java.util.zip.ZipException: invalid general purpose flag: 9

Question

I get this error on Android 6.0

java.util.zip.ZipException: Invalid General Purpose Bit Flag: 9 java.util.zip.ZipInputStream.getNextEntry(ZipInputStream.java:253)

And this is my code:

ZipInputStream zin = new ZipInputStream(getAppContext().getContentResolver().openInputStream(uri));

What does it mean? What am I doing wrong?

Answer 1

Here's the ZIP file specification: https://users.cs.jmu.edu/buchhofp/forensics/formats/pkzip.html

Flags   General purpose bit flag:
Bit 00: encrypted file
Bit 01: compression option
Bit 02: compression option
Bit 03: data descriptor
Bit 04: enhanced deflation
Bit 05: compressed patched data
Bit 06: strong encryption
Bit 07-10: unused
Bit 11: language encoding
Bit 12: reserved
Bit 13: mask header values
Bit 14-15: reserved 

So, a GPBF value of 9 has both the "encrypted file" and "data descriptor" bits set.

A peek at the Android source code here: https://chromium.googlesource.com/android_tools/+/9e9b6169a098bc19986e44fbbf65e4c29031e4bd/sdk/sources/android-22/java/util/zip/ZipFile.java (an older version, but I suspect this hasn't changed) shows this:

static final int GPBF_ENCRYPTED_FLAG = 1 << 0;

[...]

/**
 * Supported General Purpose Bit Flags Mask.
 * Bit mask of bits not supported.
 * Note: The only bit that we will enforce at this time
 * is the encrypted bit. Although other bits are not supported,
 * we must not enforce them as this could break some legitimate
 * use cases (See http://b/8617715).
 */
static final int GPBF_UNSUPPORTED_MASK = GPBF_ENCRYPTED_FLAG;

[...]

// At position 6 we find the General Purpose Bit Flag.
int gpbf = Short.reverseBytes(is.readShort()) & 0xffff;
if ((gpbf & ZipFile.GPBF_UNSUPPORTED_MASK) != 0) {
    throw new ZipException("Invalid General Purpose Bit Flag: " + gpbf);
}

So, your ZIP file claims to have encrypted the file (bit 00 of the GPBF is set), and the ZipFile implementation doesn't support reading encrypted files.