master
  1//! The .ZIP File Format Specification is found here:
  2//!    https://pkwaredownloads.blob.core.windows.net/pem/APPNOTE.txt
  3//!
  4//! Note that this file uses the abbreviation "cd" for "central directory"
  5
  6const builtin = @import("builtin");
  7const std = @import("std");
  8const File = std.fs.File;
  9const is_le = builtin.target.cpu.arch.endian() == .little;
 10const Writer = std.Io.Writer;
 11const Reader = std.Io.Reader;
 12const flate = std.compress.flate;
 13
 14pub const CompressionMethod = enum(u16) {
 15    store = 0,
 16    deflate = 8,
 17    _,
 18};
 19
 20pub const central_file_header_sig = [4]u8{ 'P', 'K', 1, 2 };
 21pub const local_file_header_sig = [4]u8{ 'P', 'K', 3, 4 };
 22pub const end_record_sig = [4]u8{ 'P', 'K', 5, 6 };
 23pub const end_record64_sig = [4]u8{ 'P', 'K', 6, 6 };
 24pub const end_locator64_sig = [4]u8{ 'P', 'K', 6, 7 };
 25pub const ExtraHeader = enum(u16) {
 26    zip64_info = 0x1,
 27    _,
 28};
 29
 30const GeneralPurposeFlags = packed struct(u16) {
 31    encrypted: bool,
 32    _: u15,
 33};
 34
 35pub const LocalFileHeader = extern struct {
 36    signature: [4]u8 align(1),
 37    version_needed_to_extract: u16 align(1),
 38    flags: GeneralPurposeFlags align(1),
 39    compression_method: CompressionMethod align(1),
 40    last_modification_time: u16 align(1),
 41    last_modification_date: u16 align(1),
 42    crc32: u32 align(1),
 43    compressed_size: u32 align(1),
 44    uncompressed_size: u32 align(1),
 45    filename_len: u16 align(1),
 46    extra_len: u16 align(1),
 47};
 48
 49pub const CentralDirectoryFileHeader = extern struct {
 50    signature: [4]u8 align(1),
 51    version_made_by: u16 align(1),
 52    version_needed_to_extract: u16 align(1),
 53    flags: GeneralPurposeFlags align(1),
 54    compression_method: CompressionMethod align(1),
 55    last_modification_time: u16 align(1),
 56    last_modification_date: u16 align(1),
 57    crc32: u32 align(1),
 58    compressed_size: u32 align(1),
 59    uncompressed_size: u32 align(1),
 60    filename_len: u16 align(1),
 61    extra_len: u16 align(1),
 62    comment_len: u16 align(1),
 63    disk_number: u16 align(1),
 64    internal_file_attributes: u16 align(1),
 65    external_file_attributes: u32 align(1),
 66    local_file_header_offset: u32 align(1),
 67};
 68
 69pub const EndRecord64 = extern struct {
 70    signature: [4]u8 align(1),
 71    end_record_size: u64 align(1),
 72    version_made_by: u16 align(1),
 73    version_needed_to_extract: u16 align(1),
 74    disk_number: u32 align(1),
 75    central_directory_disk_number: u32 align(1),
 76    record_count_disk: u64 align(1),
 77    record_count_total: u64 align(1),
 78    central_directory_size: u64 align(1),
 79    central_directory_offset: u64 align(1),
 80};
 81
 82pub const EndLocator64 = extern struct {
 83    signature: [4]u8 align(1),
 84    zip64_disk_count: u32 align(1),
 85    record_file_offset: u64 align(1),
 86    total_disk_count: u32 align(1),
 87};
 88
 89pub const EndRecord = extern struct {
 90    signature: [4]u8 align(1),
 91    disk_number: u16 align(1),
 92    central_directory_disk_number: u16 align(1),
 93    record_count_disk: u16 align(1),
 94    record_count_total: u16 align(1),
 95    central_directory_size: u32 align(1),
 96    central_directory_offset: u32 align(1),
 97    comment_len: u16 align(1),
 98
 99    pub fn need_zip64(self: EndRecord) bool {
100        return isMaxInt(self.record_count_disk) or
101            isMaxInt(self.record_count_total) or
102            isMaxInt(self.central_directory_size) or
103            isMaxInt(self.central_directory_offset);
104    }
105
106    pub const FindBufferError = error{ ZipNoEndRecord, ZipTruncated };
107
108    /// TODO audit this logic
109    pub fn findBuffer(buffer: []const u8) FindBufferError!EndRecord {
110        const pos = std.mem.lastIndexOf(u8, buffer, &end_record_sig) orelse return error.ZipNoEndRecord;
111        if (pos + @sizeOf(EndRecord) > buffer.len) return error.EndOfStream;
112        const record_ptr: *EndRecord = @ptrCast(buffer[pos..][0..@sizeOf(EndRecord)]);
113        var record = record_ptr.*;
114        if (!is_le) std.mem.byteSwapAllFields(EndRecord, &record);
115        return record;
116    }
117
118    pub const FindFileError = File.Reader.SizeError || File.SeekError || File.ReadError || error{
119        ZipNoEndRecord,
120        EndOfStream,
121        ReadFailed,
122    };
123
124    pub fn findFile(fr: *File.Reader) FindFileError!EndRecord {
125        const end_pos = try fr.getSize();
126
127        var buf: [@sizeOf(EndRecord) + std.math.maxInt(u16)]u8 = undefined;
128        const record_len_max = @min(end_pos, buf.len);
129        var loaded_len: u32 = 0;
130        var comment_len: u16 = 0;
131        while (true) {
132            const record_len: u32 = @as(u32, comment_len) + @sizeOf(EndRecord);
133            if (record_len > record_len_max)
134                return error.ZipNoEndRecord;
135
136            if (record_len > loaded_len) {
137                const new_loaded_len = @min(loaded_len + 300, record_len_max);
138                const read_len = new_loaded_len - loaded_len;
139
140                try fr.seekTo(end_pos - @as(u64, new_loaded_len));
141                const read_buf: []u8 = buf[buf.len - new_loaded_len ..][0..read_len];
142                fr.interface.readSliceAll(read_buf) catch |err| switch (err) {
143                    error.ReadFailed => return fr.err.?,
144                    error.EndOfStream => return error.EndOfStream,
145                };
146                loaded_len = new_loaded_len;
147            }
148
149            const record_bytes = buf[buf.len - record_len ..][0..@sizeOf(EndRecord)];
150            if (std.mem.eql(u8, record_bytes[0..4], &end_record_sig) and
151                std.mem.readInt(u16, record_bytes[20..22], .little) == comment_len)
152            {
153                const record: *align(1) EndRecord = @ptrCast(record_bytes.ptr);
154                if (!is_le) std.mem.byteSwapAllFields(EndRecord, record);
155                return record.*;
156            }
157
158            if (comment_len == std.math.maxInt(u16))
159                return error.ZipNoEndRecord;
160            comment_len += 1;
161        }
162    }
163};
164
165pub const Decompress = struct {
166    interface: Reader,
167    state: union {
168        inflate: flate.Decompress,
169        store: *Reader,
170    },
171
172    pub fn init(reader: *Reader, method: CompressionMethod, buffer: []u8) Reader {
173        return switch (method) {
174            .store => .{
175                .state = .{ .store = reader },
176                .interface = .{
177                    .context = undefined,
178                    .vtable = &.{ .stream = streamStore },
179                    .buffer = buffer,
180                    .end = 0,
181                    .seek = 0,
182                },
183            },
184            .deflate => .{
185                .state = .{ .inflate = .init(reader, .raw) },
186                .interface = .{
187                    .context = undefined,
188                    .vtable = &.{ .stream = streamDeflate },
189                    .buffer = buffer,
190                    .end = 0,
191                    .seek = 0,
192                },
193            },
194            else => unreachable,
195        };
196    }
197
198    fn streamStore(r: *Reader, w: *Writer, limit: std.Io.Limit) Reader.StreamError!usize {
199        const d: *Decompress = @fieldParentPtr("interface", r);
200        return d.store.read(w, limit);
201    }
202
203    fn streamDeflate(r: *Reader, w: *Writer, limit: std.Io.Limit) Reader.StreamError!usize {
204        const d: *Decompress = @fieldParentPtr("interface", r);
205        return flate.Decompress.read(&d.inflate, w, limit);
206    }
207};
208
209fn isBadFilename(filename: []const u8) bool {
210    if (filename.len == 0 or filename[0] == '/')
211        return true;
212
213    var it = std.mem.splitScalar(u8, filename, '/');
214    while (it.next()) |part| {
215        if (std.mem.eql(u8, part, ".."))
216            return true;
217    }
218
219    return false;
220}
221
222fn isMaxInt(uint: anytype) bool {
223    return uint == std.math.maxInt(@TypeOf(uint));
224}
225
226const FileExtents = struct {
227    uncompressed_size: u64,
228    compressed_size: u64,
229    local_file_header_offset: u64,
230};
231
232fn readZip64FileExtents(comptime T: type, header: T, extents: *FileExtents, data: []u8) !void {
233    var data_offset: usize = 0;
234    if (isMaxInt(header.uncompressed_size)) {
235        if (data_offset + 8 > data.len)
236            return error.ZipBadCd64Size;
237        extents.uncompressed_size = std.mem.readInt(u64, data[data_offset..][0..8], .little);
238        data_offset += 8;
239    }
240    if (isMaxInt(header.compressed_size)) {
241        if (data_offset + 8 > data.len)
242            return error.ZipBadCd64Size;
243        extents.compressed_size = std.mem.readInt(u64, data[data_offset..][0..8], .little);
244        data_offset += 8;
245    }
246
247    switch (T) {
248        CentralDirectoryFileHeader => {
249            if (isMaxInt(header.local_file_header_offset)) {
250                if (data_offset + 8 > data.len)
251                    return error.ZipBadCd64Size;
252                extents.local_file_header_offset = std.mem.readInt(u64, data[data_offset..][0..8], .little);
253                data_offset += 8;
254            }
255            if (isMaxInt(header.disk_number)) {
256                if (data_offset + 4 > data.len)
257                    return error.ZipInvalid;
258                const disk_number = std.mem.readInt(u32, data[data_offset..][0..4], .little);
259                if (disk_number != 0)
260                    return error.ZipMultiDiskUnsupported;
261                data_offset += 4;
262            }
263            if (data_offset > data.len)
264                return error.ZipBadCd64Size;
265        },
266        else => {},
267    }
268}
269
270pub const Iterator = struct {
271    input: *File.Reader,
272
273    cd_record_count: u64,
274    cd_zip_offset: u64,
275    cd_size: u64,
276
277    cd_record_index: u64 = 0,
278    cd_record_offset: u64 = 0,
279
280    pub fn init(input: *File.Reader) !Iterator {
281        const end_record = try EndRecord.findFile(input);
282
283        if (!isMaxInt(end_record.record_count_disk) and end_record.record_count_disk > end_record.record_count_total)
284            return error.ZipDiskRecordCountTooLarge;
285
286        if (end_record.disk_number != 0 or end_record.central_directory_disk_number != 0)
287            return error.ZipMultiDiskUnsupported;
288
289        {
290            const counts_valid = !isMaxInt(end_record.record_count_disk) and !isMaxInt(end_record.record_count_total);
291            if (counts_valid and end_record.record_count_disk != end_record.record_count_total)
292                return error.ZipMultiDiskUnsupported;
293        }
294
295        var result: Iterator = .{
296            .input = input,
297            .cd_record_count = end_record.record_count_total,
298            .cd_zip_offset = end_record.central_directory_offset,
299            .cd_size = end_record.central_directory_size,
300        };
301        if (!end_record.need_zip64()) return result;
302
303        const locator_end_offset: u64 = @as(u64, end_record.comment_len) + @sizeOf(EndRecord) + @sizeOf(EndLocator64);
304        const stream_len = try input.getSize();
305
306        if (locator_end_offset > stream_len)
307            return error.ZipTruncated;
308        try input.seekTo(stream_len - locator_end_offset);
309        const locator = input.interface.takeStruct(EndLocator64, .little) catch |err| switch (err) {
310            error.ReadFailed => return input.err.?,
311            error.EndOfStream => return error.EndOfStream,
312        };
313        if (!std.mem.eql(u8, &locator.signature, &end_locator64_sig))
314            return error.ZipBadLocatorSig;
315        if (locator.zip64_disk_count != 0)
316            return error.ZipUnsupportedZip64DiskCount;
317        if (locator.total_disk_count != 1)
318            return error.ZipMultiDiskUnsupported;
319
320        try input.seekTo(locator.record_file_offset);
321
322        const record64 = input.interface.takeStruct(EndRecord64, .little) catch |err| switch (err) {
323            error.ReadFailed => return input.err.?,
324            error.EndOfStream => return error.EndOfStream,
325        };
326
327        if (!std.mem.eql(u8, &record64.signature, &end_record64_sig))
328            return error.ZipBadEndRecord64Sig;
329
330        if (record64.end_record_size < @sizeOf(EndRecord64) - 12)
331            return error.ZipEndRecord64SizeTooSmall;
332        if (record64.end_record_size > @sizeOf(EndRecord64) - 12)
333            return error.ZipEndRecord64UnhandledExtraData;
334
335        if (record64.version_needed_to_extract > 45)
336            return error.ZipUnsupportedVersion;
337
338        {
339            const is_multidisk = record64.disk_number != 0 or
340                record64.central_directory_disk_number != 0 or
341                record64.record_count_disk != record64.record_count_total;
342            if (is_multidisk)
343                return error.ZipMultiDiskUnsupported;
344        }
345
346        if (isMaxInt(end_record.record_count_total)) {
347            result.cd_record_count = record64.record_count_total;
348        } else if (end_record.record_count_total != record64.record_count_total)
349            return error.Zip64RecordCountTotalMismatch;
350
351        if (isMaxInt(end_record.central_directory_offset)) {
352            result.cd_zip_offset = record64.central_directory_offset;
353        } else if (end_record.central_directory_offset != record64.central_directory_offset)
354            return error.Zip64CentralDirectoryOffsetMismatch;
355
356        if (isMaxInt(end_record.central_directory_size)) {
357            result.cd_size = record64.central_directory_size;
358        } else if (end_record.central_directory_size != record64.central_directory_size)
359            return error.Zip64CentralDirectorySizeMismatch;
360
361        return result;
362    }
363
364    pub fn next(self: *Iterator) !?Entry {
365        if (self.cd_record_index == self.cd_record_count) {
366            if (self.cd_record_offset != self.cd_size)
367                return if (self.cd_size > self.cd_record_offset)
368                    error.ZipCdOversized
369                else
370                    error.ZipCdUndersized;
371
372            return null;
373        }
374
375        const header_zip_offset = self.cd_zip_offset + self.cd_record_offset;
376        const input = self.input;
377        try input.seekTo(header_zip_offset);
378        const header = input.interface.takeStruct(CentralDirectoryFileHeader, .little) catch |err| switch (err) {
379            error.ReadFailed => return input.err.?,
380            error.EndOfStream => return error.EndOfStream,
381        };
382        if (!std.mem.eql(u8, &header.signature, &central_file_header_sig))
383            return error.ZipBadCdOffset;
384
385        self.cd_record_index += 1;
386        self.cd_record_offset += @sizeOf(CentralDirectoryFileHeader) + header.filename_len + header.extra_len + header.comment_len;
387
388        // Note: checking the version_needed_to_extract doesn't seem to be helpful, i.e. the zip file
389        // at https://github.com/ninja-build/ninja/releases/download/v1.12.0/ninja-linux.zip
390        // has an undocumented version 788 but extracts just fine.
391
392        if (header.flags.encrypted)
393            return error.ZipEncryptionUnsupported;
394        // TODO: check/verify more flags
395        if (header.disk_number != 0)
396            return error.ZipMultiDiskUnsupported;
397
398        var extents: FileExtents = .{
399            .uncompressed_size = header.uncompressed_size,
400            .compressed_size = header.compressed_size,
401            .local_file_header_offset = header.local_file_header_offset,
402        };
403
404        if (header.extra_len > 0) {
405            var extra_buf: [std.math.maxInt(u16)]u8 = undefined;
406            const extra = extra_buf[0..header.extra_len];
407
408            try input.seekTo(header_zip_offset + @sizeOf(CentralDirectoryFileHeader) + header.filename_len);
409            input.interface.readSliceAll(extra) catch |err| switch (err) {
410                error.ReadFailed => return input.err.?,
411                error.EndOfStream => return error.EndOfStream,
412            };
413
414            var extra_offset: usize = 0;
415            while (extra_offset + 4 <= extra.len) {
416                const header_id = std.mem.readInt(u16, extra[extra_offset..][0..2], .little);
417                const data_size = std.mem.readInt(u16, extra[extra_offset..][2..4], .little);
418                const end = extra_offset + 4 + data_size;
419                if (end > extra.len)
420                    return error.ZipBadExtraFieldSize;
421                const data = extra[extra_offset + 4 .. end];
422                switch (@as(ExtraHeader, @enumFromInt(header_id))) {
423                    .zip64_info => try readZip64FileExtents(CentralDirectoryFileHeader, header, &extents, data),
424                    else => {}, // ignore
425                }
426                extra_offset = end;
427            }
428        }
429
430        return .{
431            .version_needed_to_extract = header.version_needed_to_extract,
432            .flags = header.flags,
433            .compression_method = header.compression_method,
434            .last_modification_time = header.last_modification_time,
435            .last_modification_date = header.last_modification_date,
436            .header_zip_offset = header_zip_offset,
437            .crc32 = header.crc32,
438            .filename_len = header.filename_len,
439            .compressed_size = extents.compressed_size,
440            .uncompressed_size = extents.uncompressed_size,
441            .file_offset = extents.local_file_header_offset,
442        };
443    }
444
445    pub const Entry = struct {
446        version_needed_to_extract: u16,
447        flags: GeneralPurposeFlags,
448        compression_method: CompressionMethod,
449        last_modification_time: u16,
450        last_modification_date: u16,
451        header_zip_offset: u64,
452        crc32: u32,
453        filename_len: u32,
454        compressed_size: u64,
455        uncompressed_size: u64,
456        file_offset: u64,
457
458        pub fn extract(
459            self: Entry,
460            stream: *File.Reader,
461            options: ExtractOptions,
462            filename_buf: []u8,
463            dest: std.fs.Dir,
464        ) !void {
465            if (filename_buf.len < self.filename_len)
466                return error.ZipInsufficientBuffer;
467            switch (self.compression_method) {
468                .store, .deflate => {},
469                else => return error.UnsupportedCompressionMethod,
470            }
471            const filename = filename_buf[0..self.filename_len];
472            {
473                try stream.seekTo(self.header_zip_offset + @sizeOf(CentralDirectoryFileHeader));
474                try stream.interface.readSliceAll(filename);
475            }
476
477            const local_data_header_offset: u64 = local_data_header_offset: {
478                const local_header = blk: {
479                    try stream.seekTo(self.file_offset);
480                    break :blk try stream.interface.takeStruct(LocalFileHeader, .little);
481                };
482                if (!std.mem.eql(u8, &local_header.signature, &local_file_header_sig))
483                    return error.ZipBadFileOffset;
484                if (local_header.version_needed_to_extract != self.version_needed_to_extract)
485                    return error.ZipMismatchVersionNeeded;
486                if (local_header.last_modification_time != self.last_modification_time)
487                    return error.ZipMismatchModTime;
488                if (local_header.last_modification_date != self.last_modification_date)
489                    return error.ZipMismatchModDate;
490
491                if (@as(u16, @bitCast(local_header.flags)) != @as(u16, @bitCast(self.flags)))
492                    return error.ZipMismatchFlags;
493                if (local_header.crc32 != 0 and local_header.crc32 != self.crc32)
494                    return error.ZipMismatchCrc32;
495                var extents: FileExtents = .{
496                    .uncompressed_size = local_header.uncompressed_size,
497                    .compressed_size = local_header.compressed_size,
498                    .local_file_header_offset = 0,
499                };
500                if (local_header.extra_len > 0) {
501                    var extra_buf: [std.math.maxInt(u16)]u8 = undefined;
502                    const extra = extra_buf[0..local_header.extra_len];
503
504                    {
505                        try stream.seekTo(self.file_offset + @sizeOf(LocalFileHeader) + local_header.filename_len);
506                        try stream.interface.readSliceAll(extra);
507                    }
508
509                    var extra_offset: usize = 0;
510                    while (extra_offset + 4 <= local_header.extra_len) {
511                        const header_id = std.mem.readInt(u16, extra[extra_offset..][0..2], .little);
512                        const data_size = std.mem.readInt(u16, extra[extra_offset..][2..4], .little);
513                        const end = extra_offset + 4 + data_size;
514                        if (end > local_header.extra_len)
515                            return error.ZipBadExtraFieldSize;
516                        const data = extra[extra_offset + 4 .. end];
517                        switch (@as(ExtraHeader, @enumFromInt(header_id))) {
518                            .zip64_info => try readZip64FileExtents(LocalFileHeader, local_header, &extents, data),
519                            else => {}, // ignore
520                        }
521                        extra_offset = end;
522                    }
523                }
524
525                if (extents.compressed_size != 0 and
526                    extents.compressed_size != self.compressed_size)
527                    return error.ZipMismatchCompLen;
528                if (extents.uncompressed_size != 0 and
529                    extents.uncompressed_size != self.uncompressed_size)
530                    return error.ZipMismatchUncompLen;
531
532                if (local_header.filename_len != self.filename_len)
533                    return error.ZipMismatchFilenameLen;
534
535                break :local_data_header_offset @as(u64, local_header.filename_len) +
536                    @as(u64, local_header.extra_len);
537            };
538
539            if (options.allow_backslashes) {
540                std.mem.replaceScalar(u8, filename, '\\', '/');
541            } else {
542                if (std.mem.indexOfScalar(u8, filename, '\\')) |_|
543                    return error.ZipFilenameHasBackslash;
544            }
545
546            if (isBadFilename(filename))
547                return error.ZipBadFilename;
548
549            // All entries that end in '/' are directories
550            if (filename[filename.len - 1] == '/') {
551                if (self.uncompressed_size != 0)
552                    return error.ZipBadDirectorySize;
553                try dest.makePath(filename[0 .. filename.len - 1]);
554                return;
555            }
556
557            const out_file = blk: {
558                if (std.fs.path.dirname(filename)) |dirname| {
559                    var parent_dir = try dest.makeOpenPath(dirname, .{});
560                    defer parent_dir.close();
561
562                    const basename = std.fs.path.basename(filename);
563                    break :blk try parent_dir.createFile(basename, .{ .exclusive = true });
564                }
565                break :blk try dest.createFile(filename, .{ .exclusive = true });
566            };
567            defer out_file.close();
568            var out_file_buffer: [1024]u8 = undefined;
569            var file_writer = out_file.writer(&out_file_buffer);
570            const local_data_file_offset: u64 =
571                @as(u64, self.file_offset) +
572                @as(u64, @sizeOf(LocalFileHeader)) +
573                local_data_header_offset;
574            try stream.seekTo(local_data_file_offset);
575
576            // TODO limit based on self.compressed_size
577
578            switch (self.compression_method) {
579                .store => {
580                    stream.interface.streamExact64(&file_writer.interface, self.uncompressed_size) catch |err| switch (err) {
581                        error.ReadFailed => return stream.err.?,
582                        error.WriteFailed => return file_writer.err.?,
583                        error.EndOfStream => return error.ZipDecompressTruncated,
584                    };
585                },
586                .deflate => {
587                    var flate_buffer: [flate.max_window_len]u8 = undefined;
588                    var decompress: flate.Decompress = .init(&stream.interface, .raw, &flate_buffer);
589                    decompress.reader.streamExact64(&file_writer.interface, self.uncompressed_size) catch |err| switch (err) {
590                        error.ReadFailed => return stream.err.?,
591                        error.WriteFailed => return file_writer.err orelse decompress.err.?,
592                        error.EndOfStream => return error.ZipDecompressTruncated,
593                    };
594                },
595                else => return error.UnsupportedCompressionMethod,
596            }
597            try file_writer.end();
598        }
599    };
600};
601
602// returns true if `filename` starts with `root` followed by a forward slash
603fn filenameInRoot(filename: []const u8, root: []const u8) bool {
604    return (filename.len >= root.len + 1) and
605        (filename[root.len] == '/') and
606        std.mem.eql(u8, filename[0..root.len], root);
607}
608
609pub const Diagnostics = struct {
610    allocator: std.mem.Allocator,
611
612    /// The common root directory for all extracted files if there is one.
613    root_dir: []const u8 = "",
614
615    saw_first_file: bool = false,
616
617    pub fn deinit(self: *Diagnostics) void {
618        self.allocator.free(self.root_dir);
619        self.* = undefined;
620    }
621
622    // This function assumes name is a filename from a zip file which has already been verified to
623    // not start with a slash, backslashes have been normalized to forward slashes, and directories
624    // always end in a slash.
625    pub fn nextFilename(self: *Diagnostics, name: []const u8) error{OutOfMemory}!void {
626        if (!self.saw_first_file) {
627            self.saw_first_file = true;
628            std.debug.assert(self.root_dir.len == 0);
629            const root_len = std.mem.indexOfScalar(u8, name, '/') orelse return;
630            std.debug.assert(root_len > 0);
631            self.root_dir = try self.allocator.dupe(u8, name[0..root_len]);
632        } else if (self.root_dir.len > 0) {
633            if (!filenameInRoot(name, self.root_dir)) {
634                self.allocator.free(self.root_dir);
635                self.root_dir = "";
636            }
637        }
638    }
639};
640
641pub const ExtractOptions = struct {
642    /// Allow filenames within the zip to use backslashes.  Back slashes are normalized
643    /// to forward slashes before forwarding them to platform APIs.
644    allow_backslashes: bool = false,
645    diagnostics: ?*Diagnostics = null,
646    verify_checksums: bool = false,
647};
648
649/// Extract the zipped files to the given `dest` directory.
650pub fn extract(dest: std.fs.Dir, fr: *File.Reader, options: ExtractOptions) !void {
651    if (options.verify_checksums) @panic("TODO unimplemented");
652
653    var iter = try Iterator.init(fr);
654
655    var filename_buf: [std.fs.max_path_bytes]u8 = undefined;
656    while (try iter.next()) |entry| {
657        try entry.extract(fr, options, &filename_buf, dest);
658        if (options.diagnostics) |d| {
659            try d.nextFilename(filename_buf[0..entry.filename_len]);
660        }
661    }
662}