gopkg.in/go-playground/validator.v8 (go): Package validator implements value validations for structs and individual fields based on tags.  It can also handle Cross-Field and Cross-Struct validation for nested structs and has the ability to dive into arrays and maps of any type.  Why not a better error message? Because this library intends for you to handle your own error messages.  Why should I handle my own errors? Many reasons. We built an internationalized application and needed to know the field, and what validation failed so we could provide a localized error.  Doing things this way is actually the way the standard library does, see the file.Open method here:  The authors return type "error" to avoid the issue discussed in the following, where err is always != nil:  Validator only returns nil or ValidationErrors as type error; so, in your code all you need to do is check if the error returned is not nil, and if it's not type cast it to type ValidationErrors like so err.(validator.ValidationErrors).  Custom functions can be added. Example:  Cross-Field Validation can be done via the following tags:  If, however, some custom cross-field validation is required, it can be done using a custom validation.  Why not just have cross-fields validation tags (i.e. only eqcsfield and not eqfield)?  The reason is efficiency. If you want to check a field within the same struct "eqfield" only has to find the field on the same struct (1 level). But, if we used "eqcsfield" it could be multiple levels down. Example:  Multiple validators on a field will process in the order defined. Example:  Bad Validator definitions are not handled by the library. Example:  Baked In Cross-Field validation only compares fields on the same struct. If Cross-Field + Cross-Struct validation is needed you should implement your own custom validator.  Comma (",") is the default separator of validation tags. If you wish to have a comma included within the parameter (i.e. excludesall=,) you will need to use the UTF-8 hex representation 0x2C, which is replaced in the code as a comma, so the above will become excludesall=0x2C.  Pipe ("|") is the default separator of validation tags. If you wish to have a pipe included within the parameter i.e. excludesall=| you will need to use the UTF-8 hex representation 0x7C, which is replaced in the code as a pipe, so the above will become excludesall=0x7C  Here is a list of the current built in validators:  Tells the validation to skip this struct field; this is particularly handy in ignoring embedded structs from being validated. (Usage: -)  This is the 'or' operator allowing multiple validators to be used and accepted. (Usage: rbg|rgba) <-- this would allow either rgb or rgba colors to be accepted. This can also be combined with 'and' for example ( Usage: omitempty,rgb|rgba)  When a field that is a nested struct is encountered, and contains this flag any validation on the nested struct will be run, but none of the nested struct fields will be validated. This is usefull if inside of you program you know the struct will be valid, but need to verify it has been assigned. NOTE: only "required" and "omitempty" can be used on a struct itself.  Same as structonly tag except that any struct level validations will not run.  Is a special tag without a validation function attached. It is used when a field is a Pointer, Interface or Invalid and you wish to validate that it exists. Example: want to ensure a bool exists if you define the bool as a pointer and use exists it will ensure there is a value; couldn't use required as it would fail when the bool was false. exists will fail is the value is a Pointer, Interface or Invalid and is nil.  Allows conditional validation, for example if a field is not set with a value (Determined by the "required" validator) then other validation such as min or max won't run, but if a value is set validation will run.  This tells the validator to dive into a slice, array or map and validate that level of the slice, array or map with the validation tags that follow. Multidimensional nesting is also supported, each level you wish to dive will require another dive tag.  Example #1  Example #2  This validates that the value is not the data types default zero value. For numbers ensures value is not zero. For strings ensures value is not "". For slices, maps, pointers, interfaces, channels and functions ensures the value is not nil.  For numbers, max will ensure that the value is equal to the parameter given. For strings, it checks that the string length is exactly that number of characters. For slices, arrays, and maps, validates the number of items.  For numbers, max will ensure that the value is less than or equal to the parameter given. For strings, it checks that the string length is at most that number of characters. For slices, arrays, and maps, validates the number of items.  For numbers, min will ensure that the value is greater or equal to the parameter given. For strings, it checks that the string length is at least that number of characters. For slices, arrays, and maps, validates the number of items.  For strings & numbers, eq will ensure that the value is equal to the parameter given. For slices, arrays, and maps, validates the number of items.  For strings & numbers, ne will ensure that the value is not equal to the parameter given. For slices, arrays, and maps, validates the number of items.  For numbers, this will ensure that the value is greater than the parameter given. For strings, it checks that the string length is greater than that number of characters. For slices, arrays and maps it validates the number of items.  Example #1  Example #2 (time.Time)  For time.Time ensures the time value is greater than time.Now.UTC().  Same as 'min' above. Kept both to make terminology with 'len' easier.  Example #1  Example #2 (time.Time)  For time.Time ensures the time value is greater than or equal to time.Now.UTC().  For numbers, this will ensure that the value is less than the parameter given. For strings, it checks that the string length is less than that number of characters. For slices, arrays, and maps it validates the number of items.  Example #1  Example #2 (time.Time) For time.Time ensures the time value is less than time.Now.UTC().  Same as 'max' above. Kept both to make terminology with 'len' easier.  Example #1  Example #2 (time.Time)  For time.Time ensures the time value is less than or equal to time.Now.UTC().  This will validate the field value against another fields value either within a struct or passed in field.  Example #1:  Example #2:  Field Equals Another Field (relative)  This does the same as eqfield except that it validates the field provided relative to the top level struct.  This will validate the field value against another fields value either within a struct or passed in field.  Examples:  Field Does Not Equal Another Field (relative)  This does the same as nefield except that it validates the field provided relative to the top level struct.  Only valid for Numbers and time.Time types, this will validate the field value against another fields value either within a struct or passed in field. usage examples are for validation of a Start and End date:  Example #1:  Example #2:  This does the same as gtfield except that it validates the field provided relative to the top level struct.  Only valid for Numbers and time.Time types, this will validate the field value against another fields value either within a struct or passed in field. usage examples are for validation of a Start and End date:  Example #1:  Example #2:  This does the same as gtefield except that it validates the field provided relative to the top level struct.  Only valid for Numbers and time.Time types, this will validate the field value against another fields value either within a struct or passed in field. usage examples are for validation of a Start and End date:  Example #1:  Example #2:  This does the same as ltfield except that it validates the field provided relative to the top level struct.  Only valid for Numbers and time.Time types, this will validate the field value against another fields value either within a struct or passed in field. usage examples are for validation of a Start and End date:  Example #1:  Example #2:  This does the same as ltefield except that it validates the field provided relative to the top level struct.  This validates that a string value contains alpha characters only  This validates that a string value contains alphanumeric characters only  This validates that a string value contains a basic numeric value. basic excludes exponents etc...  This validates that a string value contains a valid hexadecimal.  This validates that a string value contains a valid hex color including hashtag (#)  This validates that a string value contains a valid rgb color  This validates that a string value contains a valid rgba color  This validates that a string value contains a valid hsl color  This validates that a string value contains a valid hsla color  This validates that a string value contains a valid email This may not conform to all possibilities of any rfc standard, but neither does any email provider accept all posibilities.  This validates that a string value contains a valid url This will accept any url the golang request uri accepts but must contain a schema for example http:// or rtmp://  This validates that a string value contains a valid uri This will accept any uri the golang request uri accepts  This validates that a string value contains a valid base64 value. Although an empty string is valid base64 this will report an empty string as an error, if you wish to accept an empty string as valid you can use this with the omitempty tag.  This validates that a string value contains the substring value.  This validates that a string value contains any Unicode code points in the substring value.  This validates that a string value contains the supplied rune value.  This validates that a string value does not contain the substring value.  This validates that a string value does not contain any Unicode code points in the substring value.  This validates that a string value does not contain the supplied rune value.  This validates that a string value contains a valid isbn10 or isbn13 value.  This validates that a string value contains a valid isbn10 value.  This validates that a string value contains a valid isbn13 value.  This validates that a string value contains a valid UUID.  This validates that a string value contains a valid version 3 UUID.  This validates that a string value contains a valid version 4 UUID.  This validates that a string value contains a valid version 5 UUID.  This validates that a string value contains only ASCII characters. NOTE: if the string is blank, this validates as true.  This validates that a string value contains only printable ASCII characters. NOTE: if the string is blank, this validates as true.  This validates that a string value contains one or more multibyte characters. NOTE: if the string is blank, this validates as true.  This validates that a string value contains a valid DataURI. NOTE: this will also validate that the data portion is valid base64  This validates that a string value contains a valid latitude.  This validates that a string value contains a valid longitude.  This validates that a string value contains a valid U.S. Social Security Number.  This validates that a string value contains a valid IP Adress.  This validates that a string value contains a valid v4 IP Adress.  This validates that a string value contains a valid v6 IP Adress.  This validates that a string value contains a valid CIDR Adress.  This validates that a string value contains a valid v4 CIDR Adress.  This validates that a string value contains a valid v6 CIDR Adress.  This validates that a string value contains a valid resolvable TCP Adress.  This validates that a string value contains a valid resolvable v4 TCP Adress.  This validates that a string value contains a valid resolvable v6 TCP Adress.  This validates that a string value contains a valid resolvable UDP Adress.  This validates that a string value contains a valid resolvable v4 UDP Adress.  This validates that a string value contains a valid resolvable v6 UDP Adress.  This validates that a string value contains a valid resolvable IP Adress.  This validates that a string value contains a valid resolvable v4 IP Adress.  This validates that a string value contains a valid resolvable v6 IP Adress.  This validates that a string value contains a valid Unix Adress.  This validates that a string value contains a valid MAC Adress.  Note: See Go's ParseMAC for accepted formats and types:  NOTE: When returning an error, the tag returned in "FieldError" will be the alias tag unless the dive tag is part of the alias. Everything after the dive tag is not reported as the alias tag. Also, the "ActualTag" in the before case will be the actual tag within the alias that failed.  Here is a list of the current built in alias tags:  Validator notes:  This package panics when bad input is provided, this is by design, bad code like that should not make it to production.
Keywords: error-handling|translation|validation