npapi plugin_invoke function return string value garbage characters

Question

npapi code:

bool plugin_invoke(NPObject *obj, NPIdentifier methodName, const NPVariant *args, uint32_t argCount, NPVariant *result) {
NPUTF8 *name = browser->utf8fromidentifier(methodName);
if(strcmp(name, plugin_method_name_getAddress) == 0){
    NPString password;
    if(argCount > 0) {
        password = NPVARIANT_TO_STRING(args[0]);
    }
    const char * StringVariable = password.UTF8Characters;
    char* npOutString = (char *)malloc(strlen(StringVariable+1));
    if (!npOutString)
        return false;
    strcpy(npOutString, StringVariable);
    STRINGZ_TO_NPVARIANT(npOutString, *result);
    browser->memfree(name);
    return true;
}
return false;

}

html code:

function run() {
    var plugin = document.getElementById("pluginId");
    var passwordBeforEncryption =  document.getElementById("passwordFeild");
    if(plugin){
        var value = plugin.getAddress("hello, just test it");
            alert(value);
    }else{
        alert("plugin is null");
    }

}

The right result should be: "hello, just test it", but sometimes return"hello, just test itÿÿÿÿ". It only sometimes not all time!

Please help.

possible duplicate of chrome newer version(14) does not give a null terminated string as part of NPVariant — smorgan
– smorgan, Commented Dec 17, 2012 at 9:38

Magical · Accepted Answer · 2012-12-18 02:25:28Z

2

The error is not in your html,you shuld see NPString structure.

typedef struct _NPString {
    const NPUTF8 *UTF8Characters;
    uint32_t UTF8Length;
} NPString;

The member UTF8Length indicate the length of your string,so you should do as below:

const char * StringVariable = password.UTF8Characters;
char* npOutString  = (char*)browser->memalloc(password.UTF8Length+1);
if (!npOutString) {
    return false;
}
memcpy(npOutString  , password.UTF8Characters, password.UTF8Length);
npOutString[password.UTF8Length] = 0;

answered Dec 18, 2012 at 2:25

Magical

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1 Comment

justin Over a year ago

Thanks you tell me the real problem and give me the demo code!

Captain Fantastic · Accepted Answer · 2014-05-12 23:45:19Z

1

It looks like you are allocating the memory incorrectly:

char* npOutString = (char *)malloc(strlen(StringVariable+1));

should be:

char* npOutString = (char *)malloc(strlen(StringVariable)+1);

to correct the length.

However, in order for the browser to be able to free the memory, you should be using:

char* npOutString = (char *)NPN_MemAlloc(strlen(StringVariable)+1);

edited May 12, 2014 at 23:45

answered May 12, 2014 at 23:30

Captain Fantastic

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Comments

justin · Accepted Answer · 2012-12-17 09:38:38Z

0

OK, fond the answer! In html code:

var value = plugin.getAddress("hello, just test it");

should be like this:

var value = plugin.getAddress("hello, just test it\0");

at string end need "\0"

answered Dec 17, 2012 at 9:38

justin

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2 Comments

smorgan Over a year ago

This works, but the real problem is that your plugin code is wrong. You should be using the string length (see the duplicate question), not assuming that it's a null-terminated string.

justin Over a year ago

Thanks you tell me the real problem!

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