Update body size attribute and metric definitions

CHANGELOG.md

@@ -36,6 +36,8 @@ release.
   ([#449](https://github.com/open-telemetry/semantic-conventions/pull/449))
 - Change `user_agent.original` from recommended to opt-in on HTTP client spans.
   ([#468](https://github.com/open-telemetry/semantic-conventions/pull/468))
+- Updates HTTP body size attributes and metric definitions to be the number of bytes transferred.
+  ([#461](https://github.com/open-telemetry/semantic-conventions/pull/461))
 
 ### Features
 

model/metrics/http.yaml

@@ -73,9 +73,7 @@ groups:
     instrument: histogram
     unit: "By"
     note: >
-      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.
+      This is the same as the `Content-Length` header value when that header is present and when the response body was fully transferred.
     extends: metric_attributes.http.server
 
   - id: metric.http.server.response.body.size
@@ -85,9 +83,7 @@ groups:
     instrument: histogram
     unit: "By"
     note: >
-      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.
+      This is the same as the `Content-Length` header value when that header is present and when the response body was fully transferred.
     extends: metric_attributes.http.server
 
   - id: metric.http.client.request.duration
@@ -105,9 +101,7 @@ groups:
     instrument: histogram
     unit: "By"
     note: >
-      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.
+      This is the same as the `Content-Length` header value when that header is present and when the request body was fully transferred.
     extends: metric_attributes.http.client
 
   - id: metric.http.client.response.body.size
@@ -117,7 +111,5 @@ groups:
     instrument: histogram
     unit: "By"
     note: >
-      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.
+      This is the same as the `Content-Length` header value when that header is present and when the response body was fully transferred.
     extends: metric_attributes.http.client

model/registry/http.yaml

@@ -6,11 +6,11 @@ groups:
     attributes:
       - id: request.body.size
         type: int
-        brief: >
-          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.
+        brief: Size of the HTTP request body.
         examples: 3495
+        stability: experimental  # this should not be marked stable with other HTTP attributes
+        note: >
+          This is the same as the `Content-Length` header value when that header is present and when the request body was fully transferred.
       - id: request.header
         type: template[string[]]
         brief: >
@@ -92,11 +92,11 @@ groups:
         examples: 3
       - id: response.body.size
         type: int
-        brief: >
-          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.
+        brief: Size of the HTTP response body.
         examples: 3495
+        stability: experimental  # this should not be marked stable with other HTTP attributes
+        note: >
+          This is the same as the `Content-Length` header value when that header is present and when the response body was fully transferred.
       - id: response.header
         type: template[string[]]
         brief: >