1 files changed, 106 insertions, 0 deletions
diff --git a/euler/source/stream.cpp b/euler/source/stream.cpp
new file mode 100644
index 0000000..faf2907
--- /dev/null
+++ b/euler/source/stream.cpp
@@ -0,0 +1,106 @@
+#include <euler/stream.hpp>
+#include <cstring>
+
+namespace euler {
+
+  file_stream::file_stream(
+    syscall::stream_handle handle, bool may_read,
+    uint64_t length, uint64_t position)
+  : handle(handle), may_read(may_read), buffer_loaded(false),
+    length(length), position(position) {}
+
+  syscall::stream_result file_stream::seek(
+    syscall::seek_from from, int64_t offset) {
+
+    int64_t new_position = offset +
+      (from == syscall::seek_from::beginning ? 0 :
+       from == syscall::seek_from::end ? length : position);
+
+    if (new_position < 0 || (uint64_t)new_position > length)
+      return syscall::stream_result::out_of_bounds;
+
+    position = new_position;
+    return syscall::stream_result::success;
+
+  }
+
+  std::pair<uint64_t, syscall::stream_result>
+    file_stream::read(uint64_t bytes, void *into) {
+
+    if (!may_read)
+      return {0, syscall::stream_result::not_readable};
+
+    uint64_t have_read = 0;
+    syscall::stream_result result = syscall::stream_result::success;
+
+    uint64_t end = position + bytes;
+
+    if (end > length) {
+      end = length;
+      result = syscall::stream_result::out_of_bounds;
+    }
+
+    uint64_t block_start = (position / 1024) * 1024;
+
+    while (position < end) {
+
+      uint64_t length_in_this_block =
+        std::min(end, block_start + 1024) - position;
+
+      if (buffer_loaded && buffer_start == block_start)
+        memcpy(into, buffer + position - block_start, length_in_this_block);
+
+      else if (length_in_this_block == 1024) {
+
+        syscall::stream_result seek_result =
+          syscall::seek_stream(
+            handle, syscall::seek_from::beginning, block_start);
+        if (seek_result != syscall::stream_result::success)
+          return {have_read, seek_result};
+
+        syscall::stream_result read_result =
+          syscall::read_from_stream(handle, 1024, into);
+        if (read_result != syscall::stream_result::success)
+          return {have_read, read_result};
+
+      }
+
+      else {
+
+        syscall::stream_result seek_result =
+          syscall::seek_stream(
+            handle, syscall::seek_from::beginning, block_start);
+        if (seek_result != syscall::stream_result::success)
+          return {have_read, seek_result};
+
+        uint64_t buffer_length = std::min(1024UL, length - block_start);
+
+        syscall::stream_result read_result =
+          syscall::read_from_stream(handle, buffer_length, buffer);
+        if (read_result != syscall::stream_result::success) {
+          buffer_loaded = false;
+          return {have_read, read_result};
+        }
+
+        buffer_loaded = true;
+        buffer_start = block_start;
+        memcpy(into, buffer + position - block_start, length_in_this_block);
+
+      }
+
+      into = (uint8_t *)into + length_in_this_block;
+      have_read += length_in_this_block;
+      position += length_in_this_block;
+      block_start += 1024;
+
+    }
+
+    return {have_read, result};
+
+  }
+
+  void file_stream::close() {
+    syscall::close_stream(handle);
+  }
+
+}