Introduce module specific errors

ballerina/data_mappings.bal

@@ -26,7 +26,12 @@ isolated function convertOASMessageToMessage(oas:Message response) returns Messa
 
     string? rawMessage = response.raw;
     if rawMessage is string {
-        email.raw = check base64UrlDecode(rawMessage);
+        string|error decodedMessage = base64UrlDecode(rawMessage);
+        if decodedMessage is error {
+            return error InvalidEncodedValue(
+                string `Returned message raw field${decodedMessage.message()}`, decodedMessage.cause());
+        }
+        email.raw = decodedMessage;
     }
 
     email.labelIds = response.labelIds ?: email.labelIds;
@@ -102,7 +107,13 @@ returns MessagePart|error {
         messagePart.attachmentId = body.attachmentId ?: messagePart.attachmentId;
         messagePart.size = body.size ?: messagePart.size;
         if body.data is string {
-            messagePart.data = check base64UrlDecode(body.data ?: EMPTY_STRING);
+            string|error decodedBody = base64UrlDecode(body.data ?: EMPTY_STRING);
+            if decodedBody is error {
+                return error InvalidEncodedValue(
+                    string `Returned message body part of id '${messagePart.partId}'${decodedBody.message()}`,
+                    decodedBody.cause());
+            }
+            messagePart.data = decodedBody;
         }
     }
 
@@ -234,17 +245,22 @@ isolated function getFileMessageString(AttachmentFile|ImageFile file, string emb
     if file is ImageFile {
         fileString += CONTENT_ID + COLON + file.contentId + NEW_LINE;
     }
-    fileString += NEW_LINE + check getEncodedFileContent(file.path) + NEW_LINE;
+    fileString += NEW_LINE + check getEncodedFileContent(file.path, embedType) + NEW_LINE;
     return fileString;
 }
 
 // todo check error usages
-isolated function getEncodedFileContent(string filePath) returns string|error {
-    io:ReadableByteChannel fileChannel = check io:openReadableFile(filePath);
-    io:ReadableByteChannel fileContent = check fileChannel.base64Encode();
-    io:ReadableByteChannel encodedFileChannel = fileContent;
-    byte[] readChannel = check encodedFileChannel.read(100000000);
-    return string:fromBytes(readChannel);
+isolated function getEncodedFileContent(string filePath, string embedType) returns string|error {
+    do {
+        io:ReadableByteChannel fileChannel = check io:openReadableFile(filePath);
+        io:ReadableByteChannel fileContent = check fileChannel.base64Encode();
+        io:ReadableByteChannel encodedFileChannel = fileContent;
+        byte[] readChannel = check encodedFileChannel.read(100000000);
+        return string:fromBytes(readChannel);
+    } on fail error e {
+        return error FileGenericError(
+            string `Unable to retrieve ${embedType}: ${filePath}`, e);
+    }
 }
 
 isolated function convertOASListMessagesResponseToListMessageResponse(oas:ListMessagesResponse response)
@@ -274,7 +290,13 @@ isolated function convertOASMessagePartBodyToAttachment(oas:MessagePartBody body
     attachment.size = bodyPart.size ?: attachment.size;
     string? data = bodyPart.data;
     if data is string {
-        attachment.data = check base64UrlDecode(data);
+        string|error decodedData = base64UrlDecode(data);
+        if decodedData is error {
+            return error InvalidEncodedValue(
+                string `Returned attachment message body part of id '${attachment.attachmentId ?: EMPTY_STRING}'
+                ${decodedData.message()}`, decodedData.cause());
+        }
+        attachment.data = decodedData;
     }
     return attachment;
 }

ballerina/errors.bal

@@ -0,0 +1,25 @@
+// Copyright (c) 2023, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
+//
+// WSO2 Inc. licenses this file to you under the Apache License,
+// Version 2.0 (the "License"); you may not use this file except
+// in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+# Defines the generic error type for the `gmail` module.
+public type Error distinct error;
+
+# Represents a generic error for the file path.
+public type FileGenericError distinct Error;
+
+# Represents a generic error for the file path.
+public type InvalidEncodedValue distinct Error;
+

ballerina/tests/test.bal

@@ -544,3 +544,41 @@ function testReplyTo() returns error? {
     }
     check gmailClient->/users/me/threads/[threadId].delete();
 }
+
+@test:Config {
+}
+function testUrlDecodeFailure() returns error? {
+    oas:Message receivedMsg = {
+        threadId: "qweqweqdqd",
+        id: "saDSASDASDA",
+        raw: "ASDADSADADADADADAD"
+    };
+    Message|error result = convertOASMessageToMessage(receivedMsg);
+    if result is error {
+        test:assertEquals(result.message(), "Returned message raw field is not a valid Base64 URL encoded value.",
+        msg = "Error decoding message");
+    } else {
+        test:assertFail("Expected decoded error");
+    }
+}
+
+@test:Config {
+}
+function testAttachmentSendFailure() returns error? {
+    MessageRequest sendMsg = {
+        attachments: [
+            {
+                name: "test.txt",
+                path: "asdadsa",
+                mimeType: "text/plain"
+            }
+        ]
+    };
+    oas:Message|error result = convertMessageRequestToOASMessage(sendMsg);
+    if result is error {
+        test:assertEquals(result.message(),
+        "Unable to retrieve attachment: asdadsa", msg = "Error decoding message");
+    } else {
+        test:assertFail("Expected decoded error");
+    }
+}

ballerina/utils.bal

@@ -21,6 +21,10 @@ isolated function base64UrlEncode(string contentToBeEncoded) returns string {
 }
 
 isolated function base64UrlDecode(string contentToBeDecoded) returns string|error {
-    string base64Encoded = re `_`.replaceAll(re `-`.replaceAll(contentToBeDecoded, PLUS), FORWARD_SLASH);
-    return check string:fromBytes(check array:fromBase64(base64Encoded));
+    do {
+        string base64Encoded = re `_`.replaceAll(re `-`.replaceAll(contentToBeDecoded, PLUS), FORWARD_SLASH);
+        return check string:fromBytes(check array:fromBase64(base64Encoded));
+    } on fail error e {
+        return error InvalidEncodedValue(" is not a valid Base64 URL encoded value.", e);
+    }
 }