(Go) PC/SC Wait for Smart Card Status Change (Inserted, Removed from Reader, etc.)

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Demonstrates how to synchronously wait for a status change, such as for a smart card to be inserted into a reader, or removed from a reader.

Note: This functionality was introduced in Chilkat v9.5.0.87.

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    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    scard := chilkat.NewSCard()

    // First establish a context to the PC/SC Resource Manager
    success := scard.EstablishContext("user")
    if success == false {
        fmt.Println(scard.LastErrorText())
        scard.DisposeSCard()
        return
    }

    // First we'll examine the state of all connected readers to see which have smartcards already inserted..
    // Get JSON containing information about the smartcards currently inserted into readers.
    // This also includes information about USB security tokens.
    json := chilkat.NewJsonObject()
    success = scard.FindSmartcards(json)
    if success == false {
        fmt.Println(scard.LastErrorText())
        scard.DisposeSCard()
        json.DisposeJsonObject()
        return
    }

    // When writing this example, I have 3 smart card readers plugged into my system.
    // One of them has a smart card inserted.
    // Here's the JSON returned by FindSmartcards...

    // {
    //   "reader": [
    //     {
    //       "name": "Alcor Micro USB Smart Card Reader 0",
    //       "state": "empty"
    //     },
    //     {
    //       "name": "Generic Smart Card Reader Interface 0",
    //       "state": "present",
    //       "vendorName": "Generic",
    //       "serialNumber": "3230303730383138303030303030303030",
    //       "systemName": "Generic Smart Card Reader Interface 0",
    //       "card": {
    //         "atr": "3BFC180000813180459067464A00641606F2727E00E0",
    //         "windows": {
    //           "miniDriver": "tagliov70px.dll",
    //           "cryptoProvider": "Microsoft Base Smart Card Crypto Provider",
    //           "keyStorageProvider": "Microsoft Smart Card Key Storage Provider"
    //         }
    //       }
    //     },
    //     {
    //       "name": "SCM Microsystems Inc. SCR33x USB Smart Card Reader 0",
    //       "state": "empty"
    //     }
    //   ]
    // }

    json.SetEmitCompact(false)
    fmt.Println(*json.Emit())
    fmt.Println(" ")

    // We can iterate over the JSON to find the readers with a smart card already inserted..
    var name *string = new(string)
    sbState := chilkat.NewStringBuilder()

    i := 0
    count_i := json.SizeOfArray("reader")
    for i < count_i {
        json.SetI(i)
        name = json.StringOf("reader[i].name")

        sbState.Clear()
        json.StringOfSb("reader[i].state",sbState)

        if sbState.Contains("present",true) == true {
            fmt.Println(*name, " has a smart card inserted.")
        }
        else {
            fmt.Println(*name, " does not have a smart card inserted.")
        }

        i = i + 1
    }

    fmt.Println(" ")

    // Now let's begin the code to wait for a change (where a smart card gets inserted or removed)

    // Get the list of all readers.
    stReaders := chilkat.NewStringTable()
    success = scard.ListReaders(stReaders)
    if success == false {
        fmt.Println(scard.LastErrorText())
        scard.DisposeSCard()
        json.DisposeJsonObject()
        sbState.DisposeStringBuilder()
        stReaders.DisposeStringTable()
        return
    }

    // Show the reader names..
    numReaders := stReaders.Count()
    i = 0
    for i < numReaders {
        fmt.Println(i, ": ", *stReaders.StringAt(i))
        i = i + 1
    }

    // Sample output from the above loop.
    // 0: Alcor Micro USB Smart Card Reader 0
    // 1: Generic Smart Card Reader Interface 0
    // 2: SCM Microsystems Inc. SCR33x USB Smart Card Reader 0
    // 

    // Synchronously wait 30 seconds for a card to be inserted or removed from any of the above readers.
    json2 := chilkat.NewJsonObject()
    success = scard.GetStatusChange(30000,stReaders,json2)
    if success == false {
        fmt.Println(scard.LastErrorText())
        scard.DisposeSCard()
        json.DisposeJsonObject()
        sbState.DisposeStringBuilder()
        stReaders.DisposeStringTable()
        json2.DisposeJsonObject()
        return
    }

    fmt.Println(" ")

    // Let's see what happened...
    json2.SetEmitCompact(false)
    fmt.Println(*json2.Emit())
    fmt.Println(" ")

    // This is what json2 contains.
    // A card was inserted into the reader named "SCM Microsystems Inc. SCR33x USB Smart Card Reader 0"
    // The "numChanged" indicates that one reader's status changed.  
    // The "changed":true indicates the reader that changed.   The state is now "present".

    // {
    //   "numChanged": 1,
    //   "reader": [
    //     {
    //       "name": "Alcor Micro USB Smart Card Reader 0",
    //       "changed": false,
    //       "state": "empty"
    //     },
    //     {
    //       "name": "Generic Smart Card Reader Interface 0",
    //       "changed": false,
    //       "state": "present",
    //       "atr": "3BFC180000813180459067464A00641606F2727E00E0"
    //     },
    //     {
    //       "name": "SCM Microsystems Inc. SCR33x USB Smart Card Reader 0",
    //       "changed": true,
    //       "state": "present",
    //       "atr": "3BDF96FF8131FE455A018048494443313158587300011B09"
    //     }
    //   ]
    // }

    // Find the reader that changed...
    var changed bool
    var state *string = new(string)
    var atr *string = new(string)

    numChanged := json2.IntOf("numChanged")
    fmt.Println("number of readers with a changed state: ", numChanged)

    i = 0
    count_i = json2.SizeOfArray("reader")
    for i < count_i {
        json2.SetI(i)
        changed = json2.BoolOf("reader[i].changed")
        if changed == true {
            name = json2.StringOf("reader[i].name")
            state = json2.StringOf("reader[i].state")

            fmt.Println("Changed: ")
            fmt.Println("    reader name: ", *name)
            fmt.Println("    new state: ", *state)

            // If a card is now in this reader, we should have the ATR of the card..
            if json2.HasMember("reader[i].atr") == true {
                atr = json2.StringOf("reader[i].atr")
                fmt.Println("    ATR of card inserted into this reader: ", *atr)
            }

        }

        i = i + 1
    }

    // The output from the above loop:

    // number of readers with a changed state: 1
    // Changed: 
    //     reader name: SCM Microsystems Inc. SCR33x USB Smart Card Reader 0
    //     new state: present
    //     ATR of card inserted into this reader: 3BDF96FF8131FE455A018048494443313158587300011B09

    // Applications should always release the context when finished.
    success = scard.ReleaseContext()
    if success == false {
        fmt.Println(scard.LastErrorText())
    }


    scard.DisposeSCard()
    json.DisposeJsonObject()
    sbState.DisposeStringBuilder()
    stReaders.DisposeStringTable()
    json2.DisposeJsonObject()