JSON

1import { Cursor } from "./core.js";
2import { readUVarint } from "./varint.js";
3import { readString } from "./strings.js";
4import { readDynamic } from "./dynamic.js";
5
6/**
7 * Read a `JSON` value. ClickHouse's `JSON` is NOT JSON text and NOT BSON — it is
8 * a list of (path, value) pairs built on the same machinery as `Dynamic`:
9 *
10 *   <varuint pathCount>  then pathCount x ( <String path> <Dynamic value> )
11 *
12 * Nested objects are FLATTENED to dotted paths (`{a:{b:2}}` -> path `"a.b"`), and
13 * each leaf value is a self-describing `Dynamic`, so this just loops
14 * {@link readString} + {@link readDynamic}. Returns a `Map` keyed by the flat
15 * dotted path. Path order on the wire is not significant.
16 *
17 * GOTCHA: a null-valued path is NOT stored at all — `{"a":null}` serializes as
18 * zero paths, identical to `{}`. JSON arrays come back as `Array(Nullable(T))`.
19 *
20 * LIMITATION — typed paths only. This reads a plain `JSON` column, where every
21 * path is dynamic (tagged). A `JSON(a T, ...)` with DECLARED typed paths
22 * serializes those paths' values WITHOUT a type tag, so they cannot be decoded
23 * without the schema; read each typed path with its known `T` reader instead.
24 */
25export function readJSON(state: Cursor): Map<string, unknown> {
26  const n = readUVarint(state);
27  const out = new Map<string, unknown>();
28  for (let i = 0; i < n; i++) {
29    const path = readString(state);
30    out.set(path, readDynamic(state));
31  }
32  return out;
33}