Remove dashes to underscores normalization from http header attribute keys

CHANGELOG.md

@@ -129,6 +129,8 @@ release.
   ([#350](https://github.com/open-telemetry/semantic-conventions/pull/350))
 - Improve network attribute briefs.
   ([#352](https://github.com/open-telemetry/semantic-conventions/pull/352))
+- BREAKING: remove `-` to `_` normalization from http header attribute keys.
+  ([#369](https://github.com/open-telemetry/semantic-conventions/pull/369))
 
 ## v1.21.0 (2023-07-13)
 

docs/http/http-spans.md

@@ -117,7 +117,7 @@ sections below.
 |---|---|---|---|---|
 | `error.type` | string | Describes a class of error the operation ended with. [1] | `timeout`; `name_resolution_error`; `500` | Conditionally Required: If request has ended with an error. |
 | `http.request.body.size` | int | The size of the request payload body in bytes. This is the number of bytes transferred excluding headers and is often, but not always, present as the [Content-Length](https://www.rfc-editor.org/rfc/rfc9110.html#field.content-length) header. For requests using transport encoding, this should be the compressed size. | `3495` | Recommended |
-| `http.request.header.<key>` | string[] | HTTP request headers, `<key>` being the normalized HTTP Header name (lowercase, with `-` characters replaced by `_`), the value being the header values. [2] | `http.request.header.content_type=["application/json"]`; `http.request.header.x_forwarded_for=["1.2.3.4", "1.2.3.5"]` | Opt-In |
+| `http.request.header.<key>` | string[] | HTTP request headers, `<key>` being the normalized HTTP Header name (lowercase), the value being the header values. [2] | `http.request.header.content-type=["application/json"]`; `http.request.header.x-forwarded-for=["1.2.3.4", "1.2.3.5"]` | Opt-In |
 | `http.request.method` | string | HTTP request method. [3] | `GET`; `POST`; `HEAD` | Required |
 | `http.request.method_original` | string | Original HTTP method sent by the client in the request line. | `GeT`; `ACL`; `foo` | Conditionally Required: [4] |
 | `http.response.body.size` | int | The size of the response payload body in bytes. This is the number of bytes transferred excluding headers and is often, but not always, present as the [Content-Length](https://www.rfc-editor.org/rfc/rfc9110.html#field.content-length) header. For requests using transport encoding, this should be the compressed size. | `3495` | Recommended |

model/trace/http.yaml

@@ -32,7 +32,7 @@ groups:
         type: template[string[]]
         requirement_level: opt_in
         brief: >
-          HTTP request headers, `<key>` being the normalized HTTP Header name (lowercase, with `-` characters replaced by `_`), the value being the header values.
+          HTTP request headers, `<key>` being the normalized HTTP Header name (lowercase), the value being the header values.
         note: >
           Instrumentations SHOULD require an explicit configuration of which headers are to be captured.
           Including all request headers can be a security risk - explicit configuration helps avoid leaking sensitive information.
@@ -43,7 +43,7 @@ groups:
           The attribute value MUST consist of either multiple header values as an array of strings
           or a single-item array containing a possibly comma-concatenated string, depending on the way
           the HTTP library provides access to headers.
-        examples: ['http.request.header.content_type=["application/json"]', 'http.request.header.x_forwarded_for=["1.2.3.4", "1.2.3.5"]']
+        examples: ['http.request.header.content-type=["application/json"]', 'http.request.header.x-forwarded-for=["1.2.3.4", "1.2.3.5"]']
       - id: response.header
         type: template[string[]]
         requirement_level: opt_in