(SQL Server) How to Tell if a File is .p7m or .p7s

This example explains how to detect if a file is a .p7m or .p7s. It provides as solution to the following problem:

Sometimes people submit P7S/P7M with wrong extensions. Can I check if file is P7S or P7M with Chilkat?

Also see What is a P7M or P7S File?

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

-- Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @iTmp0 int
    DECLARE @iTmp1 int
    DECLARE @iTmp2 int
    DECLARE @iTmp3 int
    -- Important: Do not use nvarchar(max).  See the warning about using nvarchar(max).
    DECLARE @sTmp0 nvarchar(4000)
    -- A .p7m or .p7s file is binary and contains PKCS7.
    -- PKCS7 is ASN.1, and always begins with a SEQUENCE tag (a byte equal to 0x30)
    -- followed by an encoded length.
    -- If the file is larger than 128 bytes (and it SHOULD be), the encoded length will begin with either 0x80, 0x81, 0x82, or 0x83.
    -- It can also begin with 0x84, but only for very large files (where the length is too large for 3 bytes).
    -- See How ASN.1 Encodes Lengths

    -- Therefore, if we have a file that might be .p7m or .p7s, we can check by
    -- examining the 1st 2 bytes of the file.

    DECLARE @bd int
    -- Use "Chilkat_9_5_0.BinData" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.BinData', @bd OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    DECLARE @success int
    EXEC sp_OAMethod @bd, 'LoadFile', @success OUT, 'qa_data/p7m/a.p7m'
    IF @success = 0
      BEGIN

        PRINT 'Failed to load the file.'
        EXEC @hr = sp_OADestroy @bd
        RETURN
      END

    DECLARE @sb int
    -- Use "Chilkat_9_5_0.StringBuilder" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.StringBuilder', @sb OUT

    EXEC sp_OAMethod @bd, 'GetEncodedChunk', @sTmp0 OUT, 0, 2, 'hex'
    EXEC sp_OAMethod @sb, 'Append', @success OUT, @sTmp0

    DECLARE @caseSensitive int
    SELECT @caseSensitive = 1
    EXEC sp_OAMethod @sb, 'ContentsEqual', @iTmp0 OUT, '3080', @caseSensitive
    EXEC sp_OAMethod @sb, 'ContentsEqual', @iTmp1 OUT, '3081', @caseSensitive
    EXEC sp_OAMethod @sb, 'ContentsEqual', @iTmp2 OUT, '3082', @caseSensitive
    EXEC sp_OAMethod @sb, 'ContentsEqual', @iTmp3 OUT, '3083', @caseSensitive
    IF @iTmp0 or @iTmp1 or @iTmp2 or @iTmp3
      BEGIN

        PRINT 'This is a .p7m or .p7s file.'
      END
    ELSE
      BEGIN

        PRINT 'This is not a .p7m or .p7s file.'
      END

    EXEC @hr = sp_OADestroy @bd
    EXEC @hr = sp_OADestroy @sb


END
GO