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CORBA is unusual among object systems for allowing a reference to be converted into a string that can be stored and converted back into a reference later This feature, although useful, is also open to abuse, so it is worthwhile to discuss stringified references in some detail 7101 Stringified Initial References Stringified references are often used to supply a client with one or more references to initial objects required for bootstrapping Although this technique works, it is inelegant and does not distribute well To get a reference from server to client, the reference must be transmitted via out-of-band means (such as e-mail), or it must be written into a file system that is shared by client and server (not a truly distributed solution) CORBA offers better and more sophisticated means of distributing initial references, and we cover them in s 18 and 19 For now, we are using stringified references for bootstrapping because they are the simplest (but not the best) way to get an initial reference from a server to a client In practice, you will almost never convert references to or from strings 7102 Size of Stringified References Stringified references begin with the prefix IOR: followed by an even number of hexadecimal digits For example:
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IOR:000000000000000d49444c3a54696d653a312e300000000000000001000000 00000000d800010100000000066d6572676500060b000000bd030231310c000016 7e0000175d360aed118129582d466163653a20267a682e2a4e394d4f77724d7152 73352a5d443948434b446a702c347634527250722f7d3f5b2b554c74644726485a 3c4d3259797c62325e642b65447a37442b21684f473c2a39795521302723373f69 633f5e7e7c7d73647b52235c722c7230694f32535d577e644f2d21455035216a64 562d2b33437362317029554d4e57627c3f303a364f67776b613c6d354b2227443c 577a215a5d234b484a517175465a200000000000000000
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As you can see, stringified IORs are quite long lengths of 200 to 800 bytes are common The exact length depends on the ORB and the length of the object key used by the application However, do not assume that because stringified IORs are long, they will
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also consume a large amount of memory For one thing, 50% of the bits of the stringified representation are wasted (because the string uses only hexadecimal digits) Second, an ORB can represent the information contained in references in a compact format in memory: if a client holds multiple references to objects in a single server, the ORB can keep a single in-memory copy to information that is identical among all the references (such as the repository ID and the addressing information) In that way, the ORB stores only the essential information unique to each reference and shares everything else to conserve memory Not all ORBs implement this optimization However, in a high-quality implementation, each additional reference in the client can consume as little as 30 bytes Nil references can be stringified as with any other reference:
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IOR:00000000000000010000000000000000
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7103 Interoperability of Stringified References The string representation of references is standardized by CORBA This means that you can safely decode a stringified reference that was produced by a different ORB Any differences among ORB environments are portably encoded in the reference itself For example, here is an alternative representation of a nil reference:
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IOR:01000000010000000000000000000000
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This reference is encoded in little-endian byte ordering (indicated by its IOR:01 prefix), whereas the nil reference in Section 7102 uses big-endian byte ordering (indicated by its IOR:00 prefix) An ORB correctly deals with such differences when it decodes a stringified reference 7104 Rules for Stringified References CORBA is very strict about what you can do with stringified references The only legal uses are Conversion of a reference to a string (object_to_string) Storage of a stringified reference for later retrieval Conversion of a stringified reference back to a reference (string_to_object) You can legally store a reference on disk or propagate it via out-of-band means (such as e-mail or even smoke signals) You can store a reference in stringified form indefinitely; the reference will continue to denote the same object provided that the object still exists when you de-stringify the reference
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Beyond that, you cannot make any assumptions about stringified references In particular, you cannot assume that stringifying a reference to an object will always produce the same string It is perfectly legal for an ORB to produce different strings for the same object at different times This happens, for example, if the ORB caches information in the reference Even though you can look at the stringified representation of a reference, you are not allowed to do that because it violates the opaqueness of references (see Section 251) If you compare stringified references to determine whether two references denote the same object, you are completely outside the CORBA object model The outcome of such a comparison is meaningless Do not ever use stringified references as database keys; that use involves comparing string representations, which is illegal Besides, their large size makes stringified IORs unsuitable as key values If you need to compare references, you can do so portably by calling the is_equivalent operation on the Object pseudo-interface (see Section 7113)
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