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https://issues.apache.org/jira/browse/HADOOP-1568?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12510841
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Chris Douglas commented on HADOOP-1568:
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Thoughts:
1) It isn't clear how one would format a list of block locations in a reply.
One could request the contents of a consecutive set of blocks by setting query
parameters or using a range header field, but XML provides a more expressive
format for that association that might also permit a consumer to contact
multiple datanodes simultaneously, from different machines, etc. We don't need
or support it now, but situations where it could be useful are not difficult to
imagine.
2) Each request for file info is a separate HTTP HEAD request. A consumer needs
to parse the link to acquire interesting information about the file, including
its name (as in the patch). If we hope to avoid assumptions about the link
syntax, a HEAD request is necessary for every file in the listing. Granted, the
link syntax is probably pretty stable, but parsing URIs for file paths doesn't
seem like a more future-proof solution than an XML schema.
Further, if we hope to implement (1), we would probably break the current
implementation of (2) or include block location URIs in header fields.
It seems prudent to restrict this servlet to meta-information, i.e. not
returning file content in response to a GET and leave that to StreamFile or
some other facility. Some of the ideas in this and in HADOOP-1563 seem very
appropriate for StreamFile, though.
> NameNode Schema for HttpFileSystem
> ----------------------------------
>
> Key: HADOOP-1568
> URL: https://issues.apache.org/jira/browse/HADOOP-1568
> Project: Hadoop
> Issue Type: New Feature
> Components: fs
> Reporter: Chris Douglas
> Assignee: Chris Douglas
>
> This issue will track the design and implementation of (the first pass of) a
> servlet on the namenode for querying its filesystem via HTTP. The proposed
> syntax for queries and responses is as follows.
> *Query*
> {noformat}GET http://<nn>:<port>/ls.jsp[<?option>[&option]*]
> HTTP/1.1{noformat}
> Where _option_ may be any of the following query parameters:
> _path_ : String (default: '/')
> _recursive_ : boolean (default: false)
> _filter_ : String (default: none)
> *Response*
> The response will be returned as an XML document in the following format:
> {noformat}
> <listing path="..." recursive="(yes|no)" filter="..."
> time="yyyy-MM-dd hh:mm:ss UTC" version="...">
> <directory path="..."/>
> <file path="..." modified="yyyy-MM-dd hh:mm:ss" blocksize="..."
> replication="..." size="..."
> dnurl="http://dn:port/streamFile?..."/>
> </listing>
> {noformat}
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