build: use more const

Mostly with `char *` types.

Also:
- mime, x509asn1, tool_operate, lib3207: drop redundant casts.
- examples/smooth-gtk-thread: add missing variable declaration.
- reduce variable scopes.
- tests/server: move `data_to_hex()` to its only user: `sws`.

Closes #20489

src/curlinfo.c

@@ -257,7 +257,7 @@ static const char *disabled[] = {
 #endif
 };
 
-int main(int argc, char **argv)
+int main(int argc, const char **argv)
 {
   size_t i;
 

src/tool_cb_hdr.c

@@ -66,8 +66,8 @@ static void write_linked_location(CURL *curl, const char *location,
 {
   /* This would so simple if CURLINFO_REDIRECT_URL were available here */
   CURLU *u = NULL;
-  char *copyloc = NULL, *locurl = NULL, *scheme = NULL, *finalurl = NULL;
-  const char *loc = location;
+  char *copyloc = NULL, *scheme = NULL, *finalurl = NULL;
+  const char *loc = location, *locurl = NULL;
   size_t llen = loclen;
   int space_skipped = 0;
   const char *vver = getenv("VTE_VERSION");

src/tool_helpers.c

@@ -96,7 +96,7 @@ int SetHTTPrequest(HttpReq req, HttpReq *store)
   return 1;
 }
 
-void customrequest_helper(HttpReq req, char *method)
+void customrequest_helper(HttpReq req, const char *method)
 {
   /* this mirrors the HttpReq enum in tool_sdecls.h */
   const char *dflt[] = {

src/tool_helpers.h

@@ -27,6 +27,6 @@
 
 const char *param2text(ParameterError error);
 int SetHTTPrequest(HttpReq req, HttpReq *store);
-void customrequest_helper(HttpReq req, char *method);
+void customrequest_helper(HttpReq req, const char *method);
 
 #endif /* HEADER_CURL_TOOL_HELPERS_H */

src/tool_operate.c

@@ -1753,7 +1753,7 @@ static CURLcode check_finished(struct parastate *s)
       struct per_transfer *ended;
       CURL *easy = msg->easy_handle;
       CURLcode tres = msg->data.result;
-      curl_easy_getinfo(easy, CURLINFO_PRIVATE, (void *)&ended);
+      curl_easy_getinfo(easy, CURLINFO_PRIVATE, &ended);
       curl_multi_remove_handle(s->multi, easy);
 
       if(ended->abort && (tres == CURLE_ABORTED_BY_CALLBACK)) {
@@ -2022,7 +2022,7 @@ static CURLcode is_using_schannel(int *pusing)
   if(using_schannel == -1) {
     CURL *curltls = curl_easy_init();
     /* The TLS backend remains, so keep the info */
-    struct curl_tlssessioninfo *tls_backend_info = NULL;
+    const struct curl_tlssessioninfo *tls_backend_info = NULL;
 
     if(!curltls)
       result = CURLE_OUT_OF_MEMORY;

src/tool_operate.h

@@ -34,7 +34,7 @@ struct per_transfer {
   struct per_transfer *next;
   struct per_transfer *prev;
   struct OperationConfig *config; /* for this transfer */
-  struct curl_certinfo *certinfo;
+  const struct curl_certinfo *certinfo;
   CURL *curl;
   long retry_remaining;
   long retry_sleep_default;

src/tool_parsecfg.c

@@ -277,7 +277,7 @@ static bool get_line(FILE *input, struct dynbuf *buf, bool *error)
   char buffer[128];
   curlx_dyn_reset(buf);
   while(1) {
-    char *b = fgets(buffer, sizeof(buffer), input);
+    const char *b = fgets(buffer, sizeof(buffer), input);
 
     if(b) {
       size_t rlen = strlen(b);

src/tool_writeout.c

@@ -86,7 +86,7 @@ static int urlpart(struct per_transfer *per, writeoutid vid,
   if(uh) {
     CURLUPart cpart = CURLUPART_HOST;
     char *part = NULL;
-    const char *url = NULL;
+    char *url = NULL;
 
     if(vid >= VAR_INPUT_URLESCHEME) {
       if(curl_easy_getinfo(per->curl, CURLINFO_EFFECTIVE_URL, &url))
@@ -162,7 +162,7 @@ static int urlpart(struct per_transfer *per, writeoutid vid,
 static void certinfo(struct per_transfer *per)
 {
   if(!per->certinfo) {
-    struct curl_certinfo *certinfo;
+    const struct curl_certinfo *certinfo;
     CURLcode result = curl_easy_getinfo(per->curl, CURLINFO_CERTINFO,
                                         &certinfo);
     per->certinfo = (!result && certinfo) ? certinfo : NULL;