Hello dear podofo-users, we currently have some issues with loading some pdf files using Podofo. When performing the load operation, the podofo code crashes with a stack overflow error.
I took a closer look at the pdf file, stepping through the Podofo code. In doing so, I found out that that this pdf file has 160 trailers / updates! This gets problematic, because parsing occurs recursively here: ReadDocumentStructure() -> ReadXRefContents() -> ReadNextTrailer() -> ReadXRefContents() -> ReadNextTrailer() ... Parsing begins with ReadDocumentStructure. At the end of the function, the (current) Xref table is read through ReadXRefContents. After the Xref table, there is a trailer, which is processed at the end of the ReadXRefContents function by calling the ReadNextTrailer function. In such a trailer, the /Prev attribute may be present, which refers to the previous version (offset to an Xref table). If such a thing is found, ReadXRefContents is called again with the new offset, and thus, ReadNextTrailer is called again later. If this also has a /Prev, the recursion continues until a trailer has no /Prev anymore. So, there are two functions calling each other repeadetly, without recursion unwinding in between. Consequently, the stack for the function calls is eventually exhausted, leading to a StackOverflow error (in my test at Update 127). We are using Podofo 0.9.8, but I checked the 0.10.x code as well, the parsing works essentially the same. So, in order to prevent stack overflows due to a large number of trailers, the code needs to be restructured from a recursive to an iterative approach. One solution could be to pass the /Prev offset from the trailer back to the caller, and then using a do-while loop until the passed back offset is zero. But I'm not familiar enough with all the details of the parsing code. Is there someone who could have a look into this? Is there maybe another, easier approach for preventing the stack overflow? Greetings, F.E.
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