lmdb.zig

// db.zig
const std = @import("std");
const warn = std.debug.warn;
const Allocator = std.mem.Allocator;
const util = @import("../util.zig");

const c = @cImport({
    @cInclude("lmdb.h");
});

var env: *c.MDB_env = undefined;
const dbpath = "./db";

pub fn init(allocator: *Allocator) !void {
  var mdb_ret: c_int = 0;
  mdb_ret = c.mdb_env_create(@ptrCast([*c]?*c.MDB_env, &env));
  if(mdb_ret != 0) {
    warn("mdb_env_create failed {}\n", mdb_ret);
    return error.BadValue;
  }
  mdb_ret = c.mdb_env_set_mapsize(env, 250 * 1024 * 1024);
  if(mdb_ret != 0) {
    warn("mdb_env_set_mapsize failed {}\n", mdb_ret);
    return error.BadValue;
  }
  std.fs.makeDir(dbpath) catch { };
  mdb_ret = c.mdb_env_open(env, util.sliceToCstr(allocator, dbpath), 0, 0o644);
  if(mdb_ret != 0) {
    warn("mdb_env_open failed {}\n", mdb_ret);
    return error.BadValue;
  }
  stats();
}

pub fn stats() void {
  var mdbStat: c.MDB_stat = undefined;
  var ret = c.mdb_env_stat(env, &mdbStat);
  warn("lmdb cache {} entries\n", mdbStat.ms_entries);
}

pub fn write(namespace: []const u8, key: []const u8, value: []const u8, allocator: *Allocator) !void {
  var txnptr = allocator.create(*c.struct_MDB_txn) catch unreachable;
  var ctxnMaybe = @ptrCast([*c]?*c.struct_MDB_txn, txnptr);
  var ret = c.mdb_txn_begin(env, null, 0, ctxnMaybe);
  if (ret == 0) {
//    warn("lmdb write {} {}={}\n", namespace, key, value);
    var dbiptr = allocator.create(c.MDB_dbi) catch unreachable;
    ret = c.mdb_dbi_open(txnptr.*, null, c.MDB_CREATE, dbiptr);
    if (ret == 0) {
      // TODO: seperator issue. perhaps 2 byte invalid utf8 sequence
      var fullkey = std.fmt.allocPrint(allocator, "{}:{}", namespace, key) catch unreachable;
      var mdb_key = mdbVal(fullkey, allocator);
      var mdb_value = mdbVal(value, allocator);
      ret = c.mdb_put(txnptr.*, dbiptr.*, mdb_key, mdb_value, 0);
      if (ret == 0) {
        ret = c.mdb_txn_commit(txnptr.*);
        if (ret == 0) {
          _ = c.mdb_dbi_close(env, dbiptr.*);
        } else {
          warn("mdb_txn_commit ERR {}\n", ret);
          return error.mdb_txn_commit;
        }
      } else {
        warn("mdb_put ERR {}\n", ret);
        return error.mdb_put;
      }
    } else {
      warn("mdb_dbi_open ERR {}\n", ret);
      return error.mdb_dbi_open;
    }
  } else {
    warn("mdb_txn_begin ERR {}\n", ret);
    return error.mdb_txn_begin;
  }
}

fn mdbVal(data: []const u8, allocator: *Allocator) *c.MDB_val {
  var dataptr = @intToPtr(?*c_void, @ptrToInt(data.ptr));
  var mdb_val = allocator.create(c.MDB_val) catch unreachable;
  mdb_val.mv_size = data.len;
  mdb_val.mv_data = dataptr;
  return mdb_val;
}

Reference: https://nest.pijul.com/donpdonp/tootdeck:master/df6b849b2d9fbdaa46