Add support for environment variable expansion

This patch teaches cgit to expand environment variables in certain
cgitrc option values (cache_root, scan-path, include) plus when
finding the location of cgitrc itself.

One use case for this feature is virtual hosting - e.g. by setting
$CGIT_CONFIG='/etc/cgitrc/$HTTP_HOST' in httpd.conf, all virtual
hosts automatically gets their own cgitrc.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

1 files changed, 71 insertions, 0 deletions

diff --git a/shared.c b/shared.c
index 5f46793..76d26dd 100644
--- a/shared.c
+++ b/shared.c
@@ -378,48 +378,119 @@ int cgit_open_filter(struct cgit_filter *filter)
         }
         close(filter->pipe_fh[0]);
         chk_non_negative(dup2(filter->pipe_fh[1], STDOUT_FILENO),
                 "Unable to use pipe as STDOUT");
         close(filter->pipe_fh[1]);
         return 0;
 }
 
 int cgit_close_filter(struct cgit_filter *filter)
 {
         chk_non_negative(dup2(filter->old_stdout, STDOUT_FILENO),
                 "Unable to restore STDOUT");
         close(filter->old_stdout);
         if (filter->pid < 0)
                 return 0;
         waitpid(filter->pid, &filter->exitstatus, 0);
         if (WIFEXITED(filter->exitstatus) && !WEXITSTATUS(filter->exitstatus))
                 return 0;
         die("Subprocess %s exited abnormally", filter->cmd);
 }
 
 /* Read the content of the specified file into a newly allocated buffer,
  * zeroterminate the buffer and return 0 on success, errno otherwise.
  */
 int readfile(const char *path, char **buf, size_t *size)
 {
         int fd, e;
         struct stat st;
 
         fd = open(path, O_RDONLY);
         if (fd == -1)
                 return errno;
         if (fstat(fd, &st)) {
                 e = errno;
                 close(fd);
                 return e;
         }
         if (!S_ISREG(st.st_mode)) {
                 close(fd);
                 return EISDIR;
         }
         *buf = xmalloc(st.st_size + 1);
         *size = read_in_full(fd, *buf, st.st_size);
         e = errno;
         (*buf)[*size] = '\0';
         close(fd);
         return (*size == st.st_size ? 0 : e);
 }
+
+int is_token_char(char c)
+{
+        return isalnum(c) || c == '_';
+}
+
+/* Replace name with getenv(name), return pointer to zero-terminating char
+ */
+char *expand_macro(char *name, int maxlength)
+{
+        char *value;
+        int len;
+
+        len = 0;
+        value = getenv(name);
+        if (value) {
+                len = strlen(value);
+                if (len > maxlength)
+                        len = maxlength;
+                strncpy(name, value, len);
+        }
+        return name + len;
+}
+
+#define EXPBUFSIZE (1024 * 8)
+
+/* Replace all tokens prefixed by '$' in the specified text with the
+ * value of the named environment variable.
+ * NB: the return value is a static buffer, i.e. it must be strdup'd
+ * by the caller.
+ */
+char *expand_macros(const char *txt)
+{
+        static char result[EXPBUFSIZE];
+        char *p, *start;
+        int len;
+
+        p = result;
+        start = NULL;
+        while (p < result + EXPBUFSIZE - 1 && txt && *txt) {
+                *p = *txt;
+                if (start) {
+                        if (!is_token_char(*txt)) {
+                                if (p - start > 0) {
+                                        *p = '\0';
+                                        len = result + EXPBUFSIZE - start - 1;
+                                        p = expand_macro(start, len) - 1;
+                                }
+                                start = NULL;
+                                txt--;
+                        }
+                        p++;
+                        txt++;
+                        continue;
+                }
+                if (*txt == '$') {
+                        start = p;
+                        txt++;
+                        continue;
+                }
+                p++;
+                txt++;
+        }
+        *p = '\0';
+        if (start && p - start > 0) {
+                len = result + EXPBUFSIZE - start - 1;
+                p = expand_macro(start, len);
+                *p = '\0';
+        }
+        return result;
+}