gopkg.in/validator.v2
Package validator implements value validations based on struct tags. In code it is often necessary to validate that a given value is valid before using it for something. A typical example might be something like this. This is a simple enough example, but it can get significantly more complex, especially when dealing with structs. You get the idea. Package validator allows one to define valid values as struct tags when defining a new struct type. Then validating a variable of type NewUserRequest becomes trivial. Here is the list of validator functions builtin in the package. Note that there are no tests to prevent conflicting validator parameters. For instance, these fields will never be valid. It is possible to define custom validation functions by using SetValidationFunc. First, one needs to create a validation function. Then one needs to add it to the list of validation funcs and give it a "tag" name. Then it is possible to use the notzz validation tag. This will print "Field A error: value cannot be ZZ" To use parameters, it is very similar. And then the code below should print "Field A error: value cannot be ABC". As well, it is possible to overwrite builtin validation functions. And you can delete a validation function by setting it to nil. Using a non-existing validation func in a field tag will always return false and with error validate.ErrUnknownTag. Finally, package validator also provides a helper function that can be used to validate simple variables/values. In case there is a reason why one would not wish to use tag 'validate' (maybe due to a conflict with a different package), it is possible to tell the package to use a different tag. Then. SetTag is permanent. The new tag name will be used until it is again changed with a new call to SetTag. A way to temporarily use a different tag exists. You may often need to have a different set of validation rules for different situations. In all the examples above, we only used the default validator but you could create a new one and set specific rules for it. For instance, you might use the same struct to decode incoming JSON for a REST API but your needs will change when you're using it to, say, create a new instance in storage vs. when you need to change something. Maybe when creating a new user, you need to make sure all values in the struct are filled, but then you use the same struct to handle incoming requests to, say, change the password, in which case you only need the Username and the Password and don't care for the others. You might use two different validators. It is also possible to do all of that using only the default validator as long as SetTag is always called before calling validator.Validate() or you chain the with WithTag().
Readme
Package validator implements variable validations
Just use go get.
go get gopkg.in/validator.v2
And then just import the package into your own code.
import (
"gopkg.in/validator.v2"
)
Please see http://godoc.org/gopkg.in/validator.v2 for detailed usage docs. A simple example would be.
type NewUserRequest struct {
Username string `validate:"min=3,max=40,regexp=^[a-zA-Z]*$"`
Name string `validate:"nonzero"`
Age int `validate:"min=21"`
Password string `validate:"min=8"`
}
nur := NewUserRequest{Username: "something", Age: 20}
if errs := validator.Validate(nur); errs != nil {
// values not valid, deal with errors here
}
Builtin validators
Here is the list of validators buildin in the package. Validators buildin
will check the element pointed to if the value to check is a pointer.
The nil pointer is treated as a valid value by validators buildin other
than nonzero, so you should to use nonzero if you don't want to
accept a nil pointer.
len
For numeric numbers, len will simply make sure 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. (Usage: len=10)
max
For numeric numbers, max will simply make sure that the
value is lesser 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. (Usage: max=10)
min
For numeric numbers, min will simply make sure 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. (Usage: min=10)
nonzero
This validates that the value is not zero. The appropriate
zero value is given by the Go spec (e.g. for int it's 0, for
string it's "", for pointers is nil, etc.) For structs, it
will not check to see if the struct itself has all zero
values, instead use a pointer or put nonzero on the struct's
keys that you care about. For pointers, the pointer's value
is used to test for nonzero in addition to the pointer itself
not being nil. To just check for not being nil, use `nonnil`.
(Usage: nonzero)
regexp
Only valid for string types, it will validate that the
value matches the regular expression provided as parameter.
Commas need to be escaped with 2 backslashes `\\`.
(Usage: regexp=^a.*b$)
nonnil
Validates that the given value is not nil. (Usage: nonnil)
Custom validators
It is possible to define custom validators by using SetValidationFunc. First, one needs to create a validation function.
// Very simple validator
func notZZ(v interface{}, param string) error {
st := reflect.ValueOf(v)
if st.Kind() != reflect.String {
return errors.New("notZZ only validates strings")
}
if st.String() == "ZZ" {
return errors.New("value cannot be ZZ")
}
return nil
}
Then one needs to add it to the list of validators and give it a "tag" name.
validator.SetValidationFunc("notzz", notZZ)
Then it is possible to use the notzz validation tag. This will print "Field A error: value cannot be ZZ"
type T struct {
A string `validate:"nonzero,notzz"`
}
t := T{"ZZ"}
if errs := validator.Validate(t); errs != nil {
fmt.Printf("Field A error: %s\n", errs["A"][0])
}
You can also have multiple sets of validator rules with SetTag().
type T struct {
A int `foo:"nonzero" bar:"min=10"`
}
t := T{5}
SetTag("foo")
validator.Validate(t) // valid as it's nonzero
SetTag("bar")
validator.Validate(t) // invalid as it's less than 10
SetTag is probably better used with multiple validators.
fooValidator := validator.NewValidator()
fooValidator.SetTag("foo")
barValidator := validator.NewValidator()
barValidator.SetTag("bar")
fooValidator.Validate(t)
barValidator.Validate(t)
This keeps the default validator's tag clean. Again, please refer to godocs for a lot of more examples and different uses.
tl;dr. Contributions are welcome.
The repository is organized in version branches. Pull requests to, say, the
v2 branch that break API compatibility will not be accepted. It is okay to
break the API in master, not in the branches.
As for validation functions, the preference is to keep the main code simple and add most new functions to the validator-contrib repository.
https://github.com/go-validator/validator-contrib
For improvements and/or fixes to the builtin validation functions, please
make sure the behaviour will not break existing functionality in the branches.
If you see a case where the functionality of the builtin will change
significantly, please send a pull request against master. We can discuss then
whether the changes should be incorporated in the version branches as well.
Copyright 2014 Roberto Teixeira robteix@robteix.com
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
FAQs
Package validator implements value validations based on struct tags. In code it is often necessary to validate that a given value is valid before using it for something. A typical example might be something like this. This is a simple enough example, but it can get significantly more complex, especially when dealing with structs. You get the idea. Package validator allows one to define valid values as struct tags when defining a new struct type. Then validating a variable of type NewUserRequest becomes trivial. Here is the list of validator functions builtin in the package. Note that there are no tests to prevent conflicting validator parameters. For instance, these fields will never be valid. It is possible to define custom validation functions by using SetValidationFunc. First, one needs to create a validation function. Then one needs to add it to the list of validation funcs and give it a "tag" name. Then it is possible to use the notzz validation tag. This will print "Field A error: value cannot be ZZ" To use parameters, it is very similar. And then the code below should print "Field A error: value cannot be ABC". As well, it is possible to overwrite builtin validation functions. And you can delete a validation function by setting it to nil. Using a non-existing validation func in a field tag will always return false and with error validate.ErrUnknownTag. Finally, package validator also provides a helper function that can be used to validate simple variables/values. In case there is a reason why one would not wish to use tag 'validate' (maybe due to a conflict with a different package), it is possible to tell the package to use a different tag. Then. SetTag is permanent. The new tag name will be used until it is again changed with a new call to SetTag. A way to temporarily use a different tag exists. You may often need to have a different set of validation rules for different situations. In all the examples above, we only used the default validator but you could create a new one and set specific rules for it. For instance, you might use the same struct to decode incoming JSON for a REST API but your needs will change when you're using it to, say, create a new instance in storage vs. when you need to change something. Maybe when creating a new user, you need to make sure all values in the struct are filled, but then you use the same struct to handle incoming requests to, say, change the password, in which case you only need the Username and the Password and don't care for the others. You might use two different validators. It is also possible to do all of that using only the default validator as long as SetTag is always called before calling validator.Validate() or you chain the with WithTag().
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