data-binary.d: clarify default content-type is x-www-form-urlencoded

- Advise user that --data-binary sends a default content type of
  x-www-form-urlencoded, and to have the data treated as arbitrary
  binary data by the server set the content-type header to octet-stream.

Ref: https://github.com/curl/curl/pull/2852#issuecomment-426465094

Closes https://github.com/curl/curl/pull/3085

diff --git a/docs/cmdline-opts/data-binary.d b/docs/cmdline-opts/data-binary.d
index c6721c6419d5782da1330a924b9ad4084e45cb36..3f6ff2dbd0a210c89a790a2e97ec91f6ef8b64fc 100644 (file)
--- a/docs/cmdline-opts/data-binary.d
+++ b/docs/cmdline-opts/data-binary.d
@@ -9,5 +9,10 @@ If you start the data with the letter @, the rest should be a filename.  Data
 is posted in a similar manner as --data does, except that newlines and
 carriage returns are preserved and conversions are never done.
 
+Like --data the default content-type sent to the server is
+application/x-www-form-urlencoded. If you want the data to be treated as
+arbitrary binary data by the server then set the content-type to octet-stream:
+-H "Content-Type: application/octet-stream".
+
 If this option is used several times, the ones following the first will append
 data as described in --data.