libgit2 has two distinct requirements that were previously solved by
`git_buf`. We require:
1. A general purpose string class that provides a number of utility APIs
for manipulating data (eg, concatenating, truncating, etc).
2. A structure that we can use to return strings to callers that they
can take ownership of.
By using a single class (`git_buf`) for both of these purposes, we have
confused the API to the point that refactorings are difficult and
reasoning about correctness is also difficult.
Move the utility class `git_buf` to be called `git_str`: this represents
its general purpose, as an internal string buffer class. The name also
is an homage to Junio Hamano ("gitstr").
The public API remains `git_buf`, and has a much smaller footprint. It
is generally only used as an "out" param with strict requirements that
follow the documentation. (Exceptions exist for some legacy APIs to
avoid breaking callers unnecessarily.)
Utility functions exist to convert a user-specified `git_buf` to a
`git_str` so that we can call internal functions, then converting it
back again.
When the failure is clearly an auth failure (as opposed to possibly an auth failure), use the error code GIT_EAUTH instead of GIT_ERROR. While we're here, fix a typo and improve an error message. Fixes #5389.
We avoid abbreviations where possible; rename git_cred to git_credential. In addition, we have standardized on a trailing `_t` for enum types, instead of using "type" in the name. So `git_credtype_t` has become `git_credential_t` and its members have become `GIT_CREDENTIAL` instead of `GIT_CREDTYPE`. Finally, the source and header files have been renamed to `credential` instead of `cred`. Keep previous name and values as deprecated, and include the new header files from the previous ones.
libgit2 does not use `type_t` suffixes as it's redundant; thus, rename `git_http_authtype_t` to `git_http_auth_t` for consistency.
The dummy negotiation scheme is used for known authentication strategies that do not wish to act. For example, when a server requests the "Negotiate" scheme but libgit2 is not built with Negotiate support, and will use the "dummy" strategy which will simply not act. Instead of setting `out` to NULL and returning a successful code, return `GIT_PASSTHROUGH` to indicate that it did not act and catch that error code.
Instead of using `is_complete` to decide whether we have connection or request affinity for authentication mechanisms, set a boolean on the mechanism definition itself.
Some authentication mechanisms (like HTTP Basic and Digest) have a one-step mechanism to create credentials, but there are more complex mechanisms like NTLM and Negotiate that require challenge/response after negotiation, requiring several round-trips. Add an `is_complete` function to know when they have round-tripped enough to be a single authentication and should now either have succeeded or failed to authenticate.
"Connection data" is an imprecise and largely incorrect name; these structures are actually parsed URLs. Provide a parser that takes a URL string and produces a URL structure (if it is valid). Separate the HTTP redirect handling logic from URL parsing, keeping a `gitno_connection_data_handle_redirect` whose only job is redirect handling logic and does not parse URLs itself.