Function findEndRecord [src]

Find and return the end record for the given seekable zip stream. Note that seekable_stream must be an instance of std.io.SeekableStream and its context must also have a .reader() method that returns an instance of std.io.Reader.

Prototype

pub fn findEndRecord(seekable_stream: anytype, stream_len: u64) !EndRecord

Parameters

stream_len: u64

Source

  pub fn findEndRecord(seekable_stream: anytype, stream_len: u64) !EndRecord {
    var buf: [@sizeOf(EndRecord) + std.math.maxInt(u16)]u8 = undefined;
    const record_len_max = @min(stream_len, buf.len);
    var loaded_len: u32 = 0;

    var comment_len: u16 = 0;
    while (true) {
        const record_len: u32 = @as(u32, comment_len) + @sizeOf(EndRecord);
        if (record_len > record_len_max)
            return error.ZipNoEndRecord;

        if (record_len > loaded_len) {
            const new_loaded_len = @min(loaded_len + 300, record_len_max);
            const read_len = new_loaded_len - loaded_len;

            try seekable_stream.seekTo(stream_len - @as(u64, new_loaded_len));
            const read_buf: []u8 = buf[buf.len - new_loaded_len ..][0..read_len];
            const len = try seekable_stream.context.reader().readAll(read_buf);
            if (len != read_len)
                return error.ZipTruncated;
            loaded_len = new_loaded_len;
        }

        const record_bytes = buf[buf.len - record_len ..][0..@sizeOf(EndRecord)];
        if (std.mem.eql(u8, record_bytes[0..4], &end_record_sig) and
            std.mem.readInt(u16, record_bytes[20..22], .little) == comment_len)
        {
            const record: *align(1) EndRecord = @ptrCast(record_bytes.ptr);
            if (builtin.target.cpu.arch.endian() != .little) {
                std.mem.byteSwapAllFields(@TypeOf(record.*), record);
            }
            return record.*;
        }

        if (comment_len == std.math.maxInt(u16))
            return error.ZipNoEndRecord;
        comment_len += 1;
    }
}  