Linux printing should work perfectly now.

To print first install printer with cups then give local printername as printer (not the URI).

Tanshu.Accounts.Print/PrinterLinux.cs

@@ -5,43 +5,86 @@ namespace Tanshu.Accounts.Print
 {
     internal class PrinterLinux : PlatformPrinter
     {
-        #region API Declarations
         // ReSharper disable InconsistentNaming
-        [DllImport("libcups", CharSet = CharSet.Ansi)]
+        #region API Declarations
-        static extern int cupsPrintFile(string printer, string filename, string title, int num_options, IntPtr options);
+        enum http_status_t              /**** HTTP status codes ****/
-        // int cupsPrintFile (const char *name, const char *filename, const char *title, int num_options, cups_option_t *options);
+        {
+            HTTP_ERROR = -1,                      /* An error response from httpXxxx() */
+            HTTP_CONTINUE = 100,                  /* Everything OK, keep going... */
+            HTTP_SWITCHING_PROTOCOLS,             /* HTTP upgrade to TLS/SSL */
+            HTTP_OK = 200,                        /* OPTIONS/GET/HEAD/POST/TRACE command was successful */
+            HTTP_CREATED,                         /* PUT command was successful */
+            HTTP_ACCEPTED,                        /* DELETE command was successful */
+            HTTP_NOT_AUTHORITATIVE,               /* Information isn't authoritative */
+            HTTP_NO_CONTENT,                      /* Successful command, no new data */
+            HTTP_RESET_CONTENT,                   /* Content was reset/recreated */
+            HTTP_PARTIAL_CONTENT,                 /* Only a partial file was recieved/sent */
+            HTTP_MULTIPLE_CHOICES = 300,          /* Multiple files match request */
+            HTTP_MOVED_PERMANENTLY,               /* Document has moved permanently */
+            HTTP_MOVED_TEMPORARILY,               /* Document has moved temporarily */
+            HTTP_SEE_OTHER,                       /* See this other link... */
+            HTTP_NOT_MODIFIED,                    /* File not modified */
+            HTTP_USE_PROXY,                       /* Must use a proxy to access this URI */
+            HTTP_BAD_REQUEST = 400,               /* Bad request */
+            HTTP_UNAUTHORIZED,                    /* Unauthorized to access host */
+            HTTP_PAYMENT_REQUIRED,                /* Payment required */
+            HTTP_FORBIDDEN,                       /* Forbidden to access this URI */
+            HTTP_NOT_FOUND,                       /* URI was not found */
+            HTTP_METHOD_NOT_ALLOWED,              /* Method is not allowed */
+            HTTP_NOT_ACCEPTABLE,                  /* Not Acceptable */
+            HTTP_PROXY_AUTHENTICATION,            /* Proxy Authentication is Required */
+            HTTP_REQUEST_TIMEOUT,                 /* Request timed out */
+            HTTP_CONFLICT,                        /* Request is self-conflicting */
+            HTTP_GONE,                            /* Server has gone away */
+            HTTP_LENGTH_REQUIRED,                 /* A content length or encoding is required */
+            HTTP_PRECONDITION,                    /* Precondition failed */
+            HTTP_REQUEST_TOO_LARGE,               /* Request entity too large */
+            HTTP_URI_TOO_LONG,                    /* URI too long */
+            HTTP_UNSUPPORTED_MEDIATYPE,           /* The requested media type is unsupported */
+            HTTP_REQUESTED_RANGE,                 /* The requested range is not satisfiable */
+            HTTP_EXPECTATION_FAILED,              /* The expectation given in an Expect header field was not met */
+            HTTP_UPGRADE_REQUIRED = 426,          /* Upgrade to SSL/TLS required */
+            HTTP_SERVER_ERROR = 500,              /* Internal server error */
+            HTTP_NOT_IMPLEMENTED,                 /* Feature not implemented */
+            HTTP_BAD_GATEWAY,                     /* Bad gateway */
+            HTTP_SERVICE_UNAVAILABLE,             /* Service is unavailable */
+            HTTP_GATEWAY_TIMEOUT,                 /* Gateway connection timed out */
+            HTTP_NOT_SUPPORTED,                   /* HTTP version not supported */
+            HTTP_AUTHORIZATION_CANCELED = 1000    /* User canceled authorization */
+        } ;
 
         [DllImport("libcups", CharSet = CharSet.Ansi)]
-        static extern int cupsCreateJob(string http, string name, string title, int num_options, IntPtr options);
+        static extern int cupsCreateJob(IntPtr http, string name, string title, int num_options, IntPtr options);
         // int cupsCreateJob (http_t *http, const char *name, const char *title, int num_options, cups_option_t *options);
 
         [DllImport("libcups", CharSet = CharSet.Ansi)]
-        static extern int cupsStartDocument(string http, string name, int job_id, string docname, string format, int last_document);
+        static extern int cupsStartDocument(IntPtr http, string name, int job_id, string docname, string format, int last_document);
         // http_status_t cupsStartDocument (http_t *http, const char *name, int job_id, const char *docname, const char *format, int last_document);
 
         [DllImport("libcups", CharSet = CharSet.Ansi)]
-        static extern int cupsWriteRequestData(string http, string buffer, int length);
+        static extern int cupsWriteRequestData(IntPtr http, string buffer, int length);
         // http_status_t cupsWriteRequestData (http_t *http, const char *buffer, size_t length);
 
         [DllImport("libcups", CharSet = CharSet.Ansi)]
-        static extern int cupsFinishDocument(string http, string name);
+        static extern int cupsFinishDocument(IntPtr http, string name);
         // ipp_status_t cupsFinishDocument (http_t *http, const char *name);
-        // ReSharper restore InconsistentNaming
+
+        const string CUPS_FORMAT_TEXT = "text/plain";
         #endregion
 
         internal override bool Print(string printerName, string documentName, string printingText)
         {
             var cupsOption = new IntPtr(0);
-            const string CUPS_HTTP_DEFAULT = "CUPS_HTTP_DEFAULT";
+            var CUPS_HTTP_DEFAULT = new IntPtr(0);
             var jobId = cupsCreateJob(CUPS_HTTP_DEFAULT, printerName, documentName, 0, cupsOption);
             if (jobId > 0)
             {
-                const string format = "CUPS_FORMAT_TEXT";
+                cupsStartDocument(CUPS_HTTP_DEFAULT, printerName, jobId, documentName, CUPS_FORMAT_TEXT, 1);
-                cupsStartDocument(CUPS_HTTP_DEFAULT, printerName, jobId, documentName, format, 1);
                 cupsWriteRequestData(CUPS_HTTP_DEFAULT, printingText, printingText.Length);
                 cupsFinishDocument(CUPS_HTTP_DEFAULT, printerName);
             }
             return jobId > 0;
         }
+        // ReSharper restore InconsistentNaming
     }
 }

Tanshu.Accounts.Print/ThermalPrinter.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Runtime.InteropServices;
 
 namespace Tanshu.Accounts.Print
 {
@@ -16,15 +15,7 @@ namespace Tanshu.Accounts.Print
         internal static bool RunningOnLinux()
         {
             var platform = (int)Environment.OSVersion.Platform;
-            if ((platform == 4) || (platform == 6) || (platform == 128))
+            return (platform == 4) || (platform == 6) || (platform == 128);
-            {
-                if (Environment.GetEnvironmentVariable("not_supported_MONO_MWF_USE_NEW_X11_BACKEND") != null ||
-                    Environment.GetEnvironmentVariable("MONO_MWF_MAC_FORCE_X11") != null)
-                {
-                    return true;
-                }
-            }
-            return false;
         }
     }
 }