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Snap type:

Read

Description:

This Snap polls the target directory and looks for file names matching the specified pattern. It continues polling at the intervals specified in the Polling interval property until the timeout (specified in the Polling timeout property) is reached. Once polling is done, the Snap lists all files whose names match the specified pattern.

Note
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, as well as to poll a directory only once.

The File Poller 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.

Expected upstream Snaps: Any Snap with a document output view, such as Mapper, JSON Generator.
Expected downstream Snaps: Any Snap with a document input view, such as File Reader, Mapper, JSON Formatter.
Expected input: 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.
Expected output: A full path in each document as a value for a key "path". If there are multiple files matching the filter, the same number of documents will be provided in the output view after each interval.

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

Prerequisites:

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Support and limitations:

Works in Ultra Pipelines.
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.

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.

Account:

This Snap uses account references created on the Accounts page of SnapLogic Manager to handle access to this endpoint. This Snap supports several account types, as listed in the table below, or no account. See Configuring Binary Accounts for information on setting up accounts that work with this Snap.

Account types supported by each protocol are as follows:

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

Note
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
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.)

Views:

Input	This Snap has at most one document input view.
Output	This Snap has exactly one document output view.
Error	This Snap has at most one document error view.

Settings

Label

Required. 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

This property is a URL path to the directory where files will be searched. The expected syntax is:

[protocol]://[host][:port]/[path]

The supported file protocols are:

s3:
file:
ftp:
ftps:
sftp:
hdfs:
sldb:
smb:
wasb:
wasbs:
gs:

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/

Default value: [None]

Note

The protocol and the rest of the URL should be separated by "://". The host name and the port number should be between "://" and "/".
Not all file protocols support "//", use "///" instead. For example, if polling files in SLDB and S3 (see the examples shown above).
This property should be an absolute path for all protocols except SLDB. For SLDB, the Snap can access only the same project directory or the shared project directory, and cannot access other project directories.
If you want this property to refer to the SLDB project (or shared project) directory where the pipeline of this Snap belongs to, enter "sldb:///" or leave it blank.
If the pipeline is created in a project other than the shared project and you want this property to refer to the shared project, enter "shared" or "sldb:///shared".
If the port number is omitted, a default port for the protocol is used. The hostname and port number are omitted in the SLDB and S3 protocols.
Ensure the file name, folder name, or the file path does not contain '?' character because it is not fully supported and when present, the Snap might fail.

File filter

Required. 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.
Example:

*.txt
ab????xx.csv

Default value: [None]

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title	Glob Pattern Interpretation Rules

Use glob patterns in this filter to select one or more files in the directory. For example:

*.java Matches file names ending in .java.
*.* Matches file names containing a dot.
*.{java,class} Matches file names ending with .java or .class.
foo.? Matches file names starting with foo. and a single character extension.

The following rules are used to interpret glob patterns:

The * character matches zero or more characters of a name component without crossing directory boundaries.
The ? character matches exactly one character of a name component.
The backslash character (\) is used to escape characters that would otherwise be interpreted as special characters. For example, the expression \\ matches a single backslash, and "\{" matches a left brace.
The ! character is used to exclude matching files from the output.
The [ ] characters are a bracket expression that match a single character of a name component out of a set of characters. For example, [abc] matches 'a', 'b', or 'c'. The hyphen (-) may be used to specify a range; so, [a-z] specifies a range that matches from 'a' to 'z' (inclusive). These forms can be mixed; so, [abce-g] matches 'a'", 'b', 'c', 'e', 'f' or 'g'. If the character after the '[' is an '!', then it is used for negation; so, [!a-c] matches any character except 'a', 'b', or 'c'.
Within a bracket expression, the *, ?, and \ characters match themselves. The (-) character matches itself if it is the first character within the brackets, or the first character after the '!', if negating.
The { } characters are a group of subpatterns, where the group matches if any subpattern in the group matches. The ',' character is used to separate subpatterns. Groups cannot be nested.
Leading period / dot characters in file names are treated as regular characters in match operations. For example, the '*' glob pattern matches file name '.login'.
Some special characters are not supported. A partial list of unsupported special characters: #, ^, â, ê, î, ç, ¿, SPACE.

Polling interval in seconds

Required. The time-gap between each poll request (in seconds).

Example: 10

Default value: 30

Polling timeout

Required. A period of time after which file polling must end.

Specify a value for polling timeout in this field and its unit in the subsequent field.

Example:

If the Polling timeout is set to greater than zero, for example 60 seconds, the polling stops after 60 seconds.
If Polling Timeout is set to 0, the Snap processes only one poll.
If Polling Timeout is set to -1, the Snap polls continually.

Default value: 30

Note
Configure this field based on the expected number of files in the target directory. If there are many files and this field's value is small, the Snap may complete the operation and stop before the file is found.

Polling-timeout unit

Unit for the polling timeout. Allowed values are SECONDS, MINUTES and HOURS.

Example: SECONDS

Default value: MINUTES

Only Output on Change

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.

Default value: Selected

Number of retries

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.

If the value is larger than 0, the Snap first downloads the target file into a temporary local file. If any error occurs during the download, the Snap waits for the time specified in the Retry interval and attempts to download the file again from the beginning. When the download is successful, the Snap streams the data from the temporary file to the downstream Pipeline. All temporary local files are deleted when they are no longer needed.

Ensure that the local drive has sufficient free disk space to store the temporary local file.

Example: 3

Minimum value: 0
Default value: 0

Retry interval (seconds)

Specifies the minimum number of seconds for which the Snap must wait before attempting recovery from a network failure.

Minimum value: 1

Default value: 1
Example: 3

Advanced properties

Use this field set to define specific settings for polling files. Click

to add a new row for defining an advanced property. This field set comprises the following fields:

Properties: Select either of the following properties.
- SAS URI
- Exit on first matches
Values

SAS URI

Specify the URI of the Shared Access Storage (SAS) you need to access. Click to add the SAS URI. 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

Note

Ensure that the URI is specified in the format described here.
If you provide SAS URI in this field, then:
- the Primary access key given in the account settings is overridden while authentication. If you do not provide the SAS URI, the Snap considers the Primary access key in the account settings.
- only this URL is used and the Snap ignores the SAS URI settings that you have configured in the associated account.

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.

Default value: false

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Troubleshooting

Error

Reason

Resolution

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 S3 data.

Examples

Writing out the List of Files in a Specific Directory Using the File Poller

In this example, you test the File Poller Snap to see whether it lists out files from a specific directory. You 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 exercise.

Download this pipeline.

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title	Understanding the pipeline

File Poller

You add a File Poller Snap and configure it to poll a directory for all files with the extension ".JSON2":

You then use a combination of JSON Formatter and File Writer Snaps to process the output and write it out to a file. You use the date.now() function to give the file a name, so every time you run the pipeline, a new file is created.

You use the JSON Formatter Snap with the default settings.

File Writer

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".

You now add a second File Poller Snap and configure it exactly as you configured 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:

This tells you that the File Poller Snap works as expected with the settings you have used.

Download this pipeline.

Polling 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

Expand

title	Understanding the 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.

Creating 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

You use the CSV Parser Snap with the default settings:

Mapper

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