前言

在近期开发的收银台项目中，需要使用打印机进行小票打印，打印流程的时序图如下所示：

在客户的使用过程中，遇到一个问题，如果机器安装了打印机驱动，那么调用厂商提供的 sdk 进行打印的话，会导致出现小票只打印一半的情况，对此，需要绕过厂商 sdk 使用系统的打印才能够解决这一问题。

在 web 端打印中，需要调用浏览器打印 api 进行网页打印。这意味着，之前后端编写的esc/pos无法复用到，同时，前端还得花费精力来编写 html 以及css 来完成打印内容的排版，这无疑增加了复杂度以及工作量。正打算开始时，得到高人指点。

可以使用 windows api 进行打印

具体参见这篇文档

于是开始这方面的研究，功夫不负有心人，使用 windows api 完成了系统的打印，于是编写这篇文章记录踩过的坑。
首先看看如何进行打印：

BOOL RawDataToPrinter(LPSTR szPrinterName, LPBYTE lpData, DWORD dwCount){ HANDLE hPrinter; DOC_INFO_1 DocInfo; DWORD dwJob; DWORD dwBytesWritten; // Need a handle to the printer. if (!OpenPrinter(szPrinterName, &hPrinter, NULL)) { int y = GetLastError(); cout << "openFail" << y << endl; return FALSE; } // Fill in the structure with info about this "document." DocInfo.pDocName = LPSTR("My Document\0"); DocInfo.pOutputFile = NULL; DocInfo.pDatatype = NULL; // LPWSTR("RAW\0"); // Inform the spooler the document is beginning. if ((dwJob = StartDocPrinter(hPrinter, 1, (LPBYTE)&DocInfo)) == 0) { int x = GetLastError(); cout << "StartDocPrinter Fail" << x << endl; ClosePrinter(hPrinter); return FALSE; } // Start a page. if (!StartPagePrinter(hPrinter)) { EndDocPrinter(hPrinter); ClosePrinter(hPrinter); return FALSE; } // Send the data to the printer. if (!WritePrinter(hPrinter, lpData, dwCount, &dwBytesWritten)) { EndPagePrinter(hPrinter); EndDocPrinter(hPrinter); ClosePrinter(hPrinter); return FALSE; } // End the page. if (!EndPagePrinter(hPrinter)) { EndDocPrinter(hPrinter); ClosePrinter(hPrinter); return FALSE; } // Inform the spooler that the document is ending. if (!EndDocPrinter(hPrinter)) { ClosePrinter(hPrinter); return FALSE; } // Tidy up the printer handle. ClosePrinter(hPrinter); // Check to see if correct number of bytes were written. if (dwBytesWritten != dwCount) return FALSE; return TRUE;}

在文档中提到，打开打印机时"OpenPrinter"可以传入 null 以使用本地打印服务，因为不知道打印机名称，于是就传入了 null，结果在 StartDocPrinter 时一直提示失败，后来了解到使用 GetLastError 可以查看 error code，得到错误码后一对照，发现是 handle 是无效的，也就意味这 OpenPrinter 这一步骤没有打开需要的打印机。于是尝试使用 设备与打印机中的打印机名称，还真就连上了，成功调用打印服务。

但客户电脑上的打印机名称是不固定的，不能使用固定打印机名称，所以得拿到已经连接了的打印机列表，于是搜索到了 EnumPrinters 这一api，具体用法如下：

void getPrinterList() { PRINTER_INFO_2* printerList; unsigned char size; unsigned long pcbNeeded; unsigned long pcReturned; EnumPrinters(PRINTER_ENUM_LOCAL, NULL, 2, NULL, 0, &pcbNeeded, &pcReturned); if ((printerList = (PRINTER_INFO_2*)malloc(pcbNeeded)) == 0) { return; } if (!EnumPrinters(PRINTER_ENUM_LOCAL, NULL, 2, (LPBYTE)printerList, pcbNeeded, &pcbNeeded, &pcReturned)) { free(printerList); return; } for (int i = 0; i < (int)pcReturned; i++) { string printName(printerList[i].pPrinterName); if (printerList[i].Attributes & PRINTER_ATTRIBUTE_NETWORK) { cout << "网络打印机" << printName << endl; } else { cout << "本地打印机" << printName << endl; } } cout << "number " << pcReturned << endl;}

通过这一方式，的确获取到了系统中可用的打印机，可是拿到可用的打印机后还是有一个问题：“如何知道哪一个是小票打印机”?

为此又进行了搜索，又找到了一个 api GetDefaultPrinter，用法如下：

string getDefaultPrinterName() { DWORD size = 0; GetDefaultPrinter(NULL, &size); if (size) { TCHAR* buffer = new TCHAR[size]; GetDefaultPrinter(buffer, &size); string printerName(buffer); return printerName; } else { return ""; }}

通过此方法获取到系统默认打印机，客户只需要设置默认的打印机为小票打印机就完美解决问题了。

以下是完整代码：

#include <iostream>#include <windows.h>#include "node.h"#include "base64.h"using namespace std;using v8::FunctionCallbackInfo;using v8::Isolate;using v8::Local;using v8::NewStringType;using v8::Object;using v8::String;using v8::Value;using v8::Integer;using v8::Int8Array;BOOL RawDataToPrinter(LPSTR szPrinterName, LPBYTE lpData, DWORD dwCount);string getDefaultPrinterName();void localPrintRawData(const FunctionCallbackInfo<Value>& args) { Isolate* isolate = args.GetIsolate(); Local<v8::Context> context = isolate->GetCurrentContext(); v8::String::Utf8Value portString(isolate, args[0]); std::string base64Str(*portString); vector<BYTE> bytes = base64_decode(base64Str); char* buffer = new char[bytes.size()]; copy(bytes.begin(), bytes.end(), buffer); string printerName = getDefaultPrinterName(); if (printerName.size() > 0) { printerName += "\0"; wstring ws(printerName.begin(), printerName.end()); RawDataToPrinter(const_cast<char*>(printerName.c_str()), &bytes[0], bytes.size()); } else { cout << "no printer" << endl; }}BOOL RawDataToPrinter(LPSTR szPrinterName, LPBYTE lpData, DWORD dwCount){ HANDLE hPrinter; DOC_INFO_1 DocInfo; DWORD dwJob; DWORD dwBytesWritten; // Need a handle to the printer. if (!OpenPrinter(szPrinterName, &hPrinter, NULL)) { int y = GetLastError(); cout << "openFial" << y << endl; return FALSE; } // Fill in the structure with info about this "document." DocInfo.pDocName = LPSTR("My Document\0"); DocInfo.pOutputFile = NULL; DocInfo.pDatatype = NULL; // LPWSTR("RAW\0"); // Inform the spooler the document is beginning. if ((dwJob = StartDocPrinter(hPrinter, 1, (LPBYTE)&DocInfo)) == 0) { int x = GetLastError(); cout << "StartDocPrinter Fial" << x << endl; ClosePrinter(hPrinter); return FALSE; } // Start a page. if (!StartPagePrinter(hPrinter)) { EndDocPrinter(hPrinter); ClosePrinter(hPrinter); return FALSE; } // Send the data to the printer. if (!WritePrinter(hPrinter, lpData, dwCount, &dwBytesWritten)) { EndPagePrinter(hPrinter); EndDocPrinter(hPrinter); ClosePrinter(hPrinter); return FALSE; } // End the page. if (!EndPagePrinter(hPrinter)) { EndDocPrinter(hPrinter); ClosePrinter(hPrinter); return FALSE; } // Inform the spooler that the document is ending. if (!EndDocPrinter(hPrinter)) { ClosePrinter(hPrinter); return FALSE; } // Tidy up the printer handle. ClosePrinter(hPrinter); // Check to see if correct number of bytes were written. if (dwBytesWritten != dwCount) return FALSE; return TRUE;}void getPrinterList() { PRINTER_INFO_2* printerList; unsigned char size; unsigned long pcbNeeded; unsigned long pcReturned; EnumPrinters(PRINTER_ENUM_LOCAL, NULL, 2, NULL, 0, &pcbNeeded, &pcReturned); if ((printerList = (PRINTER_INFO_2*)malloc(pcbNeeded)) == 0) { return; } if (!EnumPrinters(PRINTER_ENUM_LOCAL, NULL, 2, (LPBYTE)printerList, pcbNeeded, &pcbNeeded, &pcReturned)) { free(printerList); return; } for (int i = 0; i < (int)pcReturned; i++) { string printName(printerList[i].pPrinterName); if (printerList[i].Attributes & PRINTER_ATTRIBUTE_NETWORK) { cout << "网络打印机" << printName << endl; } else { cout << "本地打印机" << printName << endl; } } cout << "number " << pcReturned << endl;}string getDefaultPrinterName() { DWORD size = 0; GetDefaultPrinter(NULL, &size); if (size) { TCHAR* buffer = new TCHAR[size]; GetDefaultPrinter(buffer, &size); string printerName(buffer); return printerName; } else { return ""; }}void Initialize(Local<Object> exports) { NODE_SET_METHOD(exports, "localPrintRawData", localPrintRawData);}NODE_MODULE(zq_device, Initialize)

参考：

https://support.microsoft.com/zh-cn/help/138594/howto-send-raw-data-to-a-printer-by-using-the-win32-api

https://docs.microsoft.com/en-us/windows/win32/printdocs/openprinter

https://stackoverflow.com/questions/6682286/understanding-a-c-sample-printers-handles-strings

https://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/a27c6615-9452-44b1-90fc-9b91b15f0e50/openprinter-returing-errorinvalidprintername1801-when-called-with?forum=windowsgeneraldevelopmentissues

https://social.msdn.microsoft.com/Forums/vstudio/en-US/de7c55a1-ae63-49c9-a87a-fe3bf32822e4/how-to-use-the-enumprinters-function-to-be-able-to-classify-installed-printers-into-quot-network?forum=vclanguage

https://docs.microsoft.com/en-us/windows/win32/debug/system-error-codes--0-499-

https://docs.microsoft.com/zh-cn/windows/win32/debug/system-error-codes--1700-3999-?redirectedfrom=MSDN

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