diff --git a/third_party/zip/reader.go b/third_party/zip/reader.go
new file mode 100644
index 0000000..f6c3ead
--- /dev/null
+++ b/third_party/zip/reader.go
@@ -0,0 +1,527 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package zip
+
+import (
+	"bufio"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"hash"
+	"hash/crc32"
+	"io"
+	"os"
+)
+
+var (
+	ErrFormat    = errors.New("zip: not a valid zip file")
+	ErrAlgorithm = errors.New("zip: unsupported compression algorithm")
+	ErrChecksum  = errors.New("zip: checksum error")
+)
+
+type Reader struct {
+	r             io.ReaderAt
+	File          []*File
+	Comment       string
+	decompressors map[uint16]Decompressor
+}
+
+type ReadCloser struct {
+	f *os.File
+	Reader
+}
+
+type File struct {
+	FileHeader
+	zip          *Reader
+	zipr         io.ReaderAt
+	zipsize      int64
+	headerOffset int64
+}
+
+func (f *File) hasDataDescriptor() bool {
+	return f.Flags&0x8 != 0
+}
+
+// OpenReader will open the Zip file specified by name and return a ReadCloser.
+func OpenReader(name string) (*ReadCloser, error) {
+	f, err := os.Open(name)
+	if err != nil {
+		return nil, err
+	}
+	fi, err := f.Stat()
+	if err != nil {
+		f.Close()
+		return nil, err
+	}
+	r := new(ReadCloser)
+	if err := r.init(f, fi.Size()); err != nil {
+		f.Close()
+		return nil, err
+	}
+	r.f = f
+	return r, nil
+}
+
+// NewReader returns a new Reader reading from r, which is assumed to
+// have the given size in bytes.
+func NewReader(r io.ReaderAt, size int64) (*Reader, error) {
+	zr := new(Reader)
+	if err := zr.init(r, size); err != nil {
+		return nil, err
+	}
+	return zr, nil
+}
+
+func (z *Reader) init(r io.ReaderAt, size int64) error {
+	end, err := readDirectoryEnd(r, size)
+	if err != nil {
+		return err
+	}
+	if end.directoryRecords > uint64(size)/fileHeaderLen {
+		return fmt.Errorf("archive/zip: TOC declares impossible %d files in %d byte zip", end.directoryRecords, size)
+	}
+	z.r = r
+	z.File = make([]*File, 0, end.directoryRecords)
+	z.Comment = end.comment
+	rs := io.NewSectionReader(r, 0, size)
+	if _, err = rs.Seek(int64(end.directoryOffset), io.SeekStart); err != nil {
+		return err
+	}
+	buf := bufio.NewReader(rs)
+
+	// The count of files inside a zip is truncated to fit in a uint16.
+	// Gloss over this by reading headers until we encounter
+	// a bad one, and then only report a ErrFormat or UnexpectedEOF if
+	// the file count modulo 65536 is incorrect.
+	for {
+		f := &File{zip: z, zipr: r, zipsize: size}
+		err = readDirectoryHeader(f, buf)
+		if err == ErrFormat || err == io.ErrUnexpectedEOF {
+			break
+		}
+		if err != nil {
+			return err
+		}
+		z.File = append(z.File, f)
+	}
+	if uint16(len(z.File)) != uint16(end.directoryRecords) { // only compare 16 bits here
+		// Return the readDirectoryHeader error if we read
+		// the wrong number of directory entries.
+		return err
+	}
+	return nil
+}
+
+// RegisterDecompressor registers or overrides a custom decompressor for a
+// specific method ID. If a decompressor for a given method is not found,
+// Reader will default to looking up the decompressor at the package level.
+func (z *Reader) RegisterDecompressor(method uint16, dcomp Decompressor) {
+	if z.decompressors == nil {
+		z.decompressors = make(map[uint16]Decompressor)
+	}
+	z.decompressors[method] = dcomp
+}
+
+func (z *Reader) decompressor(method uint16) Decompressor {
+	dcomp := z.decompressors[method]
+	if dcomp == nil {
+		dcomp = decompressor(method)
+	}
+	return dcomp
+}
+
+// Close closes the Zip file, rendering it unusable for I/O.
+func (rc *ReadCloser) Close() error {
+	return rc.f.Close()
+}
+
+// DataOffset returns the offset of the file's possibly-compressed
+// data, relative to the beginning of the zip file.
+//
+// Most callers should instead use Open, which transparently
+// decompresses data and verifies checksums.
+func (f *File) DataOffset() (offset int64, err error) {
+	bodyOffset, err := f.findBodyOffset()
+	if err != nil {
+		return
+	}
+	return f.headerOffset + bodyOffset, nil
+}
+
+// Open returns a ReadCloser that provides access to the File's contents.
+// Multiple files may be read concurrently.
+func (f *File) Open() (io.ReadCloser, error) {
+	bodyOffset, err := f.findBodyOffset()
+	if err != nil {
+		return nil, err
+	}
+	size := int64(f.CompressedSize64)
+	r := io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset, size)
+	dcomp := f.zip.decompressor(f.Method)
+	if dcomp == nil {
+		return nil, ErrAlgorithm
+	}
+	var rc io.ReadCloser = dcomp(r)
+	var desr io.Reader
+	if f.hasDataDescriptor() {
+		desr = io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset+size, dataDescriptorLen)
+	}
+	rc = &checksumReader{
+		rc:   rc,
+		hash: crc32.NewIEEE(),
+		f:    f,
+		desr: desr,
+	}
+	return rc, nil
+}
+
+type checksumReader struct {
+	rc    io.ReadCloser
+	hash  hash.Hash32
+	nread uint64 // number of bytes read so far
+	f     *File
+	desr  io.Reader // if non-nil, where to read the data descriptor
+	err   error     // sticky error
+}
+
+func (r *checksumReader) Read(b []byte) (n int, err error) {
+	if r.err != nil {
+		return 0, r.err
+	}
+	n, err = r.rc.Read(b)
+	r.hash.Write(b[:n])
+	r.nread += uint64(n)
+	if err == nil {
+		return
+	}
+	if err == io.EOF {
+		if r.nread != r.f.UncompressedSize64 {
+			return 0, io.ErrUnexpectedEOF
+		}
+		if r.desr != nil {
+			if err1 := readDataDescriptor(r.desr, r.f); err1 != nil {
+				if err1 == io.EOF {
+					err = io.ErrUnexpectedEOF
+				} else {
+					err = err1
+				}
+			} else if r.hash.Sum32() != r.f.CRC32 {
+				err = ErrChecksum
+			}
+		} else {
+			// If there's not a data descriptor, we still compare
+			// the CRC32 of what we've read against the file header
+			// or TOC's CRC32, if it seems like it was set.
+			if r.f.CRC32 != 0 && r.hash.Sum32() != r.f.CRC32 {
+				err = ErrChecksum
+			}
+		}
+	}
+	r.err = err
+	return
+}
+
+func (r *checksumReader) Close() error { return r.rc.Close() }
+
+// findBodyOffset does the minimum work to verify the file has a header
+// and returns the file body offset.
+func (f *File) findBodyOffset() (int64, error) {
+	var buf [fileHeaderLen]byte
+	if _, err := f.zipr.ReadAt(buf[:], f.headerOffset); err != nil {
+		return 0, err
+	}
+	b := readBuf(buf[:])
+	if sig := b.uint32(); sig != fileHeaderSignature {
+		return 0, ErrFormat
+	}
+	b = b[22:] // skip over most of the header
+	filenameLen := int(b.uint16())
+	extraLen := int(b.uint16())
+	return int64(fileHeaderLen + filenameLen + extraLen), nil
+}
+
+// readDirectoryHeader attempts to read a directory header from r.
+// It returns io.ErrUnexpectedEOF if it cannot read a complete header,
+// and ErrFormat if it doesn't find a valid header signature.
+func readDirectoryHeader(f *File, r io.Reader) error {
+	var buf [directoryHeaderLen]byte
+	if _, err := io.ReadFull(r, buf[:]); err != nil {
+		return err
+	}
+	b := readBuf(buf[:])
+	if sig := b.uint32(); sig != directoryHeaderSignature {
+		return ErrFormat
+	}
+	f.CreatorVersion = b.uint16()
+	f.ReaderVersion = b.uint16()
+	f.Flags = b.uint16()
+	f.Method = b.uint16()
+	f.ModifiedTime = b.uint16()
+	f.ModifiedDate = b.uint16()
+	f.CRC32 = b.uint32()
+	f.CompressedSize = b.uint32()
+	f.UncompressedSize = b.uint32()
+	f.CompressedSize64 = uint64(f.CompressedSize)
+	f.UncompressedSize64 = uint64(f.UncompressedSize)
+	filenameLen := int(b.uint16())
+	extraLen := int(b.uint16())
+	commentLen := int(b.uint16())
+	b = b[4:] // skipped start disk number and internal attributes (2x uint16)
+	f.ExternalAttrs = b.uint32()
+	f.headerOffset = int64(b.uint32())
+	d := make([]byte, filenameLen+extraLen+commentLen)
+	if _, err := io.ReadFull(r, d); err != nil {
+		return err
+	}
+	f.Name = string(d[:filenameLen])
+	f.Extra = d[filenameLen : filenameLen+extraLen]
+	f.Comment = string(d[filenameLen+extraLen:])
+
+	needUSize := f.UncompressedSize == ^uint32(0)
+	needCSize := f.CompressedSize == ^uint32(0)
+	needHeaderOffset := f.headerOffset == int64(^uint32(0))
+
+	if len(f.Extra) > 0 {
+		// Best effort to find what we need.
+		// Other zip authors might not even follow the basic format,
+		// and we'll just ignore the Extra content in that case.
+		b := readBuf(f.Extra)
+		for len(b) >= 4 { // need at least tag and size
+			tag := b.uint16()
+			size := b.uint16()
+			if int(size) > len(b) {
+				break
+			}
+			if tag == zip64ExtraId {
+				// update directory values from the zip64 extra block.
+				// They should only be consulted if the sizes read earlier
+				// are maxed out.
+				// See golang.org/issue/13367.
+				eb := readBuf(b[:size])
+
+				if needUSize {
+					needUSize = false
+					if len(eb) < 8 {
+						return ErrFormat
+					}
+					f.UncompressedSize64 = eb.uint64()
+				}
+				if needCSize {
+					needCSize = false
+					if len(eb) < 8 {
+						return ErrFormat
+					}
+					f.CompressedSize64 = eb.uint64()
+				}
+				if needHeaderOffset {
+					needHeaderOffset = false
+					if len(eb) < 8 {
+						return ErrFormat
+					}
+					f.headerOffset = int64(eb.uint64())
+				}
+				break
+			}
+			b = b[size:]
+		}
+	}
+
+	// Assume that uncompressed size 2³²-1 could plausibly happen in
+	// an old zip32 file that was sharding inputs into the largest chunks
+	// possible (or is just malicious; search the web for 42.zip).
+	// If needUSize is true still, it means we didn't see a zip64 extension.
+	// As long as the compressed size is not also 2³²-1 (implausible)
+	// and the header is not also 2³²-1 (equally implausible),
+	// accept the uncompressed size 2³²-1 as valid.
+	// If nothing else, this keeps archive/zip working with 42.zip.
+	_ = needUSize
+
+	if needCSize || needHeaderOffset {
+		return ErrFormat
+	}
+
+	return nil
+}
+
+func readDataDescriptor(r io.Reader, f *File) error {
+	var buf [dataDescriptorLen]byte
+
+	// The spec says: "Although not originally assigned a
+	// signature, the value 0x08074b50 has commonly been adopted
+	// as a signature value for the data descriptor record.
+	// Implementers should be aware that ZIP files may be
+	// encountered with or without this signature marking data
+	// descriptors and should account for either case when reading
+	// ZIP files to ensure compatibility."
+	//
+	// dataDescriptorLen includes the size of the signature but
+	// first read just those 4 bytes to see if it exists.
+	if _, err := io.ReadFull(r, buf[:4]); err != nil {
+		return err
+	}
+	off := 0
+	maybeSig := readBuf(buf[:4])
+	if maybeSig.uint32() != dataDescriptorSignature {
+		// No data descriptor signature. Keep these four
+		// bytes.
+		off += 4
+	}
+	if _, err := io.ReadFull(r, buf[off:12]); err != nil {
+		return err
+	}
+	b := readBuf(buf[:12])
+	if b.uint32() != f.CRC32 {
+		return ErrChecksum
+	}
+
+	// The two sizes that follow here can be either 32 bits or 64 bits
+	// but the spec is not very clear on this and different
+	// interpretations has been made causing incompatibilities. We
+	// already have the sizes from the central directory so we can
+	// just ignore these.
+
+	return nil
+}
+
+func readDirectoryEnd(r io.ReaderAt, size int64) (dir *directoryEnd, err error) {
+	// look for directoryEndSignature in the last 1k, then in the last 65k
+	var buf []byte
+	var directoryEndOffset int64
+	for i, bLen := range []int64{1024, 65 * 1024} {
+		if bLen > size {
+			bLen = size
+		}
+		buf = make([]byte, int(bLen))
+		if _, err := r.ReadAt(buf, size-bLen); err != nil && err != io.EOF {
+			return nil, err
+		}
+		if p := findSignatureInBlock(buf); p >= 0 {
+			buf = buf[p:]
+			directoryEndOffset = size - bLen + int64(p)
+			break
+		}
+		if i == 1 || bLen == size {
+			return nil, ErrFormat
+		}
+	}
+
+	// read header into struct
+	b := readBuf(buf[4:]) // skip signature
+	d := &directoryEnd{
+		diskNbr:            uint32(b.uint16()),
+		dirDiskNbr:         uint32(b.uint16()),
+		dirRecordsThisDisk: uint64(b.uint16()),
+		directoryRecords:   uint64(b.uint16()),
+		directorySize:      uint64(b.uint32()),
+		directoryOffset:    uint64(b.uint32()),
+		commentLen:         b.uint16(),
+	}
+	l := int(d.commentLen)
+	if l > len(b) {
+		return nil, errors.New("zip: invalid comment length")
+	}
+	d.comment = string(b[:l])
+
+	// These values mean that the file can be a zip64 file
+	if d.directoryRecords == 0xffff || d.directorySize == 0xffff || d.directoryOffset == 0xffffffff {
+		p, err := findDirectory64End(r, directoryEndOffset)
+		if err == nil && p >= 0 {
+			err = readDirectory64End(r, p, d)
+		}
+		if err != nil {
+			return nil, err
+		}
+	}
+	// Make sure directoryOffset points to somewhere in our file.
+	if o := int64(d.directoryOffset); o < 0 || o >= size {
+		return nil, ErrFormat
+	}
+	return d, nil
+}
+
+// findDirectory64End tries to read the zip64 locator just before the
+// directory end and returns the offset of the zip64 directory end if
+// found.
+func findDirectory64End(r io.ReaderAt, directoryEndOffset int64) (int64, error) {
+	locOffset := directoryEndOffset - directory64LocLen
+	if locOffset < 0 {
+		return -1, nil // no need to look for a header outside the file
+	}
+	buf := make([]byte, directory64LocLen)
+	if _, err := r.ReadAt(buf, locOffset); err != nil {
+		return -1, err
+	}
+	b := readBuf(buf)
+	if sig := b.uint32(); sig != directory64LocSignature {
+		return -1, nil
+	}
+	if b.uint32() != 0 { // number of the disk with the start of the zip64 end of central directory
+		return -1, nil // the file is not a valid zip64-file
+	}
+	p := b.uint64()      // relative offset of the zip64 end of central directory record
+	if b.uint32() != 1 { // total number of disks
+		return -1, nil // the file is not a valid zip64-file
+	}
+	return int64(p), nil
+}
+
+// readDirectory64End reads the zip64 directory end and updates the
+// directory end with the zip64 directory end values.
+func readDirectory64End(r io.ReaderAt, offset int64, d *directoryEnd) (err error) {
+	buf := make([]byte, directory64EndLen)
+	if _, err := r.ReadAt(buf, offset); err != nil {
+		return err
+	}
+
+	b := readBuf(buf)
+	if sig := b.uint32(); sig != directory64EndSignature {
+		return ErrFormat
+	}
+
+	b = b[12:]                        // skip dir size, version and version needed (uint64 + 2x uint16)
+	d.diskNbr = b.uint32()            // number of this disk
+	d.dirDiskNbr = b.uint32()         // number of the disk with the start of the central directory
+	d.dirRecordsThisDisk = b.uint64() // total number of entries in the central directory on this disk
+	d.directoryRecords = b.uint64()   // total number of entries in the central directory
+	d.directorySize = b.uint64()      // size of the central directory
+	d.directoryOffset = b.uint64()    // offset of start of central directory with respect to the starting disk number
+
+	return nil
+}
+
+func findSignatureInBlock(b []byte) int {
+	for i := len(b) - directoryEndLen; i >= 0; i-- {
+		// defined from directoryEndSignature in struct.go
+		if b[i] == 'P' && b[i+1] == 'K' && b[i+2] == 0x05 && b[i+3] == 0x06 {
+			// n is length of comment
+			n := int(b[i+directoryEndLen-2]) | int(b[i+directoryEndLen-1])<<8
+			if n+directoryEndLen+i <= len(b) {
+				return i
+			}
+		}
+	}
+	return -1
+}
+
+type readBuf []byte
+
+func (b *readBuf) uint16() uint16 {
+	v := binary.LittleEndian.Uint16(*b)
+	*b = (*b)[2:]
+	return v
+}
+
+func (b *readBuf) uint32() uint32 {
+	v := binary.LittleEndian.Uint32(*b)
+	*b = (*b)[4:]
+	return v
+}
+
+func (b *readBuf) uint64() uint64 {
+	v := binary.LittleEndian.Uint64(*b)
+	*b = (*b)[8:]
+	return v
+}