You are reading an online chapter for Optimizing ColdFusion 5 by Chris

Transcription

1 APPENDIX B 1

2 2 Optimizing ColdFusion 5 You are reading an online chapter for Optimizing ColdFusion 5 by Chris Cortes (Osborne/McGraw-Hill, 2001). This online chapter is intended to supplement the printed text and provide valuable additional material to its readers. Optimizing ColdFusion 5 was designed to give ColdFusion architects and developers the tools necessary for improving many core aspects of their ColdFusion applications. For more information about this ColdFusion text and others visit or Standard HTTP Error Codes Because it seems like ColdFusion can be run on just about every web server on the planet, it would be very difficult for me to list for you all the variations of error messages that web servers return in the event an exception is thrown. What I can do, however, is list the common error code standards that the W3C has prescribed for web server error codes and messages as defined in RFC 2616, which covers HTTP errors. Although most web servers have customized or customizable variations on the definitions contained in the W3C standard, almost all of the core error code and messages remain intact. Being able to quickly understand or interpret web server error messages enables you to debug server and application problems faster, which, in effect, optimizes your debugging process. Remember that HTTP status codes, which represent errors, fall into one of two categories. 400 codes relate to errors that the client may have caused, and 500 messages relate to errors where the server is probably responsible for the problem. The following are the status codes that you are most likely to see on a regular basis. Client Side Errors HTTP status messages in the 400 range are exceptions thrown by a web server, where the client is suspected of causing an error. 400 Bad Request 400 Errors are one of the most common HTTP errors and are almost always caused by typos. When debugging 400 errors, look for very simple mistakes that you wouldn t normally worry about. And also, as mentioned in the following table, don t waste too much time with debugging these types of errors; it is usually faster to simply retype the address.

3 Appendix B Bad Request - The server, due to malformed syntax could not understand the client s request. 401 Unauthorized HTTP Status Code 401 Unauthorized The URL that was submitted by the client was probably mistyped. Watch for missed punctuation or misspelled words. Sometimes, hyphens or tildes are missing from the URL. Try retyping the address and resubmitting the request. 401 Unauthorized - The authentication has been refused. The server must authenticate the user in order to access the requested resource. Log in prior to attempting access to the requested resource. 403 Forbidden HTTP Status Code 403 Forbidden 403 Forbidden - The server understood the request, but it is refusing to fulfill it. The requested resource is not available to the client that requested it. A process commonly resulting in 403 errors is attempting to access resources with limited access. For example, when attempting to browse directories on Windows NT, if IIS has directory browsing disabled, IIS will return a 403 error message. 404 Not Found HTTP Status Code 404 Not Found 404 Not Found - The server has not found anything matching the requested address. The requested resource does not exist. Watch for misspelled words, as this is a common cause for false 404 status code reports. The 404 error is usually the result of one of two problems. First, the user may have made a typographical error when requesting the failed resource. Second, there

4 4 Optimizing ColdFusion 5 is a chance that the user is requesting a nonexistent resource, or a resource that has been moved from its previously known location. In either event, do not waste time debugging this error; instead, immediately look for spelling mistakes and punctuation errors in the URL or retype the URL and resubmit the request. 405 Method Not Allowed HTTP Status Code 405 Method Not Allowed 405 Method Not Allowed - The method identified in the header is not allowed for the resource identified by the request. You are attempting to use the incorrect protocol to access the resource. Make sure that the HTTP, HTTPS, or FTP designation is properly defined within the URL. When experiencing a 405 error message, immediately look to the beginning of the URL to make sure that you have defined the correct protocol that you want to use when making the request. Using the incorrect protocol for a specific resource is almost always the problem with 405 status codes. 408 Request Timeout HTTP Status Code 408 Request Timeout 408 Request Timeout - The client did not produce a request within the time that the server was prepared to wait. The time elapsed between the request start and end was too long, so the server stopped the request before the request could be completed. When frequently experiencing 408 messages, you should consider increasing the request timeout value for your server. If you are experiencing timeout problems when running scheduled tasks when using the CFSCHEDULE TAG, remember that you can override ColdFusion s default timeout value using the CFSCHEDULE requesttimeout attribute.

5 Appendix B 5 Server Side Errors 500 Internal Server Error HTTP Status Code 500 Internal Server Error 500 Internal Server Error - The server encountered an unexpected internal error. An unexpected error occurred, and the server is not able to complete the request. In most cases, immediately resubmitting the request will result in the request being successfully delivered. Consider that the Internet is a complex organism and that it really is a wonder that we are capable of submitting a request in Texas and seconds later receive a response originating in New York. There are many things that can go with a given request between the time that it is sent and the time that it is returned. Occasionally, requests are not successfully processed. I almost never worry about these types of errors unless they are happening in a disproportionately high percentage of the requests. 503 Service Unavailable HTTP Status Code 503 Service Unavailable 503 Service Unavailable - The server is currently unable to satisfy the request due to temporary overloading. The server is either busy or unable to fulfill the client s request, or the server is disconnected from the network or knocked offline. Common ColdFusion Error Messages Because ColdFusion applications are so diverse, the variations of problems with ColdFusion applications are endless. There are, however, a handful of classic

6 6 Optimizing ColdFusion 5 ColdFusion errors that persist across most ColdFusion applications, and ColdFusion developers can be trained to quickly pick up mistakes through visual recognition of error messages. There are basically two types of errors in ColdFusion applications that can be quickly debugged: CFML syntax errors and database configuration errors. CFML Syntax Errors CFML syntax errors can be caused by any of the following conditions: Missing or extraneous pound signs Missing or extraneous CFML ending tags Improperly positioned conditional tags such as <CFIF> and </CFIF> Missing quotes or semicolons in CFSCRIPT blocks Missing or extraneous angle brackets One thing that you should keep in mind when debugging CFML syntax errors in ColdFusion applications is that the ColdFusion Server debugging output usually places blame immediately following the actual cause of the problem. As a good rule of thumb, when you are debugging syntax errors, look at the line above the diagnosed problem to find the actual error. For example, look at the following code: 1 <cfscript> 2 3 Request.DSN = "CF5DB"; 4 Request.HomePage = "PartnerIndex.cfm" 5 6 </cfscript> NOTE In the preceding code example, I included line numbers in order to clarify my example. You cannot code line numbers into your ColdFusion templates. Notice that on line four of the preceding code example, there is a missing semicolon at the end of that line. Off the top of your head, do you know what error will be thrown if this code was executed, and where ColdFusion Application Server will put the blame? You should know the answer to this question; improving your debugging skills requires you to know what errors occur for which reasons.

7 Appendix B 7 The error that will be generated for the preceding code listing is Invalid Parser Construct, meaning that ColdFusion server expected to see a different character immediately following line four. ColdFusion will blame the first character of line six for the problem, because ColdFusion expects line four to be ended with a semicolon. In Figure B-1, you can see the error that was generated from the preceding code. Identifying patterns such as the Invalid Parser Construct error in the preceding example is an important part of building good debugging skills. In the following CFML syntax errors, there are also some common patterns in error message and syntax that can help you to quickly identify code mistakes. Figure B-1 Error caused by a missing semicolon in a CFSCRIPT block

8 8 Optimizing ColdFusion 5 NOTE ColdFusion Application Server does not handle syntax errors the same way that it handles other exceptions. In almost all instances, ColdFusion is not capable of catching syntax errors with CFCATH. An Error Occurred While Evaluating The Expression In some cases, when attempting to evaluate a variable, ColdFusion is unable to evaluate the expression and throws an error, as seen in Figure B-2. The most common cause for the error seen in Figure B-2 is a simple spelling mistake in the variable reference. When debugging this type of error, you should immediately check the spelling of the variables that you are attempting to evaluate. A second reason why this type of error may occur is an attempt to evaluate a Figure B-2 Error thrown by misspelled variable

9 Appendix B 9 variable that has not yet been created or initialized with a default value using the CFPARAM tag. Invalid Parser Construct Found Another common syntax error, which I briefly mentioned at the beginning of this section, is the invalid parser construct error, which is notorious for blaming the line following the actual error for the problem, as seen in Figure B-3. Common causes for the Invalid Parser Construct errors are: A missing semicolon inside of a CFSCRIPT block A missing quotation mark within a CFSCRIPT block or CFSET tag A missing angle bracket Figure B-3 Error caused by a missing semicolon in a CFSCRIPT block

10 10 Optimizing ColdFusion 5 Invalid Token Found Basically, Invalid Token Found is a way for ColdFusion to let you know that you have serious problems with your syntax. Look at the following example: 1 <cfscript> 2 3 Request.DSN = "getuserdata.dsn"; 4 Request.HomePage = "PartnerIndex.cfm"; 5 6 </cfscript> 7 8 <cfoutput#request.dsn#</cfoutput> NOTE In the preceding code example, I included line numbers in order to clarify my example. You cannot code line numbers into your ColdFusion templates. Notice that in line eight there is a missing close angle bracket in the opening CFOUTPUT tag. A missing close angle bracket in this case will cause the error message seen in Figure B-4. Again, being able to identify the culprits of common CFML syntax error messages, without stopping to examine your code, will enable you to more efficiently debug your ColdFusion applications. Database Errors The second type of ColdFusion problem that I want to cover are errors that you receive when attempting to attach your ColdFusion server to your database. Database errors can be caused by any of the following conditions: Spelling mistakes ColdFusion Administrator configuration problems Misused quotation marks Missing pound signs Remember that there are any number of syntax errors, such as swapping INSERT and UPDATE syntax, that occur within the SQL statement itself. I will not cover code misuse as a quickly identifiable bug.

11 Appendix B 11 Figure B-4 Invalid Token Found error caused by a missing angle bracket Data Source Not Found And No Default Driver Specified The Data Source Not Found error is an error that is thrown when the ColdFusion server is not able to locate the name that you have provided in the datasource attribute of the CFQUERY tag amongst the server s data source registrations. The Data Source Not Found error is shown in Figure B-5. In the case of the error in Figure B-5, the string Request.DSN was passed to the datasource attribute of the CFQUERY tag, while instead Request.DSN should have been passed in as a variable. There are three common causes for the Data Source Not Found error: Missing pound signs around a variable defining the datasource attribute of the CFQUERY tag. The data source name has been misspelled. The data source has not been registered on the machine where the error has been thrown.

12 12 Optimizing ColdFusion 5 My advice when debugging the Data Source Not Found error is to assume that you are missing pound signs around your data source variable, or that you have misspelled the data source name altogether. Although it is possible to have improperly configured your target data source, or have forgotten it entirely, the odds are that you will likely not forget such a big step, unless it is the first time that you are trying to connect to the target data source. Base Table Not Found The Base Table Not Found error is a result of the database not being able to find the table named in your SQL statement as a valid table within the queried database; this error is shown in Figure B-6. Figure B-5 Data Source Not Found error

13 Appendix B 13 Figure B-6 Base Table Not Found error This error is usually caused by one of the following problems in your code: The table name has been misspelled. When your application has multiple data sources, or you are reusing code from a custom tag or previous application, you may be pointed at the incorrect data source. Invalid Authorization Specification The Invalid Authorization Specification error is one that I do not see often, but one that can be tricky to debug depending on your background. Read the Invalid Authorization Specification error message in its entirety, as it is shown in Figure B-7. In Figure B-7, notice the phrase Not Associated With A Trusted SQL Server Connection. Some users mistake this message to mean that a trust relationship must

14 14 Optimizing ColdFusion 5 Figure B-7 Invalid Authorization Specification error be established between the ColdFusion server and the database server. This is an incorrect assumption; trust relationships do not need to be established between the ColdFusion server and your database, but you do need to enter a username and password, into the ColdFusion Administrator for that database, which enables ColdFusion Server to authenticate to your database server. To assign a username and password to an ODBC data source connection, follow these instructions: 1. Launch ColdFusion Administrator and enter the ODBC Datasources section. 2. Click the data source name whose connection information you want to modify. 3. Click the CF Settings >> button, in the bottom-right corner of the browser window.

15 Appendix B Under ColdFusion Login, enter a username and password. 5. Scroll down to the bottom of the window, and click the Update button in the bottom-left corner of the browser window. 6. Click the Verify link in the ODBC Datasources section to verify that your changes have successfully taken effect. Your data source should now be ready to use.