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site/content/en/docs/Archives/v2.1.x/Developer Guide/_index.md
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,12 @@ | ||
| --- | ||
| date: 2021-05-12 | ||
| title: "Developer Guide" | ||
| linkTitle: "Developer Guide" | ||
| weight: 20 | ||
| description: > | ||
| Learn about the concepts and the functionalities of the Connect File Pulse Plugin. | ||
| --- | ||
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| The Developer Guide section helps you learn about the functionalities of the File Pulse Connector and the concepts | ||
| File Pulse uses to process and transform your data, and helps you obtain a deeper understanding of how File Pulse Connector works. | ||
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.../content/en/docs/Archives/v2.1.x/Developer Guide/accessing-data-and-metadata.md
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| Original file line number | Diff line number | Diff line change |
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| --- | ||
| date: 2021-06-10 | ||
| title: "Accessing Data and Metadata" | ||
| linkTitle: "Accessing Data and Metadata" | ||
| weight: 60 | ||
| description: > | ||
| The commons configuration for Connect File Pulse. | ||
| --- | ||
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| Some filters (e.g : [AppendFilter](/kafka-connect-file-pulse/docs/developer-guide/filters/#appendfilter)) can be configured using *Simple Connect Expression Language*. | ||
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| *Simple Connect Expression Language* (ScEL for short) is an expression language based on regex that allows quick access and manipulating record fields and metadata. | ||
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| The syntaxes to define an expression are of the form : `<expression string>` or `"{{ <expression string> }}"`. | ||
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| ScEL supports the following capabilities : | ||
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| * **Literal expressions** | ||
| * **Field Selector** | ||
| * **Nested Navigation** | ||
| * **String substitution** | ||
| * **Functions** | ||
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| ## Literal expressions | ||
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| * String : `'Hello World'` | ||
| * Number : `42` | ||
| * Boolean: `True` | ||
| * Nullable: `null` | ||
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| ## Field Selector | ||
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| The expression language can be used to easily select one field from the input record : | ||
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| `$.username` | ||
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| ## Nested Navigation | ||
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| To navigate down a struct value, just use a period to indicate a nested field value : | ||
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| `$.address.city` | ||
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| ## String substitution | ||
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| The expression language can be used to easily build a new string field that concatenate multiple ones : | ||
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| `The user {{ $.username }} is living in city {{ $.address.city }}` | ||
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| ## Function | ||
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| The expression language support function call : | ||
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| `The user {{ $.username }} is living in city {{ uppercase($.address.city) }}` | ||
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| ## Dynamic Field Selector | ||
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| String substitution can be used to dynamically select a field : | ||
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| The bellow example shows how to dynamically build a field selector by concatenating `$.` and | ||
| the first element present in the array field `$.values`. | ||
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| `{{ '$.'extract_array($.values, 0) }}` | ||
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| Note the use of double-quotes to define a substitution expressions | ||
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| ## Built-in Functions | ||
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| ScEL supports a number of predefined functions that can be used to apply a single transformation on a field. | ||
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| | Function | Description | Syntax | | ||
| | ----------------|---------------|-----------| | ||
| | `concat` | Concatenate two or more string expressions. | `{{ concat(expr1, expr2, ...) }}` | | ||
| | `concat_ws` | Concatenate two or more string expressions, using the specified separator between each. | `{{ concat_ws(separator, prefix, suffix, expr1, expr2, ...) }}` | | ||
| | `contains` | Returns `true` if an array field's value contains the specified value | `{{ contains(array, 'value') }}` | | ||
| | `converts` | Converts a field's value into the specified type | `{{ converts(field_expr, INTEGER) }}` | | ||
| | `ends_with` | Returns `true` if a string field's value end with the specified string suffix | `{{ ends_with(field_expr, 'suffix') }}` | | ||
| | `equals` | Returns `true` if a string or number fields's value equals the specified value | `{{ equals(field_expr, value) }}` | | ||
| | `exists` | Returns `true` if an object has the specified field | `{{ exists(obj_expr, field_expr) }}` | | ||
| | `extract_array` | Returns the element at the specified position of the specified array | `{{ extract_array(array, 0) }}` | | ||
| | `hash` | Hash a given string expression, using murmur2 algorithm | `{{ hash(field_expr) }}` | | ||
| | `is_null` | Returns `true` if a field's value is null | `{{ is_null(field) }}` | | ||
| | `length` | Returns the number of elements into an array of the length of an string field | `{{ length(array) }}` | | ||
| | `lowercase` | Converts all of the characters in a string field's value to lower case | `{{ lowercase(field) }}` | | ||
| | `matches` | Returns `true` if a field's value match the specified regex | `{{ matches(field_expr, 'regex') }}` | | ||
| | `md5` | Compute the MD5 hash of string expression | `{{ md5(field_expr) }}` | | ||
| | `nlv` | Sets a default value if a field's value is null | `{{ length(array) }}` | | ||
| | `replace_all ` | Replaces every subsequence of the field's value that matches the given pattern with the given replacement string. | `{{ replace_all(field_expr, 'regex', 'replacement') }}` | | ||
| | `split` | Split a string field's value into an array using the specified regex or character | `{{ split(field_expr, regex) }}` or `{{ split(field_expr, regex, limit) }}` | | ||
| | `starts_with` | Returns `true` if an a string field's value start with the specified string prefix | `{{ starts_with(field_expr, 'prefix') }}` | | ||
| | `trim` | Trims the spaces from the beginning and end of a string. | `{{ trim(field_expr) }}` | | ||
| | `uppercase` | Converts all of the characters in a string field's value to upper case | `{{ uppercase(field_expr) }}` | | ||
| | `uuid` | Create a Universally Unique Identifier (UUID) | `{{ uuid() }}` | | ||
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| In addition, ScEL supports nested functions. | ||
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| For example, the following expression can be used to replace all whitespace characters after transforming our field's value into lowercase. | ||
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| ``` | ||
| replace_all(lowercase($.field), '\\s', '-') | ||
| ``` | ||
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| {{% alert title="Limitation" color="warning" %}} | ||
| Currently, FilePulse does not support user-defined functions (UDFs). So you cannot register your own functions to enrich the expression language. | ||
| {{% /alert %}} | ||
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| ## Scopes | ||
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| In the previous section, we have shown how to use the expression language to select a specific field. | ||
| The selected field was part of our the current record being processed. | ||
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| Actually, ScEL allows you to get access to additional fields through the used of scopes. | ||
| Basically, a scope defined the root object on which a selector expression must evaluated. | ||
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| The syntax to define an expression with a scope is of the form : "`$<scope>.<selector expression string>`". | ||
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| By default, if no scope is defined in the expression, the scope `$value` is implicitly used. | ||
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| ScEL supports a number of predefined scopes that can be used for example : | ||
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| - **To define the topic for the record.** | ||
| - **To define the key for the record.** | ||
| - **To get access to metadata about the source file.** | ||
| - Etc. | ||
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| | Scope | Description | Type | | ||
| |--- | --- |--- | | ||
| | `$headers` | The record headers | - | | ||
| | `$key` | The record key | `string` | | ||
| | `$metadata` | The file metadata | `struct` | | ||
| | `$offset` | The offset information of this record into the source file | `struct` | | ||
| | `$system` | The system environment variables and runtime properties | `struct` | | ||
| | `$timestamp` | The record timestamp | `long` | | ||
| | `$topic` | The output topic | `string` | | ||
| | `$value` | The record value| `struct` | | ||
| | `$variables` | The contextual filter-chain variables| `map[string, object]` | | ||
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| Note, that in case of failures more fields are added to the current filter context (see : [Handling Failures](/kafka-connect-file-pulse/docs/developer-guide/handling-failures/)) | ||
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| ### Record Headers | ||
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| The scope `headers` allows defining the headers of the output record. | ||
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| ### Record key | ||
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| The scope `key` allows defining the key of the output record. Only string key is currently supported. | ||
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| ### Source Metadata | ||
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| The scope `metadata` allows read access to information about the file being processing. | ||
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| | Predefined Fields (ScEL) | Description | Type | | ||
| |--- | --- |--- | | ||
| | `$metadata.name` | The file name | `string` | | ||
| | `$metadata.path` | The file directory path | `string` | | ||
| | `$metadata.absolutePath` | The file absolute path | `string` | | ||
| | `$metadata.hash` | The file CRC32 hash | `int` | | ||
| | `$metadata.lastModified` | The file last modified time. | `long` | | ||
| | `$metadata.size` | The file size | `long` | | ||
| | `$metadata.inode` | The file Unix inode | `long` | | ||
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| ## Record Offset | ||
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| The scope `offset` allows read access to information about the original position of the record into the source file. | ||
| The available fields depend on the configured FileInputRecord. | ||
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| | Predefined Fields (ScEL) | Description | Type | | ||
| |--- | --- |--- | | ||
| | `$offset.timestamp` | The creation time of the record (millisecond) | `long` | | ||
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| Information only available if `RowFilterReader` is configured. | ||
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| | Predefined Fields (ScEL) | Description | Type | | ||
| |--- | --- |--- | | ||
| | `$offset.startPosition` | The start position of the record into the source file | `long` | | ||
| | `$offset.endPosition` | The end position of the record into the source file | `long` | | ||
| | `$offset.size` | The size in bytes | `long` | | ||
| | `$offset.row` | The row number of the record into the source | `long` | | ||
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| Information only available if `BytesArrayInputReader` is configured. | ||
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| | Predefined Fields (ScEL) | Description | Type | | ||
| |--- | --- |--- | | ||
| | `$offset.startPosition` | The start position of the record into the source file (always equals to 0) | `long` | | ||
| | `$offset.endPosition` | The end position of the record into the source file (equals to the file size) | `long` | | ||
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| Information only available if `AvroFilterInputReader` is configured. | ||
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| | Predefined Fields (ScEL) | Description | Type | | ||
| |--- | --- |--- | | ||
| | `$offset.blockStart` | The start position of the current block | `long` | | ||
| | `$offset.position` | The position into the current block. | `long` | | ||
| | `$offset.records` | The number of record read into the current block. | `long` | | ||
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| ## System | ||
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| The scope `system` allows accessing to the system environment variables and runtime properties. | ||
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| | Predefined Fields (ScEL) | Description | Type | | ||
| |--- | --- |--- | | ||
| | `$system.env` | The system environment variables. | `map[string, string]` | | ||
| | `$system.props` | The system environment properties. | `map[string, string]` | | ||
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| ## Timestamp | ||
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| The scope `$timestamp` allows defining the timestamp of the output record. | ||
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| ## Topic | ||
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| The scope `$topic` allows defining the target topic of the output record. | ||
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| ## Value | ||
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| The scope `$value` allows defining the fields of the output record | ||
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| ## Variables | ||
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| The scope `$variables` allows read/write access to a simple key-value map structure. | ||
| This scope can be used to share user-defined variables between [Processing Filters](/kafka-connect-file-pulse/docs/developer-guide/filters/). | ||
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| Note : variables are not cached between records. |
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