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Support java class files #142

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Support java class files #142

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Binary file added fixtures/sample.class
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2 changes: 2 additions & 0 deletions match_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -54,6 +54,7 @@ func TestMatchFile(t *testing.T) {
{"zst"},
{"exr"},
{"avif"},
{"class"},
}

for _, test := range cases {
Expand All @@ -77,6 +78,7 @@ func TestMatchReader(t *testing.T) {
{bytes.NewBuffer([]byte{0xFF, 0xD8, 0xFF}), "jpg"},
{bytes.NewBuffer([]byte{0xFF, 0xD8, 0x00}), "unknown"},
{bytes.NewBuffer([]byte{0x89, 0x50, 0x4E, 0x47}), "png"},
{bytes.NewBuffer([]byte{0xCA, 0xFE, 0xBA, 0xBE, 0x00, 0x00, 0x00, 0xff}), "class"},
}

for _, test := range cases {
Expand Down
21 changes: 20 additions & 1 deletion matchers/archive.go
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@ var (
TypeDcm = newType("dcm", "application/dicom")
TypeIso = newType("iso", "application/x-iso9660-image")
TypeMachO = newType("macho", "application/x-mach-binary") // Mach-O binaries have no common extension.
TypeClass = newType("class", "application/java-vm") // Java class files
)

var Archive = Map{
Expand Down Expand Up @@ -67,6 +68,7 @@ var Archive = Map{
TypeDcm: Dcm,
TypeIso: Iso,
TypeMachO: MachO,
TypeClass: Class,
}

var (
Expand Down Expand Up @@ -184,7 +186,24 @@ func MachO(buf []byte) bool {
// Big endian versions below here...
(buf[0] == 0xCF && buf[1] == 0xFA && buf[2] == 0xED && buf[3] == 0xFE) ||
(buf[0] == 0xCE && buf[1] == 0xFA && buf[2] == 0xED && buf[3] == 0xFE) ||
(buf[0] == 0xCA && buf[1] == 0xFE && buf[2] == 0xBA && buf[3] == 0xBE))
// Java class files have a 0xCAFEBABE magic number. As the Class func can disambiguate,
// if buf has 0xCAFEBABE as a magic number but Class returns false, assume it's a MachO.
(buf[0] == 0xCA && buf[1] == 0xFE && buf[2] == 0xBA && buf[3] == 0xBE && !Class(buf)))
}

// Class matches Java class files which are pretty tricky.
// They have the same magic number as some MachO FAT files.
// Reference: https://opensource.apple.com/source/file/file-80.40.2/file/magic/Magdir/cafebabe.auto.html
func Class(buf []byte) bool {
if len(buf) < 8 {
return false
}

if !(buf[0] == 0xCA && buf[1] == 0xFE && buf[2] == 0xBA && buf[3] == 0xBE) {
return false
}

return binary.BigEndian.Uint32(buf[4:8]) >= 44 // Java 1.0 corresponds to major version 44.
}

// Zstandard compressed data is made of one or more frames.
Expand Down
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