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://docs.microsoft.com/en-us/windows/win32/printdocs/openprinter
https://stackoverflow.com/questions/6682286/understanding-a-c-sample-printers-handles-strings
https://docs.microsoft.com/en-us/windows/win32/debug/system-error-codes--0-499-
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