---

"_Honestly, what you've built looks super solid and polished. In many ways, it's what I wanted **Hug** to be - it's really inspiring to see someone build that._"

# Settings and Environment Variables { #settings-and-environment-variables }

In many cases your application could need some external settings or configurations, for example secret keys, database credentials, credentials for email services, etc.

Most of these settings are variable (can change), like database URLs. And many could be sensitive, like secrets.

For this reason it's common to provide them in environment variables that are read by the application.

/// tip

 * specific language governing permissions and limitations
 * under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

package okhttp3.internal.http

    assertEquals("a&quot;b&lt;c&gt;d&amp;", htmlEscaper().escape("a\"b<c>d&"));

    // Test two escapes in a row.
    assertEquals("foo&amp;&amp;bar", htmlEscaper().escape("foo&&bar"));

    // Test many non-escaped characters.
    s =
        "!@#$%^*()_+=-/?\\|]}[{,.;:"
            + "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
            + "1234567890";
    assertSame(s, htmlEscaper().escape(s));
  }

    inadvertently changed this behavior when we introduced the `mockwebserver3` API.


## Version 5.0.0-alpha.17

_2025-06-29_

This release stabilizes many APIs for the imminent OkHttp 5.0.0 release.

 *  New: `TrailersSource`, a public API for HTTP trailers. Production callers shouldn't need this

const (
	HasOne    RelationshipType = "has_one"      // HasOneRel has one relationship
	HasMany   RelationshipType = "has_many"     // HasManyRel has many relationship
	BelongsTo RelationshipType = "belongs_to"   // BelongsToRel belongs to relationship
	Many2Many RelationshipType = "many_to_many" // Many2ManyRel many to many relationship
	has       RelationshipType = "has"
)

type Relationships struct {
	HasOne    []*Relationship

In many cases it's not very obvious how environment variables would be useful and applicable right away. But they keep showing up in many different scenarios when you are developing, so it's good to know about them.

   * {@link SortedMultiset#tailMultiset}, the {@code size()} and {@code iterator()} methods of
   * {@link SortedMultiset#entrySet}, and {@link SortedMultiset#remove(Object, int)}. In many
   * situations, you may wish to override {@link SortedMultiset#elementSet} to forward to this
   * implementation or a subclass thereof.
   *
   * @since 15.0
   */

This is normally the best way to contribute to the project.

## External Contributions

External contributions are very welcome and appreciated, including answering questions, submitting PRs, etc. 🙇‍♂️

All the dependencies we have seen are a fixed function or class.

But there could be cases where you want to be able to set parameters on the dependency, without having to declare many different functions or classes.

Let's imagine that we want to have a dependency that checks if the query parameter `q` contains some fixed content.

But we want to be able to parameterize that fixed content.