Hadoop httpfs API的使用

CoderSunYu發表於2018-09-12
HadoopHTTPAPI

參照官方rest介面的使用方式：WebHDFS REST API

Operations

FileSystem URIs vs HTTP URLs

The FileSystem scheme of WebHDFS is "webhdfs://". A WebHDFS FileSystem URI has the following format.

  webhdfs://<HOST>:<HTTP_PORT>/<PATH>
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The above WebHDFS URI corresponds to the below HDFS URI.

  hdfs://<HOST>:<RPC_PORT>/<PATH>
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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://<HOST>:<HTTP_PORT>/webhdfs/v1/<PATH>?op=...
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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.

  1. Authentication when security is off:
    curl -i "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?[user.name=<USER>&]op=..."
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  2. Authentication using Kerberos SPNEGO when security is on:
    curl -i --negotiate -u : "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=..."
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  3. Authentication using Hadoop delegation token when security is on:
    curl -i "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?delegation=<TOKEN>&op=..."
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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.

  1. A proxy request when security is off:
curl -i "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?[user.name=<USER>&]doas=<USER>&op=..."
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  1. A proxy request using Kerberos SPNEGO when security is on:
curl -i --negotiate -u : "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?doas=<USER>&op=..."
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  1. A proxy request using Hadoop delegation token when security is on:
curl -i "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?delegation=<TOKEN>&op=..."
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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://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=CREATE
                    [&overwrite=<true|false>][&blocksize=<LONG>][&replication=<SHORT>]
                    [&permission=<OCTAL>][&buffersize=<INT>]"
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The request is redirected to a datanode where the file data is to be written:

HTTP/1.1 307 TEMPORARY_REDIRECT
Location: http://<DATANODE>:<PORT>/webhdfs/v1/<PATH>?op=CREATE...
Content-Length: 0
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  • 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 <LOCAL_FILE> "http://<DATANODE>:<PORT>/webhdfs/v1/<PATH>?op=CREATE..."
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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://<HOST>:<PORT>/<PATH>
Content-Length: 0
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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://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=APPEND[&buffersize=<INT>]"
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The request is redirected to a datanode where the file data is to be appended:

HTTP/1.1 307 TEMPORARY_REDIRECT
Location: http://<DATANODE>:<PORT>/webhdfs/v1/<PATH>?op=APPEND...
Content-Length: 0
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  • 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 <LOCAL_FILE> "http://<DATANODE>:<PORT>/webhdfs/v1/<PATH>?op=APPEND..."
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The client receives a response with zero content length:

HTTP/1.1 200 OK
Content-Length: 0
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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://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=OPEN
                    [&offset=<LONG>][&length=<LONG>][&buffersize=<INT>]"
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The request is redirected to a datanode where the file data can be read:

HTTP/1.1 307 TEMPORARY_REDIRECT
Location: http://<DATANODE>:<PORT>/webhdfs/v1/<PATH>?op=OPEN...
Content-Length: 0
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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!
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See also: offset, length, buffersize, FileSystem.open

Make a Directory

  • Submit a HTTP PUT request.
curl -i -X PUT "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=MKDIRS[&permission=<OCTAL>]"
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The client receives a response with a boolean JSON object:

HTTP/1.1 200 OK
Content-Type: application/json
Transfer-Encoding: chunked

{"boolean": true}
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See also: permission, FileSystem.mkdirs

Create a Symbolic Link

  • Submit a HTTP PUT request.
curl -i -X PUT "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=CREATESYMLINK
                              &destination=<PATH>[&createParent=<true|false>]"
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The client receives a response with zero content length:

HTTP/1.1 200 OK
Content-Length: 0
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See also: destination, createParent, FileSystem.createSymlink

Rename a File/Directory

  • Submit a HTTP PUT request.
curl -i -X PUT "<HOST>:<PORT>/webhdfs/v1/<PATH>?op=RENAME&destination=<PATH>"
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The client receives a response with a boolean JSON object:

HTTP/1.1 200 OK
Content-Type: application/json
Transfer-Encoding: chunked

{"boolean": true}
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See also: destination, FileSystem.rename

Delete a File/Directory

  • Submit a HTTP DELETE request.
curl -i -X DELETE "http://<host>:<port>/webhdfs/v1/<path>?op=DELETE
                              [&recursive=<true|false>]"
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The client receives a response with a boolean JSON object:

HTTP/1.1 200 OK
Content-Type: application/json
Transfer-Encoding: chunked

{"boolean": true}
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See also: recursive, FileSystem.delete

Status of a File/Directory

  • Submit a HTTP GET request.
curl -i  "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=GETFILESTATUS"
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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}
  }
}
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See also: FileSystem.getFileStatus

List a Directory

Submit a HTTP GET request.

curl -i  "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=LISTSTATUS"
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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"
      },
      ...
    ]
  }
}
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See also: FileSystem.listStatus

Other File System Operations

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