From cbbff786b4c347b6ef7c6ae6c18cf9ea09dfc40a Mon Sep 17 00:00:00 2001
From: Dan Fandrich <dan@coneharvesters.com>
Date: Thu, 4 Nov 2021 22:02:05 -0700
Subject: tool_cb_hdr: Turn the Location: into a terminal hyperlink

This turns even relative URLs into clickable hyperlinks in a supported
terminal when --styled-output is enabled. Many terminals already turn
URLs into clickable links but there is not enough information in a
relative URL to do this automatically otherwise.
---
 src/tool_cb_hdr.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)

diff --git a/src/tool_cb_hdr.c b/src/tool_cb_hdr.c
index 67ea10447..a93d5f2ec 100644
--- a/src/tool_cb_hdr.c
+++ b/src/tool_cb_hdr.c
@@ -47,6 +47,10 @@ static char *parse_filename(const char *ptr, size_t len);
    bold-off code (21) isn't supported everywhere - like in the mac
    Terminal. */
 #define BOLDOFF "\x1b[0m"
+/* OSC 8 hyperlink escape sequence */
+#define LINK "\x1b]8;;"
+#define LINKST "\x1b\\"
+#define LINKOFF LINK LINKST
 #endif
 
 /*
@@ -204,7 +208,89 @@ size_t tool_header_cb(char *ptr, size_t size, size_t nmemb, void *userdata)
     if(value) {
       size_t namelen = value - ptr;
       fprintf(outs->stream, BOLD "%.*s" BOLDOFF ":", namelen, ptr);
+#ifndef LINK
       fwrite(&value[1], cb - namelen - 1, 1, outs->stream);
+#else
+      if(curl_strnequal("Location", ptr, namelen)) {
+        /* Treat the Location: header specially, by writing a special escape
+         * sequence that adds a hyperlink to the displayed text. This makes
+         * the absolute URL of the redirect clickable in supported terminals,
+         * which couldn't happen otherwise for relative URLs. The Location:
+         * header is supposed to always be absolute so this theoretically
+         * shouldn't be needed but the real world returns plenty of relative
+         * URLs here.
+         */
+
+        /* This would so simple if CURLINFO_REDIRECT_URL were available here */
+        char *location = &value[1];
+        size_t llen = cb - namelen - 1;
+        CURLU *u = NULL;
+        char *copyloc = NULL, *locurl = NULL, *scheme = NULL, *finalurl = NULL;
+
+        /* Strip leading whitespace of the redirect URL */
+        while(llen && *location == ' ') {
+          ++location;
+          --llen;
+        }
+
+        /* Strip the trailing end-of-line characters, normally "\r\n" */
+        while(llen && (location[llen-1] == '\n' || location[llen-1] == '\r'))
+          --llen;
+
+        /* CURLU makes it easy to handle the relative URL case */
+        u = curl_url();
+        if(!u)
+          goto locout;
+
+        /* Create a NUL-terminated and whitespace-stripped copy of Location: */
+        copyloc = malloc(llen + 1);
+        if(!copyloc)
+          goto locout;
+        memcpy(copyloc, location, llen);
+        copyloc[llen] = 0;
+
+        /* The original URL to use as a base for a relative redirect URL */
+        if(curl_easy_getinfo(per->curl, CURLINFO_EFFECTIVE_URL, &locurl))
+          goto locout;
+        if(curl_url_set(u, CURLUPART_URL, locurl, 0))
+          goto locout;
+
+        /* Redirected location. This can be either absolute or relative. */
+        if(curl_url_set(u, CURLUPART_URL, copyloc, 0))
+          goto locout;
+
+        if(curl_url_get(u, CURLUPART_URL, &finalurl, CURLU_NO_DEFAULT_PORT))
+          goto locout;
+
+        if(curl_url_get(u, CURLUPART_SCHEME, &scheme, 0))
+          goto locout;
+
+        if(!strcmp("http", scheme) ||
+           !strcmp("https", scheme) ||
+           !strcmp("ftp", scheme) ||
+           !strcmp("ftps", scheme)) {
+          fprintf(outs->stream, LINK "%s" LINKST "%.*s" LINKOFF,
+                  finalurl, cb - namelen - 1, &value[1]);
+          goto locdone;
+        }
+
+        /* Not a "safe" URL: don't linkify it */
+
+locout:
+        /* Write the normal output in case of error or unsafe */
+        fwrite(&value[1], cb - namelen - 1, 1, outs->stream);
+
+locdone:
+        if(u) {
+          curl_url_cleanup(u);
+          free(copyloc);
+          free(scheme);
+          free(finalurl);
+        }
+      }
+      else
+        fwrite(&value[1], cb - namelen - 1, 1, outs->stream);
+#endif
     }
     else
       /* not "handled", just show it */
-- 
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