Refactor out the 'find string at start of any line' logic.

We do this in too many places throughout the code; it's time to start
clamping down.

Also, refactor Karsten's patch to use strchr-then-strndup, rather than
malloc-then-strlcpy-then-strchr-then-clear.

2 files changed, 25 insertions, 0 deletions

diff --git a/src/common/util.c b/src/common/util.c
index e70a9ea5f3..6177a3e736 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -682,6 +682,29 @@ find_whitespace_eos(const char *s, const char *eos)
   return s;
 }
 
+/** Return the the first occurrence of <b>needle</b> in <b>haystack</b> that
+ * occurs at the start of a line (that is, at the beginning of <b>haystack</b>
+ * or immediately after a newline).  Return NULL if no such string is found.
+ */
+const char *
+find_str_at_start_of_line(const char *haystack, const char *needle)
+{
+  size_t needle_len = strlen(needle);
+
+  do {
+    if (!strncmp(haystack, needle, needle_len))
+      return haystack;
+
+    haystack = strchr(haystack, '\n');
+    if (!haystack)
+      return NULL;
+    else
+      ++haystack;
+  } while (*haystack);
+
+  return NULL;
+}
+
 /** Return true iff the 'len' bytes at 'mem' are all zero. */
 int
 tor_mem_is_zero(const char *mem, size_t len)
diff --git a/src/common/util.h b/src/common/util.h
index 17cbb4a44f..b55bb91c51 100644
--- a/src/common/util.h
+++ b/src/common/util.h
@@ -195,6 +195,8 @@ const char *eat_whitespace_no_nl(const char *s) ATTR_PURE;
 const char *eat_whitespace_eos_no_nl(const char *s, const char *eos) ATTR_PURE;
 const char *find_whitespace(const char *s) ATTR_PURE;
 const char *find_whitespace_eos(const char *s, const char *eos) ATTR_PURE;
+const char *find_str_at_start_of_line(const char *haystack, const char *needle)
+  ATTR_PURE;
 int tor_mem_is_zero(const char *mem, size_t len) ATTR_PURE;
 int tor_digest_is_zero(const char *digest) ATTR_PURE;
 int tor_digest256_is_zero(const char *digest) ATTR_PURE;