Question

I must be doing something wrong… Or this may be a bug in YAJL, but I highly doubt that.
I’m unable to retrieve the first element from a json object. I went back to the YAJL source to test this with the example parse_config.c and it failed as well.

Using the sample.config

/*
 * The configuration file for Yahoo! BrowserPlus, included in the YAJL
 * tree as a sample configuration file for parsing.
 *
 * This is the configuration file for BrowserPlus
 */

{
    // The type of build this is, which is accessible to JavaScript via
    // BrowserPlus.getPlatformInfo(); 
    // Different build types should only differ in signatures accepted
    // (BrowserPlus.crt) and configured distribution servers.
    "BuildType": "ephemeral",

    // the base url for the "primary" distribution server.  This server will
    // be the single source of truth for Permissions, and will used to 
    // attain services
    "DistServer": "http://browserplus.yahoo.com",

    // An array of "secondary" distribution servers, which will be checked
    // in order for services if the primary server has no components
    // available which match an issued require statement.
    "SecondaryDistServers": [
      "http://first.fictional.server",
      "http://second.fictional.server"
    ],

    // Logging Setup
    "Logging" :
    {
        // Log level.  Values: "debug"|"info"|"warn"|"error"|"fatal"|"off"
        "level": "BP_LOG_LEVEL",

        // Destination.  Values: "file"|"console"|"win32"
        "dest": "BP_LOG_DEST",

        // Log message layout.  Values: "standard"|"source"|"raw"
        "layout": "standard",

        // Time format.  Values: "utc"|"local"|"msec"
        "timeFormat": "utc",

        // File size in KB which will trigger a rollover
        "fileRolloverKB": 2048,

        // Whether to send file logging from each service to a distinct file.
        // Values: "combined"|"separate"
        "serviceLogMode": "combined"
    },

    // Daemon setup
    // Syntax: "Options": "option1 option2 etc"
    // -fg        run in foreground, log to console
    "Options":"",

    // Auto-shutdown daemon if idle for this time.  Use 0 for no auto-shutdown.
    "MaxIdleSecs": 5,

    // At the end of each BrowserPlus session a small web request is made
    // to yahoo to indicate that BrowserPlus was used.  This report includes
    // * information about the browser being used
    // * an "installation id", which is a unique token that's generated
    //   the first time BrowserPlus runs.
    //
    // By design, there is *no information* in this request that gives
    // Yahoo! information about:
    //   a) the site that the user is visiting (see, "url": false)
    //   b) who the user is (the installation token cannot be tracked to a
    //      specific user).
    //
    // This information is primarily captured to help Yahoo! understand
    // adoption and usage of the BrowserPlus platform.
    "UsageReporting":
    {
       "enabled": true,
       "url": false,
       "id": true
    },

    // "Breakpoints" is an array of strings holding named breakpoints.
    // Platform code checks for specific entries at certain key points, and if 
    // a matching entry is found here a DebugBreak will be performed.
    // For developers with Visual Studio installed, the DebugBreak will cause an
    // opportunity to perform just-in-time attachment of an existing or new 
    // debugger instance.
    // The currently-defined breakpoints are listed below:
    //      runServiceProcess - A DebugBreak is performed in the service 
    //                          "harness" just prior to service load.
    //      ax.FinalConstruct - A DebugBreak is performed at entry to 
    //                          FinalConstruct of the ActiveX plugin.
    //      PluginInit -        Very early in the NPAPI plugin initialization.
    //                          A wonderful spot to stop and set more
    //                          breakpoints.
    //"Breakpoints": ["runServiceProcess"],

    // How often we check for service updates.  We guarantee at least this
    // much time will pass between checks, though the true time may be
    // much more if sites which use browserplus are not visited.
    // The time is in seconds.
    "ServiceUpdatePollPeriod": 86400
}

I try and retrieve the “BuildType” <– the first element of the JSON object.

I changed the parse_config.c file to do this… here’s the code:

int
main(void)
{
    size_t rd;
    yajl_val node;
    char errbuf[1024];

    /* null plug buffers */
    fileData[0] = errbuf[0] = 0;

    /* read the entire config file */
    rd = fread((void *) fileData, 1, sizeof(fileData) - 1, stdin);

    /* file read error handling */
    if (rd == 0 && !feof(stdin)) {
        fprintf(stderr, "error encountered on file read\n");
        return 1;
    } else if (rd >= sizeof(fileData) - 1) {
        fprintf(stderr, "config file too big\n");
        return 1;
    }

    /* we have the whole config file in memory.  let's parse it ... */
    node = yajl_tree_parse((const char *) fileData, errbuf, sizeof(errbuf));

    /* parse error handling */
    if (node == NULL) {
        fprintf(stderr, "parse_error: ");
        if (strlen(errbuf)) fprintf(stderr, " %s", errbuf);
        else fprintf(stderr, "unknown error");
        fprintf(stderr, "\n");
        return 1;
    }

    /* ... and extract a nested value from the config file */
    {
        //const char * path[] = { "Logging", "timeFormat", (const char *) 0 };

Note: If I try to get “DistServer” it works just fine, but “BuildType” returns NULL.

        const char * path[] = { "BuildType", (const char *) 0 };
        //const char * path[] = { "DistServer", (const char *) 0 };
        yajl_val v = yajl_tree_get(node, path, yajl_t_string);
        if (v) printf("%s: %s\n", path[0], YAJL_GET_STRING(v));
        else   printf("no such node: %s\n", path[0] );
        //if (v) printf("%s/%s: %s\n", path[0], path[1], YAJL_GET_STRING(v));
        //else   printf("no such node: %s/%s\n", path[0], path[1]);
    }

    yajl_tree_free(node);

    return 0;
}

I’m using the latest YAJL version: 2.0.2.

Thanks in advance!

EDIT:

Here’s my command output:

./parse_config  < ../../example/sample.config 
no such node: BuildType

Note, the parse_config that I’m running is in the one in the build/example directory

My gcc version is:
gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5)

EDIT 2
For the record, this is the sample code that comes with This code came with YAJL. I purposely used it instead of my own code to make sure that the problem wasn’t only related to my application. Meanwhile I’ve worked around the problem by using the callback mechanism the library provides and using

yajl_parse()
and 
yajl_complete_parse()

But I still would like to know why the original code wasn’t working.

Answer 1

I just hit this same bug, using version 2.0.2. It appears to be a bug in yajl and has been fixed in github (“validate the length of the correct object in yajl_tree_get”, commit 9c2948a33165c650122d131f31140c15321908f5).

I’ve applied this patch and I’m now able to read the first item fine.