src/user/knob/file.c


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#include <pland/syscall.h>
#include <knob/format.h>
#include <knob/heap.h>
#include <knob/env.h>

struct file {
  _file_handle_t handle;
  uint32_t position;
  uint32_t length;
};

static const char *try_remove_prefix(const char *path, uint8_t *dn_out) {
  if ((path[0] != 's') || (path[1] != 'd'))
    return 0;

  const char *num_part = path + 2;
  for (uint32_t i = 0; num_part[i]; ++i)
    if (num_part[i] == ':') {

      uint32_t dn_large;
      if (!try_sntoi(num_part, i, &dn_large) || dn_large > 255)
        return 0;

      *dn_out = (uint8_t)dn_large;
      return num_part + i + 1;
    }

  return 0;
}

struct file *open_file(const char *path) {
  uint8_t dn;
  const char *path_part = try_remove_prefix(path, &dn);
  if (path_part)
    path = path_part;
  else
    dn = current_drive;

  _file_handle_t h = _open_file(dn, path);
  if (!h)
    return 0;

  struct file *f = get_block(sizeof(struct file));
  f->handle = h;
  f->position = 0;
  f->length = _file_size(h);

  return f;
}

void close_file(struct file *f) {
  _close_file(f->handle);
  free_block(f);
}

uint32_t read_from_file(struct file *f, uint32_t max, void *buf) {
  if (f->position + max > f->length)
    max = f->length - f->position;

  uint32_t read = _file_read(f->handle, f->position, max, buf);

  f->position += read;
  return read;
}

uint32_t seek_file_to(struct file *f, uint32_t to) {
  if (to > f->length)
    to = f->length;
  return f->position = to;
}

int32_t seek_file_by(struct file *f, int32_t by) {
  uint32_t old = f->position;
  uint32_t to = old + by > f->length ? f->length : old + by;
  f->position = to;
  return to - old;
}

__attribute__ ((pure))
uint32_t file_size(struct file *f) {
  return f->length;
}