):
+                bufferCount += Int(MAX_PATH)
+                return nil
+            case (_, let errorCode):
+                throw Win32Error(errorCode)
+            }
+        }) {
+            return result
+        }
+    }
+    preconditionFailure("unreachable")
+}
+#endif

Sources/SWBUtil/POSIX.swift

@@ -35,7 +35,7 @@ public enum POSIX: Sendable {
             }
             return try withUnsafeTemporaryAllocation(of: WCHAR.self, capacity: Int(dwLength)) {
                 switch GetEnvironmentVariableW(wName, $0.baseAddress!, DWORD($0.count)) {
-                case dwLength - 1:
+                case 1..<dwLength:
                     return String(decodingCString: $0.baseAddress!, as: CInterop.PlatformUnicodeEncoding.self)
                 case 0 where GetLastError() == ERROR_ENVVAR_NOT_FOUND:
                     return nil

Sources/SWBUtil/ProcessInfo.swift

@@ -62,8 +62,10 @@ extension ProcessInfo {
         var capacity = UNLEN + 1
         let pointer = UnsafeMutablePointer<CInterop.PlatformChar>.allocate(capacity: Int(capacity))
         defer { pointer.deallocate() }
-        GetUserNameW(pointer, &capacity)
-        return String(platformString: pointer)
+        if GetUserNameW(pointer, &capacity) {
+            return String(platformString: pointer)
+        }
+        return ""
         #else
         let uid = geteuid().orIfZero(getuid())
         return (getpwuid(uid)?.pointee.pw_name).map { String(cString: $0) } ?? String(uid)

Tests/SwiftBuildTests/ConsoleCommands/CLIConnection.swift

@@ -12,7 +12,7 @@
 
 import Foundation
 import SWBTestSupport
-import SWBUtil
+@_spi(Testing) import SWBUtil
 import SWBCore
 import SWBLibc
 import SwiftBuild
@@ -319,25 +319,7 @@ fileprivate func swiftRuntimePath() throws -> Path? {
         guard let handle = GetModuleHandleW(wName) else {
             throw Win32Error(GetLastError())
         }
-
-        var capacity = MAX_PATH
-        var path = ""
-        while path.isEmpty {
-            try withUnsafeTemporaryAllocation(of: WCHAR.self, capacity: Int(capacity)) {
-                let dwLength = GetModuleFileNameW(handle, $0.baseAddress!, DWORD($0.count))
-                switch dwLength {
-                case 0:
-                    throw Win32Error(GetLastError())
-                default:
-                    if GetLastError() == ERROR_INSUFFICIENT_BUFFER {
-                        capacity *= 2
-                    } else {
-                        path = String(decodingCString: $0.baseAddress!, as: CInterop.PlatformUnicodeEncoding.self)
-                    }
-                }
-            }
-        }
-        return Path(path).dirname
+        return try Path(SWB_GetModuleFileNameW(handle)).dirname
     }
     #else
     return nil
@@ -352,10 +334,12 @@ fileprivate func systemRoot() throws -> Path? {
     }
     return try withUnsafeTemporaryAllocation(of: WCHAR.self, capacity: Int(dwLength)) {
         switch GetWindowsDirectoryW($0.baseAddress!, DWORD($0.count)) {
+        case 1..<dwLength:
+            return Path(String(decodingCString: $0.baseAddress!, as: CInterop.PlatformUnicodeEncoding.self))
         case 0:
             throw Win32Error(GetLastError())
         default:
-            return Path(String(decodingCString: $0.baseAddress!, as: CInterop.PlatformUnicodeEncoding.self))
+            throw Win32Error(DWORD(ERROR_INSUFFICIENT_BUFFER))
         }
     }
     #else