A customer was getting this error from their Web server:<\/p>\n
Server Error in ‘\/’ Application.<\/p>\n
The environment block used to start a process cannot be longer than 65535 bytes. Your environment block is 70009 bytes long. Remove some environment variables and try again.<\/p>\n
Description<\/b>: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.<\/p>\n
Details<\/b>: System.InvalidOperationException: The environment block used to start a process cannot be longer than 65535 bytes. Your environment block is 70009 bytes long. Remove some environment variables and try again.<\/p>\n<\/div>\n
Windows imposes no hard-coded limit on the size of a Unicode environment block. Here’s a test program that shows that a 256KB environment block is no problem:<\/p>\n
#include <windows.h>\r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n auto n = 65535*2;\r\n auto p = new WCHAR[n];\r\n for (int i = 0; i < n; i++) {\r\n p[i] = L'x';\r\n }\r\n p[1] = L'=';\r\n p[n-1] = 0;\r\n p[n-2] = 0;\r\n STARTUPINFO si = { sizeof(si) };\r\n PROCESS_INFORMATION pi;\r\n wchar_t cmdline[] = L\"notepad.exe\";\r\n printf(\"CreateProcess result is %d\\n\",\r\n CreateProcessW(nullptr, cmdline, nullptr, nullptr, false,\r\n CREATE_UNICODE_ENVIRONMENT, p, nullptr, &si, &pi));\r\n return 0;\r\n}\r\n<\/pre>\nThis program creates an environment block that holds only one variable, named x<\/code> whose value is 131,067 copies of the letter x<\/code>. It’s not glamourous, and certainly not useful, but it does show that Windows is fine with it.<\/p>\nThis claimed 65535 byte limit must therefore be coming from somewhere else. After some investigation, the customer found it<\/a>:<\/p>\nnamespace System.Diagnostics\r\n{\r\n \/* ... *\/\r\n\r\n internal static class EnvironmentBlock {\r\n public static byte[] ToByteArray(StringDictionary sd, bool unicode) {\r\n \/* ... *\/\r\n\r\n if (unicode) {\r\n envBlock = Encoding.Unicode.GetBytes(stringBuff.ToString());\r\n } else {\r\n envBlock = Encoding.Default.GetBytes(stringBuff.ToString());\r\n\r\n if (envBlock.Length > UInt16.MaxValue)\r\n throw new InvalidOperationException(\r\n SR.GetString(SR.EnvironmentBlockTooLong,\r\n envBlock.Length));<\/span>\r\n }\r\n\r\n return envBlock;\r\n }\r\n }\r\n}\r\n<\/pre>\nThe exception is coming from the C# base class library.<\/p>\n
Note that the check is inside the else<\/code> branch, which means that somebody is passing an ANSI environment block to the CreateProcess function, and ANSI environment blocks are documented as supported up to 32,767 characters.<\/p>\n