# HTTP Configuration Settings

HTTP exposes a [variety of settings](https://golang.org/pkg/net/http/).
Several of these settings are available for configuration within individual
receivers or exporters.

## Client Configuration

[Exporters](https://github.com/open-telemetry/opentelemetry-collector/blob/main/exporter/README.md)
leverage client configuration.

Note that client configuration supports TLS configuration, the
configuration parameters are also defined under `tls` like server
configuration. For more information, see [configtls
README](../configtls/README.md).

- `endpoint`: address:port
- [`tls`](../configtls/README.md)
- [`headers`](https://pkg.go.dev/net/http#Request): name/value pairs added to the HTTP request headers
  - certain headers such as Content-Length and Connection are automatically written when needed and values in Header may be ignored.
  - `Host` header is automatically derived from `endpoint` value. However, this automatic assignment can be overridden by explicitly setting the Host field in the headers field.
  - if `Host` header is provided then it overrides `Host` field in [Request](https://pkg.go.dev/net/http#Request) which results as an override of `Host` header value.
- [`read_buffer_size`](https://golang.org/pkg/net/http/#Transport)
- [`timeout`](https://golang.org/pkg/net/http/#Client)
- [`write_buffer_size`](https://golang.org/pkg/net/http/#Transport)
- `compression`: Compression type to use among `gzip`, `zstd`, `snappy`, `zlib`, `deflate`, and `lz4`.
  - look at the documentation for the server-side of the communication.
  - `none` will be treated as uncompressed, and any other inputs will cause an error.
- `compression_params` : Configure advanced compression options
  - `level`: Configure compression level for `compression` type
  - The following are valid combinations of `compression` and `level`
    - `gzip`
      - BestSpeed: `1`
      - BestCompression: `9`
      - DefaultCompression: `-1`
    - `zlib`
      - BestSpeed: `1`
      - BestCompression: `9`
      - DefaultCompression: `-1`
    - `deflate`
      - BestSpeed: `1`
      - BestCompression: `9`
      - DefaultCompression: `-1`
    - `zstd`
      - SpeedFastest: `1`
      - SpeedDefault: `3`
      - SpeedBetterCompression: `6`
      - SpeedBestCompression: `11`
    - `snappy`
      No compression levels supported yet
    - `x-snappy-framed` (When feature gate `confighttp.framedSnappy` is enabled)
      No compression levels supported yet
- [`max_idle_conns`](https://golang.org/pkg/net/http/#Transport)
- [`max_idle_conns_per_host`](https://golang.org/pkg/net/http/#Transport)
- [`max_conns_per_host`](https://golang.org/pkg/net/http/#Transport)
- [`idle_conn_timeout`](https://golang.org/pkg/net/http/#Transport)
- [`auth`](../configauth/README.md)
- [`disable_keep_alives`](https://golang.org/pkg/net/http/#Transport)
- [`force_attempt_http2`](https://golang.org/pkg/net/http/#Transport)
- [`http2_read_idle_timeout`](https://pkg.go.dev/golang.org/x/net/http2#Transport)
- [`http2_ping_timeout`](https://pkg.go.dev/golang.org/x/net/http2#Transport)
- [`cookies`](https://pkg.go.dev/net/http#CookieJar)
  - [`enabled`] if enabled, the client will store cookies from server responses and reuse them in subsequent requests.
- [`middlewares`](../configmiddleware/README.md)

Example:

```yaml
exporter:
  otlphttp:
    endpoint: otelcol2:55690
    auth:
      authenticator: some-authenticator-extension
    tls:
      ca_file: ca.pem
      cert_file: cert.pem
      key_file: key.pem
    headers:
      test1: "value1"
      "test 2": "value 2"
    compression: gzip
    compression_params:
      level: 1
    cookies:
      enabled: true
```

## Server Configuration

[Receivers](https://github.com/open-telemetry/opentelemetry-collector/blob/main/receiver/README.md)
leverage server configuration.

- [`cors`](https://github.com/rs/cors#parameters): Configure [CORS][cors],
allowing the receiver to accept traces from web browsers, even if the receiver
is hosted at a different [origin][origin]. If left blank or set to `null`, CORS
will not be enabled.
  - `allowed_origins`: A list of [origins][origin] allowed to send requests to
  the receiver. An origin may contain a wildcard (`*`) to replace 0 or more
  characters (e.g., `https://*.example.com`). **Do not use** a plain wildcard
  `["*"]`, as our CORS response includes `Access-Control-Allow-Credentials: true`, which makes browsers to **disallow a plain wildcard** (this is a security standard). To allow any origin, you can specify at least the protocol, for example `["https://*", "http://*"]`. If no origins are listed, CORS will not be enabled.
  - `allowed_headers`: Allow CORS requests to include headers outside the
  [default safelist][cors-headers]. By default, safelist headers and
  `X-Requested-With` will be allowed. To allow any request header, set to
  `["*"]`.
  - `max_age`: Sets the value of the [`Access-Control-Max-Age`][cors-cache]
  header, allowing clients to cache the response to CORS preflight requests. If
  not set, browsers use a default of 5 seconds.
- `endpoint`: Valid value syntax available [here](https://github.com/grpc/grpc/blob/master/doc/naming.md)
- `max_request_body_size`: configures the maximum allowed body size in bytes for a single request. Default: `20971520` (20MiB)
- `compression_algorithms`: configures the list of compression algorithms the server can accept. Default: ["", "gzip", "zstd", "zlib", "snappy", "deflate", "lz4"]
  - `x-snappy-framed` can be used if feature gate `confighttp.snappyFramed` is enabled.
- [`tls`](../configtls/README.md)
- [`auth`](../configauth/README.md)
  - `request_params`: a list of query parameter names to add to the auth context, along with the HTTP headers
- [`middlewares`](../configmiddleware/README.md)

You can enable [`attribute processor`][attribute-processor] to append any http header to span's attribute using custom key. You also need to enable the "include_metadata"

Example:

```yaml
receivers:
  otlp:
    protocols:
      http:
        include_metadata: true
        auth:
          request_params:
          - token
          authenticator: some-authenticator-extension
        cors:
          allowed_origins:
            - https://foo.bar.com
            - https://*.test.com
          allowed_headers:
            - Example-Header
          max_age: 7200
        endpoint: 0.0.0.0:55690
        compression_algorithms: ["", "gzip"]
processors:
  attributes:
    actions:
      - key: http.client_ip
        from_context: metadata.x-forwarded-for
        action: upsert
```

[cors]: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS
[cors-headers]: https://developer.mozilla.org/en-US/docs/Glossary/CORS-safelisted_request_header
[cors-cache]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Max-Age
[origin]: https://developer.mozilla.org/en-US/docs/Glossary/Origin
[attribute-processor]: https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/processor/attributesprocessor/README.md
