参照官方rest接口的使用方式：WebHDFS REST API
Operations
- HTTP GET
- OPEN (see FileSystem.open)
- GETFILESTATUS (see FileSystem.getFileStatus)
- LISTSTATUS (see FileSystem.listStatus)
- GETCONTENTSUMMARY (see FileSystem.getContentSummary)
- GETFILECHECKSUM (see FileSystem.getFileChecksum)
- GETHOMEDIRECTORY (see FileSystem.getHomeDirectory)
- GETDELEGATIONTOKEN (see FileSystem.getDelegationToken)
- GETDELEGATIONTOKENS (see FileSystem.getDelegationTokens)
- GETXATTRS (see FileSystem.getXAttr)
- GETXATTRS (see FileSystem.getXAttrs)
- GETXATTRS (see FileSystem.getXAttrs)
- LISTXATTRS (see FileSystem.listXAttrs)
- CHECKACCESS (see FileSystem.access)
- HTTP PUT
- CREATE (see FileSystem.create)
- MKDIRS (see FileSystem.mkdirs)
- CREATESYMLINK (see FileContext.createSymlink)
- RENAME (see FileSystem.rename)
- SETREPLICATION (see FileSystem.setReplication)
- SETOWNER (see FileSystem.setOwner)
- SETPERMISSION (see FileSystem.setPermission)
- SETTIMES (see FileSystem.setTimes)
- RENEWDELEGATIONTOKEN (see FileSystem.renewDelegationToken)
- CANCELDELEGATIONTOKEN (see FileSystem.cancelDelegationToken)
- CREATESNAPSHOT (see FileSystem.createSnapshot)
- RENAMESNAPSHOT (see FileSystem.renameSnapshot)
- SETXATTR (see FileSystem.setXAttr)
- REMOVEXATTR (see FileSystem.removeXAttr)
- HTTP POST
- APPEND (see FileSystem.append)
- CONCAT (see FileSystem.concat)
- HTTP DELETE
- DELETE (see FileSystem.delete)
- DELETESNAPSHOT (see FileSystem.deleteSnapshot)
FileSystem URIs vs HTTP URLs
The FileSystem scheme of WebHDFS is "webhdfs://". A WebHDFS FileSystem URI has the following format.
webhdfs://:/
复制代码 The above WebHDFS URI corresponds to the below HDFS URI.
hdfs://:/
复制代码 In the REST API, the prefix "/webhdfs/v1" is inserted in the path and a query is appended at the end. Therefore, the corresponding HTTP URL has the following format.
http://:/webhdfs/v1/?op=...
复制代码 HDFS Configuration Options
Below are the HDFS configuration options for WebHDFS.
| Property Name | Description |
|---|---|
| dfs.webhdfs.enabled | Enable/disable WebHDFS in Namenodes and Datanodes |
| dfs.web.authentication.kerberos.principal | The HTTP Kerberos principal used by Hadoop-Auth in the HTTP endpoint. The HTTP Kerberos principal MUST start with 'HTTP/' per Kerberos HTTP SPNEGO specification. A value of "*" will use all HTTP principals found in the keytab. |
| dfs.web.authentication.kerberos.keytab | The Kerberos keytab file with the credentials for the HTTP Kerberos principal used by Hadoop-Auth in the HTTP endpoint. |
Authentication
When security is off, the authenticated user is the username specified in the user.name query parameter. If the user.name parameter is not set, the server may either set the authenticated user to a default web user, if there is any, or return an error response.
When security is on, authentication is performed by either Hadoop delegation token or Kerberos SPNEGO. If a token is set in the delegation query parameter, the authenticated user is the user encoded in the token. If the delegation parameter is not set, the user is authenticated by Kerberos SPNEGO.
Below are examples using the curl command tool.
- Authentication when security is off:
curl -i "http://: 复制代码/webhdfs/v1/ ?[user.name= &]op=..." - Authentication using Kerberos SPNEGO when security is on:
curl -i --negotiate -u : "http://: 复制代码/webhdfs/v1/ ?op=..." - Authentication using Hadoop delegation token when security is on:
curl -i "http://: 复制代码/webhdfs/v1/ ?delegation= &op=..."
See also: Authentication for Hadoop HTTP web-consoles
Proxy Users
When the proxy user feature is enabled, a proxy user P may submit a request on behalf of another user U. The username of U must be specified in the doas query parameter unless a delegation token is presented in authentication. In such case, the information of both users P and U must be encoded in the delegation token.
- A proxy request when security is off:
curl -i "http://:/webhdfs/v1/?[user.name=&]doas=&op=..."
复制代码- A proxy request using Kerberos SPNEGO when security is on:
curl -i --negotiate -u : "http://:/webhdfs/v1/?doas=&op=..."
复制代码- A proxy request using Hadoop delegation token when security is on:
curl -i "http://:/webhdfs/v1/?delegation=&op=..."
复制代码File and Directory Operations
Create and Write to a File
- Step 1: Submit a HTTP PUT request without automatically following redirects and without sending the file data.
curl -i -X PUT "http://:/webhdfs/v1/?op=CREATE
[&overwrite=][&blocksize=][&replication=]
[&permission=][&buffersize=]"
复制代码The request is redirected to a datanode where the file data is to be written:
HTTP/1.1 307 TEMPORARY_REDIRECT
Location: http://:/webhdfs/v1/?op=CREATE...
Content-Length: 0
复制代码 - Step 2: Submit another HTTP PUT request using the URL in the Location header with the file data to be written.
curl -i -X PUT -T "http://:/webhdfs/v1/?op=CREATE..."
复制代码 The client receives a 201 Created response with zero content length and the WebHDFS URI of the file in the Location header:
HTTP/1.1 201 Created
Location: webhdfs://:/
Content-Length: 0
复制代码 Note that the reason of having two-step create/append is for preventing clients to send out data before the redirect. This issue is addressed by the "Expect: 100-continue" header in HTTP/1.1; see RFC 2616, Section 8.2.3. Unfortunately, there are software library bugs (e.g. Jetty 6 HTTP server and Java 6 HTTP client), which do not correctly implement "Expect: 100-continue". The two-step create/append is a temporary workaround for the software library bugs.
See also: overwrite, blocksize, replication, permission, buffersize, FileSystem.create
Append to a File
- Step 1: Submit a HTTP POST request without automatically following redirects and without sending the file data.
curl -i -X POST "http://:/webhdfs/v1/?op=APPEND[&buffersize=]"
复制代码The request is redirected to a datanode where the file data is to be appended:
HTTP/1.1 307 TEMPORARY_REDIRECT
Location: http://:/webhdfs/v1/?op=APPEND...
Content-Length: 0
复制代码 - Step 2: Submit another HTTP POST request using the URL in the Location header with the file data to be appended.
curl -i -X POST -T "http://:/webhdfs/v1/?op=APPEND..."
复制代码 The client receives a response with zero content length:
HTTP/1.1 200 OK
Content-Length: 0
复制代码See the note in the previous section for the description of why this operation requires two steps.
See also: buffersize, FileSystem.append
Open and Read a File
- Submit a HTTP GET request with automatically following redirects.
curl -i -L "http://:/webhdfs/v1/?op=OPEN
[&offset=][&length=][&buffersize=]"
复制代码The request is redirected to a datanode where the file data can be read:
HTTP/1.1 307 TEMPORARY_REDIRECT
Location: http://:/webhdfs/v1/?op=OPEN...
Content-Length: 0
复制代码 The client follows the redirect to the datanode and receives the file data:
HTTP/1.1 200 OK
Content-Type: application/octet-stream
Content-Length: 22
Hello, webhdfs user!
复制代码See also: offset, length, buffersize, FileSystem.open
Make a Directory
- Submit a HTTP PUT request.
curl -i -X PUT "http://:/webhdfs/v1/?op=MKDIRS[&permission=]"
复制代码The client receives a response with a boolean JSON object:
HTTP/1.1 200 OK
Content-Type: application/json
Transfer-Encoding: chunked
{"boolean": true}
复制代码See also: permission, FileSystem.mkdirs
Create a Symbolic Link
- Submit a HTTP PUT request.
curl -i -X PUT "http://:/webhdfs/v1/?op=CREATESYMLINK
&destination=[&createParent=]"
复制代码The client receives a response with zero content length:
HTTP/1.1 200 OK
Content-Length: 0
复制代码See also: destination, createParent, FileSystem.createSymlink
Rename a File/Directory
- Submit a HTTP PUT request.
curl -i -X PUT ":/webhdfs/v1/?op=RENAME&destination="
复制代码The client receives a response with a boolean JSON object:
HTTP/1.1 200 OK
Content-Type: application/json
Transfer-Encoding: chunked
{"boolean": true}
复制代码See also: destination, FileSystem.rename
Delete a File/Directory
- Submit a HTTP DELETE request.
curl -i -X DELETE "http://:/webhdfs/v1/?op=DELETE
[&recursive=]"
复制代码The client receives a response with a boolean JSON object:
HTTP/1.1 200 OK
Content-Type: application/json
Transfer-Encoding: chunked
{"boolean": true}
复制代码See also: recursive, FileSystem.delete
Status of a File/Directory
- Submit a HTTP GET request.
curl -i "http://:/webhdfs/v1/?op=GETFILESTATUS"
复制代码The client receives a response with a FileStatus JSON object:
HTTP/1.1 200 OK
Content-Type: application/json
Transfer-Encoding: chunked
{
"FileStatus":
{
"accessTime" : 0,
"blockSize" : 0,
"childrenNum" : 1,
"fileId" : 16386,
"group" : "supergroup",
"length" : 0, //in bytes, zero for directories
"modificationTime": 1320173277227,
"owner" : "webuser",
"pathSuffix" : "",
"permission" : "777",
"replication" : 0,
"type" : "DIRECTORY" //enum {FILE, DIRECTORY, SYMLINK}
}
}
复制代码See also: FileSystem.getFileStatus
List a Directory
Submit a HTTP GET request.
curl -i "http://:/webhdfs/v1/?op=LISTSTATUS"
复制代码The client receives a response with a FileStatuses JSON object:
HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 427
{
"FileStatuses":
{
"FileStatus":
[
{
"accessTime" : 1320171722771,
"blockSize" : 33554432,
"childrenNum" : 0,
"fileId" : 16387,
"group" : "supergroup",
"length" : 24930,
"modificationTime": 1320171722771,
"owner" : "webuser",
"pathSuffix" : "a.patch",
"permission" : "644",
"replication" : 1,
"type" : "FILE"
},
{
"accessTime" : 0,
"blockSize" : 0,
"childrenNum" : 2,
"fileId" : 16388,
"group" : "supergroup",
"length" : 0,
"modificationTime": 1320895981256,
"owner" : "szetszwo",
"pathSuffix" : "bar",
"permission" : "711",
"replication" : 0,
"type" : "DIRECTORY"
},
...
]
}
}
复制代码See also: FileSystem.listStatus
Other File System Operations