Remove unneeded uses of std::map::operator[] (#2642)

These unintentionally mutate the map.  Script suggested by @danmar.

Makefile.am

@@ -51,6 +51,7 @@ cppcheck:
             --suppress=useStlAlgorithm \
             --suppress=checkLevelNormal \
             --suppress=normalCheckLevelMaxBranches \
+            --addon=test/map-subscript-read.py \
             src/ test/
 
 #

src/s3fs.cpp

@@ -4004,8 +4004,9 @@ static int s3fs_removexattr(const char* path, const char* name)
     }
     if(need_put_header){
         // not found opened file.
-        if(updatemeta["x-amz-meta-xattr"].empty()){
-            updatemeta.erase("x-amz-meta-xattr");
+        auto iter = updatemeta.find("x-amz-meta-xattr");
+        if(iter != updatemeta.end() && iter->second.empty()){
+            updatemeta.erase(iter);
         }
 
         merge_headers(meta, updatemeta, true);

src/s3fs_cred.cpp

@@ -514,19 +514,32 @@ bool S3fsCred::SetIAMCredentials(const char* response)
         return false;
     }
 
-    AWSAccessToken = keyval[IAM_token_field];
+    auto aws_access_token = keyval.find(IAM_token_field);
+    if(aws_access_token == keyval.end()){
+        return false;
+    }
 
     if(is_ibm_iam_auth){
+        auto access_token_expire = keyval.find(IAM_expiry_field);
         off_t tmp_expire = 0;
-        if(!s3fs_strtoofft(&tmp_expire, keyval[IAM_expiry_field].c_str(), /*base=*/ 10)){
+        if(access_token_expire == keyval.end() || !s3fs_strtoofft(&tmp_expire, access_token_expire->second.c_str(), /*base=*/ 10)){
             return false;
         }
         AWSAccessTokenExpire = static_cast<time_t>(tmp_expire);
     }else{
-        AWSAccessKeyId       = keyval[S3fsCred::IAMCRED_ACCESSKEYID];
-        AWSSecretAccessKey   = keyval[S3fsCred::IAMCRED_SECRETACCESSKEY];
-        AWSAccessTokenExpire = cvtIAMExpireStringToTime(keyval[IAM_expiry_field].c_str());
+        auto access_key_id = keyval.find(S3fsCred::IAMCRED_ACCESSKEYID);
+        auto secret_access_key = keyval.find(S3fsCred::IAMCRED_SECRETACCESSKEY);
+        auto access_token_expire = keyval.find(IAM_expiry_field);
+        if(access_key_id == keyval.end() || secret_access_key == keyval.end() || access_token_expire == keyval.end()){
+            return false;
+        }
+
+        AWSAccessKeyId = access_key_id->second;
+        AWSSecretAccessKey = secret_access_key->second;
+        AWSAccessTokenExpire = cvtIAMExpireStringToTime(access_token_expire->second.c_str());
     }
+
+    AWSAccessToken = aws_access_token->second;
     return true;
 }
 

test/map-subscript-read.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+#
+# locate map operator [] reads
+#
+# Example usage of this addon (scan a sourcefile main.cpp)
+# cppcheck --dump main.cpp
+# python map-subscript-read.py main.cpp.dump
+
+import cppcheckdata
+import sys
+
+
+DEBUG = ('-debug' in sys.argv)
+
+
+def reportError(token, severity, msg, id):
+    cppcheckdata.reportError(token, severity, msg, 'map', id)
+
+
+def simpleMatch(token, pattern):
+    return cppcheckdata.simpleMatch(token, pattern)
+
+
+def check_map_subscript(data):
+    #if data.language != 'cpp':
+    #    return
+    for cfg in data.iterconfigurations():
+        for token in cfg.tokenlist:
+            if token.str != '[' or token.astOperand1 is None or token.astOperand2 is None:
+                continue
+            if token.astParent and token.astParent.str == '=' and token.astParent.astOperand1 == token:
+                continue
+            m = token.astOperand1
+            if m.variable is None:
+                continue
+            if simpleMatch(m.variable.typeStartToken, 'std :: map <'):
+                reportError(token, 'style', 'Reading from std::map with subscript operator [].', 'mapSubscriptRead')
+            elif simpleMatch(m.variable.typeStartToken, 'std :: unordered_map <'):
+                reportError(token, 'style', 'Reading from std::unordered_map with subscript operator [].', 'mapSubscriptRead')
+
+
+for arg in sys.argv[1:]:
+    if arg == '--cli':
+        continue
+    data = cppcheckdata.CppcheckData(arg)
+    check_map_subscript(data)
+
+sys.exit(cppcheckdata.EXIT_CODE)