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fix: exception message mismatch in in-memory emulator #55

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Copilot Apr 23, 2026
9d9f6f9
fix: exception message mismatch in in-memory emulator (v4.0.6)
Copilot Apr 23, 2026
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96 changes: 65 additions & 31 deletions src/CosmosDB.InMemoryEmulator/InMemoryContainer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,13 @@ namespace CosmosDB.InMemoryEmulator;
/// </remarks>
internal class InMemoryContainer : Container, IContainerTestSetup
{
// Ref: https://learn.microsoft.com/en-us/rest/api/cosmos-db/
// Error message constants matching real Cosmos DB REST API response bodies.
private const string MessageEntityDoesNotExist = "Entity with the specified id does not exist in the system.";
private const string MessageEntityAlreadyExists = "Entity with the specified id already exists in the system.";
// Ref: https://learn.microsoft.com/en-us/rest/api/cosmos-db/replace-a-document (412 response)
private const string MessagePreconditionFailed = "One of the specified pre-condition is not met";

private static readonly JsonSerializerSettings JsonSettings = new()
{
TypeNameHandling = TypeNameHandling.None,
Expand Down Expand Up @@ -717,7 +724,7 @@ public override async Task<ItemResponse<T>> CreateItemAsync<T>(
ValidateUniqueKeys(jObj, pk);
if (!_items.TryAdd(key, json))
{
throw new InMemoryCosmosException($"Entity with the specified id already exists in the system. id = {itemId}",
throw new InMemoryCosmosException($"{MessageEntityAlreadyExists} id = {itemId}",
HttpStatusCode.Conflict, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
}
}
Expand All @@ -726,7 +733,7 @@ public override async Task<ItemResponse<T>> CreateItemAsync<T>(
{
if (!_items.TryAdd(key, json))
{
throw new InMemoryCosmosException($"Entity with the specified id already exists in the system. id = {itemId}",
throw new InMemoryCosmosException($"{MessageEntityAlreadyExists} id = {itemId}",
HttpStatusCode.Conflict, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
}
}
Expand Down Expand Up @@ -786,7 +793,7 @@ public override Task<ItemResponse<T>> ReadItemAsync<T>(
if (!_items.TryGetValue(key, out var json) || IsExpired(key))
{
EvictIfExpired(key);
throw new InMemoryCosmosException($"Entity with the specified id does not exist in the system. id = {id}",
throw new InMemoryCosmosException($"{MessageEntityDoesNotExist} id = {id}",
HttpStatusCode.NotFound, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
}

Expand Down Expand Up @@ -824,7 +831,7 @@ public override async Task<ItemResponse<T>> UpsertItemAsync<T>(

if (requestOptions?.IfMatchEtag is not null && !_items.ContainsKey(key))
{
throw new InMemoryCosmosException($"Entity with the specified id does not exist. id = {itemId}",
throw new InMemoryCosmosException($"{MessageEntityDoesNotExist} id = {itemId}",
HttpStatusCode.NotFound, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
}

Expand Down Expand Up @@ -934,7 +941,7 @@ public override async Task<ItemResponse<T>> ReplaceItemAsync<T>(
if (!_items.ContainsKey(key) || IsExpired(key))
{
EvictIfExpired(key);
throw new InMemoryCosmosException($"Entity with the specified id does not exist. id = {id}",
throw new InMemoryCosmosException($"{MessageEntityDoesNotExist} id = {id}",
HttpStatusCode.NotFound, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
}

Expand Down Expand Up @@ -1018,7 +1025,7 @@ public override async Task<ItemResponse<T>> DeleteItemAsync<T>(
if (!_items.TryGetValue(key, out var existingJson) || IsExpired(key))
{
EvictIfExpired(key);
throw new InMemoryCosmosException($"Entity with the specified id does not exist. id = {id}",
throw new InMemoryCosmosException($"{MessageEntityDoesNotExist} id = {id}",
HttpStatusCode.NotFound, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
}

Expand Down Expand Up @@ -1099,7 +1106,7 @@ private ItemResponse<T> PatchItemCore<T>(
if (!_items.TryGetValue(key, out var existingJson) || IsExpired(key))
{
EvictIfExpired(key);
throw new InMemoryCosmosException($"Entity with the specified id does not exist. id = {id}",
throw new InMemoryCosmosException($"{MessageEntityDoesNotExist} id = {id}",
HttpStatusCode.NotFound, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
}

Expand All @@ -1118,7 +1125,7 @@ private ItemResponse<T> PatchItemCore<T>(
new Dictionary<string, object>(), null);
if (!matches)
{
throw new InMemoryCosmosException("Precondition Failed",
throw new InMemoryCosmosException(MessagePreconditionFailed,
HttpStatusCode.PreconditionFailed, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
}
}
Expand Down Expand Up @@ -1208,16 +1215,19 @@ public override async Task<ResponseMessage> CreateItemStreamAsync(
lock (_uniqueKeyWriteLock)
{
if (!ValidateUniqueKeysStream(jObj, pk))
return CreateResponseMessage(HttpStatusCode.Conflict);
return CreateResponseMessage(HttpStatusCode.Conflict,
reason: $"{MessageEntityAlreadyExists} id = {itemId}");

if (!_items.TryAdd(key, json))
return CreateResponseMessage(HttpStatusCode.Conflict);
return CreateResponseMessage(HttpStatusCode.Conflict,
reason: $"{MessageEntityAlreadyExists} id = {itemId}");
}
}
else
{
if (!_items.TryAdd(key, json))
return CreateResponseMessage(HttpStatusCode.Conflict);
return CreateResponseMessage(HttpStatusCode.Conflict,
reason: $"{MessageEntityAlreadyExists} id = {itemId}");
}

var etag = GenerateETag();
Expand Down Expand Up @@ -1258,7 +1268,8 @@ public override Task<ResponseMessage> ReadItemStreamAsync(
if (!_items.TryGetValue(key, out var json) || IsExpired(key))
{
EvictIfExpired(key);
return Task.FromResult(CreateResponseMessage(HttpStatusCode.NotFound));
return Task.FromResult(CreateResponseMessage(HttpStatusCode.NotFound,
reason: $"{MessageEntityDoesNotExist} id = {id}"));
}
var etag = _etags.GetValueOrDefault(key);
if (!CheckIfNoneMatchStream(requestOptions, key))
Expand Down Expand Up @@ -1306,12 +1317,14 @@ public override async Task<ResponseMessage> UpsertItemStreamAsync(
// IfMatch on non-existent item: return NotFound (matching real Cosmos)
if (requestOptions?.IfMatchEtag is not null && !_items.ContainsKey(key))
{
return CreateResponseMessage(HttpStatusCode.NotFound);
return CreateResponseMessage(HttpStatusCode.NotFound,
reason: $"{MessageEntityDoesNotExist} id = {itemId}");
}

if (!CheckIfMatchStream(requestOptions, key))
{
return CreateResponseMessage(HttpStatusCode.PreconditionFailed);
return CreateResponseMessage(HttpStatusCode.PreconditionFailed,
reason: MessagePreconditionFailed);
}
bool existed;
string etag;
Expand All @@ -1324,7 +1337,8 @@ public override async Task<ResponseMessage> UpsertItemStreamAsync(
lock (_uniqueKeyWriteLock)
{
if (!ValidateUniqueKeysStream(jObj, pk, excludeItemId: itemId))
return CreateResponseMessage(HttpStatusCode.Conflict);
return CreateResponseMessage(HttpStatusCode.Conflict,
reason: $"{MessageEntityAlreadyExists} id = {itemId}");
existed = _items.TryGetValue(key, out previousJson);
if (existed) { previousEtag = _etags.GetValueOrDefault(key); previousTimestamp = _timestamps.GetValueOrDefault(key); }
etag = GenerateETag();
Expand All @@ -1337,7 +1351,8 @@ public override async Task<ResponseMessage> UpsertItemStreamAsync(
else
{
if (!ValidateUniqueKeysStream(jObj, pk, excludeItemId: itemId))
return CreateResponseMessage(HttpStatusCode.Conflict);
return CreateResponseMessage(HttpStatusCode.Conflict,
reason: $"{MessageEntityAlreadyExists} id = {itemId}");
existed = _items.TryGetValue(key, out previousJson);
if (existed) { previousEtag = _etags.GetValueOrDefault(key); previousTimestamp = _timestamps.GetValueOrDefault(key); }
etag = GenerateETag();
Expand Down Expand Up @@ -1412,12 +1427,14 @@ public override async Task<ResponseMessage> ReplaceItemStreamAsync(
if (!_items.TryGetValue(key, out var previousJson) || IsExpired(key))
{
EvictIfExpired(key);
return CreateResponseMessage(HttpStatusCode.NotFound);
return CreateResponseMessage(HttpStatusCode.NotFound,
reason: $"{MessageEntityDoesNotExist} id = {id}");
}

if (!CheckIfMatchStream(requestOptions, key))
{
return CreateResponseMessage(HttpStatusCode.PreconditionFailed);
return CreateResponseMessage(HttpStatusCode.PreconditionFailed,
reason: MessagePreconditionFailed);
}

var previousEtag = _etags.GetValueOrDefault(key);
Expand All @@ -1437,7 +1454,8 @@ public override async Task<ResponseMessage> ReplaceItemStreamAsync(
lock (_uniqueKeyWriteLock)
{
if (!ValidateUniqueKeysStream(jObj, pk, excludeItemId: id))
return CreateResponseMessage(HttpStatusCode.Conflict);
return CreateResponseMessage(HttpStatusCode.Conflict,
reason: $"{MessageEntityAlreadyExists} id = {id}");
etag = GenerateETag();
_etags[key] = etag;
_timestamps[key] = DateTimeOffset.UtcNow;
Expand All @@ -1448,7 +1466,8 @@ public override async Task<ResponseMessage> ReplaceItemStreamAsync(
else
{
if (!ValidateUniqueKeysStream(jObj, pk, excludeItemId: id))
return CreateResponseMessage(HttpStatusCode.Conflict);
return CreateResponseMessage(HttpStatusCode.Conflict,
reason: $"{MessageEntityAlreadyExists} id = {id}");
etag = GenerateETag();
_etags[key] = etag;
_timestamps[key] = DateTimeOffset.UtcNow;
Expand Down Expand Up @@ -1494,12 +1513,14 @@ public override async Task<ResponseMessage> DeleteItemStreamAsync(
if (!_items.TryGetValue(key, out var existingJson) || IsExpired(key))
{
EvictIfExpired(key);
return CreateResponseMessage(HttpStatusCode.NotFound);
return CreateResponseMessage(HttpStatusCode.NotFound,
reason: $"{MessageEntityDoesNotExist} id = {id}");
}

if (!CheckIfMatchStream(requestOptions, key))
{
return CreateResponseMessage(HttpStatusCode.PreconditionFailed);
return CreateResponseMessage(HttpStatusCode.PreconditionFailed,
reason: MessagePreconditionFailed);
}

ExecutePreTriggers(requestOptions, JsonParseHelpers.ParseJson(existingJson), "Delete");
Expand Down Expand Up @@ -1582,12 +1603,14 @@ private ResponseMessage PatchItemStreamCore(
if (!_items.TryGetValue(key, out var existingJson) || IsExpired(key))
{
EvictIfExpired(key);
return CreateResponseMessage(HttpStatusCode.NotFound);
return CreateResponseMessage(HttpStatusCode.NotFound,
reason: $"{MessageEntityDoesNotExist} id = {id}");
}

if (!CheckIfMatchStream(requestOptions, key))
{
return CreateResponseMessage(HttpStatusCode.PreconditionFailed);
return CreateResponseMessage(HttpStatusCode.PreconditionFailed,
reason: MessagePreconditionFailed);
}

var jObj = JsonParseHelpers.ParseJson(existingJson);
Expand All @@ -1602,7 +1625,8 @@ private ResponseMessage PatchItemStreamCore(
new Dictionary<string, object>(), null);
if (!matches)
{
return CreateResponseMessage(HttpStatusCode.PreconditionFailed);
return CreateResponseMessage(HttpStatusCode.PreconditionFailed,
reason: MessagePreconditionFailed);
}
}
}
Expand All @@ -1625,7 +1649,8 @@ private ResponseMessage PatchItemStreamCore(
lock (_uniqueKeyWriteLock)
{
if (!ValidateUniqueKeysStream(jObj, pk, excludeItemId: id))
return CreateResponseMessage(HttpStatusCode.Conflict);
return CreateResponseMessage(HttpStatusCode.Conflict,
reason: $"{MessageEntityAlreadyExists} id = {id}");
etag = GenerateETag();
_etags[key] = etag;
_timestamps[key] = DateTimeOffset.UtcNow;
Expand Down Expand Up @@ -3094,7 +3119,7 @@ private void CheckIfMatch(ItemRequestOptions requestOptions, (string Id, string

if (requestOptions.IfMatchEtag != currentEtag)
{
throw new InMemoryCosmosException("Precondition Failed", HttpStatusCode.PreconditionFailed, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
throw new InMemoryCosmosException(MessagePreconditionFailed, HttpStatusCode.PreconditionFailed, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
}
}

Expand Down Expand Up @@ -3129,12 +3154,12 @@ private void CheckIfNoneMatchForWrite(ItemRequestOptions requestOptions, (string

if (requestOptions.IfNoneMatchEtag == "*" && _etags.ContainsKey(key))
{
throw new InMemoryCosmosException("Precondition Failed", HttpStatusCode.PreconditionFailed, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
throw new InMemoryCosmosException(MessagePreconditionFailed, HttpStatusCode.PreconditionFailed, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
}

if (_etags.TryGetValue(key, out var currentEtag) && requestOptions.IfNoneMatchEtag == currentEtag)
{
throw new InMemoryCosmosException("Precondition Failed", HttpStatusCode.PreconditionFailed, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
throw new InMemoryCosmosException(MessagePreconditionFailed, HttpStatusCode.PreconditionFailed, 0, Guid.NewGuid().ToString(), SyntheticRequestCharge);
}
}

Expand Down Expand Up @@ -3245,14 +3270,23 @@ public InMemoryItemResponse(
public override string ETag => _etag;
}

private ResponseMessage CreateResponseMessage(HttpStatusCode statusCode, string json = null, string etag = null, int subStatusCode = 0)
private ResponseMessage CreateResponseMessage(HttpStatusCode statusCode, string json = null, string etag = null, int subStatusCode = 0, string reason = null)
{
var errorMessage = (int)statusCode >= 400
? $"Response status code does not indicate success: {statusCode} ({(int)statusCode})"
: null;

// When a specific error reason is provided, embed it as a JSON body so the Cosmos SDK
// can extract it into CosmosException.Message when this response flows through the
// FakeCosmosHandler HTTP pipeline (ConvertToHttpResponse → SDK parses response body).
// Ref: https://learn.microsoft.com/en-us/rest/api/cosmos-db/ — error response body format.
var contentJson = json ?? (reason is not null
? new JObject { ["message"] = reason }.ToString(Formatting.None)
: null);

var msg = new ResponseMessage(statusCode, requestMessage: null, errorMessage: errorMessage)
{
Content = json is not null ? ToStream(json) : null
Content = contentJson is not null ? ToStream(contentJson) : null
};
msg.Headers["x-ms-activity-id"] = Guid.NewGuid().ToString();
msg.Headers["x-ms-request-charge"] = SyntheticRequestCharge.ToString(CultureInfo.InvariantCulture);
Expand Down
2 changes: 1 addition & 1 deletion src/Directory.Build.props
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@
<!-- Shared NuGet package metadata for all source (packable) projects -->
<PropertyGroup>
<IsPackable>true</IsPackable>
<Version>4.0.5</Version>
<Version>4.0.6</Version>
<Authors>lemonlion</Authors>
<Copyright>Copyright (c) 2026 lemonlion</Copyright>
<PackageLicenseExpression>MIT</PackageLicenseExpression>
Expand Down
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