Format Date Header for ISO8601 Compliance

source/include/sigv4.h

@@ -67,6 +67,8 @@
 
 /**< Length of the date header in ISO 8601 format. */
 #define SIGV4_ISO_STRING_LEN                        16U
+/**< Length of the date header found in AWS IoT's HTTP response. */
+#define SIGV4_EXPECTED_AWS_IOT_DATE_LEN             20U
 /** @}*/
 
 /**
@@ -379,9 +381,12 @@ SigV4Status_t SigV4_GenerateHTTPAuthorization( const SigV4Parameters_t * pParams
 
 /**
  * @brief Parse the date header value from the AWS IoT response.
+ *
  * The AWS IoT response date is of the form: 2018-01-18T09:18:06Z.
+ * The ISO8601-formatted date is: 20180118T091806Z.
  *
- * @param[in] pDate The date header value.
+ * @param[in] pDate The RFC3339-formatted date header value, found in the HTTP
+ * response returned by AWS IoT (ex. "2018-01-18T09:18:06Z").
  * @param[in] dateLen length of the pDate header value.
  * @param[out] pDateISO8601 The ISO8601 format compliant date. This buffer must
  * be large enough to hold both the ISO8601-formatted date (16 characters) and

source/sigv4.c

@@ -0,0 +1,114 @@
+/*
+ * SigV4 Utility Library v1.0.0
+ * Copyright (C) 2020 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+/**
+ * @file sigv4.c
+ * @brief Implements the user-facing functions in sigv4.h
+ */
+
+#include <stdio.h>
+#include <assert.h>
+#include <string.h>
+#include <time.h>
+
+#include "sigv4.h"
+
+/*-----------------------------------------------------------*/
+
+SigV4Status_t SigV4_AwsIotDateToIso8601( const char * pDate,
+                                         size_t dateLen,
+                                         char * pDateISO8601,
+                                         size_t dateISO8601Len )
+{
+    SigV4Status_t returnStatus = SigV4InvalidParameter;
+
+    /* Check for NULL parameters. */
+    if( pDate == NULL )
+    {
+        LogError( ( "Parameter check failed: pDate is NULL." ) );
+    }
+    else if( pDateISO8601 == NULL )
+    {
+        LogError( ( "Parameter check failed: pDateISO8601 is NULL." ) );
+    }
+
+    /* Check that the date buffer provided is not shorter than the expected
+     * input format. */
+    else if( dateLen < SIGV4_EXPECTED_AWS_IOT_DATE_LEN )
+    {
+        LogError( ( "Parameter check failed: dateLen must be at least %u.",
+                    SIGV4_EXPECTED_AWS_IOT_DATE_LEN ) );
+    }
+
+    /* Check that the output buffer provided is large enough for the formatted
+     * string. */
+    else if( dateISO8601Len < SIGV4_ISO_STRING_LEN + 1 )
+    {
+        LogError( ( "Parameter check failed: dateISO8601Len must be at least %u.",
+                    SIGV4_ISO_STRING_LEN + 1 ) );
+    }
+    else
+    {
+        struct tm dateInfo = { 0 };
+
+        /* Parse pDate according to the input's expected string format, and
+         * populate the date struct with its components.  */
+        if( sscanf( pDate, "%4d-%2d-%2dT%2d:%2d:%2dZ",
+                    &dateInfo.tm_year,
+                    &dateInfo.tm_mon,
+                    &dateInfo.tm_mday,
+                    &dateInfo.tm_hour,
+                    &dateInfo.tm_min,
+                    &dateInfo.tm_sec ) != 6 )
+        {
+            LogError( ( "sscanf() failed to parse the date string using the format expected." ) );
+            returnStatus = SigV4ISOFormattingError;
+        }
+        else
+        {
+            size_t lenFormatted = 0U;
+
+            /* Standardize month and year values for struct tm's specifications:
+             *  - tm_mon = "months from January" (0-11)
+             *  - tm_year = "years since 1900" */
+            dateInfo.tm_mon--;
+            dateInfo.tm_year -= 1900;
+
+            /* Construct ISO 8601 string using members of populated date struct. */
+            lenFormatted = strftime( pDateISO8601, SIGV4_ISO_STRING_LEN + 1, "%Y%m%dT%H%M%SZ", &dateInfo );
+
+            if( lenFormatted != SIGV4_ISO_STRING_LEN )
+            {
+                LogError( ( "Failed to generate ISO 8601 date: Call to strftime() for string formatting failed: "
+                            "ExpectedReturnValue=%u, ActualReturnValue=%lu.",
+                            SIGV4_ISO_STRING_LEN, lenFormatted ) );
+                returnStatus = SigV4ISOFormattingError;
+            }
+            else
+            {
+                returnStatus = SigV4Success;
+            }
+        }
+    }
+
+    return returnStatus;
+}