private async Task GenerateResponseFromStore(HttpContext httpContext, bool updateLastModified = true)
{
var logInformation = string.Empty;
var headers = httpContext.Response.Headers;
// set the ETag & Last-Modified date.
// remove any other ETag and Last-Modified headers (could be set
// by other pieces of code)
headers.Remove(HeaderNames.ETag);
headers.Remove(HeaderNames.LastModified);
// generate key
var storeKey = await _storeKeyGenerator.GenerateStoreKey(
ConstructStoreKeyContext(httpContext.Request, _validationModelOptions));
// take ETag value from the store (if it's found)
var savedResponse = await _store.GetAsync(storeKey);
if (savedResponse?.ETag != null)
{
var eTag = new ETag(savedResponse.ETag.ETagType, savedResponse.ETag.Value);
headers[HeaderNames.ETag] = savedResponse.ETag.ToString();
logInformation = $"ETag: {eTag.ETagType}, {eTag}, ";
}
DateTimeOffset lastModified;
if (updateLastModified)
{
// set LastModified
lastModified = await _lastModifiedInjector.CalculateLastModified(
new ResourceContext(httpContext.Request, storeKey, savedResponse));
}
else
{
lastModified = savedResponse.LastModified;
}
var lastModifiedValue = await _dateParser.LastModifiedToString(lastModified);
headers[HeaderNames.LastModified] = lastModifiedValue;
logInformation += $"Last-Modified: {lastModifiedValue}.";
_logger.LogInformation($"Generation done. {logInformation}");
}
private async Task GenerateResponseFromStore(HttpContext httpContext)
{
var headers = httpContext.Response.Headers;
// set the ETag & Last-Modified date.
// remove any other ETag and Last-Modified headers (could be set
// by other pieces of code)
headers.Remove(HeaderNames.ETag);
headers.Remove(HeaderNames.LastModified);
// generate key
var requestKey = GenerateRequestKey(httpContext.Request);
// set LastModified
// r = RFC1123 pattern (https://msdn.microsoft.com/en-us/library/az4se3k1(v=vs.110).aspx)
var lastModified = GetUtcNowWithoutMilliseconds();
headers[HeaderNames.LastModified] = lastModified.ToString("r", CultureInfo.InvariantCulture);
ETag eTag = null;
// take ETag value from the store (if it's found)
var savedResponse = await _store.GetAsync(requestKey);
if (savedResponse?.ETag != null)
{
eTag = new ETag(savedResponse.ETag.ETagType, savedResponse.ETag.Value);
headers[HeaderNames.ETag] = savedResponse.ETag.Value;
}
// store (overwrite)
await _store.SetAsync(requestKey, new ValidationValue(eTag, lastModified));
var logInformation = string.Empty;
if (eTag != null)
{
logInformation = $"ETag: {eTag.ETagType.ToString()}, {eTag.Value}, ";
}
logInformation += $"Last-Modified: {lastModified.ToString("r", CultureInfo.InvariantCulture)}.";
_logger.LogInformation($"Generation done. {logInformation}");
}
private static bool ETagsMatch(
ETag eTag,
string eTagToCompare,
bool useStrongComparisonFunction)
{
// for If-None-Match (cache) checks, weak comparison should be used.
// for If-Match (concurrency) check, strong comparison should be used.
//The example below shows the results for a set of entity-tag pairs and
//both the weak and strong comparison function results:
//+--------+--------+-------------------+-----------------+
//| ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |
//+--------+--------+-------------------+-----------------+
//| W/"1" | W/"1" | no match | match |
//| W/"1" | W/"2" | no match | no match |
//| W/"1" | "1" | no match | match |
//| "1" | "1" | match | match |
//+--------+--------+-------------------+-----------------+
if (useStrongComparisonFunction)
{
// to match, both eTags must be strong & be an exact match.
var eTagToCompareIsStrong = !eTagToCompare.StartsWith("W/");
return(eTagToCompareIsStrong &&
eTag.ETagType == ETagType.Strong &&
string.Equals(eTag.ToString(), eTagToCompare, StringComparison.OrdinalIgnoreCase));
}
// for weak comparison, we only compare the parts of the eTags after the "W/"
var firstValueToCompare = eTag.ETagType == ETagType.Weak ? eTag.ToString().Substring(2) : eTag.ToString();
var secondValueToCompare = eTagToCompare.StartsWith("W/") ? eTagToCompare.Substring(2) : eTagToCompare;
return(string.Equals(firstValueToCompare, secondValueToCompare, StringComparison.OrdinalIgnoreCase));
}
private void GenerateValidationHeadersOnResponse(HttpContext httpContext)
{
// don't generate these for 304 - that's taken care of at the
// start of the request
if (httpContext.Response.StatusCode == StatusCodes.Status304NotModified)
{
return;
}
// This takes care of storing new tags, also after a succesful PUT/POST/PATCH.
// Other PUT/POST/PATCH requests must thus include the new ETag as If-Match,
// otherwise the precondition will fail.
//
// If an API returns a 204 No Content after PUT/PATCH, the ETag will be generated
// from an empty response - any other user/cache must GET the response again
// before updating it. Getting it will result in a new ETag value being generated.
//
// If an API returns a 200 Ok after PUT/PATCH, the ETag will be generated from
// that response body - if the update was succesful but nothing was changed,
// in those cases the original ETag for other users/caches will still be sufficient.
// if the response body cannot be read, we can never
// generate correct ETags (and it should never be cached)
if (!httpContext.Response.Body.CanRead)
{
return;
}
_logger.LogInformation("Generating Validation headers.");
var headers = httpContext.Response.Headers;
// remove any other ETag and Last-Modified headers (could be set
// by other pieces of code)
headers.Remove(HeaderNames.ETag);
headers.Remove(HeaderNames.LastModified);
// Save the ETag in a store.
// Key = generated from request URI & headers (if VaryBy is
// set, only use those headers)
// ETag itself is generated from the key + response body
// (strong ETag)
// get the request key
var requestKey = GenerateRequestKey(httpContext.Request);
var requestKeyAsBytes = Encoding.UTF8.GetBytes(requestKey);
// get the response bytes
if (httpContext.Response.Body.CanSeek)
{
httpContext.Response.Body.Position = 0;
}
var responseBodyContent = new StreamReader(httpContext.Response.Body).ReadToEnd();
var responseBodyContentAsBytes = Encoding.UTF8.GetBytes(responseBodyContent);
// combine both to generate an etag
var combinedBytes = Combine(requestKeyAsBytes, responseBodyContentAsBytes);
var eTag = new ETag(ETagType.Strong, GenerateETag(combinedBytes));
var lastModified = GetUtcNowWithoutMilliseconds();
// store the ETag & LastModified date with the request key as key in the ETag store
_store.SetAsync(requestKey, new ValidationValue(eTag, lastModified));
// set the ETag and LastModified header
headers[HeaderNames.ETag] = eTag.Value;
headers[HeaderNames.LastModified] = lastModified.ToString("r", CultureInfo.InvariantCulture);
_logger.LogInformation($"Validation headers generated. ETag: {eTag.Value}. Last-Modified: {lastModified.ToString("r", CultureInfo.InvariantCulture)}");
}
private async Task <bool> ConditionalPUTorPATCHIsValid(HttpContext httpContext)
{
_logger.LogInformation("Checking for conditional PUT/PATCH.");
// Preconditional checks are used for concurrency checks only,
// on updates: PUT or PATCH
if (!(httpContext.Request.Method == HttpMethod.Put.ToString() ||
httpContext.Request.Method == "PATCH"))
{
_logger.LogInformation("Not valid - method isn't PUT or PATCH.");
// for all the other methods, return true (no 412 response)
return(true);
}
// the precondition is valid if one of the ETags submitted through
// IfMatch matches with the saved ETag, AND if the If-UnModified-Since
// value is smaller than the saved date. Both must be valid if both
// are submitted.
// If both headers are missing, we should
// always return true (the precondition is missing, so it's valid)
// We don't need to check anything, and can never return a 412 response
if (!(httpContext.Request.Headers.Keys.Contains(HeaderNames.IfMatch) ||
httpContext.Request.Headers.Keys.Contains(HeaderNames.IfUnmodifiedSince)))
{
_logger.LogInformation("Not valid - no If Match or If Unmodified-Since headers.");
return(true);
}
// generate the request key
var requestKey = GenerateRequestKey(httpContext.Request);
// find the validationValue with this key in the store
var validationValue = await _store.GetAsync(requestKey);
// if there is no validation value in the store, we return false:
// there is nothing to compare to, so the precondition can
// never be ok - return a 412 response
if (validationValue == null || validationValue.ETag == null)
{
_logger.LogInformation("No saved response found in store.");
return(false);
}
var eTagIsValid = false;
var ifUnModifiedSinceIsValid = false;
// check the ETags
if (httpContext.Request.Headers.Keys.Contains(HeaderNames.IfMatch))
{
var ifMatchHeaderValue = httpContext.Request.Headers[HeaderNames.IfMatch].ToString().Trim();
_logger.LogInformation($"Checking If-Match: {ifMatchHeaderValue}.");
// if the value is *, the check is valid.
if (ifMatchHeaderValue == "*")
{
eTagIsValid = true;
}
else
{
// otherwise, check the actual ETag(s)
var ETagsFromIfMatchHeader = ifMatchHeaderValue
.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
foreach (var ETag in ETagsFromIfMatchHeader)
{
// check the ETag. If one of the ETags matches, the
// ETag precondition is valid.
// for concurrency checks, we use the strong
// comparison function.
if (ETagsMatch(validationValue.ETag,
ETag.Trim(),
true))
{
_logger.LogInformation($"ETag valid: {validationValue.ETag}.");
eTagIsValid = true;
break;
}
}
}
}
else
{
_logger.LogInformation("No If-Match header, don't check ETag.");
// if there is no IfMatch header, the tag precondition is valid.
eTagIsValid = true;
}
// if there is an IfMatch header but none of the ETags match,
// the precondition is already invalid. We don't have to
// continue checking.
if (!eTagIsValid)
{
_logger.LogInformation("Not valid. No match found for ETag.");
return(false);
}
// Either the ETag matches (or one of them), or there was no IfMatch header.
// Continue with checking the IfUnModifiedSince header, if it exists.
if (httpContext.Request.Headers.Keys.Contains(HeaderNames.IfUnmodifiedSince))
{
// if the LastModified date is smaller than the IfUnmodifiedSince date,
// the precondition is valid.
var ifUnModifiedSinceValue = httpContext.Request.Headers[HeaderNames.IfUnmodifiedSince].ToString();
_logger.LogInformation($"Checking If-Unmodified-Since: {ifUnModifiedSinceValue}");
DateTimeOffset parsedIfUnModifiedSince;
if (DateTimeOffset.TryParseExact(ifUnModifiedSinceValue, "r",
CultureInfo.InvariantCulture.DateTimeFormat, DateTimeStyles.AdjustToUniversal,
out parsedIfUnModifiedSince))
{
// If the LastModified date is smaller than the IfUnmodifiedSince date,
// the precondition is valid.
ifUnModifiedSinceIsValid = validationValue.LastModified.CompareTo(parsedIfUnModifiedSince) < 0;
}
else
{
// can only check if we can parse it. Invalid values must
// be ignored.
ifUnModifiedSinceIsValid = true;
_logger.LogInformation("Cannot parse If-Unmodified-Since value as date, header is ignored.");
}
}
else
{
_logger.LogInformation("No If-Unmodified-Since header.");
// if there is no IfUnmodifiedSince header, the check is valid.
ifUnModifiedSinceIsValid = true;
}
// return the combined result of all validators.
return(ifUnModifiedSinceIsValid && eTagIsValid);
}
private async Task <bool> ConditionalGETorHEADIsValid(HttpContext httpContext)
{
_logger.LogInformation("Checking for conditional GET/HEAD.");
if (!(httpContext.Request.Method == HttpMethod.Get.ToString()) ||
httpContext.Request.Method == "HEAD")
{
_logger.LogInformation("Not valid - method isn't GET or HEAD.");
return(false);
}
// we should check ALL If-None-Match values (can be multiple eTags) (if available),
// and the If-Modified-Since date (if available AND an eTag matches). See issue #2 @Github.
// So, this is a valid conditional GET/HEAD (304) if one of the ETags match and, if it's
// available, the If-Modified-Since date is larger than what's saved.
// if both headers are missing, we should
// always return false - we don't need to check anything, and
// can never return a 304 response
if (!(httpContext.Request.Headers.Keys.Contains(HeaderNames.IfNoneMatch) ||
httpContext.Request.Headers.Keys.Contains(HeaderNames.IfModifiedSince)))
{
_logger.LogInformation("Not valid - no If-None-Match or If-Modified-Since headers.");
return(false);
}
// generate the request key
var requestKey = GenerateRequestKey(httpContext.Request);
// find the validationValue with this key in the store
var validationValue = await _store.GetAsync(requestKey);
// if there is no validation value in the store, always
// return false - we have nothing to compare to, and can
// never return a 304 response
if (validationValue == null || validationValue.ETag == null)
{
_logger.LogInformation("No saved response found in store.");
return(false);
}
bool eTagIsValid = false;
bool ifModifiedSinceIsValid = false;
// check the ETags
if (httpContext.Request.Headers.Keys.Contains(HeaderNames.IfNoneMatch))
{
_logger.LogInformation("Checking If-None-Match.");
var ifNoneMatchHeaderValue = httpContext.Request.Headers[HeaderNames.IfNoneMatch].ToString().Trim();
_logger.LogInformation($"Checking If-None-Match: {ifNoneMatchHeaderValue}.");
// if the value is *, the check is valid.
if (ifNoneMatchHeaderValue == "*")
{
eTagIsValid = true;
}
else
{
var ETagsFromIfNoneMatchHeader = ifNoneMatchHeaderValue
.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
foreach (var ETag in ETagsFromIfNoneMatchHeader)
{
// check the ETag. If one of the ETags matches, we're good to
// go and can return a 304 Not Modified.
// For conditional GET/HEAD, we use weak comparison.
if (ETagsMatch(validationValue.ETag,
ETag.Trim(),
false))
{
eTagIsValid = true;
_logger.LogInformation($"ETag valid: {validationValue.ETag}.");
break;
}
}
// if there is an IfNoneMatch header, but none of the eTags match, we don't take the
// If-Modified-Since headers into account.
//
// cfr: "If none of the entity tags match, then the server MAY perform the requested method as if the
// If-None-Match header field did not exist, but MUST also ignore any If-Modified-Since header field(s)
// in the request. That is, if no entity tags match, then the server MUST NOT return a 304(Not Modified) response."
if (!eTagIsValid)
{
_logger.LogInformation("Not valid. No match found for ETag.");
return(false);
}
}
}
else
{
_logger.LogInformation("No If-None-Match header, don't check ETag.");
eTagIsValid = true;
}
if (httpContext.Request.Headers.Keys.Contains(HeaderNames.IfModifiedSince))
{
// if the LastModified date is smaller than the IfModifiedSince date,
// we can return a 304 Not Modified (IF there's also a matching ETag).
// By adding an If-Modified-Since date
// to a GET/HEAD request, the consumer is stating that (s)he only wants the resource
// to be returned if if has been modified after that.
var ifModifiedSinceValue = httpContext.Request.Headers[HeaderNames.IfModifiedSince].ToString();
_logger.LogInformation($"Checking If-Modified-Since: {ifModifiedSinceValue}");
DateTimeOffset parsedIfModifiedSince;
if (DateTimeOffset.TryParseExact(ifModifiedSinceValue, "r",
CultureInfo.InvariantCulture.DateTimeFormat, DateTimeStyles.AdjustToUniversal,
out parsedIfModifiedSince))
{
// can only check if we can parse it.
ifModifiedSinceIsValid = validationValue.LastModified.CompareTo(parsedIfModifiedSince) < 0;
}
else
{
ifModifiedSinceIsValid = true;
_logger.LogInformation("Cannot parse If-Modified-Since value as date, header is ignored.");
}
}
else
{
_logger.LogInformation("No If-Modified-Since header.");
ifModifiedSinceIsValid = true;
}
return(eTagIsValid && ifModifiedSinceIsValid);
}
public ValidatorValue(ETag eTag, DateTimeOffset lastModified)
{
ETag = eTag;
LastModified = lastModified;
}