zig server-sent events parser

sse.zig

const std = @import("std");

pub const Event = struct {
    event: ?[]const u8,
    data: ?std.ArrayListUnmanaged(u8),
    id: ?[]const u8,
    retry: ?u64,

    pub fn deinit(event: Event, ally: std.mem.Allocator) void {
        inline for (.{ event.event, event.id }) |mx| if (mx) |x| ally.free(x);
        if (event.data) |d| {
            var mut_d = d;
            mut_d.deinit(ally);
        }
    }

    pub const empty = .{ .event = null, .data = null, .id = null, .retry = null };
};

pub const EventStreamParser = struct {
    event: Event = Event.empty,

    pub fn feed(state: *EventStreamParser, line: []const u8, ally: std.mem.Allocator) !?Event {
        if (line.len == 0) {
            defer state.event = Event.empty;
            // free up some memory
            if (state.event.data) |d| d.shrinkAndFree(ally, d.items.len);
            return state.event;
        }

        const index_of_colon = std.mem.indexOfScalar(u8, line, ':') orelse line.len;
        if (index_of_colon == 0) return null; // comment

        const kind = line[0..index_of_colon];
        const raw_value = line[@min(index_of_colon + 1, line.len)..];
        const value = if (std.mem.startsWith(u8, raw_value, " ")) raw_value[1..] else raw_value;

        if (std.mem.eql(u8, kind, "data")) {
            if (state.event.data) |d| {
                try d.append(ally, '\n');
            } else {
                state.event.data = std.ArrayListUnmanaged(u8){};
            }

            try state.event.data.?.appendSlice(ally, value);
        } else if (std.mem.eql(u8, kind, "event")) {
            if (state.event.event != null) return error.DuplicateEvent;

            state.event.event = try ally.dupe(u8, value);
        } else if (std.mem.eql(u8, kind, "id")) {
            if (state.event.id != null) return error.DuplicateId;

            state.event.id = try ally.dupe(u8, value);
        } else if (std.mem.eql(u8, kind, "retry")) {
            state.event.retry = std.fmt.parseInt(u64, value, 10) catch null;
        }

        return null;
    }
};