Curl handle as a FILE *

From: Patrick Monnerat via curl-library <curl-library_at_lists.haxx.se>
Date: Tue, 6 Dec 2022 13:01:48 +0100

Hi friends,

Please find the source code and use examples of functions curl_fopen()
and curl_fdopen() in attachement.

These allow associating an URL or a curl handle with a standard C FILE
pointer and use the standard C IO API on it.

There is a built-in CRLF conversion feature and a no-wait mode.

I wrote them for fun and as a proof of concept, so there is no doc. Look
at the prototypes and examples.

I think it can be useful for the community or as a base of a
non-callback API for our project, but I don't really know what to do it
with now that it mostly works! May be a curl doc example?

You will find use examples embedded within the source: simple download,
mail sending, copy a handle to another, mixing protocols and even using
an handle as the data source for another one.

Please feel free to use it at your convenience.


Now, the main drawbacks:

- It uses the GNU-specific function fopencookie(): there is no support
for other environment yet. An equivalent facility exists in BSD
(funopen), but I did not find one for other systems.

- Chunked output MUST be enabled, as we don't know the write data size
in advance.

- There is no way to get the CURL handle from the file outside the
package itself.

- A FILE-attached CURL handle is not reusable outside this context:
closing the FILE deletes it.

- Only limited seek support is available (of course!): rewind and flush
to request termination.

- By the non-callback nature of the C IO API, one must know at each time
if input or output is expected.

- Because file:// URLs do not support pausing, they are open as normal C
files.

- There's a lot of buffer copying, probably adding overhead (I did not
measure perfomance).

- As it is built outside libcurl, it has no access to the internal
structures.

- Redirection of upload/post request is not possible. This probably is
also the case for multi-pass authentication.

- FILE/curl tuned buffer size is important: better not change it!


Have fun!

Patrick

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Received on 2022-12-06