1 files changed, 153 insertions, 0 deletions
diff --git a/src/rgw/rgw_tar.h b/src/rgw/rgw_tar.h
new file mode 100644
index 000000000..b06943a3c
--- /dev/null
+++ b/src/rgw/rgw_tar.h
@@ -0,0 +1,153 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab ft=cpp
+
+#pragma once
+
+#include <algorithm>
+#include <array>
+#include <cstring>
+#include <string_view>
+#include <tuple>
+#include <utility>
+
+#include <boost/optional.hpp>
+#include <boost/range/adaptor/reversed.hpp>
+
+namespace rgw {
+namespace tar {
+
+static constexpr size_t BLOCK_SIZE = 512;
+
+
+static inline std::pair<class StatusIndicator,
+                        boost::optional<class HeaderView>>
+interpret_block(const StatusIndicator& status, ceph::bufferlist& bl);
+
+
+class StatusIndicator {
+  friend std::pair<class StatusIndicator,
+                   boost::optional<class HeaderView>>
+  interpret_block(const StatusIndicator& status, ceph::bufferlist& bl);
+
+  bool is_empty;
+  bool is_eof;
+
+  StatusIndicator()
+    : is_empty(false),
+      is_eof(false) {
+  }
+
+  StatusIndicator(const StatusIndicator& prev_status,
+                  const bool is_empty)
+  : is_empty(is_empty),
+    is_eof(is_empty && prev_status.empty()) {
+  }
+
+public:
+  bool empty() const {
+    return is_empty;
+  }
+
+  bool eof() const {
+    return is_eof;
+  }
+
+  static StatusIndicator create() {
+    return StatusIndicator();
+  }
+} /* class StatusIndicator */;
+
+
+enum class FileType : char {
+  UNKNOWN = '\0',
+
+  /* The tar format uses ASCII encoding. */
+  NORMAL_FILE = '0',
+  DIRECTORY = '5'
+}; /* enum class FileType */
+
+class HeaderView {
+protected:
+  /* Everything is char here (ASCII encoding), so we don't need to worry about
+   * the struct padding. */
+  const struct header_t {
+    char filename[100];
+    char __filemode[8];
+    char __owner_id[8];
+    char __group_id[8];
+    char filesize[12];
+    char lastmod[12];
+    char checksum[8];
+    char filetype;
+    char __padding[355];
+  } *header;
+
+  static_assert(sizeof(*header) == BLOCK_SIZE,
+                "The TAR header must be exactly BLOCK_SIZE length");
+
+  /* The label is far more important from what the code really does. */
+  static size_t pos2len(const size_t pos) {
+    return pos + 1;
+  }
+
+public:
+  explicit HeaderView(const char (&header)[BLOCK_SIZE])
+    : header(reinterpret_cast<const header_t*>(header)) {
+  }
+
+  FileType get_filetype() const {
+    switch (header->filetype) {
+      case static_cast<char>(FileType::NORMAL_FILE):
+        return FileType::NORMAL_FILE;
+      case static_cast<char>(FileType::DIRECTORY):
+        return FileType::DIRECTORY;
+      default:
+        return FileType::UNKNOWN;
+    }
+  }
+
+  std::string_view get_filename() const {
+    return std::string_view(header->filename,
+                             std::min(sizeof(header->filename),
+                                      strlen(header->filename)));
+  }
+
+  size_t get_filesize() const {
+    /* The string_ref is pretty suitable here because tar encodes its
+     * metadata in ASCII. */
+    const std::string_view raw(header->filesize, sizeof(header->filesize));
+
+    /* We need to find where the padding ends. */
+    const auto pad_ends_at = std::min(raw.find_last_not_of('\0'),
+                                      raw.find_last_not_of(' '));
+    const auto trimmed = raw.substr(0,
+      pad_ends_at == std::string_view::npos ? std::string_view::npos
+                                             : pos2len(pad_ends_at));
+
+    size_t sum = 0, mul = 1;
+    for (const char c : boost::adaptors::reverse(trimmed)) {
+      sum += (c - '0') * mul;
+      mul *= 8;
+    }
+
+    return sum;
+  }
+}; /* class Header */
+
+
+static inline std::pair<StatusIndicator,
+                        boost::optional<HeaderView>>
+interpret_block(const StatusIndicator& status, ceph::bufferlist& bl) {
+  static constexpr std::array<char, BLOCK_SIZE> zero_block = {0, };
+  const char (&block)[BLOCK_SIZE] = \
+    reinterpret_cast<const char (&)[BLOCK_SIZE]>(*bl.c_str());
+
+  if (std::memcmp(zero_block.data(), block, BLOCK_SIZE) == 0) {
+    return std::make_pair(StatusIndicator(status, true), boost::none);
+  } else {
+    return std::make_pair(StatusIndicator(status, false), HeaderView(block));
+  }
+}
+
+} /* namespace tar */
+} /* namespace rgw */