feat: add appendSegment and rowPrefix

src/index.zig

@@ -0,0 +1,155 @@
+const std = @import("std");
+const dbmod = @import("db.zig");
+const row = @import("row.zig");
+
+const Allocator = std.mem.Allocator;
+const Db = dbmod.Db;
+const Value = row.Value;
+
+/// Keyspace layout shared by every table and index living inside a single
+/// Db instance:
+///   "R\x00" table "\x00" orderedPk                 -> encoded Row
+///   "I\x00" table "\x00" field "\x00" orderedValue orderedPk -> encoded pk Value
+///   "J\x00" table "\x00" indexName "\x00" orderedValue1 .. orderedValueN orderedPk -> encoded pk Value
+///   "M\x00INDEXES\x00" table                        -> encoded list of indexed field names
+///   "M\x00CINDEXES\x00" table                       -> encoded list of composite index specs
+///   "M\x00UNIQUE\x00" table                         -> encoded list of UNIQUE-constrained field names
+///   "M\x00FKEYS\x00" table                          -> encoded list of FOREIGN KEY specs (field, refTable, refField)
+///   "M\x00CHECKS\x00" table                         -> encoded list of CHECK constraint specs (name, expr source)
+///   "M\x00REFBY\x00" table                          -> encoded list of reverse FK specs (childTable, childField, refField),
+///                                                       one entry per OTHER table's FOREIGN KEY that names this table+refField
+///
+/// All namespaces share one flat LSM keyspace (there is only one Db), so the
+/// leading tag byte plus NUL separators keep tables, single-field indexes,
+/// composite indexes, and metadata from ever colliding or shadowing each
+/// other during a scan. A composite index entry's value columns are just N
+/// single-column `row.appendOrdered` encodings concatenated in the index's
+/// declared field order ahead of the primary key's - each encoding is
+/// already self-delimiting (fixed width for none/boolean/int/float, a
+/// 0x00 0x00 terminator for text/bytes with 0x00 bytes escaped), so the
+/// concatenation compares byte-for-byte in exactly the same order as
+/// comparing the value tuples component by component. That is what makes a
+/// prefix scan over the leading K of N components ("leftmost prefix" rule,
+/// same as a real multi-column B-tree index) a correct equality lookup on
+/// just those K columns, unconstrained on the rest.
+pub const rowTag: u8 = 'R';
+pub const indexTag: u8 = 'I';
+pub const compositeIndexTag: u8 = 'J';
+pub const metaTag: u8 = 'M';
+const sep: u8 = 0x00;
+
+fn appendSegment(out: *std.ArrayList(u8), segment: []const u8) !void {
+    try out.appendSlice(segment);
+    try out.append(sep);
+}
+
+pub fn rowPrefix(allocator: Allocator, table: []const u8) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(rowTag);
+    try appendSegment(&out, table);
+    return out.toOwnedSlice();
+}
+
+pub fn rowKey(allocator: Allocator, table: []const u8, pk: Value) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(rowTag);
+    try appendSegment(&out, table);
+    try row.appendOrdered(&out, pk);
+    return out.toOwnedSlice();
+}
+
+pub fn indexPrefix(allocator: Allocator, table: []const u8, field: []const u8) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(indexTag);
+    try appendSegment(&out, table);
+    try appendSegment(&out, field);
+    return out.toOwnedSlice();
+}
+
+pub fn indexEntryKey(allocator: Allocator, table: []const u8, field: []const u8, value: Value, pk: Value) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(indexTag);
+    try appendSegment(&out, table);
+    try appendSegment(&out, field);
+    try row.appendOrdered(&out, value);
+    try row.appendOrdered(&out, pk);
+    return out.toOwnedSlice();
+}
+
+pub fn indexValueBound(allocator: Allocator, table: []const u8, field: []const u8, value: Value) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(indexTag);
+    try appendSegment(&out, table);
+    try appendSegment(&out, field);
+    try row.appendOrdered(&out, value);
+    return out.toOwnedSlice();
+}
+
+fn metaKey(allocator: Allocator, table: []const u8) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(metaTag);
+    try appendSegment(&out, "INDEXES");
+    try out.appendSlice(table);
+    return out.toOwnedSlice();
+}
+
+fn compositeMetaKey(allocator: Allocator, table: []const u8) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(metaTag);
+    try appendSegment(&out, "CINDEXES");
+    try out.appendSlice(table);
+    return out.toOwnedSlice();
+}
+
+fn uniqueMetaKey(allocator: Allocator, table: []const u8) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(metaTag);
+    try appendSegment(&out, "UNIQUE");
+    try out.appendSlice(table);
+    return out.toOwnedSlice();
+}
+
+fn foreignKeyMetaKey(allocator: Allocator, table: []const u8) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(metaTag);
+    try appendSegment(&out, "FKEYS");
+    try out.appendSlice(table);
+    return out.toOwnedSlice();
+}
+
+fn checkMetaKey(allocator: Allocator, table: []const u8) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(metaTag);
+    try appendSegment(&out, "CHECKS");
+    try out.appendSlice(table);
+    return out.toOwnedSlice();
+}
+
+fn referencedByMetaKey(allocator: Allocator, table: []const u8) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(metaTag);
+    try appendSegment(&out, "REFBY");
+    try out.appendSlice(table);
+    return out.toOwnedSlice();
+}
+
+pub fn compositeIndexPrefix(allocator: Allocator, table: []const u8, indexName: []const u8) ![]u8 {
+    var out = std.ArrayList(u8).init(allocator);
+    errdefer out.deinit();
+    try out.append(compositeIndexTag);
+    try appendSegment(&out, table);
+    try appendSegment(&out, indexName);
+    return out.toOwnedSlice();
+}
+