在C中使用YAJL解析json

Question

我一定做错了什么......或者这可能是 YAJL 中的一个错误，但我非常怀疑这一点。 我无法从 json 对象中检索第一个元素。我回到 YAJL 源代码并使用示例 parse_config.c 对此进行测试，但它也失败了。

使用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
}

我尝试检索“BuildType”<--JSON 对象的第一个元素。

我更改了 parse_config.c 文件来执行此操作...这是代码：

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 };

注意：如果我尝试获取“DistServer”，它工作得很好，但“BuildType”返回 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;
}

我正在使用最新的 YAJL 版本：2.0.2。

提前致谢！

编辑：

这是我的命令输出：

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

注意，我正在运行的 parse_config 位于 build/example 目录中

我的 gcc 版本是： gcc 版本 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5)

编辑 2 作为记录，这是随 YAJL 附带的示例代码。我故意使用它而不是我自己的代码，以确保问题不仅仅与我的应用程序有关。同时，我通过使用库提供的回调机制解决了这个问题，并使用

yajl_parse()
and 
yajl_complete_parse()

但我仍然想知道为什么原始代码不起作用。

Answer 1

我刚刚使用 2.0.2 版本遇到了同样的错误。这似乎是 yajl 中的一个错误，并已在 github 中修复（“验证 yajl_tree_get 中正确对象的长度”，提交 9c2948a33165c650122d131f31140c15321908f5）。

我已经应用了这个补丁，现在我可以很好地阅读第一个项目了。

Answer 2

这看起来像是 yajl 中的一个 bug ...

哇，我没想到本来就是这样。