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diff --git a/git-curl-compat.h b/git-curl-compat.h
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+#ifndef GIT_CURL_COMPAT_H
+#define GIT_CURL_COMPAT_H
+#include <curl/curl.h>
+
+/**
+ * This header centralizes the declaration of our libcurl dependencies
+ * to make it easy to discover the oldest versions we support, and to
+ * inform decisions about removing support for older libcurl in the
+ * future.
+ *
+ * The oldest supported version of curl is documented in the "INSTALL"
+ * document.
+ *
+ * The source of truth for what versions have which symbols is
+ * https://github.com/curl/curl/blob/master/docs/libcurl/symbols-in-versions;
+ * the release dates are taken from curl.git (at
+ * https://github.com/curl/curl/).
+ *
+ * For each X symbol we need from curl we define our own
+ * GIT_CURL_HAVE_X. If multiple similar symbols with the same prefix
+ * were defined in the same version we pick one and check for that name.
+ *
+ * We may also define a missing CURL_* symbol to its known value, if
+ * doing so is sufficient to add support for it to older versions that
+ * don't have it.
+ *
+ * Keep any symbols in date order of when their support was
+ * introduced, oldest first, in the official version of cURL library.
+ */
+
+/**
+ * Versions before curl 7.66.0 (September 2019) required manually setting the
+ * transfer-encoding for a streaming POST; after that this is handled
+ * automatically.
+ */
+#if LIBCURL_VERSION_NUM < 0x074200
+#define GIT_CURL_NEED_TRANSFER_ENCODING_HEADER
+#endif
+
+/**
+ * CURLOPT_PROTOCOLS_STR and CURLOPT_REDIR_PROTOCOLS_STR were added in 7.85.0,
+ * released in August 2022.
+ */
+#if LIBCURL_VERSION_NUM >= 0x075500
+#define GIT_CURL_HAVE_CURLOPT_PROTOCOLS_STR 1
+#endif
+
+/**
+ * CURLOPT_TCP_KEEPCNT was added in 8.9.0, released in July, 2024.
+ */
+#if LIBCURL_VERSION_NUM >= 0x080900
+#define GIT_CURL_HAVE_CURLOPT_TCP_KEEPCNT
+#endif
+
+#endif