From d21966a76d7d356417bc33dda4548560f46681ea Mon Sep 17 00:00:00 2001 From: Johannes Schindelin Date: Sun, 7 May 2023 22:05:33 +0200 Subject: [PATCH] http: when loading libcurl lazily, allow for multiple SSL backends The previous commits introduced a compile-time option to load libcurl lazily, but it uses the hard-coded name "libcurl-4.dll" (or equivalent on platforms other than Windows). To allow for installing multiple libcurl flavors side by side, where each supports one specific SSL/TLS backend, let's first look whether `libcurl--4.dll` exists, and only use `libcurl-4.dll` as a fall back. That will allow us to ship with a libcurl by default that only supports the Secure Channel backend for the `https://` protocol. This libcurl won't suffer from any dependency problem when upgrading OpenSSL to a new major version (which will change the DLL name, and hence break every program and library that depends on it). This is crucial because Git for Windows relies on libcurl to keep working when building and deploying a new OpenSSL package because that library is used by `git fetch` and `git clone`. Note that this feature is by no means specific to Windows. On Ubuntu, for example, a `git` built using `LAZY_LOAD_LIBCURL` will use `libcurl.so.4` for `http.sslbackend=openssl` and `libcurl-gnutls.so.4` for `http.sslbackend=gnutls`. Signed-off-by: Johannes Schindelin --- compat/lazyload-curl.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/compat/lazyload-curl.c b/compat/lazyload-curl.c index 98d73fb0f2a66f..2f2b2ebc27993e 100644 --- a/compat/lazyload-curl.c +++ b/compat/lazyload-curl.c @@ -172,17 +172,26 @@ static curl_easy_setopt_pointer_type curl_easy_setopt_pointer_func; typedef CURLcode (*curl_easy_setopt_off_t_type)(CURL *curl, CURLoption opt, curl_off_t value); static curl_easy_setopt_off_t_type curl_easy_setopt_off_t_func; +static char ssl_backend[64]; + static void lazy_load_curl(void) { static int initialized; - void *libcurl; + void *libcurl = NULL; func_t curl_easy_getinfo_func, curl_easy_setopt_func; if (initialized) return; initialized = 1; - libcurl = load_library(LIBCURL_FILE_NAME("libcurl")); + if (ssl_backend[0]) { + char dll_name[64 + 16]; + snprintf(dll_name, sizeof(dll_name) - 1, + LIBCURL_FILE_NAME("libcurl-%s"), ssl_backend); + libcurl = load_library(dll_name); + } + if (!libcurl) + libcurl = load_library(LIBCURL_FILE_NAME("libcurl")); if (!libcurl) die("failed to load library '%s'", LIBCURL_FILE_NAME("libcurl")); @@ -246,6 +255,9 @@ CURLcode curl_global_init(long flags) CURLsslset curl_global_sslset(curl_sslbackend id, const char *name, const curl_ssl_backend ***avail) { + if (name && strlen(name) < sizeof(ssl_backend)) + strlcpy(ssl_backend, name, sizeof(ssl_backend)); + lazy_load_curl(); return curl_global_sslset_func(id, name, avail); }