Reddit slash links

README.md

@@ -104,6 +104,8 @@ some extensions or allowing some deviations from the specification.
 
  * With the flag `MD_FLAG_NOINDENTEDCODEBLOCKS`, indented code blocks are
    disabled.
+
+ * With the flag `MD_FLAG_REDDITAUTOLINKS`, Reddit subreddit and user links such as r/test or /u/me are detected
 
 
 ## Input/Output Encoding

md2html/md2html.c

@@ -195,6 +195,7 @@ static const option cmdline_options[] = {
     { "version",                    'v', 'v', OPTION_ARG_NONE },
     { "commonmark",                  0,  'c', OPTION_ARG_NONE },
     { "github",                      0,  'g', OPTION_ARG_NONE },
+    { "reddit",                      0,  'r', OPTION_ARG_NONE },
     { "fverbatim-entities",          0,  'E', OPTION_ARG_NONE },
     { "fpermissive-atx-headers",     0,  'A', OPTION_ARG_NONE },
     { "fpermissive-url-autolinks",   0,  'U', OPTION_ARG_NONE },
@@ -208,6 +209,7 @@ static const option cmdline_options[] = {
     { "fcollapse-whitespace",        0,  'W', OPTION_ARG_NONE },
     { "ftables",                     0,  'T', OPTION_ARG_NONE },
     { "fstrikethrough",              0,  'S', OPTION_ARG_NONE },
+    { "freddit-autolinks",           0,  'R', OPTION_ARG_NONE },
     { 0 }
 };
 
@@ -229,6 +231,7 @@ usage(void)
         "(note these are equivalent to some combinations of flags below)\n"
         "      --commonmark     CommonMark (this is default)\n"
         "      --github         Github Flavored Markdown\n"
+        "      --reddit         Reddit's dialect of Markdown\n"
         "\n"
         "Markdown extension options:\n"
         "      --fcollapse-whitespace\n"
@@ -253,6 +256,8 @@ usage(void)
         "      --fno-html-spans\n"
         "                       Disable raw HTML spans\n"
         "      --fno-html       Same as --fno-html-blocks --fno-html-spans\n"
+        "      --freddit-autolinks\n"
+        "                       Enable Reddit autolinks of the form /u/x, /r/x, u/x, r/x\n"
         "      --ftables        Enable tables\n"
         "      --fstrikethrough Enable strikethrough spans\n"
     );
@@ -288,6 +293,7 @@ cmdline_callback(int opt, char const* value, void* data)
 
         case 'c':   parser_flags = MD_DIALECT_COMMONMARK; break;
         case 'g':   parser_flags = MD_DIALECT_GITHUB; break;
+        case 'r':   parser_flags = MD_DIALECT_REDDIT; break;
 
         case 'E':   renderer_flags |= MD_RENDER_FLAG_VERBATIM_ENTITIES; break;
         case 'A':   parser_flags |= MD_FLAG_PERMISSIVEATXHEADERS; break;
@@ -302,6 +308,7 @@ cmdline_callback(int opt, char const* value, void* data)
         case 'V':   parser_flags |= MD_FLAG_PERMISSIVEAUTOLINKS; break;
         case 'T':   parser_flags |= MD_FLAG_TABLES; break;
         case 'S':   parser_flags |= MD_FLAG_STRIKETHROUGH; break;
+        case 'R':   parser_flags |= MD_FLAG_REDDITAUTOLINKS; break;
 
         default:
             fprintf(stderr, "Illegal option: %s\n", value);

md2html/render_html.c

@@ -310,6 +310,22 @@ render_open_a_span(MD_RENDER_HTML* r, const MD_SPAN_A_DETAIL* det)
     RENDER_LITERAL(r, "\">");
 }
 
+static void
+render_reddit_link(MD_RENDER_HTML* r, const MD_REDDIT_SLASH_DETAIL* det)
+{
+    RENDER_LITERAL(r, "<a href=\"https://www.reddit.com/");
+    if (det->type == MD_REDDIT_SUBREDDIT)
+    {
+        RENDER_LITERAL(r, "r/");
+    }
+    else
+    {
+        RENDER_LITERAL(r, "u/");
+    }
+    render_text(r, det->name, det->size);
+    RENDER_LITERAL(r, "\">");
+}
+
 static void
 render_open_img_span(MD_RENDER_HTML* r, const MD_SPAN_IMG_DETAIL* det)
 {
@@ -413,6 +429,7 @@ enter_span_callback(MD_SPANTYPE type, void* detail, void* userdata)
         case MD_SPAN_IMG:       render_open_img_span(r, (MD_SPAN_IMG_DETAIL*) detail); break;
         case MD_SPAN_CODE:      RENDER_LITERAL(r, "<code>"); break;
         case MD_SPAN_DEL:       RENDER_LITERAL(r, "<del>"); break;
+        case MD_REDDIT_SLASH_LINK: render_reddit_link(r, (MD_REDDIT_SLASH_DETAIL*)detail); break;
     }
 
     return 0;
@@ -438,6 +455,7 @@ leave_span_callback(MD_SPANTYPE type, void* detail, void* userdata)
         case MD_SPAN_IMG:       /*noop, handled above*/ break;
         case MD_SPAN_CODE:      RENDER_LITERAL(r, "</code>"); break;
         case MD_SPAN_DEL:       RENDER_LITERAL(r, "</del>"); break;
+        case MD_REDDIT_SLASH_LINK: RENDER_LITERAL(r, "</a>"); break;
     }
 
     return 0;

md4c/md4c.c

@@ -2696,7 +2696,8 @@ md_build_mark_char_map(MD_CTX* ctx)
     ctx->mark_char_map['!'] = 1;
     ctx->mark_char_map[']'] = 1;
     ctx->mark_char_map['\0'] = 1;
-
+    if (ctx->r.flags & MD_FLAG_REDDITAUTOLINKS)
+        ctx->mark_char_map['/'] = 1;
     if(ctx->r.flags & MD_FLAG_STRIKETHROUGH)
         ctx->mark_char_map['~'] = 1;
 
@@ -2912,11 +2913,48 @@ md_collect_marks(MD_CTX* ctx, const MD_LINE* lines, int n_lines, int table_mode)
                     /* Push a dummy as a reserve for a closer. */
                     PUSH_MARK('D', off, off, 0);
                 }
-
                 off++;
                 continue;
             }
 
+            /* A potential permissive Reddit autolink */
+            if(ch == _T('/')) {
+                if(line->beg + 1 <= off && (CH(off - 1) == 'u' || CH(off - 1) == 'r') &&
+                      (line->beg + 1 == off ||
+                         (CH(off - 2) != '/' && (ISUNICODEPUNCTBEFORE(off - 1) || ISUNICODEWHITESPACE(off - 2)))) &&
+                      line->end > off + 1 && ISALNUM(off + 1)) 
+                {
+                    OFF index = off + 2;
+                    while (index <= line->end)
+                    {
+                        if (!(ISALNUM(index) || (CH(index) == '_')))
+                            break;
+                        index++;
+                    }
+                    /* u/something or r/something */
+                    PUSH_MARK('/', off - 1, index, MD_MARK_RESOLVED);
+                    off = index;
+                } 
+                else if (line->end > off + 3 && ((CH(off + 2) == '/') && (CH(off + 1) == 'u' || CH(off + 1) == 'r') &&
+                    ISALNUM(off + 3)))
+                {
+                    OFF index = off + 4;
+                    while (index <= line->end)
+                    {
+                        if (!(ISALNUM(index) || (CH(index) == '_')))
+                            break;
+                            index++;
+                    }
+                    PUSH_MARK('/', off, index, MD_MARK_RESOLVED);
+                    off = index;
+                }
+                else
+                {
+                    off++;
+                }
+                continue;
+            }
+
             /* A potential permissive URL autolink. */
             if(ch == _T(':')) {
                 static struct {
@@ -3605,6 +3643,9 @@ md_analyze_permissive_url_autolink(MD_CTX* ctx, int mark_index)
     OFF off = opener->end;
     int seen_dot = FALSE;
     int seen_underscore_or_hyphen[2] = { FALSE, FALSE };
+    if (opener->end == opener->beg) {
+        opener->ch = '/';
+    }
 
     /* Check for domain. */
     while(off < ctx->size) {
@@ -3711,7 +3752,6 @@ md_analyze_permissive_email_autolink(MD_CTX* ctx, int mark_index)
     closer->end = end;
     md_resolve_range(ctx, NULL, mark_index, closer_index);
 }
-
 static inline void
 md_analyze_marks(MD_CTX* ctx, const MD_LINE* lines, int n_lines,
                  int mark_beg, int mark_end, const CHAR* mark_chars)
@@ -3752,6 +3792,7 @@ md_analyze_marks(MD_CTX* ctx, const MD_LINE* lines, int n_lines,
             case '_':   md_analyze_underscore(ctx, i); break;
             case '~':   md_analyze_tilde(ctx, i); break;
             case '.':   /* Pass through. */
+            case '/':   /* Pass through */
             case ':':   md_analyze_permissive_url_autolink(ctx, i); break;
             case '@':   md_analyze_permissive_email_autolink(ctx, i); break;
         }
@@ -3970,22 +4011,51 @@ md_process_inlines(MD_CTX* ctx, const MD_LINE* lines, int n_lines)
                     const MD_MARK* closer = &ctx->marks[opener->next];
                     const CHAR* dest = STR(opener->end);
                     SZ dest_size = closer->beg - opener->end;
-
-                    if(opener->ch == '@' || opener->ch == '.') {
+                    if (opener->ch == '@' || opener->ch == '.') {
                         dest_size += 7;
                         MD_TEMP_BUFFER(dest_size * sizeof(CHAR));
                         memcpy(ctx->buffer,
-                                (opener->ch == '@' ? _T("mailto:") : _T("http://")),
-                                7 * sizeof(CHAR));
-                        memcpy(ctx->buffer + 7, dest, (dest_size-7) * sizeof(CHAR));
+                            (opener->ch == '@' ? _T("mailto:") : _T("http://")),
+                            7 * sizeof(CHAR));
+                        memcpy(ctx->buffer + 7, dest, (dest_size - 7) * sizeof(CHAR));
                         dest = ctx->buffer;
                     }
-
-                    MD_CHECK(md_enter_leave_span_a(ctx, (mark->flags & MD_MARK_OPENER),
-                                MD_SPAN_A, dest, dest_size, TRUE, NULL, 0));
+                    MD_CHECK(md_enter_leave_span_a(ctx, (mark->flags & MD_MARK_OPENER), MD_SPAN_A, dest, dest_size, TRUE, NULL, 0));
                     break;
                 }
-
+                case '/':       /* Permissive Reddit autolinks */
+                {
+                    MD_REDDIT_SLASH_DETAIL det;
+                    if (CH(mark->beg) == '/')
+                    {
+                        det.name = ctx->text + mark->beg + 3;
+                        det.size = mark->end - mark->beg - 3;
+                        if (CH(mark->beg + 1) == 'r')
+                        {
+                            det.type = MD_REDDIT_SUBREDDIT;
+                        }
+                        else
+                        {
+                            det.type = MD_REDDIT_USER;
+                        }
+                    }
+                    else // u/something or r/something instead of /r/something
+                    {
+                        det.name = ctx->text + mark->beg + 2;
+                        det.size = mark->end - mark->beg - 2;
+                        if (CH(mark->beg) == 'r')
+                        {
+                            det.type = MD_REDDIT_SUBREDDIT;
+                        }
+                        else
+                        {
+                            det.type = MD_REDDIT_USER;
+                        }
+                    }
+                    MD_ENTER_SPAN(MD_REDDIT_SLASH_LINK, &det);
+                    MD_TEXT(text_type, STR(mark->beg), mark->end - mark->beg);
+                    MD_LEAVE_SPAN(MD_REDDIT_SLASH_LINK, &det);
+                }break;
                 case '&':       /* Entity. */
                     MD_TEXT(MD_TEXT_ENTITY, STR(mark->beg), mark->end - mark->beg);
                     break;

md4c/md4c.h

@@ -131,7 +131,8 @@ typedef enum MD_SPANTYPE {
     /* <del>...</del>
      * Note: Recognized only when MD_FLAG_STRIKETHROUGH is enabled.
      */
-    MD_SPAN_DEL
+    MD_SPAN_DEL,
+    MD_REDDIT_SLASH_LINK
 } MD_SPANTYPE;
 
 /* Text is the actual textual contents of span. */
@@ -172,8 +173,10 @@ typedef enum MD_TEXTTYPE {
      * The text contains verbatim '\n' for the new lines. */
     MD_TEXT_HTML
 } MD_TEXTTYPE;
-
-
+typedef enum MD_REDDIT_SLASH_TYPE
+{
+    MD_REDDIT_USER, MD_REDDIT_SUBREDDIT
+} MD_REDDIT_SLASH_TYPE;
 /* Alignment enumeration. */
 typedef enum MD_ALIGN {
     MD_ALIGN_DEFAULT = 0,   /* When unspecified. */
@@ -245,7 +248,12 @@ typedef struct MD_SPAN_A_DETAIL {
     MD_ATTRIBUTE href;
     MD_ATTRIBUTE title;
 } MD_SPAN_A_DETAIL;
-
+typedef struct MD_REDDIT_SLASH_DETAIL
+{
+    MD_REDDIT_SLASH_TYPE type; //whether it's a user or subreddit
+    unsigned char size; 
+    MD_CHAR * name;
+}MD_REDDIT_SLASH_DETAIL;
 /* Detailed info for MD_SPAN_IMG. */
 typedef struct MD_SPAN_IMG_DETAIL {
     MD_ATTRIBUTE src;
@@ -271,6 +279,8 @@ typedef struct MD_SPAN_IMG_DETAIL {
 
 #define MD_FLAG_PERMISSIVEAUTOLINKS         (MD_FLAG_PERMISSIVEEMAILAUTOLINKS | MD_FLAG_PERMISSIVEURLAUTOLINKS | MD_FLAG_PERMISSIVEWWWAUTOLINKS)
 #define MD_FLAG_NOHTML                      (MD_FLAG_NOHTMLBLOCKS | MD_FLAG_NOHTMLSPANS)
+#define MD_FLAG_REDDITAUTOLINKS             0x8000  /* Enable Reddit autolinks */
+
 
 /* Convenient sets of flags corresponding to well-known Markdown dialects.
  * Note we may only support subset of features of the referred dialect.
@@ -279,6 +289,7 @@ typedef struct MD_SPAN_IMG_DETAIL {
  */
 #define MD_DIALECT_COMMONMARK               0
 #define MD_DIALECT_GITHUB                   (MD_FLAG_PERMISSIVEAUTOLINKS | MD_FLAG_TABLES | MD_FLAG_STRIKETHROUGH)
+#define MD_DIALECT_REDDIT               (MD_FLAG_PERMISSIVEATXHEADERS | MD_FLAG_PERMISSIVEAUTOLINKS | MD_FLAG_NOHTML | MD_FLAG_REDDITAUTOLINKS | MD_FLAG_STRIKETHROUGH)
 
 /* Renderer structure.
  */

scripts/run-tests.sh

@@ -54,6 +54,10 @@ echo
 echo "Strikethrough extension:"
 $PYTHON "$TEST_DIR/spec_tests.py" -s "$TEST_DIR/strikethrough.txt" -p "$PROGRAM --fstrikethrough"
 
+echo
+echo "Reddit autolinks extension:"
+$PYTHON "$TEST_DIR/spec_tests.py" -s "$TEST_DIR/reddit-autolinks.txt" -p "$PROGRAM --freddit-autolinks"
+
 echo
 echo "Pathological input:"
 $PYTHON "$TEST_DIR/pathological_tests.py" -p "$PROGRAM"

test/reddit-autolinks.txt

@@ -0,0 +1,22 @@
+
+# Reddit Autolinks
+
+With the flag `MD_FLAG_REDDITAUTOLINKS`, MD4C enables extension for recognition Reddit usernames and subreddits.
+
+For reference, here is snudown's (Reddit's markdown parser) implementation [link](https://github.com/reddit/snudown/blob/master/src/autolink.c).
+
+Reddit autolinks can be prefixed by a a forward slash or not: r/test and /r/test both work. A link ends when a non-alphanumeric character is hit. The only such character allowed it an underscore.
+
+```````````````````````````````` example
+Here is a link to /r/askreddit by u/me.
+.
+<p>Here is a link to <a href="https://www.reddit.com/r/askreddit">/r/askreddit</a> by <a href="https://www.reddit.com/u/me">u/me</a>.</p>
+````````````````````````````````
+
+A link can show up in the middle of the word if prefixed by a forward slash (you don't need a whitespace before).
+
+```````````````````````````````` example
+World/r/news vs /r/worldnew;s
+.
+<p>World<a href="https://www.reddit.com/r/news">/r/news</a> vs <a href="https://www.reddit.com/r/worldnew">/r/worldnew</a>;s</p>
+````````````````````````````````