diff --git a/dataformats.c b/dataformats.c
index feb4a69e..7789ed0c 100644
--- a/dataformats.c
+++ b/dataformats.c
@@ -32,27 +32,38 @@ int cmp_sid_t(const sid_t *a, const sid_t *b)
 
 int str_to_sid_t(sid_t *sidp, const char *hex)
 {
-  const char *end;
-  return strn_to_sid_t(sidp, hex, SIZE_MAX, &end) != -1 && *end == '\0' ? 0 : -1;
+  return parse_sid_t(sidp, hex, -1, NULL); // checks for nul terminator
 }
 
-int strn_to_sid_t(sid_t *sidp, const char *hex, size_t hexlen, const char **endp)
+int strn_to_sid_t(sid_t *sidp, const char *hex, size_t hexlen)
 {
-  if (strn_startswith(hex, hexlen, "broadcast", endp)) {
+  return parse_sid_t(sidp, hex, hexlen, NULL); // does not check for nul terminator
+}
+
+int parse_sid_t(sid_t *sidp, const char *hex, ssize_t hexlen, const char **endp)
+{
+  const char *end = NULL;
+  if (strn_startswith(hex, hexlen, "broadcast", &end)) {
+    if (endp)
+      *endp = end;
+    else if (hexlen == -1 && *end != '\0')
+      return -1;
     if (sidp)
       *sidp = SID_BROADCAST;
     return 0;
   }
-  sid_t tmp;
-  if (hexlen < sizeof tmp.binary * 2)
+  if (hexlen != -1 && hexlen != SID_STRLEN)
     return -1;
+  sid_t tmp;
   int n = fromhex(tmp.binary, hex, sizeof tmp.binary);
   if (n != sizeof tmp.binary)
     return -1;
+  if (endp)
+    *endp = hex + SID_STRLEN;
+  else if (hexlen == -1 && hex[SID_STRLEN] != '\0')
+    return -1;
   if (sidp)
     *sidp = tmp;
-  if (endp)
-    *endp = hex + sizeof tmp.binary * 2;
   return 0;
 }
 
@@ -84,19 +95,28 @@ int cmp_rhizome_bid_t(const rhizome_bid_t *a, const rhizome_bid_t *b)
 
 int str_to_rhizome_bid_t(rhizome_bid_t *bid, const char *hex)
 {
-  return bid ? fromhexstr(bid->binary, hex, sizeof bid->binary) : is_xstring(hex, RHIZOME_BUNDLE_ID_STRLEN) ? 0 : -1;
+  return parse_rhizome_bid_t(bid, hex, -1, NULL); // checks for nul terminator
 }
 
-int strn_to_rhizome_bid_t(rhizome_bid_t *bid, const char *hex, const char **endp)
+int strn_to_rhizome_bid_t(rhizome_bid_t *bid, const char *hex, size_t hexlen)
 {
+  return parse_rhizome_bid_t(bid, hex, hexlen, NULL); // does not check for nul terminator
+}
+
+int parse_rhizome_bid_t(rhizome_bid_t *bid, const char *hex, ssize_t hexlen, const char **endp)
+{
+  if (hexlen != -1 && hexlen != RHIZOME_BUNDLE_ID_STRLEN)
+    return -1;
   rhizome_bid_t tmp;
   int n = fromhex(tmp.binary, hex, sizeof tmp.binary);
   if (n != sizeof tmp.binary)
     return -1;
+  if (endp)
+    *endp = hex + RHIZOME_BUNDLE_ID_STRLEN;
+  else if (hexlen == -1 && hex[RHIZOME_BUNDLE_ID_STRLEN] != '\0')
+    return -1;
   if (bid)
     *bid = tmp;
-  if (endp)
-    *endp = hex + sizeof tmp.binary * 2;
   return 0;
 }
 
@@ -107,37 +127,55 @@ int cmp_rhizome_filehash_t(const rhizome_filehash_t *a, const rhizome_filehash_t
 
 int str_to_rhizome_filehash_t(rhizome_filehash_t *hashp, const char *hex)
 {
-  return hashp ? fromhexstr(hashp->binary, hex, sizeof hashp->binary) : is_xstring(hex, RHIZOME_FILEHASH_STRLEN) ? 0 : -1;
+  return parse_rhizome_filehash_t(hashp, hex, -1, NULL); // checks for nul terminator
 }
 
-int strn_to_rhizome_filehash_t(rhizome_filehash_t *hashp, const char *hex, const char **endp)
+int strn_to_rhizome_filehash_t(rhizome_filehash_t *hashp, const char *hex, size_t hexlen)
 {
+  return parse_rhizome_filehash_t(hashp, hex, hexlen, NULL); // does not check for nul terminator
+}
+
+int parse_rhizome_filehash_t(rhizome_filehash_t *hashp, const char *hex, ssize_t hexlen, const char **endp)
+{
+  if (hexlen != -1 && hexlen != RHIZOME_FILEHASH_STRLEN)
+    return -1;
   rhizome_filehash_t tmp;
   int n = fromhex(tmp.binary, hex, sizeof tmp.binary);
   if (n != sizeof tmp.binary)
     return -1;
+  if (endp)
+    *endp = hex + RHIZOME_FILEHASH_STRLEN;
+  else if (hexlen == -1 && hex[RHIZOME_FILEHASH_STRLEN] != '\0')
+    return -1;
   if (hashp)
     *hashp = tmp;
-  if (endp)
-    *endp = hex + sizeof tmp.binary * 2;
   return 0;
 }
 
 int str_to_rhizome_bk_t(rhizome_bk_t *bkp, const char *hex)
 {
-  return bkp ? fromhexstr(bkp->binary, hex, sizeof bkp->binary) : is_xstring(hex, RHIZOME_BUNDLE_KEY_STRLEN) ? 0 : -1;
+  return parse_rhizome_bk_t(bkp, hex, -1, NULL); // checks for nul terminator
 }
 
-int strn_to_rhizome_bk_t(rhizome_bk_t *bkp, const char *hex, const char **endp)
+int strn_to_rhizome_bk_t(rhizome_bk_t *bkp, const char *hex, size_t hexlen)
 {
+  return parse_rhizome_bk_t(bkp, hex, hexlen, NULL); // does not check for nul terminator
+}
+
+int parse_rhizome_bk_t(rhizome_bk_t *bkp, const char *hex, ssize_t hexlen, const char **endp)
+{
+  if (hexlen != -1 && hexlen != RHIZOME_BUNDLE_KEY_STRLEN)
+    return -1;
   rhizome_bk_t tmp;
   int n = fromhex(tmp.binary, hex, sizeof tmp.binary);
   if (n != sizeof tmp.binary)
     return -1;
+  if (endp)
+    *endp = hex + RHIZOME_BUNDLE_KEY_STRLEN;
+  else if (hexlen == -1 && hex[RHIZOME_BUNDLE_KEY_STRLEN] != '\0')
+    return -1;
   if (bkp)
     *bkp = tmp;
-  if (endp)
-    *endp = hex + sizeof tmp.binary * 2;
   return 0;
 }
 
@@ -157,7 +195,7 @@ int strn_to_rhizome_bsk_t(rhizome_bk_t *bskp, const char *text, size_t textlen)
       strn_digest_passphrase(bskp->binary, sizeof bskp->binary, text, textlen);
     return 0;
   }
-  return strn_to_rhizome_bk_t(bskp, text, NULL);
+  return strn_to_rhizome_bk_t(bskp, text, textlen);
 }
 
 int rhizome_strn_is_bundle_crypt_key(const char *key)
diff --git a/mdp_filter.c b/mdp_filter.c
index 8245cb13..ad6a7ddc 100644
--- a/mdp_filter.c
+++ b/mdp_filter.c
@@ -452,7 +452,7 @@ static int _endpoint(Cursor c, uint8_t *flagsp, uint8_t port_flag, struct subscr
   preload(c, SID_STRLEN);
   if (skip(c, "*")) {
     *subscr = NULL;
-  } else if (strn_to_sid_t(&sid, preloaded(c), available(c), &end) == 0) {
+  } else if (parse_sid_t(&sid, preloaded(c), available(c), &end) == 0) {
     if ((*subscr = find_subscriber(sid.binary, sizeof sid.binary, 1)) == NULL)
       return 0;
     advance_to(c, end);
diff --git a/meshms_restful.c b/meshms_restful.c
index 970925d7..9c04325e 100644
--- a/meshms_restful.c
+++ b/meshms_restful.c
@@ -124,7 +124,7 @@ int restful_meshms_(httpd_request *r, const char *remainder)
   http_size_t content_length = CONTENT_LENGTH_UNKNOWN;
   HTTP_HANDLER *handler = NULL;
   const char *end;
-  if (strn_to_sid_t(&r->sid1, remainder, SIZE_MAX, &end) != -1) {
+  if (parse_sid_t(&r->sid1, remainder, -1, &end) != -1) {
     remainder = end;
     if (strcmp(remainder, "/conversationlist.json") == 0) {
       handler = restful_meshms_conversationlist_json;
@@ -136,7 +136,7 @@ int restful_meshms_(httpd_request *r, const char *remainder)
       content_length = 0;
       remainder = "";
     }
-    else if (*remainder == '/' && strn_to_sid_t(&r->sid2, remainder + 1, SIZE_MAX, &end) != -1) {
+    else if (*remainder == '/' && parse_sid_t(&r->sid2, remainder + 1, -1, &end) != -1) {
       remainder = end;
       if (strcmp(remainder, "/messagelist.json") == 0) {
 	handler = restful_meshms_messagelist_json;
diff --git a/rhizome_bundle.c b/rhizome_bundle.c
index 3a2b35d0..61ccbdf6 100644
--- a/rhizome_bundle.c
+++ b/rhizome_bundle.c
@@ -524,7 +524,7 @@ int rhizome_manifest_inspect(const char *buf, size_t len, struct rhizome_manifes
 	    eol = p;
 	  if (has_bid == 1) {
 	    const char *e;
-	    if (strn_to_rhizome_bid_t(&summ->bid, begin, &e) == 0 && e == eol)
+	    if (parse_rhizome_bid_t(&summ->bid, begin, eol - begin, &e) == 0 && e == eol)
 	      has_bid = 2;
 	    else
 	      state = Error; // invalid "id" field
diff --git a/rhizome_restful.c b/rhizome_restful.c
index 3820979e..bb8a34e2 100644
--- a/rhizome_restful.c
+++ b/rhizome_restful.c
@@ -559,7 +559,7 @@ static int insert_mime_part_end(struct http_request *hr)
   httpd_request *r = (httpd_request *) hr;
   if (r->u.insert.current_part == PART_AUTHOR) {
     if (   r->u.insert.author_hex_len != sizeof r->u.insert.author_hex
-	|| strn_to_sid_t(&r->u.insert.author, r->u.insert.author_hex, sizeof r->u.insert.author_hex, NULL) == -1
+	|| strn_to_sid_t(&r->u.insert.author, r->u.insert.author_hex, sizeof r->u.insert.author_hex) == -1
     )
       return http_response_form_part(r, "Invalid", PART_AUTHOR, r->u.insert.author_hex, r->u.insert.author_hex_len);
     r->u.insert.received_author = 1;
@@ -738,7 +738,7 @@ int restful_rhizome_(httpd_request *r, const char *remainder)
   HTTP_HANDLER *handler = NULL;
   rhizome_bid_t bid;
   const char *end;
-  if (strn_to_rhizome_bid_t(&bid, remainder, &end) != -1) {
+  if (parse_rhizome_bid_t(&bid, remainder, -1, &end) != -1) {
     if (strcmp(end, ".rhm") == 0) {
       handler = restful_rhizome_bid_rhm;
       remainder = "";
diff --git a/rhizome_types.h b/rhizome_types.h
index 5a66a00b..92c688fb 100644
--- a/rhizome_types.h
+++ b/rhizome_types.h
@@ -80,7 +80,8 @@ typedef struct rhizome_bid_binary {
 #define alloca_tohex_rhizome_bid_t(bid) alloca_tohex((bid).binary, sizeof (*(rhizome_bid_t*)0).binary)
 int cmp_rhizome_bid_t(const rhizome_bid_t *a, const rhizome_bid_t *b);
 int str_to_rhizome_bid_t(rhizome_bid_t *bid, const char *hex);
-int strn_to_rhizome_bid_t(rhizome_bid_t *bid, const char *hex, const char **endp);
+int strn_to_rhizome_bid_t(rhizome_bid_t *bid, const char *hex, size_t hexlen);
+int parse_rhizome_bid_t(rhizome_bid_t *bid, const char *hex, ssize_t hexlen, const char **endp);
 
 /* Fundamental data type: Rhizome File Hash
  *
@@ -97,7 +98,8 @@ typedef struct rhizome_filehash_binary {
 #define alloca_tohex_rhizome_filehash_t(fh) alloca_tohex((fh).binary, sizeof (*(rhizome_filehash_t*)0).binary)
 int cmp_rhizome_filehash_t(const rhizome_filehash_t *a, const rhizome_filehash_t *b);
 int str_to_rhizome_filehash_t(rhizome_filehash_t *fh, const char *hex);
-int strn_to_rhizome_filehash_t(rhizome_filehash_t *fh, const char *hex, const char **endp);
+int strn_to_rhizome_filehash_t(rhizome_filehash_t *fh, const char *hex, size_t hexlen);
+int parse_rhizome_filehash_t(rhizome_filehash_t *fh, const char *hex, ssize_t hexlen, const char **endp);
 
 /* Fundamental data type: Rhizome Bundle Key (BK)
  *
@@ -119,7 +121,8 @@ int cmp_rhizome_bk_t(const rhizome_bk_t *a, const rhizome_bk_t *b);
 
 // The BK field can only be in hex format
 int str_to_rhizome_bk_t(rhizome_bk_t *bk, const char *hex);
-int strn_to_rhizome_bk_t(rhizome_bk_t *bk, const char *hex, const char **endp);
+int strn_to_rhizome_bk_t(rhizome_bk_t *bk, const char *hex, size_t hexlen);
+int parse_rhizome_bk_t(rhizome_bk_t *bk, const char *hex, ssize_t hexlen, const char **endp);
 
 // The Bundle Secret can be given as hex or as a passphrase
 int str_to_rhizome_bsk_t(rhizome_bk_t *bsk, const char *text);
diff --git a/serval_types.h b/serval_types.h
index 7eb7ee93..466e63e5 100644
--- a/serval_types.h
+++ b/serval_types.h
@@ -54,7 +54,8 @@ typedef struct sid_binary {
 
 int cmp_sid_t(const sid_t *a, const sid_t *b);
 int str_to_sid_t(sid_t *sid, const char *hex);
-int strn_to_sid_t(sid_t *sid, const char *hex, size_t hexlen, const char **endp);
+int strn_to_sid_t(sid_t *sid, const char *hex, size_t hexlen);
+int parse_sid_t(sid_t *sid, const char *hex, ssize_t hexlen, const char **endp);
 
 #define alloca_tohex_sas(sas)           alloca_tohex((sas), SAS_SIZE)
 
diff --git a/str.c b/str.c
index 06a062c2..1eebb509 100644
--- a/str.c
+++ b/str.c
@@ -563,8 +563,9 @@ int str_startswith(const char *str, const char *substring, const char **afterp)
   return 1;
 }
 
-int strn_startswith(const char *str, size_t len, const char *substring, const char **afterp)
+int strn_startswith(const char *str, ssize_t len, const char *substring, const char **afterp)
 {
+  // if len == -1 then str must be nul terminated
   while (len && *substring && *substring == *str)
     --len, ++substring, ++str;
   if (*substring)
diff --git a/str.h b/str.h
index 4294419f..43a6e01c 100644
--- a/str.h
+++ b/str.h
@@ -371,9 +371,11 @@ int str_startswith(const char *str, const char *substring, const char **afterp);
  * sub-string.  If so, return 1 and, if afterp is not NULL, set *afterp to point to the character
  * immediately following the substring.  Otherwise return 0.
  *
+ * If len == -1 then is equivalent to str_startswith().
+ *
  * @author Andrew Bettison <andrew@servalproject.com>
  */
-int strn_startswith(const char *str, size_t len, const char *substring, const char **afterp);
+int strn_startswith(const char *str, ssize_t len, const char *substring, const char **afterp);
 
 /* Case-insensitive form of str_startswith().
  * @author Andrew Bettison <andrew@servalproject.com>