.NET/Java PDF, Tiff, Barcode SDK Library

over time. The more people parsing, the more people waiting in line to latch the shared pool, the longer the queues, the longer the wait. Executing SQL statements without bind variables is very much like compiling a subroutine before each method call. Imagine shipping Java source code to your customers where, before calling a method in a class, they had to invoke the Java compiler, compile the class, run the method, and then throw away the byte code. Next time they wanted to execute the same method, they would do the same thing: compile it, run it, and throw it away. You would never consider doing this in your application; you should never consider doing this in your database either. Another impact of not using bind variables, for developers employing string concatenation, is security specifically something called SQL injection. If you are not familiar with this term, I encourage you to put aside this book for a moment and, using the search engine of your choice, look up SQL injection. There are almost one million hits returned for it as I write this edition. The problem of SQL injection is well-documented.

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1. Languages targeting .NET are not affected by these interoperability issues since they share the same CLR runtime.

Note SQL injection is a security hole whereby the developer accepts input from an end user and concatenates that

must be known at compile time) or acquired at run time by accessing component metadata in the form of an interface named IDispatch or a database called type library Since COM components can be compiled by any compiler supporting the generation of memory layouts compatible with the standard, it is necessary that the client shares the same layout for data structures that must be passed or returned by the component methods The standard type system for COM, defined in oledll, defines a simple and restricted set of types COM types correspond to the Variant type of Visual Basic and provide only basic types and arrays For structured types, COM requires a custom marshaller to be developed, but this has been rarely used in components that are widely available The COM infrastructure provides a memory manager that uses reference counting to automatically free components when they are not used anymore.

input into a query, then compiles and executes that query. In effect, the developer accepts snippets of SQL code from the end user, then compiles and executes those snippets. That approach allows the end user to potentially modify the SQL statement so that it does something the application developer never intended. It s almost like leaving a terminal open with a SQL Plus session logged in and connected as SYSDBA. You are just begging someone to come by and type in some command, compile it, and then execute it. The results can be disastrous.

It is a fact that if you do not use bind variables, that if you use the string concatenation technique in PROC2 shown earlier, your code is subject to SQL injection attacks and must be carefully reviewed. And it should be reviewed by people who don t actually like the developer who wrote the code because the code must be reviewed critically and objectively. If the reviewers are peers of the code author, or worse, friends or subordinates, the review will not be as critical as it should be. Developed code that does not use bind variables must be viewed with suspicion it should be the exceptional case where bind variables are not used, not the norm. To demonstrate how insidious SQL injection can be, I present this small routine: ops$tkyte%ORA11GR2> create or replace procedure inj( p_date in date ) 2 as 3 l_rec all_users%rowtype; 4 c sys_refcursor; 5 l_query long; 6 begin 7 l_query := ' 8 select * 9 from all_users 10 where created = ''' ||p_date ||''''; 11 12 dbms_output.put_line( l_query ); 13 open c for l_query; 14 15 for i in 1 .. 5 16 loop 17 fetch c into l_rec;

Whenever a copy of a pointer to an interface is copied, the programmer is required to invoke the AddRef method of the IUnknown interface (every interface inherits from IUnknown), and when the pointer is no longer required, the Release method should be called to decrement the counter inside the component When the counter reaches zero, the component is automatically freed This strategy of memory management, though more automatic than the traditional malloc/free handling of the heap, has proven to be error prone, because programmers often forget to increment the counter when pointers are copied (risk of dangling pointers) or decrement when a pointer is no longer needed (risk of memory wasted in garbage).