How to read print job content using ReadPrinter method

Question

I'd like to get content of a document sent to printing. Google said an only way to do that is to use WinAPI method ReadPrinter(). I've implemented a sketch but can't get it work. A trouble is the ReadPrinter() method always returns nothing.

Please give me a hint what is wrong.

Simplified code below:

string printerName = "Microsoft XPS Document Writer";
const uint firstJob = 0u;
const uint noJobs = 10u;
const uint level = 1u;
uint bytesNeeded;
uint returned;
uint bytesCopied;
uint structsCopied;

// Open printer
IntPtr printerHandle = OpenPrinterW(printerName.Normalize(), out printerHandle, IntPtr.Zero);

// Get byte size required for a data
EnumJobsW(printerHandle, firstJob, noJobs, level, IntPtr.Zero, 0, out bytesNeeded, out returned);

// Now we know how much memory we need to read the data (bytesNeeded value)
IntPtr pJob = Marshal.AllocHGlobal((int)bytesNeeded);

// Read the data
EnumJobsW(printerHandle, firstJob, noJobs, level, pJob, bytesNeeded, out bytesCopied, out structsCopied);

// Convert pJob to jobInfos
JOB_INFO_1W[] jobInfos = null;

// ... actual convert code missed ...

//  Iterate through the jobs and try to get their content
foreach (JOB_INFO_1W jobInfo in jobInfos)
{
    // Open print job
    string printJobName = string.Format("{0}, Job {1}", printerName, jobInfo.JobId);
    IntPtr printJobHandle;

    OpenPrinterW(printJobName.Normalize(), out printJobHandle, IntPtr.Zero);

    // Read print job
    const int printJobBufLen = 1024;
    StringBuilder printJobSb = new StringBuilder(printJobBufLen);
    int printJobBytesRead = 0;

    while (printJobBytesRead == 0)
    {
        ReadPrinter(printJobHandle, printJobSb, printJobBufLen, out printJobBytesRead);

        // !!! printJobBytesRead is 0 and printJobSb is empty
    }

    // Close print job
    ClosePrinter(printJobHandle);
}

// Close printer
ClosePrinter(printerHandle);

P/Invoke signatures:

[DllImport("winspool.drv", EntryPoint = "OpenPrinterW", SetLastError = true, CharSet = CharSet.Unicode, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
public static extern int OpenPrinterW(
    [In] string pPrinterName,
    [Out] out IntPtr phPrinter,
    [In] IntPtr pDefault);

[DllImport("spoolss.dll", EntryPoint = "ClosePrinter", SetLastError = true, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
public static extern int ClosePrinter(
    [In] IntPtr hPrinter);

[DllImport("winspool.drv", EntryPoint = "EnumJobsW", SetLastError = true, CharSet = CharSet.Unicode, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
public static extern int EnumJobsW(
    [In] IntPtr hPrinter,
    [In] uint FirstJob,
    [In] uint NoJobs,
    [In] uint Level,
    [Out] IntPtr pJob,
    [In] uint cbBuf,
    [Out] out uint pcbNeeded,
    [Out] out uint pcReturned);

[DllImport("spoolss.dll", EntryPoint = "ReadPrinter", SetLastError = true, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
public static extern int ReadPrinter(
    [In] IntPtr hPrinter,
    [Out] StringBuilder data,
    [In] Int32 cbBuf,
    [Out] out Int32 pNoBytesRead);

Answer 1

Is this code inside a driver's Print Processor component? (Link updated to web archive.) If not, I don't think it will work.

So you either use a print driver component, or read from the spool file on disk. See here.