1 files changed, 232 insertions, 0 deletions
diff --git a/src/io.cc b/src/io.cc
new file mode 100644
index 0000000..99c0518
--- /dev/null
+++ b/src/io.cc
@@ -0,0 +1,232 @@
+#include "io.hh"
+
+#include "unique_fd.hh"
+
+#include <algorithm>
+#include <cerrno>
+#include <cstdio>
+#include <cstring>
+#include <expected>
+#include <fcntl.h>
+#include <limits>
+#include <memory>
+#include <optional>
+#include <string>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <utility>
+
+namespace io {
+
+namespace {
+
+class BasicReader : public Reader {
+ public:
+  explicit BasicReader(unique_fd fd) : fd_(std::move(fd)) {}
+
+  [[nodiscard]]
+  std::expected<size_t, ReadError> read(void* dst, size_t max) override {
+    ssize_t ret = ::read(
+        fd_.get(), dst,
+        std::min(static_cast<size_t>(std::numeric_limits<ssize_t>::max()),
+                 max));
+    if (ret < 0) {
+      switch (errno) {
+        case EINTR:
+          return read(dst, max);
+        default:
+          return std::unexpected(ReadError::Error);
+      }
+    } else if (ret == 0 && max > 0) {
+      return std::unexpected(ReadError::Eof);
+    }
+    offset_ += ret;
+    return ret;
+  }
+
+  [[nodiscard]]
+  std::expected<size_t, ReadError> skip(size_t max) override {
+    off_t ret;
+    if (sizeof(size_t) > sizeof(off_t)) {
+      ret = lseek(
+          fd_.get(),
+          // NOLINTNEXTLINE(bugprone-narrowing-conversions)
+          std::min(static_cast<size_t>(std::numeric_limits<off_t>::max()), max),
+          SEEK_CUR);
+    } else {
+      ret = lseek(fd_.get(), static_cast<off_t>(max), SEEK_CUR);
+    }
+    if (ret < 0) {
+      return std::unexpected(ReadError::Error);
+    }
+    // Don't want skip to go past (cached) file end.
+    if (!size_.has_value() || ret >= size_.value()) {
+      // When going past end, double check that it still is the end.
+      off_t ret2 = lseek(fd_.get(), 0, SEEK_END);
+      if (ret2 < 0) {
+        // We're screwed, but try to go back to original position and then
+        // return error.
+        size_.reset();
+        lseek(fd_.get(), offset_, SEEK_SET);
+        return std::unexpected(ReadError::Error);
+      }
+      size_ = ret2;
+      if (ret >= ret2) {
+        auto distance = ret2 - offset_;
+        offset_ = ret2;
+        if (distance == 0 && max > 0)
+          return std::unexpected(ReadError::Eof);
+        return distance;
+      }
+      // Seek back to where we should be
+      if (lseek(fd_.get(), ret, SEEK_SET) < 0) {
+        return std::unexpected(ReadError::Error);
+      }
+    }
+    auto distance = ret - offset_;
+    offset_ = ret;
+    return distance;
+  }
+
+ private:
+  unique_fd fd_;
+  off_t offset_{0};
+  std::optional<off_t> size_;
+};
+
+class MemoryReader : public Reader {
+ public:
+  MemoryReader(void* ptr, size_t size) : ptr_(ptr), size_(size) {}
+
+  [[nodiscard]]
+  std::expected<size_t, ReadError> read(void* dst, size_t max) override {
+    size_t avail = size_ - offset_;
+    if (avail == 0 && max > 0)
+      return std::unexpected(io::ReadError::Eof);
+    size_t ret = std::min(max, avail);
+    memcpy(dst, reinterpret_cast<char*>(ptr_) + offset_, ret);
+    offset_ += ret;
+    return ret;
+  }
+
+  [[nodiscard]]
+  std::expected<size_t, ReadError> skip(size_t max) override {
+    size_t avail = size_ - offset_;
+    size_t ret = std::min(max, avail);
+    offset_ += ret;
+    return ret;
+  }
+
+ protected:
+  void* ptr_;
+  size_t const size_;
+
+ private:
+  size_t offset_{0};
+};
+
+class MmapReader : public MemoryReader {
+ public:
+  MmapReader(unique_fd fd, void* ptr, size_t size)
+      : MemoryReader(ptr, size), fd_(std::move(fd)) {}
+
+  ~MmapReader() override { munmap(ptr_, size_); }
+
+ private:
+  unique_fd fd_;
+};
+
+class StringReader : public MemoryReader {
+ public:
+  explicit StringReader(std::string data)
+      : MemoryReader(nullptr, data.size()), data_(std::move(data)) {
+    ptr_ = data_.data();
+  }
+
+ private:
+  std::string data_;
+};
+
+}  // namespace
+
+std::expected<size_t, ReadError> Reader::repeat_read(void* dst, size_t max) {
+  auto ret = read(dst, max);
+  if (!ret.has_value() || ret.value() == max)
+    return ret;
+
+  char* d = reinterpret_cast<char*>(dst);
+  size_t offset = ret.value();
+  while (true) {
+    ret = read(d + offset, max - offset);
+    if (!ret.has_value())
+      break;
+    offset += ret.value();
+    if (offset == max)
+      break;
+  }
+  return offset;
+}
+
+std::expected<size_t, ReadError> Reader::repeat_skip(size_t max) {
+  auto ret = skip(max);
+  if (!ret.has_value() || ret.value() == max)
+    return ret;
+
+  size_t offset = ret.value();
+  while (true) {
+    ret = skip(max - offset);
+    if (!ret.has_value())
+      break;
+    offset += ret.value();
+    if (offset == max)
+      break;
+  }
+  return offset;
+}
+
+std::expected<std::unique_ptr<Reader>, OpenError> open(
+    const std::string& file_path) {
+  return openat(AT_FDCWD, file_path);
+}
+
+std::expected<std::unique_ptr<Reader>, OpenError> openat(
+    int dirfd, const std::string& file_path) {
+  unique_fd fd(::openat(dirfd, file_path.c_str(), O_RDONLY));
+  if (fd) {
+    struct stat buf;
+    if (fstat(fd.get(), &buf) == 0) {
+      if (std::cmp_less_equal(buf.st_size,
+                              std::numeric_limits<size_t>::max())) {
+        auto size = static_cast<size_t>(buf.st_size);
+        void* ptr = mmap(nullptr, size, PROT_READ, MAP_PRIVATE, fd.get(), 0);
+        if (ptr != MAP_FAILED) {
+          return std::make_unique<MmapReader>(std::move(fd), ptr, size);
+        }
+      }
+    }
+    return std::make_unique<BasicReader>(std::move(fd));
+  }
+  OpenError err;
+  switch (errno) {
+    case EINTR:
+      return openat(dirfd, file_path);
+    case EACCES:
+      err = OpenError::NoAccess;
+      break;
+    case ENOENT:
+      err = OpenError::NoSuchFile;
+      break;
+    default:
+      err = OpenError::Error;
+      break;
+  }
+  return std::unexpected(err);
+}
+
+std::unique_ptr<Reader> memory(std::string data) {
+  return std::make_unique<StringReader>(std::move(data));
+}
+
+}  // namespace io