# Fixes sync issues caused by locale-sensitive lowercasing
# of HTTP headers.
# See https://github.com/laurent22/joplin/issues/10681
diff --git a/android/src/main/java/com/RNFetchBlob/RNFetchBlobConfig.java b/android/src/main/java/com/RNFetchBlob/RNFetchBlobConfig.java
index 8ac9e7a855162cefbf99024eb013c8a3b11de1ec..1c639cf9d84821b6ffc132960e2d1c044bedbd48 100644
--- a/android/src/main/java/com/RNFetchBlob/RNFetchBlobConfig.java
+++ b/android/src/main/java/com/RNFetchBlob/RNFetchBlobConfig.java
@@ -2,6 +2,7 @@ package com.RNFetchBlob;
 
 import com.facebook.react.bridge.ReadableArray;
 import com.facebook.react.bridge.ReadableMap;
+import java.util.Locale;
 
 class RNFetchBlobConfig {
 
@@ -33,7 +34,7 @@ class RNFetchBlobConfig {
         }
         if(options.hasKey("binaryContentTypes"))
             this.binaryContentTypes = options.getArray("binaryContentTypes");
-        if(this.path != null && path.toLowerCase().contains("?append=true")) {
+        if(this.path != null && path.toLowerCase(Locale.ROOT).contains("?append=true")) {
             this.overwrite = false;
         }
         if(options.hasKey("overwrite"))
diff --git a/android/src/main/java/com/RNFetchBlob/RNFetchBlobFS.java b/android/src/main/java/com/RNFetchBlob/RNFetchBlobFS.java
index a4d70153f41e6c14eec65412b5b59822f1c6750b..d98c439f7b0aeb79afc82ab9f653e9c021086426 100644
--- a/android/src/main/java/com/RNFetchBlob/RNFetchBlobFS.java
+++ b/android/src/main/java/com/RNFetchBlob/RNFetchBlobFS.java
@@ -29,6 +29,7 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.UUID;
+import java.util.Locale;
 
 class RNFetchBlobFS {
 
@@ -210,7 +211,7 @@ class RNFetchBlobFS {
                 return;
             }
 
-            switch (encoding.toLowerCase()) {
+            switch (encoding.toLowerCase(Locale.ROOT)) {
                 case "base64" :
                     promise.resolve(Base64.encodeToString(bytes, Base64.NO_WRAP));
                     break;
@@ -1050,7 +1051,7 @@ class RNFetchBlobFS {
         if(encoding.equalsIgnoreCase("ascii")) {
             return data.getBytes(Charset.forName("US-ASCII"));
         }
-        else if(encoding.toLowerCase().contains("base64")) {
+        else if(encoding.toLowerCase(Locale.ROOT).contains("base64")) {
             return Base64.decode(data, Base64.NO_WRAP);
 
         }
diff --git a/android/src/main/java/com/RNFetchBlob/RNFetchBlobReq.java b/android/src/main/java/com/RNFetchBlob/RNFetchBlobReq.java
index a8abd71833879201e3438b2fa51d712a311c4551..b70cc13c004229f69157de5f82ae5ec3abf4358e 100644
--- a/android/src/main/java/com/RNFetchBlob/RNFetchBlobReq.java
+++ b/android/src/main/java/com/RNFetchBlob/RNFetchBlobReq.java
@@ -49,6 +49,7 @@ import java.security.KeyStore;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Locale;
 import java.util.HashMap;
 
 import java.util.concurrent.TimeUnit;
@@ -300,14 +301,14 @@ public class RNFetchBlobReq extends BroadcastReceiver implements Runnable {
                             responseFormat = ResponseFormat.UTF8;
                     }
                     else {
-                        builder.header(key.toLowerCase(), value);
-                        mheaders.put(key.toLowerCase(), value);
+                        builder.header(key.toLowerCase(Locale.ROOT), value);
+                        mheaders.put(key.toLowerCase(Locale.ROOT), value);
                     }
                 }
             }
 
             if(method.equalsIgnoreCase("post") || method.equalsIgnoreCase("put") || method.equalsIgnoreCase("patch")) {
-                String cType = getHeaderIgnoreCases(mheaders, "Content-Type").toLowerCase();
+                String cType = getHeaderIgnoreCases(mheaders, "Content-Type").toLowerCase(Locale.ROOT);
 
                 if(rawRequestBodyArray != null) {
                     requestType = RequestType.Form;
@@ -323,7 +324,7 @@ public class RNFetchBlobReq extends BroadcastReceiver implements Runnable {
                             || rawRequestBody.startsWith(RNFetchBlobConst.CONTENT_PREFIX)) {
                         requestType = RequestType.SingleFile;
                     }
-                    else if (cType.toLowerCase().contains(";base64") || cType.toLowerCase().startsWith("application/octet")) {
+                    else if (cType.toLowerCase(Locale.ROOT).contains(";base64") || cType.toLowerCase(Locale.ROOT).startsWith("application/octet")) {
                         cType = cType.replace(";base64","").replace(";BASE64","");
                         if(mheaders.containsKey("content-type"))
                             mheaders.put("content-type", cType);
@@ -686,7 +687,7 @@ public class RNFetchBlobReq extends BroadcastReceiver implements Runnable {
         boolean isCustomBinary = false;
         if(options.binaryContentTypes != null) {
             for(int i = 0; i< options.binaryContentTypes.size();i++) {
-                if(ctype.toLowerCase().contains(options.binaryContentTypes.getString(i).toLowerCase())) {
+                if(ctype.toLowerCase(Locale.ROOT).contains(options.binaryContentTypes.getString(i).toLowerCase(Locale.ROOT))) {
                     isCustomBinary = true;
                     break;
                 }
@@ -698,13 +699,13 @@ public class RNFetchBlobReq extends BroadcastReceiver implements Runnable {
     private String getHeaderIgnoreCases(Headers headers, String field) {
         String val = headers.get(field);
         if(val != null) return val;
-        return headers.get(field.toLowerCase()) == null ? "" : headers.get(field.toLowerCase());
+        return headers.get(field.toLowerCase(Locale.ROOT)) == null ? "" : headers.get(field.toLowerCase(Locale.ROOT));
     }
 
     private String getHeaderIgnoreCases(HashMap<String,String> headers, String field) {
         String val = headers.get(field);
         if(val != null) return val;
-        String lowerCasedValue = headers.get(field.toLowerCase());
+        String lowerCasedValue = headers.get(field.toLowerCase(Locale.ROOT));
         return lowerCasedValue == null ? "" : lowerCasedValue;
     }