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<!--
title: "Parser"
custom_edit_url: https://github.com/netdata/netdata/blob/master/parser/README.md
sidebar_label: "Parser"
learn_status: "Published"
learn_topic_type: "References"
learn_rel_path: "Developers/Database"
-->
#### Introduction
The parser will be used to process streaming and plugins input as well as metadata
Usage
1. Define a structure that will be used to share user state across calls
1. Initialize the parser using `parser_init`
2. Register keywords and associated callback function using `parser_add_keyword`
3. Register actions on the keywords
4. Start a loop until EOF
1. Fetch the next line using `parser_next`
2. Process the line using `parser_action`
1. The registered callbacks are executed to parse the input
2. The registered action for the callback is called for processing
4. Release the parser using `parser_destroy`
5. Release the user structure
#### Functions
TODO:
##### parse_init(RRDHOST *host, void *user, void *input, int flags)
Initialize an internal parser with the specified user defined data structure that will be shared across calls.
Input
- Host
- The host this parser will be dealing with. For streaming with SSL enabled for this host
- user
- User defined structure that is passed in all the calls
- input
- Where the parser will get the input from
- flags
- flags to define processing on the input
Output
- A parser structure
##### parse_push(PARSER *parser, char *line)
Push a new line for processing
Input
- parser
- The parser object as returned by the `parser_init`
- line
- The new line to process
Output
- The line will be injected into the stream and will be the next one to be processed
Returns
- 0 line added
- 1 error detected
##### parse_add_keyword(PARSER *parser, char *keyword, keyword_function callback_function)
The function will add callbacks for keywords. The callback function is defined as
`typedef PARSER_RC (*keyword_function)(char **, void *);`
Input
- parser
- The parser object as returned by the `parser_init`
- keyword
- The keyword to register
- keyword_function
- The callback that will handle the keyword processing
* The callback function should return one of the following
* PARSER_RC_OK - Callback was successful (continue with other callbacks)
* PARSER_RC_STOP - Stop processing callbacks (return OK)
* PARSER_RC_ERROR - Callback failed, exit
Output
- The corresponding keyword and callback will be registered
Returns
- 0 maximum callbacks already registered for this keyword
- > 0 which is the number of callbacks associated with this keyword.
##### parser_next(PARSER *parser)
Return the next item to parse
Input
- parser
- The parser object as returned by the `parser_init`
Output
- The parser will store internally the next item to parse
Returns
- 0 Next item fetched successfully
- 1 No more items to parse
##### parser_action(PARSER *parser, char *input)
Return the next item to parse
Input
- parser
- The parser object as returned by the `parser_init`
- input
- Process the input specified instead of using the internal buffer
Output
- The current keyword will be processed by calling all the registered callbacks
Returns
- 0 Callbacks called successfully
- 1 Failed
##### parser_destroy(PARSER *parser)
Cleanup a previously allocated parser
Input
- parser
- The parser object as returned by the `parser_init`
Output
- The parser is deallocated
Returns
- none
##### parser_recover_input(PARSER *parser)
Cleanup a previously allocated parser
Input
- parser
- The parser object as returned by the `parser_init`
Output
- The parser is deallocated
Returns
- none
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