hexdump: Replace Core::File with Core::Stream::File

Previously, hexdump used Core::File to read input into a fixed buffer.
This PR rewrites the file handling to use the more modern
Core::Stream::File, which reads data into spans. By using spans, we
can also simplify the rest of the code, which previously used memcpy
for array manipulation and relied on manual bookkeeping to keep track of
offsets.

Userland/Utilities/hexdump.cpp

@@ -1,12 +1,13 @@
 /*
  * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, Eli Youngs <eli.m.youngs@gmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
 #include <AK/Array.h>
 #include <LibCore/ArgsParser.h>
-#include <LibCore/File.h>
+#include <LibCore/Stream.h>
 #include <LibCore/System.h>
 #include <LibMain/Main.h>
 #include <ctype.h>
@@ -25,7 +26,7 @@ ErrorOr<int> serenity_main(Main::Arguments args)
     TRY(Core::System::pledge("stdio rpath"));
 
     Core::ArgsParser args_parser;
-    char const* path = nullptr;
+    StringView path;
     bool verbose = false;
     Optional<size_t> max_bytes;
 
@@ -35,18 +36,13 @@ ErrorOr<int> serenity_main(Main::Arguments args)
 
     args_parser.parse(args);
 
-    RefPtr<Core::File> file;
+    auto file = TRY(Core::Stream::File::open_file_or_standard_stream(path, Core::Stream::OpenMode::Read));
 
-    if (!path)
-        file = Core::File::standard_input();
-    else
-        file = TRY(Core::File::open(path, Core::OpenMode::ReadOnly));
-
-    auto print_line = [](u8* buf, size_t size) {
-        VERIFY(size <= LINE_LENGTH_BYTES);
+    auto print_line = [](Bytes line) {
+        VERIFY(line.size() <= LINE_LENGTH_BYTES);
         for (size_t i = 0; i < LINE_LENGTH_BYTES; ++i) {
-            if (i < size)
-                out("{:02x} ", buf[i]);
+            if (i < line.size())
+                out("{:02x} ", line[i]);
             else
                 out("   ");
 
@@ -56,9 +52,9 @@ ErrorOr<int> serenity_main(Main::Arguments args)
 
         out("  |");
 
-        for (size_t i = 0; i < size; ++i) {
-            if (isprint(buf[i]))
-                putchar(buf[i]);
+        for (auto const& byte : line) {
+            if (isprint(byte))
+                putchar(byte);
             else
                 putchar('.');
         }
@@ -68,42 +64,42 @@ ErrorOr<int> serenity_main(Main::Arguments args)
     };
 
     Array<u8, BUFSIZ> contents;
-    Span<u8> previous_line;
+    Bytes bytes;
+    Bytes previous_line;
     static_assert(LINE_LENGTH_BYTES * 2 <= contents.size(), "Buffer is too small?!");
-    size_t bytes_in_buffer = 0;
     size_t total_bytes_read = 0;
-    size_t bytes_remaining = 0;
-    size_t bytes_to_read = 0;
 
-    int nread;
     auto state = State::Print;
     bool is_input_remaining = true;
     while (is_input_remaining) {
-        bytes_to_read = BUFSIZ - bytes_in_buffer;
+        auto bytes_to_read = contents.size() - bytes.size();
 
         if (max_bytes.has_value()) {
-            bytes_remaining = max_bytes.value() - total_bytes_read;
+            auto bytes_remaining = max_bytes.value() - total_bytes_read;
             if (bytes_remaining < bytes_to_read) {
                 bytes_to_read = bytes_remaining;
                 is_input_remaining = false;
             }
         }
 
-        nread = file->read(&contents[bytes_in_buffer], (int)bytes_to_read);
-        if (nread <= 0)
-            break;
+        bytes = contents.span().slice(0, bytes_to_read);
+        bytes = TRY(file->read(bytes));
+
+        total_bytes_read += bytes.size();
+
+        if (bytes.size() < bytes_to_read) {
+            is_input_remaining = false;
+        }
 
-        total_bytes_read += nread;
-        bytes_in_buffer += nread;
+        while (bytes.size() > LINE_LENGTH_BYTES) {
+            auto current_line = bytes.slice(0, LINE_LENGTH_BYTES);
+            bytes = bytes.slice(LINE_LENGTH_BYTES);
 
-        size_t offset;
-        for (offset = 0; offset + LINE_LENGTH_BYTES - 1 < bytes_in_buffer; offset += LINE_LENGTH_BYTES) {
             if (verbose) {
-                print_line(&contents[offset], LINE_LENGTH_BYTES);
+                print_line(current_line);
                 continue;
             }
 
-            auto current_line = contents.span().slice(offset, LINE_LENGTH_BYTES);
             bool is_same_contents = (current_line == previous_line);
             if (!is_same_contents)
                 state = State::Print;
@@ -113,7 +109,7 @@ ErrorOr<int> serenity_main(Main::Arguments args)
             // Coalesce repeating lines
             switch (state) {
             case State::Print:
-                print_line(&contents[offset], LINE_LENGTH_BYTES);
+                print_line(current_line);
                 break;
             case State::PrintFiller:
                 outln("*");
@@ -124,18 +120,10 @@ ErrorOr<int> serenity_main(Main::Arguments args)
             }
             previous_line = current_line;
         }
-
-        bytes_in_buffer -= offset;
-        VERIFY(bytes_in_buffer < LINE_LENGTH_BYTES);
-        // If we managed to make the buffer exactly full, &contents[BUFSIZ] would blow up.
-        if (bytes_in_buffer > 0) {
-            // Regions cannot overlap due to above static_assert.
-            memcpy(&contents[0], &contents[offset], bytes_in_buffer);
-        }
     }
-    VERIFY(bytes_in_buffer <= LINE_LENGTH_BYTES - 1);
-    if (bytes_in_buffer > 0)
-        print_line(&contents[0], bytes_in_buffer);
+
+    if (bytes.size() > 0)
+        print_line(bytes);
 
     return 0;
 }