/*
 * Structure representing a DEX file.
 *
 * Code should regard DexFile as opaque, using the API calls provided here
 * to access specific structures.
 */
struct DexFile {
    /* directly-mapped "opt" header */
    const DexOptHeader* pOptHeader;

    /* pointers to directly-mapped structs and arrays in base DEX */
    const DexHeader*    pHeader;
    const DexStringId*  pStringIds;
    const DexTypeId*    pTypeIds;
    const DexFieldId*   pFieldIds;
    const DexMethodId*  pMethodIds;
    const DexProtoId*   pProtoIds;
    const DexClassDef*  pClassDefs;
    const DexLink*      pLinkData;

    /*
     * These are mapped out of the "auxillary" section, and may not be
     * included in the file.
     */
    const DexClassLookup* pClassLookup;
    const void*         pRegisterMapPool;       // RegisterMapClassPool

    /* points to start of DEX file data */
    const u1*           baseAddr;

    /* track memory overhead for auxillary structures */
    int                 overhead;

    /* additional app-specific data structures associated with the DEX */
    //void*               auxData;
};

struct DexFile{
    DexHeader    Header;
    DexStringId  StringIds[stringIdsSize];
    DexTypeId    TypeIds[typeIdsSize];
    DexFieldId   FieldIds[fieldIdsSize];
    DexMethodId  MethodIds[methodIdsSize];
    DexProtoId   ProtoIds[protoIdsSize];
    DexClassDef  ClassDefs[classDefsSize];
    DexData      Data[];
    DexLink      LinkData;
};

/*
 * 160-bit SHA-1 digest.
 */
enum { kSHA1DigestLen = 20,
       kSHA1DigestOutputLen = kSHA1DigestLen*2 +1 };

/*
 * Direct-mapped "header_item" struct.
 */
struct DexHeader {
    u1  magic[8];           /* 版本标识 */
    u4  checksum;           /* adler32 检验 */
    u1  signature[kSHA1DigestLen]; /* SHA-1 哈希值 */
    u4  fileSize;           /* 整个文件大小 */
    u4  headerSize;         /* DexHeader 大小 */
    u4  endianTag;          /* 字节序标记 */
    u4  linkSize;           /* 链接段大小 */
    u4  linkOff;            /* 链接段偏移 */
    u4  mapOff;             /* DexMapList 的文件偏移 */
    u4  stringIdsSize;      /* DexStringId 的个数 */
    u4  stringIdsOff;       /* DexStringId 的文件偏移 */
    u4  typeIdsSize;        /* DexTypeId 的个数 */
    u4  typeIdsOff;         /* DexTypeId 的文件偏移 */
    u4  protoIdsSize;       /* DexProtoId 的个数 */
    u4  protoIdsOff;        /* DexProtoId 的文件偏移 */
    u4  fieldIdsSize;       /* DexFieldId 的个数 */
    u4  fieldIdsOff;        /* DexFieldId 的文件偏移 */
    u4  methodIdsSize;      /* DexMethodId 的个数 */
    u4  methodIdsOff;       /* DexMethodId 的文件偏移 */
    u4  classDefsSize;      /* DexClassDef 的个数 */
    u4  classDefsOff;       /* DexClassDef 的文件偏移 */
    u4  dataSize;           /* 数据段的大小 */
    u4  dataOff;            /* 数据段的文件偏移 */
};

ubyte[8] DEX_FILE_MAGIC = { 0x64 0x65 0x78 0x0a 0x30 0x33 0x35 0x00 }
                        = "dex\n035\0"

uint ENDIAN_CONSTANT = 0x12345678;
uint REVERSE_ENDIAN_CONSTANT = 0x78563412;

00000000  64 65 78 0a 30 33 35 00  3b ba fe c3 83 7e aa be  |dex.035.;....~..|
00000010  09 97 71 1e 17 96 9f e9  0c bd 01 60 b4 2a 1a c9  |..q........`.*..|
00000020  c4 10 00 00 70 00 00 00  78 56 34 12 00 00 00 00  |....p...xV4.....|
00000030  00 00 00 00 00 10 00 00  5c 00 00 00 70 00 00 00  |........\...p...|
00000040  19 00 00 00 e0 01 00 00  12 00 00 00 44 02 00 00  |............D...|
00000050  01 00 00 00 1c 03 00 00  2b 00 00 00 24 03 00 00  |........+...$...|
00000060  02 00 00 00 7c 04 00 00  08 0c 00 00 bc 04 00 00  |....|...........|

import struct

class DexStruct(object):
    DexHeader = {
          "magic": 0,
          "checkSum": 0,
          'signature': 0,
          'fileSize': 0,
          "headerSize": 0,
          "endianTag": 0,
          "linkSize": 0,
          "linkOff": 0,
          "mapOff": 0,
          "stringIdsSize": 0,
          "stringIdsOff": 0,
          "typeIdsSize": 0,
          "typeIdsOff": 0,
          "protoIdsSize": 0,
          "protoIdsOff": 0,
          "fieldIdsSize": 0,
          "fieldIdsOff": 0,
          "methodIdsSize": 0,
          "methodIdsOff": 0,
          "classDefsSize": 0,
          "classDefsOff": 0,
          "dataSize": 0,
          "dataOff": 0,   }


def parseHeader(header_data):

        header_list = [header_data[i:i+4] for i in range(32,112,4)]
        header_list.insert(0,header_data[12:32])
        header_list.insert(0,header_data[8:12])
        header_list.insert(0,header_data[:8])

        DexStruct.DexHeader['magic'] = struct.unpack('8s',header_list[0])[0]
        if DexStruct.DexHeader['magic'] != "dex\n035\0":
            print 'invalid dex file.'
            exit(-1)
        DexStruct.DexHeader['checkSum'] = struct.unpack('I',header_list[1])[0]
        DexStruct.DexHeader['signature'] = struct.unpack('20s',header_list[2])[0]
        DexStruct.DexHeader['fileSize'] = struct.unpack('I',header_list[3])[0]
        DexStruct.DexHeader['headerSize'] = struct.unpack('I',header_list[4])[0]
        DexStruct.DexHeader['endianTag'] = struct.unpack('I',header_list[5])[0]
        DexStruct.DexHeader['linkSize'] = struct.unpack('I',header_list[6])[0]
        DexStruct.DexHeader['linkOff'] = struct.unpack('I',header_list[7])[0]
        DexStruct.DexHeader['mapOff'] = struct.unpack('I',header_list[8])[0]
        DexStruct.DexHeader['stringIdsSize'] = struct.unpack('I',header_list[9])[0]
        DexStruct.DexHeader['stringIdsOff'] = struct.unpack('I',header_list[10])[0]
        DexStruct.DexHeader['typeIdsSize'] = struct.unpack('I',header_list[11])[0]
        DexStruct.DexHeader['typeIdsOff'] = struct.unpack('I',header_list[12])[0]
        DexStruct.DexHeader['protoIdsSize'] = struct.unpack('I',header_list[13])[0]
        DexStruct.DexHeader['protoIdsOff'] = struct.unpack('I',header_list[14])[0]
        DexStruct.DexHeader['fieldIdsSize'] = struct.unpack('I',header_list[15])[0]
        DexStruct.DexHeader['fieldIdsOff'] = struct.unpack('I',header_list[16])[0]
        DexStruct.DexHeader['methodIdsSize'] = struct.unpack('I',header_list[17])[0]
        DexStruct.DexHeader['methodIdsOff'] = struct.unpack('I',header_list[18])[0]
        DexStruct.DexHeader['classDefsSize'] = struct.unpack('I',header_list[19])[0]
        DexStruct.DexHeader['classDefsOff'] = struct.unpack('I',header_list[20])[0]
        DexStruct.DexHeader['dataSize'] = struct.unpack('I',header_list[21])[0]
        DexStruct.DexHeader['dataOff'] = struct.unpack('I',header_list[22])[0]


if __name__ == '__main__':

    with open("classes.dex", 'rb') as f:
        parseHeader(f.read(0x70))
        for x in DexStruct.DexHeader:
            print x, hex(DexStruct.DexHeader[x])