HTTPCaller
Accesses a URL via HTTP or HTTPS, performing a GET, PUT, POST, DELETE, HEAD, PATCH or OPTIONS operation.
This transformer replaces the HTTPFetcher, HTTPUploader, HTTPFileUploader, HTTPMultipartUploader, HTTPDeleter and HTTPHeader transformers.
Output
The HTTP response body may be saved to an attribute, or a file. By default the body is saved to the attribute identified by the Response Body Attribute parameter.
The HTTP response status code will be stored in the attribute named by the Status Code Attribute parameter. By default this is the _http_status_code attribute. For more information on HTTP Status Codes, please refer to http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html.
In addition, the HTTP response headers will be saved in the list attribute specified by the List Attribute for Response Headers parameter. By default the headers are stored in the _headers{} list attribute. For a list of common HTTP response headers, please refer to http://en.wikipedia.org/wiki/List_of_HTTP_header_fields.
If an error occurs while accessing the URL, the feature will be output via the <Rejected> port. In addition, an error message will be set in the attribute named by the Error Attribute parameter.
Parameters
Request
This parameter identifies the HTTP method which will be used to access the server. Most requests will use the GET method. Requests which upload data will use the PUT, POST or PATCH method. The HEAD,DELETE and OPTIONS methods can be useful when accessing a REST API.
This parameter identifies the URL which will be accessed by the transformer. The transformer can access http and https URLs. The URL can be entered directly in the transformer, or be built up from attribute values.
Query String Parameters
This table can be used to create additional URL query parameters. The parameters will be appended to the URL given in the Request URL parameter. This can be useful when accessing a REST API endpoint which requires many parameters. The parameter names and values can be entered directly or constructed from attribute values.
Headers
This table can be used to create custom HTTP headers which will be sent along with the request. This can be used to customize the request that FME will make to the server. Header names and values can be entered directly or constructed from attribute values. In addition, the Name column provides a list of commonly used header names.
Body
The parameters in this group are only enabled when the HTTP Method parameter is set to PUT, POST or PATCH.
This parameter identifies the type of data that will be uploaded. The transformer can upload a file, a string value, or a multi-part combination of file and string values.
Upload data may be entered using this parameter. The data may be entered directly into the transformer or constructed from attribute values.
When uploading a file, this parameter provides the file path. The path may be entered directly into the transformer or set from an attribute value.
When uploading a string value or a file, this parameter provides the data content type. The value of this parameter will be sent in the Content-Type request header. The drop-down list contains a number of commonly-used content type values. If a different value is required, it can be typed into the text field, or derived from an attribute value.
This table is used to construct multipart uploads. Each part in a multipart upload must have a name, which is given in the first column. The second column identifies the type of part – either a file or a string value. The third column provides the data and MIME type for the part.
Response
This parameter allows users to set the destination for the HTTP response body. The body may be saved to an attribute, or to a file.
Note: If you are downloading a very large response body with the HTTPCaller, it is recommended that you save it to a file. This avoids creating a large attribute on the feature.
When saving the response body to an attribute, this parameter names the attribute which will be used. The default attribute name is _response_body. When performing a HTTP HEAD request, this attribute will be empty.
This parameter is used to indicate the character encoding of the target attribute. By default, the attribute encoding will be automatically determined from the HTTP response headers. Alternatively, a specific encoding may be selected from the list. When downloading binary data, the parameter should be set to Binary or Auto Detect from HTTP Headers.
Save Response Body To File
This parameter controls the manner in which the transformer will save response bodies to files. There are two modes:
- No: The response body will be saved to the file specified in the Output Filename parameter.
- Yes: A new file will be created for each feature, and saved in the folder specified in the Output Folder parameter.
When the Create a New File Per Feature parameter is set to No, the transformer will save HTTP response bodies to the file specified in this parameter. The file may be selected directly, or set from an attribute. Note that if the file is selected directly, the file will be overwritten by each feature passing through the transformer. If more than one feature is passing through the transformer, it is recommended that the file path be set to a unique attribute value, or that the transformer be configured to create a new file for each feature.
When the Create a New File Per Feature parameter is set to Yes, the transformer will create a new file for each feature passing through the transformer. The files will be saved in the folder specified in this parameter.
If Create a New File Per Feature is Yes, this parameter specifies the file type extension for the new file names. Select from a list of common file types, type in manually, or automatically set based on the Content-Type header in the HTTP response.
After the response body has been saved to a file, the attribute named in this parameter will be set to the file path.
Response Headers and Status
This parameter is optional. If it is set to a list attribute name, then HTTP headers returned by the server will be stored in the list attribute. The headers will be split into names and values. For example:
`_headers{0}.name' has value `X-XSS-Protection'
`_headers{0}.value' has value `1; mode=block'
`_headers{1}.name' has value `Date'
`_headers{1}.value' has value `Wed, 25 May 2011 17:20:20 GMT'
`_headers{2}.name' has value `Transfer-Encoding'
`_headers{2}.value' has value `chunked'
`_headers{3}.name' has value `Content-Type'
`_headers{3}.value' has value `text/html; charset=ISO-8859-1'
`_headers{4}.name' has value `Cache-Control'
`_headers{4}.value' has value `private, max-age=0'
This parameter is optional. If it is set to an attribute name, then the HTTP response code returned by the server will be stored in the attribute.
This parameter is optional. If an error occurs, the feature will be output through the <Rejected> output port, and the attribute named in this parameter will contain a brief error message.
HTTP Client Options
If this parameter is set to Yes, any saved cookies that correspond to the URL being accessed will be sent with the request. In addition, any cookies contained in the response will be saved for use with subsequent HTTP requests.
Saved cookies will persist for the duration of the translation – they cannot be used in subsequent translations.
- An HTTPCaller transformer is used to log in to the web service and a session cookie is saved.
- A second HTTPCaller transformer is used to access the web service, utilizing the saved session cookie.
- A third HTTPCaller is used to log out of the web service, which invalidates the saved cookie.
If this parameter is set to Yes, the transformer will follow any URL redirects it encounters, making a second request to a new location.
If this parameter is set to Yes, the transformer will verify SSL certificates. This is done in two stages:
- Ensure that the certificate is for the host we are trying to connect to.
- Ensure that the certificate is valid.
This parameter can be used to set a timeout on HTTP connection requests. If a connection to the server cannot be created within the given number of seconds, the request will fail, and the feature will be output through the <Rejected> port. The default connection timeout is 60 seconds. If 0 is entered, there will be no timeout, and the transformer will wait indefinitely for a successful connection.
This parameter can be used to set a timeout on HTTP transfers. If data stops being transferred for more than the given number of seconds, the request will fail, and the feature will be output through the <Rejected> port. The default transfer timeout is 90 seconds. If 0 is entered, there will be no timeout, and the transformer will wait indefinitely for data to resume being transferred.
Authentication Parameters
The transformer supports user authentication in two ways: Named Connections and username/password authentication.
The Named Connection option allows the selection of a stored Named Connection, which will authenticate the user with the appropriate Web Service. To add a new Named Connection, select “Add Connection…” from the Named Connection dropdown menu. The Named Connection option allows for OAuth2 authentication with supported Web Services.
When authenticating with a username and password, the basic, digest and NTLM access authentication methods are supported:
- Basic (HTTP Basic authentication): This is the default choice, and the only method in widespread use and supported virtually everywhere. This sends the username and password over the network in plain text, easily captured by others.
- Digest (HTTP Digest authentication): Digest authentication is more secure over public networks than the Basic method.
- NTLM (HTTP NTLM authentication): NTLM is a proprietary protocol invented and used by Microsoft. It uses a challenge-response and hash concept similar to Digest to prevent the password from being eavesdropped.
Note: Note that although the HTTP Basic access authentication is a mechanism designed to allow a client to provide credentials to a server on the assumption that the connection between them is trusted and secure, be aware that any credentials passed from client to server can be easily intercepted through an insecure connection.
Editing Transformer Parameters
Using a set of menu options, transformer parameters can be assigned by referencing other elements in the workspace. More advanced functions, such as an advanced editor and an arithmetic editor, are also available in some transformers. To access a menu of these options, click beside the applicable parameter. For more information, see Transformer Parameter Menu Options.
Transformer Categories
FME Licensing Level
FME Professional edition and above
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Tags Keywords: URLFetcher