[jira] [Commented] (HDFS-14172) Avoid NPE when SectionName#fromString() returns null

["Yiqun Lin (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-14172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16757056#comment-16757056 ] 

Yiqun Lin commented on HDFS-14172:
----------------------------------

{quote}Regarding the behavior against an unknown section, I would prefer logging a warn/error to throwing a descriptive IOException and aborting the program.
{quote}
Re-looking into this, as HDFS-7076 is not merged, I think a descriptive IOException and aborting the program will be a more appropriate way. I mean that, it's safe for NN that it loads an unknown section and it should aborts the program.

So a descriptive IOException throwing should be enough, can we revert additional change and make this JIRA more clear, [~water]?
{code:java}
         SectionName sectionName = SectionName.fromString(n);
        if (sectionName == null) {
          throw new IOException("Unrecognized section {}" + n);
        }
        
        switch (sectionName) {
        case NS_INFO:
          loadNameSystemSection(in);
          break;
        ...
{code}

> Avoid NPE when SectionName#fromString() returns null
> ----------------------------------------------------
>
>                 Key: HDFS-14172
>                 URL: https://issues.apache.org/jira/browse/HDFS-14172
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Xiang Li
>            Assignee: Xiang Li
>            Priority: Minor
>         Attachments: HADOOP-14172.000.patch, HADOOP-14172.001.patch, HADOOP-14172.002.patch
>
>
> In FSImageFormatProtobuf.SectionName#fromString(), as follows:
> {code:java}
> public static SectionName fromString(String name) {
>   for (SectionName n : values) {
>     if (n.name.equals(name))
>       return n;
>   }
>   return null;
> }
> {code}
> When the code meets an unknown section from the fsimage, the function will return null. Callers always operates the return value with a "switch" clause, like FSImageFormatProtobuf.Loader#loadInternal(), as:
> {code:java}
> switch (SectionName.fromString(n))
> {code}
> NPE will be thrown here.
> For self-protection, shall we add a default section name in the enum of SectionName, like "UNKNOWN", to steer clear of NPE?



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