What is causing Ghostscript to return an error of

问题:

So, I am using Matthew Ephraim's GhostscriptSharp, which is a simple C# wrapper for the unmanaged Win32 Ghostscript DLL in my ASP.Net MVC project. Some background:

What I am attempting to do is have a user upload a PDF, and then convert that document into an image that I can then save off into whatever directory I choose (as well as do some other OOP to tie that new image to my site).

I decided to use Mr. Ephraim's wrapper class (GhostscriptSharp) because it was simple enough to use, and it gives me relatively clean access to the DLL's API.

To test it, I created a dummy C# console application to make sure I could load the DLL, access it, hand it a PDF file on the local disk and then have it write a JPG to the same local disk. After a few learning experiences, I had success. I would hand it C:\INPUT.pdf, it would hand me C:\OUTPUT.jpg.

However, after integrating the GhostScriptSharp code that I had in the console application into my ASP.NET MVC project to the point of where I was calling the DLL with P/invoke, Ghostscript is returning with the int/error code -100, which is a fatal error (is called E_Fatal in the GhostScript source code). I get the same result with both the file that is uploaded through the HTML form, and if I hand it the exact same hard-coded paths that I used in my working console application.

For reference, the lines which the exception is thrown are 93-97 in GhostScriptSharp.cs (which is in the CallApi function):

int result = InitAPI(gsInstancePtr, args.Length, args);

if (result < 0) {
  throw new ExternalException("Ghostscript conversion error", result);
}

Obviously the exception is thrown because result is -100.

When InitAPI is called, the instance ptr is a valid int (though I don't know if the instance of GS is correct or not), args has a length of 20 (is a string[]) of valid GhostScript options (including the correctly-escaped paths to my input & output files).

Long story short, what am I doing wrong? The error code -100 seems like a catch-all because there is no documentation that states what could possibly be going wrong here.

Any help is much appreciated, thank you in advance.

回答1:

The -100 error is a generic "fatal error" in GhostScript.

A few things to check:

1) Permissions (al operations require file access)

2) Scope, you want to add the GS bin folder to the PATH variables

3) Consider not calling GhostScript directly from asp.net, GS can be very CPU intensive, rather process files in a separate service

I have also created a wrapper, send me an email (address on profile) and I will send it you. It allows one to pass in the GS bin folder which helps.

回答2:

Most likely the process running the web application does not have permission to write to the directories that you are using. I'd suggest creating some specific directory for the app to use and a local id to use to run the app pool, then give that id enough privileges to read/write the directory you've created.

回答3:

So, ended up being an ID10T error that was derailing me here in this specific instance.

In Matthew Ephraim's GhostscriptSharp code, he uses a couple of enums to define the options set forth for Ghostscript, and two in particular were the GhostscriptDevices and GhostscriptPageSizes enums. Problem is, the way they're written Resharper (Jetbrains Visual Studio plugin) has default rules for naming Enum members. Not thinking, I fixed all of these definitions to please Resharper not realizing that these are passed directly to Ghostscript, so instead of getting a7 for -sPAPERSIZE GS was getting A7, and for -sDEVICE it was getting Jpeg instead of jpeg.

For the time being permissions weren't a problem on my end, but only because I run the Cassini web dev test server in Visual Studio.

Thanks to @MarkRedman and @tvanfosson for their helpful suggestions!