feat(lsm): add entry data reading

lsm/example/test.c

@@ -1,5 +1,46 @@
+#include <assert.h>
 #include <stdio.h>
 
 #include "lsm.h"
+#include "lsm/store.h"
+#include "lsm/str.h"
 
-int main() { printf("yuh"); }
+int main() {
+  lsm_str *db_path, *data_dir;
+  lsm_str_init_copy(&db_path, "data/data.db");
+  lsm_str_init_copy(&data_dir, "data");
+
+  lsm_store *store;
+  lsm_store_load(&store, db_path, data_dir);
+
+  lsm_str *key;
+  lsm_str_init_copy(&key, "key");
+
+  lsm_entry_handle *handle;
+  assert(lsm_store_insert(&handle, store, key) == lsm_error_ok);
+
+  lsm_str *data;
+  lsm_str_init_copy(&data, "hello");
+
+  for (int i = 0; i < 50; i++) {
+    lsm_entry_data_append(store, handle, data);
+  }
+
+  lsm_entry_close(handle);
+
+  assert(lsm_store_open_read(&handle, store, key) == lsm_error_ok);
+
+  char buf[24];
+  uint64_t read;
+  uint64_t total = 0;
+
+  lsm_entry_data_read(&read, buf, handle, 24);
+  total += read;
+
+  while (read > 0) {
+    printf("%.*s", read, buf);
+    lsm_entry_data_read(&read, buf, handle, 24);
+    total += read;
+  }
+  printf("\n%lu", total);
+}

lsm/include/lsm/store.h

@@ -151,4 +151,16 @@ lsm_error lsm_store_insert(lsm_entry_handle **out, lsm_store *store,
 lsm_error lsm_entry_data_append(lsm_store *store, lsm_entry_handle *handle,
                                 lsm_str *data);
 
+/**
+ * Read a number of bytes from the entry's data field. The position from which
+ * data is read is dependent on previous read calls.
+ *
+ * @param out where to write how many bytes were read
+ * @param buf buffer to store read data in
+ * @param handle entry handle to read from
+ * @param len how many bytes to read at most
+ */
+lsm_error lsm_entry_data_read(uint64_t *out, char *buf,
+                              lsm_entry_handle *handle, uint64_t len);
+
 #endif

lsm/src/_include/lsm/store_internal.h

@@ -62,6 +62,7 @@ void lsm_entry_wrapper_free(lsm_entry_wrapper *wrapper);
 struct lsm_entry_handle {
   lsm_entry_wrapper *wrapper;
   FILE *f;
+  uint64_t pos;
 };
 
 lsm_error lsm_entry_handle_init(lsm_entry_handle **out);

lsm/src/store/lsm_store.c

@@ -259,3 +259,34 @@ lsm_error lsm_entry_data_append(lsm_store *store, lsm_entry_handle *handle,
 
   return lsm_error_ok;
 }
+
+lsm_error lsm_entry_data_read(uint64_t *out, char *buf,
+                              lsm_entry_handle *handle, uint64_t len) {
+  lsm_entry *entry = handle->wrapper->entry;
+
+  if (entry->data.len == 0) {
+    *out = 0;
+
+    return lsm_error_ok;
+  }
+
+  uint64_t read;
+
+  if (entry->data.on_disk) {
+    read = fread(buf, sizeof(char), len, handle->f);
+
+    if ((read == 0) && (ferror(handle->f) != 0)) {
+      return lsm_error_failed_io;
+    }
+  } else {
+    read = (entry->data.len - handle->pos) < len
+               ? (entry->data.len - handle->pos)
+               : len;
+    memcpy(buf, &entry->data.value.ptr[handle->pos], read * sizeof(char));
+  }
+
+  handle->pos += read;
+  *out = read;
+
+  return lsm_error_ok;
+}