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# UUID
UUIDs metrics are used to record values that uniquely identify some entity, such as a client id.
## Recording API
### `generateAndSet`
Sets a UUID metric to a randomly generated [UUID](https://datatracker.ietf.org/doc/html/rfc4122) value (UUID v4) .
{{#include ../../../shared/tab_header.md}}
<div data-lang="Kotlin" class="tab">
```Kotlin
import org.mozilla.yourApplication.GleanMetrics.User
// Generate a new UUID and record it
User.clientId.generateAndSet()
```
</div>
<div data-lang="Java" class="tab">
```Java
import org.mozilla.yourApplication.GleanMetrics.User;
// Generate a new UUID and record it
User.INSTANCE.clientId().generateAndSet();
```
</div>
<div data-lang="Swift" class="tab">
```Swift
// Generate a new UUID and record it
User.clientId.generateAndSet()
```
</div>
<div data-lang="Python" class="tab">
```Python
from glean import load_metrics
metrics = load_metrics("metrics.yaml")
# Generate a new UUID and record it
metrics.user.client_id.generate_and_set()
```
</div>
<div data-lang="Rust" class="tab">
```Rust
use uuid::Uuid;
use glean_metrics::user;
// Generate a new UUID and record it
user::client_id.generate_and_set();
```
</div>
<div data-lang="JavaScript" class="tab">
```js
import * as user from "./path/to/generated/files/user.js";
user.clientId.generateAndSet();
```
</div>
<div data-lang="Firefox Desktop" class="tab">
**C++**
```c++
#include "mozilla/glean/GleanMetrics.h"
// Generate a new UUID and record it.
mozilla::glean::user::client_id.GenerateAndSet();
```
**JavaScript**
```js
// Generate a new UUID and record it.
Glean.user.clientId.generateAndSet();
```
</div>
{{#include ../../../shared/tab_footer.md}}
### `set`
Sets a UUID metric to a specific value.
Accepts any UUID version.
{{#include ../../../shared/tab_header.md}}
<div data-lang="Kotlin" class="tab">
```Kotlin
import org.mozilla.yourApplication.GleanMetrics.User
// Set a UUID explicitly
User.clientId.set(UUID.randomUUID()) // Set a UUID explicitly
```
</div>
<div data-lang="Java" class="tab">
```Java
import org.mozilla.yourApplication.GleanMetrics.User;
// Set a UUID explicitly
User.INSTANCE.clientId().set(UUID.randomUUID());
```
</div>
<div data-lang="Swift" class="tab">
```Swift
User.clientId.set(UUID()) // Set a UUID explicitly
```
</div>
<div data-lang="Python" class="tab">
```Python
import uuid
from glean import load_metrics
metrics = load_metrics("metrics.yaml")
# Set a UUID explicitly
metrics.user.client_id.set(uuid.uuid4())
```
</div>
<div data-lang="Rust" class="tab">
```Rust
use uuid::Uuid;
use glean_metrics::user;
// Set a UUID explicitly
user::client_id.set(Uuid::new_v4());
```
</div>
<div data-lang="JavaScript" class="tab">
```js
import * as user from "./path/to/generated/files/user.js";
const uuid = "decafdec-afde-cafd-ecaf-decafdecafde";
user.clientId.set(uuid);
```
</div>
<div data-lang="Firefox Desktop" class="tab">
**C++**
```c++
#include "mozilla/glean/GleanMetrics.h"
// Set a specific value.
nsCString kUuid("decafdec-afde-cafd-ecaf-decafdecafde");
mozilla::glean::user::client_id.Set(kUuid);
```
**JavaScript**
```js
// Set a specific value.
const uuid = "decafdec-afde-cafd-ecaf-decafdecafde";
Glean.user.clientId.set(uuid);
```
</div>
{{#include ../../../shared/tab_footer.md}}
#### Recorded errors
* [`invalid_value`](../../user/metrics/error-reporting.md): if the value is set to a string that is not a UUID (only applies for dynamically-typed languages, such as Python).
* [`invalid_type`](../../user/metrics/error-reporting.md): if a non-string or non-UUID value is given.
## Testing API
### `testGetValue`
Gets the recorded value for a given UUID metric.
Returns a UUID if data is stored.
Returns a language-specific empty/null value if no data is stored.
Has an optional argument to specify the name of the ping you wish to retrieve data from, except
in Rust where it's required. `None` or no argument will default to the first value found for `send_in_pings`.
{{#include ../../../shared/tab_header.md}}
<div data-lang="Kotlin" class="tab">
```Kotlin
import org.mozilla.yourApplication.GleanMetrics.User
// Was it the expected value?
assertEquals(uuid, User.clientId.testGetValue())
```
</div>
<div data-lang="Java" class="tab">
```Java
import org.mozilla.yourApplication.GleanMetrics.User;
// Was it the expected value?
assertEquals(uuid, User.INSTANCE.clientId().testGetValue());
```
</div>
<div data-lang="Swift" class="tab">
```Swift
// Was it the expected value?
XCTAssertEqual(uuid, try User.clientId.testGetValue())
```
</div>
<div data-lang="Python" class="tab">
```Python
from glean import load_metrics
metrics = load_metrics("metrics.yaml")
# Was it the expected value?
assert uuid == metrics.user.client_id.test_get_value()
```
</div>
<div data-lang="Rust" class="tab">
```Rust
use uuid::Uuid;
use glean_metrics::user;
let u = Uuid::new_v4();
// Does it have the expected value?
assert_eq!(u, user::client_id.test_get_value(None).unwrap());
```
</div>
<div data-lang="JavaScript" class="tab">
```js
import * as user from "./path/to/generated/files/user.js";
const uuid = "decafdec-afde-cafd-ecaf-decafdecafde";
assert(uuid, await user.clientId.testGetValue());
```
</div>
<div data-lang="Firefox Desktop" class="tab">
**C++**
```c++
#include "mozilla/glean/GleanMetrics.h"
// Is it clear of errors?
ASSERT_TRUE(mozilla::glean::user::client_id.TestGetValue().isOk());
// Does it have an expected values?
ASSERT_STREQ(kUuid.get(), mozilla::glean::user::client_id.TestGetValue().unwrap().value().get());
```
**JavaScript**
```js
const uuid = "decafdec-afde-cafd-ecaf-decafdecafde";
// testGetValue will throw NS_ERROR_LOSS_OF_SIGNIFICANT_DATA on error.
Assert.equal(Glean.user.clientId.testGetValue(), uuid);
```
</div>
{{#include ../../../shared/tab_footer.md}}
### `testGetNumRecordedErrors`
Gets the number of errors recorded for a given UUID metric.
{{#include ../../../shared/tab_header.md}}
<div data-lang="Kotlin" class="tab">
```Kotlin
import org.mozilla.yourApplication.GleanMetrics.User
assertEquals(
0,
User.clientId.testGetNumRecordedErrors(ErrorType.INVALID_VALUE)
)
```
</div>
<div data-lang="Java" class="tab">
```Java
import org.mozilla.yourApplication.GleanMetrics.User;
assertEquals(
0,
User.INSTANCE.clientId().testGetNumRecordedErrors(ErrorType.INVALID_VALUE)
);
```
</div>
<div data-lang="Swift" class="tab">
```Swift
XCTAssertEqual(0, User.clientId.testGetNumRecordedErrors(.invalidValue))
```
</div>
<div data-lang="Python" class="tab">
```Python
from glean import load_metrics
metrics = load_metrics("metrics.yaml")
from glean.testing import ErrorType
assert 0 == metrics.user.client_id.test_get_num_recorded_errors(
ErrorType.INVALID_VALUE
)
```
</div>
<div data-lang="Rust" class="tab">
```Rust
use glean::ErrorType;
use glean_metrics::user;
assert_eq!(
0,
user::client_id.test_get_num_recorded_errors(
ErrorType::InvalidValue
)
);
```
</div>
<div data-lang="JavaScript" class="tab">
```js
import * as user from "./path/to/generated/files/user.js";
import { ErrorType } from "@mozilla/glean/error";
// Was the string truncated, and an error reported?
assert.strictEqual(
0,
await user.clientId.testGetNumRecordedErrors(ErrorType.InvalidValue)
);
```
</div>
<div data-lang="Firefox Desktop" class="tab" data-info="Firefox Desktop uses testGetValue to communicate errors"></div>
{{#include ../../../shared/tab_footer.md}}
## Metric Parameters
You first need to add an entry for it to the `metrics.yaml` file:
```YAML
user:
client_id:
type: uuid
description: >
A unique identifier for the client's profile
bugs:
data_reviews:
notification_emails:
- me@mozilla.com
expires: 2020-10-01
```
For a full reference on metrics parameters common to all metric types,
refer to the [metrics YAML registry format](../yaml/metrics.md) reference page.
### Extra metric parameters
N/A
## Data questions
* A unique identifier for the client.
## Reference
* [Swift API docs](../../../swift/Classes/UuidMetricType.html)
* [Python API docs](../../../python/glean/metrics/index.html#glean.metrics.UuidMetricType)
* [Rust API docs](../../../docs/glean/private/uuid/struct.UuidMetric.html)