In this article

1 Overview
- 1.1 Snap Type
- 1.2 Prerequisites
- 1.3 Support for Ultra Pipelines
- 1.4 Limitations
- 1.5 Known Issues
- 1.6 Behavior Change
- 1.7 Supported Protocols
2 Snap Views
3 Snap Settings
4 Troubleshooting
5 Examples
- 5.1 Write a List of Files in a Specific Directory
- 5.2 Poll a Directory Using a Trigger Task from ServiceNow
6 Downloads
7 Snap Pack History

Overview

You can use this Snap to poll the target directory and find file names matching the specified pattern.

The Snap continues polling at the intervals specified in the Polling interval property until the timeout (specified in the Polling timeout property) is reached. After polling is done, the Snap lists all files whose names match the specified pattern.
This Snap can be used in situations where an operation must be triggered when a specific file is found in the target directory. The pipeline can be configured with additional Snaps to process the Snap's output and delete the matched file before the Polling interval value is reached.
The File Poller Snap uses the case-sensitive filter pattern, regardless of the operating system.

This Snap polls the target directory only. Subdirectories, if any, are ignored. Use the Directory Browser Snap if you want to poll files in the directory and all subdirectories, and to poll a directory only once.

Snap Type

The File Poller Snap is a Read-type Snap.

Prerequisites

Support for Ultra Pipelines

Works in Ultra Pipelines.

Limitations

For S3 folders, the Snap currently supports polling the target directory for a maximum of 10,000 files. If there are more than that, the Snap does not provide any output.

Known Issues

The Snap is expected to fail if there is no account selected. However, the Snap may execute successfully without any account if all the following conditions exist:

The Snap is executed in an EC2-instance Snaplex where your pipeline runs with an IAM role.
The S3 bucket accessed by the Snap includes the necessary permissions for use with the specific IAM role.
The following global property is set as a node property in the plex:
jcc.jvm_options = -DIAM_CREDENTIAL_FOR_S3=TRUE

Behavior Change

The File Poller Snap now honors the value specified in the Polling timeout field instead of polling indefinitely in case of poor file polling operations. To handle indefinite polling operations the polling is done in a separate thread. However, when the execution time exceeds the value specified in the Polling timeout, a timeout exception is written to the log to prevent the polling from getting stuck and the Snap continues polling depending on the Polling timeout.

If the Polling timeout value is greater than 0, the Snap polls until the end of polling window.
If it is less than 0, the Snap stops polling.
If it is -1, the Snap continues polling.

Supported Protocols

Account types supported by each protocol are as follows:

Protocol	Account types

Protocol	Account types
sldb	no account
s3	AWS S3
ftp	Basic Auth
sftp	Basic Auth, SSH Auth
ftps	Basic Auth
hdfs	no account
smb	SMB
wasb	Azure Storage
wasbs	Azure Storage
gs	Google Storage
file	Local file system

The FTPS file protocol works only in explicit mode. The implicit mode is not supported.

Required settings for account types are as follows:

Account Type	Settings

Account Type	Settings
Basic Auth	Username, Password
AWS S3	Access-key ID, Secret key
SSH Auth	Username, Private key, Key Passphrase
SMB	Domain, Username, Password
Azure Storage	Account name, Primary access key
Google Storage	Approval prompt, Application scope, Auto-refresh token (Read-only properties are Access token, Refresh token, Access token expiration, OAuth2 Endpoint, OAuth2 token and Access type.)

Snap Views

Type	Format	Number of Views	Examples of Upstream and Downstream Snaps	Description

Type

Format

Number of Views

Examples of Upstream and Downstream Snaps

Description

Input

Document

Min: 1
Max: 1

Mapper
JSON Generator

An optional document to evaluate expressions in the Directory and/or File filter properties. Note that each input document will trigger the execution of the Snap.

Output

Document

Min: 1
Max: 1

Mapper
File Reader
JSON Formatter

A full path in each document as a value for a key "path". If multiple files match the filter, the same number of documents will be provided in the output view after each interval.

[
        {
                "path" :  "sftp://sftp.smart.com/home/voo/test1.csv"
        },
        {
                "path" :  "sftp://sftp.smart.com/home/voo/test2.csv"
        }
]

Error

Error handling is a generic way to handle errors without losing data or failing the Snap execution. You can handle the errors that the Snap might encounter when running the pipeline by choosing one of the following options from the When errors occur list under the Views tab:

Stop Pipeline Execution: Stops the current pipeline execution if the Snap encounters an error.
Discard Error Data and Continue: Ignores the error, discards that record, and continues with the remaining records.
Route Error Data to Error View: Routes the error data to an error view without stopping the Snap execution.

Learn more about Error handling in Pipelines.

Snap Settings

Field Name		Field Type	Description
Label* Default Value: File Poller Example: File Poller		String	Specify the name for the Snap. You can modify this to be more specific, especially if you have more than one of the same Snap in your pipeline.
Directory Default Value: N/A Example: `s3:///<S3_bucket_name>@s3.<region_name>.amazonaws.com/<path>` For region names and their details, see AWS Regions and Endpoints. sftp://ftp.snaplogic.com:22/home/test/dir `ftp://ftp.snaplogic.com/test/csv` `$directory` `_directory` (A key-value pair with "directory" key should be defined as a pipeline parameter. Ensure that the '=' button is enabled when using parameters.) `file:///D:/testFolder/` (if the Snap is executed in the Windows Groundplex and needs to access the D: drive) `wasb:///Snaplogic/testDir/` or `wasbs:///Snaplogic/testDir/` `gs:///testBucket/testDir/`		String/Expression	Specify the URL path to the directory where files will be searched in the following format: `[protocol]://[host][:port]/[path]` The supported file protocols are: s3: file: ftp: ftps: sftp: hdfs: sldb: smb: wasb: wasbs: gs:
File filter* Default Value: N/A Example: .txt ab????xx.csv*		String/Expression	Specify a GLOB pattern to be applied to select one or more files in the directory. The File filter property can be a JavaScript expression which will be evaluated with values from the input view document. [None]
Polling interval in seconds* Default value: 30 Example: 10		Integer	Specify the time gap between each poll request (in seconds).
Polling timeout* Default value: 30 Example: 20		Integer	Specify a period of time after which file polling must end. If the Polling timeout is set to: Greater than 0, for example, 60 seconds, the polling stops after 60 seconds. 0, the Snap processes only one poll. -1, the Snap polls continually.
Polling-timeout unit Default value: MINUTES Example: SECONDS		Dropdown list	Specify a value for polling timeout.
Only Output on Change Default value: Selected		Checkbox	Select this check box to instruct the Snap to provide an output only when there is a change in the contents of the polled directory. When selected, the Snap provides an output during its initial run if it finds matching documents. However, it provides polling results in the next run only if the polled directory has newer files that match the pattern specified.
Number of retries Minimum value: 0 Default value: 0 Example: 3		Integer	Specify the maximum number of retry attempts that the Snap must make in case there is a network failure, and the Snap is unable to read the target file.
Retry interval (seconds) Minimum value: 1 Default value: 1 Example: 3		Integer	Specify the minimum number of seconds for which the Snap must wait before attempting recovery from a network failure.
Advanced properties	Use this field set to define specific settings for polling files.
	Properties	Dropdown list	Choose either of the following options: SAS URI Exit on first matches
	Values	String/Expression	If you choose SAS URI, specify the URI of the Shared Access Storage (SAS) you need to access. You can generate the SAS URI either from the SAS Generator Snap or from the Azure portal → Shared access signature. The supported SAS types are: Service SAS on a container Service SAS on blob If you choose Exit on first matches, set this field to true to stop the Snap from executing after writing the first list of file paths that match the filter pattern to the output view. If the field is not configured or is set to false, then the Snap continues to poll the directory until the Polling timeout is reached.
Snap execution Default Value: Validate & Execute Example: Execute only		Dropdown list	Select one of the following three modes in which the Snap executes: Validate & Execute: Performs limited execution of the Snap, and generates a data preview during Pipeline validation. Subsequently, performs full execution of the Snap (unlimited records) during Pipeline runtime. Execute only: Performs full execution of the Snap during Pipeline execution without generating preview data. Disabled: Disables the Snap and all Snaps that are downstream from it.

Troubleshooting

Error	Reason	Resolution

Error

Reason

Resolution

Algorithm negotiation fail: algorithmName="server_host_key" jschProposal="<algorithms>" serverProposal="ssh-rsa"

The library that we use for SFTP connections no longer supports deprecated signature protocols by default. This changed with the 4.33 GA release.

Add the algorithm to the serverProposal in the global properties.
You can also enable support for RSA-SHA1 authentication in the Node Properties tab on the Update Snaplex dialog in SnapLogic Manager.

In the Node Properties tab of your target Snaplex, add the following Key Value pair under Global Properties:
Key: jcc.jvm_options
Value: -Djsch.server_host_key=ssh-rsa -Djsch.client_pubkey=ssh-rsa
Click Update, and then restart the Snaplex node.

Learn more: Configuration Options

com.amazonaws.AbortedException - Cannot access AWS S3 service

If you have set the Polling Timeout value to a few seconds, it results in the S3 request getting canceled.

Increase the value of Polling Timeout (in seconds) for the Snap to work successfully.

We recommend that you set the Polling Timeout value to the default value of 30 minutes or more to fetch all the data from S3.

Examples

Write a List of Files in a Specific Directory

This example pipeline demonstrates how to list out files from a specific directory. After the Poller Snap lists the files, then write the output to a file and run the File Poller Snap again to check whether the new file was created as expected. To ensure that the File Poller Snap doesn't pick up any existing files, you use an unusual extension for this example.

Configure the File Poller Snap to poll a directory for all files with the extension ".JSON2".

Connect JSON Formatter and File Writer Snaps to process the output and write it to a file. Use the JSON Formatter Snap with the default settings. In the File Writer Snap, use the date.now() function to give the file a name, so a new file is created every time you run the pipeline.

When used in production, the output from the File Poller Snap can be used to trigger specific tasks as needed. In this example, you write it to a file. As expected, the file contains no output, as there is no file in the target directory with the extension ".JSON2".

Next, add the second File Poller Snap and configure it exactly as the first one. Once again, you add a JSON Formatter and File Writer Snap with the same settings as for the previous pair. But this time, the file created is not blank: It lists out the file that you created using the first three Snaps in the pipeline:

Download this pipeline.

Poll a Directory Using a Trigger Task from ServiceNow

In this example, you call a Trigger Task from ServiceNow to poll a directory for files of a specific type.

Download this pipeline

To make this example work, you must perform the following tasks:

Create a pipeline that receives specifications from ServiceNow on the file type for which you want to poll a directory.
Create a Trigger Task that will make the pipeline available as a REST API.
Create a REST call in ServiceNow that will trigger the Task created in Step 2 above.

Create the File Poller Pipeline

You design a pipeline containing the following Snaps:

CSV Parser: Parses the data coming in from ServiceNow as a CSV document.
Mapper: Makes the contents of the input CSV document available as a parameter.
File Poller: Polls a specific directory for files matching the pattern specified in the parameter received from the Mapper Snap.

You will note that the File Poller has open input and output views. This is because it receives data from the Trigger Task associated with it and returns processed data back to the same Trigger Task.

CSV Parser: Use the CSV Parser Snap with the default settings:

Mapper: Configure the Mapper Snap to receive the parsed CSV data and map the message in the CSV document to the $msg variable:

File Poller: Configure the File Poller Snap to poll the /QA/Documentation/File Poller/ directory for all files that match the pattern contained in the $msg variable, which you use as a file filter parameter:

Create a Trigger Task for the File Poller Pipeline: Save the pipeline, click the (Create Task) button, and configure the Trigger Task:

Click Update to complete setting up the task; then navigate to the Manager to view the Trigger Task's properties:

You copy the Cloud URL and authorization bearer token, and navigate to ServiceNow to set up the API call.

Create a REST call in ServiceNow: Create a REST Call in ServiceNow by appending the authorization token to the Cloud URL that you copied in the previous step:

For details on how to set up REST calls using ServiceNow, see ServiceNow documentation.

While configuring the REST call, ensure that:

HTTP Method is POST.
Endpoint contains the Cloud URL concatenated with the bearer token.
HTTP Parameters > Content contains the variable and extension value that you want to use.

You click Test to check the REST call. For a successful execution, the pipeline returns a list of files whose extension matches the value in the Content field: