builtins: make ltrimstr and rtrimstr error for non-string inputs

I also refactored the code in rtrimstr to make it more similar to the
code used by ltrimstr.

Previously, ltrimstr/rtrimstr would just the input pass through for
non-string inputs or arguments.

That was happening because, they were leaking the errors returned by
startswith/endswith treating them as if they were jv_false().

This patch also fixes that memory leak discovered by oss-fuzz

Ref: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=64946

src/builtin.c

@@ -295,7 +295,13 @@ static jv f_endswith(jq_state *jq, jv a, jv b) {
 }
 
 static jv f_ltrimstr(jq_state *jq, jv input, jv left) {
-  if (jv_get_kind(f_startswith(jq, jv_copy(input), jv_copy(left))) != JV_KIND_TRUE) {
+  jv startswith = f_startswith(jq, jv_copy(input), jv_copy(left));
+  if (!jv_is_valid(startswith)) {
+    jv_free(input);
+    jv_free(left);
+    return startswith;
+  }
+  if (jv_get_kind(startswith) != JV_KIND_TRUE) {
     jv_free(left);
     return input;
   }
@@ -311,14 +317,21 @@ static jv f_ltrimstr(jq_state *jq, jv input, jv left) {
 }
 
 static jv f_rtrimstr(jq_state *jq, jv input, jv right) {
-  if (jv_get_kind(f_endswith(jq, jv_copy(input), jv_copy(right))) == JV_KIND_TRUE) {
-    jv res = jv_string_sized(jv_string_value(input),
-                             jv_string_length_bytes(jv_copy(input)) - jv_string_length_bytes(right));
+  jv endswith = f_endswith(jq, jv_copy(input), jv_copy(right));
+  if (!jv_is_valid(endswith)) {
     jv_free(input);
-    return res;
+    jv_free(right);
+    return endswith;
   }
-  jv_free(right);
-  return input;
+  if (jv_get_kind(endswith) != JV_KIND_TRUE) {
+    jv_free(right);
+    return input;
+  }
+  int suffixlen = jv_string_length_bytes(right);
+  jv res = jv_string_sized(jv_string_value(input),
+                           jv_string_length_bytes(jv_copy(input)) - suffixlen);
+  jv_free(input);
+  return res;
 }
 
 jv binop_minus(jv a, jv b) {

tests/jq.test

@@ -2091,3 +2091,18 @@ try ("foobar" | .[1.5]) catch .
 null
 "Cannot index string with number"
 
+# ltrimstr/1 and rtrimstr/1 don't leak, and return an error for
+# non-string arguments. #2969
+.[] as [$x, $y] | try ["ok", ($x | ltrimstr($y))] catch ["ko", .]
+[["hi",1],[1,"hi"],["hi","hi"],[1,1]]
+["ko","startswith() requires string inputs"]
+["ko","startswith() requires string inputs"]
+["ok",""]
+["ko","startswith() requires string inputs"]
+
+.[] as [$x, $y] | try ["ok", ($x | rtrimstr($y))] catch ["ko", .]
+[["hi",1],[1,"hi"],["hi","hi"],[1,1]]
+["ko","endswith() requires string inputs"]
+["ko","endswith() requires string inputs"]
+["ok",""]
+["ko","endswith() requires string inputs"]