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9432fec612
The examples now use `fs.access` instead of the deprecated `fs.exists`. I have also rewritten the async/await example, since as of Node.js v15 the default behaviour for uncaught exceptions has changed to terminating the process instead of logging a warning, making the previous advice incorrect.
83 lines
1.9 KiB
XML
83 lines
1.9 KiB
XML
<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>
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Servers handle requests from clients until terminated
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deliberately by a server administrator. A client request that results
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in an uncaught server-side exception causes the current server
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response generation to fail, and should not have an effect on
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subsequent client requests.
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</p>
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<p>
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Under some circumstances, uncaught exceptions can however
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cause the entire server to terminate abruptly. Such a behavior is
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highly undesirable, especially if it gives malicious users the ability
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to turn off the server at will, which is an efficient
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denial-of-service attack.
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</p>
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</overview>
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<recommendation>
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<p>
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Ensure that the processing of client requests can not cause
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uncaught exceptions to terminate the entire server abruptly.
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</p>
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</recommendation>
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<example>
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<p>
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The following server code checks if a client-provided file path is valid
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before saving data to it. It would be reasonable to expect that the
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server responds with an error response to client requests with invalid
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file paths. However, the server instead throws an exception, which is
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uncaught in the context of the asynchronous callback invocation
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(<code>fs.access(...)</code>). This causes the entire server to
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terminate abruptly.
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</p>
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<sample src="examples/server-crash.BAD.js"/>
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<p>
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To remedy this, the server can catch the exception explicitly with
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a <code>try/catch</code> block, and generate an appropriate error
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response instead:
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</p>
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<sample src="examples/server-crash.GOOD-A.js"/>
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<p>
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To simplify exception handling, it may be advisable to switch to
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async/await syntax instead of using callbacks, which allows wrapping the
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entire request handler in a <code>try/catch</code> block:
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</p>
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<sample src="examples/server-crash.GOOD-B.js"/>
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</example>
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<references>
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</references>
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</qhelp>
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