146 lines
6.8 KiB
Go
146 lines
6.8 KiB
Go
// Package gcfg reads "INI-style" text-based configuration files with
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// "name=value" pairs grouped into sections (gcfg files).
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//
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// This package is still a work in progress; see the sections below for planned
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// changes.
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//
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// Syntax
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//
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// The syntax is based on that used by git config:
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// http://git-scm.com/docs/git-config#_syntax .
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// There are some (planned) differences compared to the git config format:
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// - improve data portability:
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// - must be encoded in UTF-8 (for now) and must not contain the 0 byte
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// - include and "path" type is not supported
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// (path type may be implementable as a user-defined type)
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// - internationalization
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// - section and variable names can contain unicode letters, unicode digits
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// (as defined in http://golang.org/ref/spec#Characters ) and hyphens
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// (U+002D), starting with a unicode letter
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// - disallow potentially ambiguous or misleading definitions:
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// - `[sec.sub]` format is not allowed (deprecated in gitconfig)
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// - `[sec ""]` is not allowed
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// - use `[sec]` for section name "sec" and empty subsection name
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// - (planned) within a single file, definitions must be contiguous for each:
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// - section: '[secA]' -> '[secB]' -> '[secA]' is an error
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// - subsection: '[sec "A"]' -> '[sec "B"]' -> '[sec "A"]' is an error
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// - multivalued variable: 'multi=a' -> 'other=x' -> 'multi=b' is an error
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//
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// Data structure
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//
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// The functions in this package read values into a user-defined struct.
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// Each section corresponds to a struct field in the config struct, and each
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// variable in a section corresponds to a data field in the section struct.
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// The mapping of each section or variable name to fields is done either based
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// on the "gcfg" struct tag or by matching the name of the section or variable,
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// ignoring case. In the latter case, hyphens '-' in section and variable names
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// correspond to underscores '_' in field names.
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// Fields must be exported; to use a section or variable name starting with a
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// letter that is neither upper- or lower-case, prefix the field name with 'X'.
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// (See https://code.google.com/p/go/issues/detail?id=5763#c4 .)
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//
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// For sections with subsections, the corresponding field in config must be a
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// map, rather than a struct, with string keys and pointer-to-struct values.
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// Values for subsection variables are stored in the map with the subsection
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// name used as the map key.
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// (Note that unlike section and variable names, subsection names are case
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// sensitive.)
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// When using a map, and there is a section with the same section name but
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// without a subsection name, its values are stored with the empty string used
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// as the key.
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// It is possible to provide default values for subsections in the section
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// "default-<sectionname>" (or by setting values in the corresponding struct
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// field "Default_<sectionname>").
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//
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// The functions in this package panic if config is not a pointer to a struct,
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// or when a field is not of a suitable type (either a struct or a map with
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// string keys and pointer-to-struct values).
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//
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// Parsing of values
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//
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// The section structs in the config struct may contain single-valued or
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// multi-valued variables. Variables of unnamed slice type (that is, a type
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// starting with `[]`) are treated as multi-value; all others (including named
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// slice types) are treated as single-valued variables.
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//
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// Single-valued variables are handled based on the type as follows.
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// Unnamed pointer types (that is, types starting with `*`) are dereferenced,
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// and if necessary, a new instance is allocated.
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//
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// For types implementing the encoding.TextUnmarshaler interface, the
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// UnmarshalText method is used to set the value. Implementing this method is
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// the recommended way for parsing user-defined types.
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//
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// For fields of string kind, the value string is assigned to the field, after
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// unquoting and unescaping as needed.
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// For fields of bool kind, the field is set to true if the value is "true",
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// "yes", "on" or "1", and set to false if the value is "false", "no", "off" or
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// "0", ignoring case. In addition, single-valued bool fields can be specified
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// with a "blank" value (variable name without equals sign and value); in such
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// case the value is set to true.
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//
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// Predefined integer types [u]int(|8|16|32|64) and big.Int are parsed as
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// decimal or hexadecimal (if having '0x' prefix). (This is to prevent
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// unintuitively handling zero-padded numbers as octal.) Other types having
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// [u]int* as the underlying type, such as os.FileMode and uintptr allow
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// decimal, hexadecimal, or octal values.
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// Parsing mode for integer types can be overridden using the struct tag option
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// ",int=mode" where mode is a combination of the 'd', 'h', and 'o' characters
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// (each standing for decimal, hexadecimal, and octal, respectively.)
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//
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// All other types are parsed using fmt.Sscanf with the "%v" verb.
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//
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// For multi-valued variables, each individual value is parsed as above and
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// appended to the slice. If the first value is specified as a "blank" value
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// (variable name without equals sign and value), a new slice is allocated;
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// that is any values previously set in the slice will be ignored.
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//
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// The types subpackage for provides helpers for parsing "enum-like" and integer
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// types.
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//
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// Error handling
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//
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// There are 3 types of errors:
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//
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// - programmer errors / panics:
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// - invalid configuration structure
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// - data errors:
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// - fatal errors:
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// - invalid configuration syntax
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// - warnings:
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// - data that doesn't belong to any part of the config structure
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//
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// Programmer errors trigger panics. These are should be fixed by the programmer
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// before releasing code that uses gcfg.
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//
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// Data errors cause gcfg to return a non-nil error value. This includes the
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// case when there are extra unknown key-value definitions in the configuration
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// data (extra data).
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// However, in some occasions it is desirable to be able to proceed in
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// situations when the only data error is that of extra data.
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// These errors are handled at a different (warning) priority and can be
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// filtered out programmatically. To ignore extra data warnings, wrap the
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// gcfg.Read*Into invocation into a call to gcfg.FatalOnly.
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//
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// TODO
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//
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// The following is a list of changes under consideration:
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// - documentation
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// - self-contained syntax documentation
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// - more practical examples
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// - move TODOs to issue tracker (eventually)
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// - syntax
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// - reconsider valid escape sequences
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// (gitconfig doesn't support \r in value, \t in subsection name, etc.)
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// - reading / parsing gcfg files
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// - define internal representation structure
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// - support multiple inputs (readers, strings, files)
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// - support declaring encoding (?)
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// - support varying fields sets for subsections (?)
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// - writing gcfg files
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// - error handling
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// - make error context accessible programmatically?
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// - limit input size?
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//
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package gcfg // import "github.com/src-d/gcfg"
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