Fetch symbols in Rust rather than with symchk.exe

[DrChat]

The process of fetching symbols seems to be pretty simple. To do so, you need the PDB filename and hash, and then you can issue a request to Microsoft's symbol server.

E.g: for ntoskrnl.exe

http://msdl.microsoft.com/download/symbols/ntkrnlmp.pdb/F3A4F64B6F639A058AD6F33155ACA4F61/ntkrnlmp.pdb

Or, for the compressed copy:

http://msdl.microsoft.com/download/symbols/ntkrnlmp.pdb/F3A4F64B6F639A058AD6F33155ACA4F61/ntkrnlmp.pd_

The symbol string commonly stored in _NT_SYMBOL_PATH takes the following form:

SRV*<path>*<URL>

E.g:

SRV*C:\symcache*http://msdl.microsoft.com/download/symbols

More advanced forms here.

Implementation

In lieu of supporting the full _NT_SYMBOL_PATH syntax, we'll just support the server and folder portions.

• Basic symbol fetching
• Fetching compressed symbols
• Fetching symbols from alternate server layout

References

https://randomascii.wordpress.com/2013/03/09/symbols-the-microsoft-way/
https://randomascii.wordpress.com/2020/03/14/creating-a-public-symbol-server-easily/
https://docs.microsoft.com/en-us/windows-hardware/drivers/debugger/symbol-store-folder-tree
https://docs.microsoft.com/en-us/windows-hardware/drivers/debugger/advanced-symsrv-use