man: add handling of "man links", by Ivana Varekova <varekova AT redhat.com>

function                                             old     new   delta
run_pipe                                             102     354    +252
show_manpage                                           -     126    +126
man_main                                             705     615     -90
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/1 up/down: 378/-90)           Total: 288 bytes

1 files changed, 62 insertions, 11 deletions

diff --git a/miscutils/man.c b/miscutils/man.c
index f499fef62..91b995cf4 100644
--- a/miscutils/man.c
+++ b/miscutils/man.c
@@ -27,10 +27,19 @@ echo ".pl \n(nlu+10"
 #define STR_catNULmanNUL "cat\0man"
 #define STR_cat          "cat\0man"
 
-static int run_pipe(const char *unpacker, const char *pager, char *man_filename, int man)
+//TODO: make gz/bz2 support conditional on FEATURE_SEAMLESS_GZ/BZ2,
+// add SEAMLESS_LZMA support
+
+static int show_manpage(const char *pager, char *man_filename, int man, int level);
+
+static int run_pipe(const char *unpacker, const char *pager, char *man_filename, int man, int level)
 {
         char *cmd;
 
+        /* Prevent man page link loops */
+        if (level > 10)
+                return 0;
+
         if (access(man_filename, R_OK) != 0)
                 return 0;
 
@@ -39,6 +48,53 @@ static int run_pipe(const char *unpacker, const char *pager, char *man_filename,
                 return 1;
         }
 
+        if (man) { /* man page, not cat page */
+                /* Test whether the man page is not a link to another one. */
+                /* The link has the following on the first line: */
+                /* ".so another_man_page" */
+                struct stat sb;
+                char *line;
+                char *linkname, *p;
+
+                /* On my system:
+                 * man1/genhostid.1.gz: 203 bytes - smallest real manpage
+                 * man2/path_resolution.2.gz: 114 bytes - largest link
+                 */
+                xstat(man_filename, &sb);
+                if (sb.st_size > 300) /* err on the safe side */
+                        goto ordinary_manpage;
+
+                line = xmalloc_open_zipped_read_close(man_filename, NULL);
+                if (!line || strncmp(line, ".so ", 4) != 0) {
+                        free(line);
+                        goto ordinary_manpage;
+                }
+                /* Example: man2/path_resolution.2.gz contains
+                 * ".so man7/path_resolution.7\n<junk>"
+                 */
+                *strchrnul(line, '\n') = '\0';
+                linkname = p = skip_whitespace(&line[4]);
+                while (1) {
+                        char *newname_slash, *oldname_slash;
+
+                        oldname_slash = strrchr(man_filename, '/');
+                        if (!oldname_slash)
+                                goto ordinary_manpage;
+                        *oldname_slash = '\0';
+                        newname_slash = strchr(p, '/');
+                        if (!newname_slash)
+                                break;
+                        p = newname_slash + 1;
+                }
+                man_filename = xasprintf("%s/%s" ".bz2", man_filename, linkname);
+                free(line);
+                /* Note: we leak "new" man_filename string as well... */
+                if (show_manpage(pager, man_filename, man, level + 1))
+                        return 1;
+                /* else: show the link, it's better than nothing */
+        }
+
+ ordinary_manpage:
         /* "2>&1" is added so that nroff errors are shown in pager too.
          * Otherwise it may show just empty screen */
         cmd = xasprintf(
@@ -51,22 +107,22 @@ static int run_pipe(const char *unpacker, const char *pager, char *man_filename,
 }
 
 /* man_filename is of the form "/dir/dir/dir/name.s.bz2" */
-static int show_manpage(const char *pager, char *man_filename, int man)
+static int show_manpage(const char *pager, char *man_filename, int man, int level)
 {
         int len;
 
-        if (run_pipe("bunzip2 -c", pager, man_filename, man))
+        if (run_pipe("bunzip2 -c", pager, man_filename, man, level))
                 return 1;
 
         len = strlen(man_filename) - 1;
 
         man_filename[len] = '\0'; /* ".bz2" -> ".gz" */
         man_filename[len - 2] = 'g';
-        if (run_pipe("gunzip -c", pager, man_filename, man))
+        if (run_pipe("gunzip -c", pager, man_filename, man, level))
                 return 1;
 
         man_filename[len - 3] = '\0'; /* ".gz" -> "" */
-        if (run_pipe(STR_cat, pager, man_filename, man))
+        if (run_pipe(STR_cat, pager, man_filename, man, level))
                 return 1;
 
         return 0;
@@ -121,11 +177,6 @@ int man_main(int argc UNUSED_PARAM, char **argv)
         }
         config_close(parser);
 
-// TODO: my man3/getpwuid.3.gz contains just one line:
-// .so man3/getpwnam.3
-// (and I _dont_ have man3/getpwnam.3, I have man3/getpwnam.3.gz)
-// need to support this...
-
         not_found = 0;
         do { /* for each argv[] */
                 int found = 0;
@@ -151,7 +202,7 @@ int man_main(int argc UNUSED_PARAM, char **argv)
                                                                 sect_len, cur_sect,
                                                                 *argv,
                                                                 sect_len, cur_sect);
-                                                found_here = show_manpage(pager, man_filename, cat0man1);
+                                                found_here = show_manpage(pager, man_filename, cat0man1, 0);
                                                 found |= found_here;
                                                 cat0man1 += found_here + 1;
                                                 free(man_filename);