Support/PathV2: Implement get_magic.

llvm-svn: 123544

include/llvm/Support/FileSystem.h

@@ -455,9 +455,11 @@ error_code has_magic(const Twine &path, const Twine &magic, bool &result);
 /// @param path Input path.
 /// @param len Number of magic bytes to get.
 /// @param result Set to the first \a len bytes in the file pointed to by
-///               \a path.
-/// @results errc::success if result has been successfully set, otherwise a
-///          platform specific error_code.
+///               \a path. Or the entire file if file_size(path) < len, in which
+///               case result.size() returns the size of the file.
+/// @results errc::success if result has been successfully set,
+///          errc::value_too_large if len is larger then the file pointed to by
+///          \a path, otherwise a platform specific error_code.
 error_code get_magic(const Twine &path, uint32_t len,
                      SmallVectorImpl<char> &result);
 

lib/Support/Unix/PathV2.inc

@@ -462,6 +462,37 @@ error_code directory_iterator_increment(directory_iterator& it) {
   return success;
 }
 
+error_code get_magic(const Twine &path, uint32_t len,
+                     SmallVectorImpl<char> &result) {
+  SmallString<128> PathStorage;
+  StringRef Path = path.toNullTerminatedStringRef(PathStorage);
+  result.set_size(0);
+
+  // Open path.
+  std::FILE *file = std::fopen(Path.data(), "rb");
+  if (file == 0)
+    return error_code(errno, system_category());
+
+  // Reserve storage.
+  result.reserve(len);
+
+  // Read magic!
+  size_t size = std::fread(result.data(), 1, len, file);
+  if (std::ferror(file) != 0) {
+    std::fclose(file);
+    return error_code(errno, system_category());
+  } else if (size != result.size()) {
+    if (std::feof(file) != 0) {
+      std::fclose(file);
+      result.set_size(size);
+      return make_error_code(errc::value_too_large);
+    }
+  }
+  std::fclose(file);
+  result.set_size(len);
+  return success;
+}
+
 } // end namespace fs
 } // end namespace sys
 } // end namespace llvm

lib/Support/Windows/PathV2.inc

@@ -616,6 +616,48 @@ retry_create_file:
   return success;
 }
 
+error_code get_magic(const Twine &path, uint32_t len,
+                     SmallVectorImpl<char> &result) {
+  SmallString<128> path_storage;
+  SmallVector<wchar_t, 128> path_utf16;
+  result.set_size(0);
+
+  // Convert path to UTF-16.
+  if (error_code ec = UTF8ToUTF16(path.toStringRef(path_storage),
+                                  path_utf16))
+    return ec;
+
+  // Open file.
+  HANDLE file = ::CreateFileW(c_str(path_utf16),
+                              GENERIC_READ,
+                              FILE_SHARE_READ,
+                              NULL,
+                              OPEN_EXISTING,
+                              FILE_ATTRIBUTE_READONLY,
+                              NULL);
+  if (file == INVALID_HANDLE_VALUE)
+    return windows_error(::GetLastError());
+
+  // Allocate buffer.
+  result.reserve(len);
+
+  // Get magic!
+  DWORD bytes_read = 0;
+  BOOL read_success = ::ReadFile(file, result.data(), len, &bytes_read, NULL);
+  error_code ec = windows_error(::GetLastError());
+  ::CloseHandle(file);
+  if (!read_success || (bytes_read != len)) {
+    // Set result size to the number of bytes read if it's valid.
+    if (bytes_read >= 0 && bytes_read <= len)
+      result.set_size(bytes_read);
+    // ERROR_HANDLE_EOF is mapped to errc::value_too_large.
+    return ec;
+  }
+
+  result.set_size(len);
+  return success;
+}
+
 error_code directory_iterator_construct(directory_iterator &it, StringRef path){
   SmallVector<wchar_t, 128> path_utf16;
 

lib/Support/Windows/system_error.inc

@@ -79,6 +79,7 @@ _system_error_category::default_error_condition(int ev) const {
   MAP_ERR_TO_COND(ERROR_FILE_EXISTS,         file_exists);
   MAP_ERR_TO_COND(ERROR_FILE_NOT_FOUND,      no_such_file_or_directory);
   MAP_ERR_TO_COND(ERROR_HANDLE_DISK_FULL,    no_space_on_device);
+  MAP_ERR_TO_COND(ERROR_HANDLE_EOF,          value_too_large);
   MAP_ERR_TO_COND(ERROR_INVALID_ACCESS,      permission_denied);
   MAP_ERR_TO_COND(ERROR_INVALID_DRIVE,       no_such_device);
   MAP_ERR_TO_COND(ERROR_INVALID_FUNCTION,    function_not_supported);