1# LIBUCL 2 3[![Build Status](https://travis-ci.org/vstakhov/libucl.svg?branch=master)](https://travis-ci.org/vstakhov/libucl) 4[![Coverity](https://scan.coverity.com/projects/4138/badge.svg)](https://scan.coverity.com/projects/4138) 5[![Coverage Status](https://coveralls.io/repos/github/vstakhov/libucl/badge.svg?branch=master)](https://coveralls.io/github/vstakhov/libucl?branch=master) 6 7**Table of Contents** *generated with [DocToc](http://doctoc.herokuapp.com/)* 8 9- [Introduction](#introduction) 10- [Basic structure](#basic-structure) 11- [Improvements to the json notation](#improvements-to-the-json-notation) 12 - [General syntax sugar](#general-syntax-sugar) 13 - [Automatic arrays creation](#automatic-arrays-creation) 14 - [Named keys hierarchy](#named-keys-hierarchy) 15 - [Convenient numbers and booleans](#convenient-numbers-and-booleans) 16- [General improvements](#general-improvements) 17 - [Comments](#comments) 18 - [Macros support](#macros-support) 19 - [Variables support](#variables-support) 20 - [Multiline strings](#multiline-strings) 21- [Emitter](#emitter) 22- [Validation](#validation) 23- [Performance](#performance) 24- [Conclusion](#conclusion) 25 26## Introduction 27 28This document describes the main features and principles of the configuration 29language called `UCL` - universal configuration language. 30 31If you are looking for the libucl API documentation you can find it at [this page](doc/api.md). 32 33## Basic structure 34 35UCL is heavily infused by `nginx` configuration as the example of a convenient configuration 36system. However, UCL is fully compatible with `JSON` format and is able to parse json files. 37For example, you can write the same configuration in the following ways: 38 39* in nginx like: 40 41```nginx 42param = value; 43section { 44 param = value; 45 param1 = value1; 46 flag = true; 47 number = 10k; 48 time = 0.2s; 49 string = "something"; 50 subsection { 51 host = { 52 host = "hostname"; 53 port = 900; 54 } 55 host = { 56 host = "hostname"; 57 port = 901; 58 } 59 } 60} 61``` 62 63* or in JSON: 64 65```json 66{ 67 "param": "value", 68 "param1": "value1", 69 "flag": true, 70 "subsection": { 71 "host": [ 72 { 73 "host": "hostname", 74 "port": 900 75 }, 76 { 77 "host": "hostname", 78 "port": 901 79 } 80 ] 81 } 82} 83``` 84 85## Improvements to the json notation. 86 87There are various things that make ucl configuration more convenient for editing than strict json: 88 89### General syntax sugar 90 91* Braces are not necessary to enclose a top object: it is automatically treated as an object: 92 93```json 94"key": "value" 95``` 96is equal to: 97```json 98{"key": "value"} 99``` 100 101* There is no requirement of quotes for strings and keys, moreover, `:` may be replaced `=` or even be skipped for objects: 102 103```nginx 104key = value; 105section { 106 key = value; 107} 108``` 109is equal to: 110```json 111{ 112 "key": "value", 113 "section": { 114 "key": "value" 115 } 116} 117``` 118 119* No commas mess: you can safely place a comma or semicolon for the last element in an array or an object: 120 121```json 122{ 123 "key1": "value", 124 "key2": "value", 125} 126``` 127### Automatic arrays creation 128 129* Non-unique keys in an object are allowed and are automatically converted to the arrays internally: 130 131```json 132{ 133 "key": "value1", 134 "key": "value2" 135} 136``` 137is converted to: 138```json 139{ 140 "key": ["value1", "value2"] 141} 142``` 143 144### Named keys hierarchy 145 146UCL accepts named keys and organize them into objects hierarchy internally. Here is an example of this process: 147```nginx 148section "blah" { 149 key = value; 150} 151section foo { 152 key = value; 153} 154``` 155 156is converted to the following object: 157 158```nginx 159section { 160 blah { 161 key = value; 162 } 163 foo { 164 key = value; 165 } 166} 167``` 168 169Plain definitions may be more complex and contain more than a single level of nested objects: 170 171```nginx 172section "blah" "foo" { 173 key = value; 174} 175``` 176 177is presented as: 178 179```nginx 180section { 181 blah { 182 foo { 183 key = value; 184 } 185 } 186} 187``` 188 189### Convenient numbers and booleans 190 191* Numbers can have suffixes to specify standard multipliers: 192 + `[kKmMgG]` - standard 10 base multipliers (so `1k` is translated to 1000) 193 + `[kKmMgG]b` - 2 power multipliers (so `1kb` is translated to 1024) 194 + `[s|min|d|w|y]` - time multipliers, all time values are translated to float number of seconds, for example `10min` is translated to 600.0 and `10ms` is translated to 0.01 195* Hexadecimal integers can be used by `0x` prefix, for example `key = 0xff`. However, floating point values can use decimal base only. 196* Booleans can be specified as `true` or `yes` or `on` and `false` or `no` or `off`. 197* It is still possible to treat numbers and booleans as strings by enclosing them in double quotes. 198 199## General improvements 200 201### Comments 202 203UCL supports different style of comments: 204 205* single line: `#` 206* multiline: `/* ... */` 207 208Multiline comments may be nested: 209```c 210# Sample single line comment 211/* 212 some comment 213 /* nested comment */ 214 end of comment 215*/ 216``` 217 218### Macros support 219 220UCL supports external macros both multiline and single line ones: 221```nginx 222.macro_name "sometext"; 223.macro_name { 224 Some long text 225 .... 226}; 227``` 228 229Moreover, each macro can accept an optional list of arguments in braces. These 230arguments themselves are the UCL object that is parsed and passed to a macro as 231options: 232 233```nginx 234.macro_name(param=value) "something"; 235.macro_name(param={key=value}) "something"; 236.macro_name(.include "params.conf") "something"; 237.macro_name(#this is multiline macro 238param = [value1, value2]) "something"; 239.macro_name(key="()") "something"; 240``` 241 242UCL also provide a convenient `include` macro to load content from another files 243to the current UCL object. This macro accepts either path to file: 244 245```nginx 246.include "/full/path.conf" 247.include "./relative/path.conf" 248.include "${CURDIR}/path.conf" 249``` 250 251or URL (if ucl is built with url support provided by either `libcurl` or `libfetch`): 252 253 .include "http://example.com/file.conf" 254 255`.include` macro supports a set of options: 256 257* `try` (default: **false**) - if this option is `true` than UCL treats errors on loading of 258this file as non-fatal. For example, such a file can be absent but it won't stop the parsing 259of the top-level document. 260* `sign` (default: **false**) - if this option is `true` UCL loads and checks the signature for 261a file from path named `<FILEPATH>.sig`. Trusted public keys should be provided for UCL API after 262parser is created but before any configurations are parsed. 263* `glob` (default: **false**) - if this option is `true` UCL treats the filename as GLOB pattern and load 264all files that matches the specified pattern (normally the format of patterns is defined in `glob` manual page 265for your operating system). This option is meaningless for URL includes. 266* `url` (default: **true**) - allow URL includes. 267* `path` (default: empty) - A UCL_ARRAY of directories to search for the include file. 268Search ends after the first match, unless `glob` is true, then all matches are included. 269* `prefix` (default false) - Put included contents inside an object, instead 270of loading them into the root. If no `key` is provided, one is automatically generated based on each files basename() 271* `key` (default: <empty string>) - Key to load contents of include into. If 272the key already exists, it must be the correct type 273* `target` (default: object) - Specify if the `prefix` `key` should be an 274object or an array. 275* `priority` (default: 0) - specify priority for the include (see below). 276* `duplicate` (default: 'append') - specify policy of duplicates resolving: 277 - `append` - default strategy, if we have new object of higher priority then it replaces old one, if we have new object with less priority it is ignored completely, and if we have two duplicate objects with the same priority then we have a multi-value key (implicit array) 278 - `merge` - if we have object or array, then new keys are merged inside, if we have a plain object then an implicit array is formed (regardless of priorities) 279 - `error` - create error on duplicate keys and stop parsing 280 - `rewrite` - always rewrite an old value with new one (ignoring priorities) 281 282Priorities are used by UCL parser to manage the policy of objects rewriting during including other files 283as following: 284 285* If we have two objects with the same priority then we form an implicit array 286* If a new object has bigger priority then we overwrite an old one 287* If a new object has lower priority then we ignore it 288 289By default, the priority of top-level object is set to zero (lowest priority). Currently, 290you can define up to 16 priorities (from 0 to 15). Includes with bigger priorities will 291rewrite keys from the objects with lower priorities as specified by the policy. 292 293### Variables support 294 295UCL supports variables in input. Variables are registered by a user of the UCL parser and can be presented in the following forms: 296 297* `${VARIABLE}` 298* `$VARIABLE` 299 300UCL currently does not support nested variables. To escape variables one could use double dollar signs: 301 302* `$${VARIABLE}` is converted to `${VARIABLE}` 303* `$$VARIABLE` is converted to `$VARIABLE` 304 305However, if no valid variables are found in a string, no expansion will be performed (and `$$` thus remains unchanged). This may be a subject 306to change in future libucl releases. 307 308### Multiline strings 309 310UCL can handle multiline strings as well as single line ones. It uses shell/perl like notation for such objects: 311``` 312key = <<EOD 313some text 314splitted to 315lines 316EOD 317``` 318 319In this example `key` will be interpreted as the following string: `some text\nsplitted to\nlines`. 320Here are some rules for this syntax: 321 322* Multiline terminator must start just after `<<` symbols and it must consist of capital letters only (e.g. `<<eof` or `<< EOF` won't work); 323* Terminator must end with a single newline character (and no spaces are allowed between terminator and newline character); 324* To finish multiline string you need to include a terminator string just after newline and followed by a newline (no spaces or other characters are allowed as well); 325* The initial and the final newlines are not inserted to the resulting string, but you can still specify newlines at the beginning and at the end of a value, for example: 326 327``` 328key <<EOD 329 330some 331text 332 333EOD 334``` 335 336## Emitter 337 338Each UCL object can be serialized to one of the three supported formats: 339 340* `JSON` - canonic json notation (with spaces indented structure); 341* `Compacted JSON` - compact json notation (without spaces or newlines); 342* `Configuration` - nginx like notation; 343* `YAML` - yaml inlined notation. 344 345## Validation 346 347UCL allows validation of objects. It uses the same schema that is used for json: [json schema v4](http://json-schema.org). UCL supports the full set of json schema with the exception of remote references. This feature is unlikely useful for configuration objects. Of course, a schema definition can be in UCL format instead of JSON that simplifies schemas writing. Moreover, since UCL supports multiple values for keys in an object it is possible to specify generic integer constraints `maxValues` and `minValues` to define the limits of values count in a single key. UCL currently is not absolutely strict about validation schemas themselves, therefore UCL users should supply valid schemas (as it is defined in json-schema draft v4) to ensure that the input objects are validated properly. 348 349## Performance 350 351Are UCL parser and emitter fast enough? Well, there are some numbers. 352I got a 19Mb file that consist of ~700 thousand lines of json (obtained via 353http://www.json-generator.com/). Then I checked jansson library that performs json 354parsing and emitting and compared it with UCL. Here are results: 355 356``` 357jansson: parsed json in 1.3899 seconds 358jansson: emitted object in 0.2609 seconds 359 360ucl: parsed input in 0.6649 seconds 361ucl: emitted config in 0.2423 seconds 362ucl: emitted json in 0.2329 seconds 363ucl: emitted compact json in 0.1811 seconds 364ucl: emitted yaml in 0.2489 seconds 365``` 366 367So far, UCL seems to be significantly faster than jansson on parsing and slightly faster on emitting. Moreover, 368UCL compiled with optimizations (-O3) performs significantly faster: 369``` 370ucl: parsed input in 0.3002 seconds 371ucl: emitted config in 0.1174 seconds 372ucl: emitted json in 0.1174 seconds 373ucl: emitted compact json in 0.0991 seconds 374ucl: emitted yaml in 0.1354 seconds 375``` 376 377You can do your own benchmarks by running `make check` in libucl top directory. 378 379## Conclusion 380 381UCL has clear design that should be very convenient for reading and writing. At the same time it is compatible with 382JSON language and therefore can be used as a simple JSON parser. Macro logic provides an ability to extend configuration 383language (for example by including some lua code) and comments allow to disable or enable the parts of a configuration 384quickly. 385