metalink: remove

Warning: this will make existing curl command lines that use metalink to
stop working.

Reasons for removal:

1. We've found several security problems and issues involving the
   metalink support in curl. The issues are not detailed here. When
   working on those, it become apparent to the team that several of the
   problems are due to the system design, metalink library API and what
   the metalink RFC says. They are very hard to fix on the curl side
   only.

2. The metalink usage with curl was only very briefly documented and was
   not following the "normal" curl usage pattern in several ways, making
   it surprising and non-intuitive which could lead to further security
   issues.

3. The metalink library was last updated 6 years ago and wasn't so
   active the years before that either. An unmaintained library means
   there's a security problem waiting to happen. This is probably reason
   enough.

4. Metalink requires an XML parsing library, which is complex code (even
   the smaller alternatives) and to this day often gets security
   updates.

5. Metalink is not a widely used curl feature. In the 2020 curl user
   survey, only 1.4% of the responders said that they'd are using it. In
   2021 that number was 1.2%. Searching the web also show very few
   traces of it being used, even with other tools.

6. The torrent format and associated technology clearly won for
   downloading large files from multiple sources in parallel.

Cloes #7176

1 files changed, 0 insertions, 165 deletions

diff --git a/src/tool_metalink.h b/src/tool_metalink.h
deleted file mode 100644
index d03dbf737..000000000
--- a/src/tool_metalink.h
+++ /dev/null
@@ -1,165 +0,0 @@
-#ifndef HEADER_CURL_TOOL_METALINK_H
-#define HEADER_CURL_TOOL_METALINK_H
-/***************************************************************************
- *                                  _   _ ____  _
- *  Project                     ___| | | |  _ \| |
- *                             / __| | | | |_) | |
- *                            | (__| |_| |  _ <| |___
- *                             \___|\___/|_| \_\_____|
- *
- * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
- *
- * This software is licensed as described in the file COPYING, which
- * you should have received as part of this distribution. The terms
- * are also available at https://curl.se/docs/copyright.html.
- *
- * You may opt to use, copy, modify, merge, publish, distribute and/or sell
- * copies of the Software, and permit persons to whom the Software is
- * furnished to do so, under the terms of the COPYING file.
- *
- * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
- * KIND, either express or implied.
- *
- ***************************************************************************/
-#include "tool_setup.h"
-#include "tool_sdecls.h"
-
-struct GlobalConfig;
-struct OperationConfig;
-
-/* returns 1 for success, 0 otherwise (we use OpenSSL *_Init fncs directly) */
-typedef int (*digest_init_func)(void *context);
-
-typedef void (*digest_update_func)(void *context,
-                                   const unsigned char *data,
-                                   unsigned int len);
-typedef void (*digest_final_func)(unsigned char *result, void *context);
-
-struct digest_params {
-  digest_init_func     digest_init;   /* Initialize context procedure */
-  digest_update_func   digest_update; /* Update context with data */
-  digest_final_func    digest_final;  /* Get final result procedure */
-  unsigned int         digest_ctxtsize;  /* Context structure size */
-  unsigned int         digest_resultlen; /* Result length (bytes) */
-};
-
-struct digest_context {
-  const struct digest_params *digest_hash; /* Hash function definition */
-  void                  *digest_hashctx;   /* Hash function context */
-};
-
-struct metalink_digest_def {
-  const char *hash_name;
-  const struct digest_params *dparams;
-};
-
-struct metalink_digest_alias {
-  const char *alias_name;
-  const struct metalink_digest_def *digest_def;
-};
-
-struct metalink_checksum {
-  const struct metalink_digest_def *digest_def;
-  /* raw digest value, not ascii hex digest */
-  unsigned char *digest;
-};
-
-struct metalink_resource {
-  struct metalink_resource *next;
-  char *url;
-};
-
-struct metalinkfile {
-  struct metalinkfile *next;
-  char *filename;
-  struct metalink_checksum *checksum;
-  struct metalink_resource *resource;
-};
-
-#ifdef USE_METALINK
-
-/*
- * curl requires libmetalink 0.1.0 or newer
- */
-#define CURL_REQ_LIBMETALINK_MAJOR  0
-#define CURL_REQ_LIBMETALINK_MINOR  1
-#define CURL_REQ_LIBMETALINK_PATCH  0
-
-#define CURL_REQ_LIBMETALINK_VERS  ((CURL_REQ_LIBMETALINK_MAJOR * 10000) + \
-                                    (CURL_REQ_LIBMETALINK_MINOR * 100) + \
-                                     CURL_REQ_LIBMETALINK_PATCH)
-
-extern const struct digest_params MD5_DIGEST_PARAMS[1];
-extern const struct digest_params SHA1_DIGEST_PARAMS[1];
-extern const struct digest_params SHA256_DIGEST_PARAMS[1];
-
-#include <metalink/metalink.h>
-
-/*
- * Counts the resource in the metalinkfile.
- */
-int count_next_metalink_resource(struct metalinkfile *mlfile);
-
-void delete_metalinkfile(struct metalinkfile *mlfile);
-void clean_metalink(struct OperationConfig *config);
-
-/*
- * Performs final parse operation and extracts information from
- * Metalink and creates metalinkfile structs.
- *
- * This function returns 0 if it succeeds without warnings, or one of
- * the following negative error codes:
- *
- * -1: Parsing failed; or no file is found
- * -2: Parsing succeeded with some warnings.
- */
-int parse_metalink(struct OperationConfig *config, struct OutStruct *outs,
-                   const char *metalink_url);
-
-/*
- * Callback function for CURLOPT_WRITEFUNCTION
- */
-size_t metalink_write_cb(void *buffer, size_t sz, size_t nmemb,
-                         void *userdata);
-
-/*
- * Returns nonzero if content_type includes "application/metalink+xml"
- * media-type. The check is done in case-insensitive manner.
- */
-int check_metalink_content_type(const char *content_type);
-
-/*
- * Check checksum of file denoted by filename.
- *
- * This function returns 1 if the checksum matches or one of the
- * following integers:
- *
- * 0:
- *   Checksum didn't match.
- * -1:
- *   Could not open file; or could not read data from file.
- * -2:
- *   No checksum in Metalink supported, hash algorithm not available, or
- *   Metalink does not contain checksum.
- */
-int metalink_check_hash(struct GlobalConfig *config,
-                        struct metalinkfile *mlfile,
-                        const char *filename);
-
-/*
- * Release resources allocated at global scope.
- */
-void metalink_cleanup(void);
-
-#else /* USE_METALINK */
-
-#define count_next_metalink_resource(x)  0
-#define delete_metalinkfile(x)  (void)x
-#define clean_metalink(x)  (void)x
-
-/* metalink_cleanup() takes no arguments */
-#define metalink_cleanup() Curl_nop_stmt
-
-#endif /* USE_METALINK */
-
-#endif /* HEADER_CURL_TOOL_METALINK_H */