HTTPCaller

The HTTP method to access the server. Most requests will use the GET method. Requests that upload data will typically use the PUT, POST or PATCH method, although an upload body can also be provided with the DELETE 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.

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.

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.

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.

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.

This parameter controls how features are processed through the transformer. The value of this parameter indicates the maximum number of transfers that will be in progress at the same time.

When the parameter is set to 1, a transfer will be fully processed before the next transfer can begin.

When the parameter is set to a value greater than 1, the transformer will not wait for each transfer to finish before starting the next one. There may be multiple transfers occurring at the same time. This can provide significant performance benefits. This value should be adjusted based on the ability of the HTTP server to handle multiple requests at the same time, taking into consideration that multiple HTTPCaller transformers may be accessing the server at the same time.

This parameter must be set to 1 if the transformer is being used inside a custom transformer which has a loop output.

This is the maximum number of HTTP requests the transformer will start in a particular time interval. For example, if you wanted to limit the transformer to 50 requests per minute, you would set this parameter to 50.

This is the time period over which requests will be limited. For example, if you wanted to limit the transformer to 50 requests per minute, you would set this parameter to 60. Some preset values are provided in the parameter list, or any number may be manually entered.

This controls the way that transfers are started within the time interval. There are two options:

• Start requests as soon as possible: When this value is selected, requests will be started as soon as possible, as long as the maximum number of requests started in the preceding time interval does not exceed the maximum. This may lead to many requests being started at the beginning of the time interval, and then nothing happening until the interval has passed.

• Start requests evenly through the interval: When this value is selected, the transformer will attempt to start requests evenly through the interval. That is, it will divide the interval length by the maximum number of requests, and then ensure that at least this much time elapses between starting each request. This is equivalent to inserting a Decelerator transformer before the HTTPCaller, and can ease the load on an HTTP server.

This parameter allows users to control which version of the HTTP protocol is used in the transformer. When Restrict to HTTP/1.1 is selected, the use of HTTP/2 will be disabled and only HTTP/1.1 will be used. When Use HTTP/2 if possible is selected, HTTP/2 may be used if the HTTP server supports it. Otherwise HTTP/1.1 will be used. Typically this parameter should be configured to allow the use of HTTP/2. Restricting the transformer to HTTP/1.1 should only be used when connecting to servers which do not handle HTTP/2 correctly.

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.

Saving cookies is useful when a web service keeps a "session". Then the following sequence of operations might be used:

1. An HTTPCaller transformer is used to log in to the web service and a session cookie is saved.
2. A second HTTPCaller transformer is used to access the web service, utilizing the saved session cookie.
3. 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:

1. Ensure that the certificate is for the host we are trying to connect to.
2. 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.

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.  

Using the Text Editor

The Text Editor provides a convenient way to construct text strings (including regular expressions) from various data sources, such as attributes, parameters, and constants, where the result is used directly inside a parameter.

Text Editor

Using the Arithmetic Editor

The Arithmetic Editor provides a convenient way to construct math expressions from various data sources, such as attributes, parameters, and feature functions, where the result is used directly inside a parameter.

Arithmetic Editor

Conditional Values

Set values depending on one or more test conditions that either pass or fail.

Parameter Condition Definition Dialog

Content

Expressions and strings can include a number of functions, characters, parameters, and more.

When setting values - whether entered directly in a parameter or constructed using one of the editors - strings and expressions containing String, Math, Date/Time or FME Feature Functions will have those functions evaluated. Therefore, the names of these functions (in the form @<function_name>) should not be used as literal string values.

Content Types

String Functions	These functions manipulate and format strings.
Special Characters	A set of control characters is available in the Text Editor.
Math Functions	Math functions are available in both editors.
Date/Time Functions	Date and time functions are available in the Text Editor.
Math Operators	These operators are available in the Arithmetic Editor.
FME Feature Functions	These return primarily feature-specific values.
FME Parameters	FME and workspace-specific parameters may be used.
Creating and Modifying User Parameters	Create your own editable parameters.

Note: Not all tools are available in all transformers.