Fix: URL-encoded special characters in $filter and $orderby break OData parsing #3080

Copilot · 2026-01-23T21:08:03Z

Why make this change?

HttpUtility.ParseQueryString() decodes query parameter values, causing double-decoding when DAB constructs OData filter strings. A URL like ?$filter=title eq 'A %26 B' becomes title eq 'A & B', where the literal & is interpreted as a query parameter separator, truncating the filter to title eq 'A and producing "unterminated string literal" errors.

What is this change?

Preserve URL encoding for OData parameters by extracting raw values before ParseQueryString() decodes them:

RestRequestContext: Added RawQueryString property to store original encoded query
RestService: Populate RawQueryString alongside ParsedQueryString
RequestParser: New ExtractRawQueryParameter() extracts encoded values by splitting on unencoded & separators
$filter/$orderby parsing: Use raw values instead of decoded values when constructing OData query strings
Error handling: Added explicit null checks that throw DataApiBuilderException if parameter extraction fails unexpectedly

// Extract raw parameter preserving encoding
private static string? ExtractRawQueryParameter(string queryString, string parameterName)
{
    if (string.IsNullOrWhiteSpace(queryString)) return null;
    foreach (string param in queryString.TrimStart('?').Split('&'))
    {
        int idx = param.IndexOf('=');
        if (idx >= 0 && param.Substring(0, idx).Equals(parameterName, StringComparison.OrdinalIgnoreCase))
            return idx < param.Length - 1 ? param.Substring(idx + 1) : string.Empty;
    }
    return null;
}

Database-agnostic: operates at HTTP parsing layer before any DB-specific processing.

How was this tested?

Integration Tests - Added test data and queries across all DB types (MsSql, PostgreSQL, MySQL, DwSql)
- 4 integration test methods testing various special characters: &, +, =, %
- Test data includes books with titles: filter & test, A+B=C, Tom & Jerry, 100% Complete
Unit Tests - 20 tests validating encoding preservation for diverse special characters
- Tests cover: &, =, +, %, #, <, >, :, /, ?
- Tests validate edge cases: duplicate parameters, case-insensitive matching, malformed queries

Sample Request(s)

REST - Before (fails):

GET /api/Book?$filter=title eq 'filter & test'
→ 400 Bad Request: "unterminated string literal at position 17 in 'title eq 'filter'."

GET /api/Book?$filter=title eq 'A+B=C'
→ 400 Bad Request: similar parsing error

REST - After (succeeds):

GET /api/Book?$filter=title eq 'filter & test'
→ 200 OK: [{"id": 22, "title": "filter & test", "publisher_id": 1234}]

GET /api/Book?$filter=title eq 'A+B=C'
→ 200 OK: [{"id": 23, "title": "A+B=C", "publisher_id": 1234}]

GET /api/Book?$filter=title eq 'Tom & Jerry'
→ 200 OK: [{"id": 24, "title": "Tom & Jerry", "publisher_id": 1234}]

GET /api/Book?$filter=title eq '100% Complete'
→ 200 OK: [{"id": 25, "title": "100% Complete", "publisher_id": 1234}]

Works with any URL-encoded special character: %26 (&), %3D (=), %2B (+), %25 (%), %23 (#), %3C (<), %3E (>), %3A (:), %2F (/), %3F (?), etc.

Original prompt

This section details on the original issue you should resolve

<issue_title>[Bug]: Special characters in filter clause</issue_title>
<issue_description>### What happened?

Tried filtering on the string "filter & test"

Original URL: https://localhost:5001/api/my_entity?$filter=region eq 'filter & test'
Encoded URL: https://localhost:5001/api/my_entity?$filter=region%20eq%20%27filter%20%26%20test%27

I get this response when using the encoded URL:
{
"error": {
"code": "BadRequest",
"message": "There is an unterminated string literal at position 17 in 'region eq 'filter'.",
"status": 400
}
}

Version

1.6.84

What database are you using?

Azure SQL

What hosting model are you using?

Container Apps

Which API approach are you accessing DAB through?

REST

Relevant log output
Azure.DataApiBuilder.Service.Exceptions.DataApiBuilderException: There is an unterminated string literal at position 17 in 'region eq 'filter'.
       ---> Microsoft.OData.ODataException: There is an unterminated string literal at position 17 in 'region eq 'filter'.
         at Microsoft.OData.UriParser.UriQueryExpressionParser.ParseComparison()
         at Microsoft.OData.UriParser.UriQueryExpressionParser.ParseLogicalAnd()
         at Microsoft.OData.UriParser.UriQueryExpressionParser.ParseLogicalOr()
         at Microsoft.OData.UriParser.UriQueryExpressionParser.ParseExpression()
         at Microsoft.OData.UriParser.UriQueryExpressionParser.ParseExpressionText(String expressionText)
         at Microsoft.OData.UriParser.ODataQueryOptionParser.ParseFilterImplementation(String filter, ODataUriParserConfiguration configuration, ODataPathInfo odataPathInfo)
         at Azure.DataApiBuilder.Core.Parsers.ODataParser.GetFilterClause(String filterQueryString, String resourcePath, ODataUriResolver customResolver) in /_/src/Core/Parsers/FilterParser.cs:line 64
         --- End of inner exception stack trace ---
         at Azure.DataApiBuilder.Core.Parsers.ODataParser.GetFilterClause(String filterQueryString, String resourcePath, ODataUriResolver customResolver) in /_/src/Core/Parsers/FilterParser.cs:line 68
         at Azure.DataApiBuilder.Core.Parsers.RequestParser.ParseQueryString(RestRequestContext context, ISqlMetadataProvider sqlMetadataProvider) in /_/src/Core/Parsers/RequestParser.cs:line 99
         at Azure.DataApiBuilder.Core.Services.RestService.ExecuteAsync(String entityName, EntityActionOperation operationType, String primaryKeyRoute) in /_/src/Core/Services/RestService.cs:line 178
         at Azure.DataApiBuilder.Service.Controllers.RestController.HandleOperation(String route, EntityActionOperation operationType) in /_/src/Service/Controllers/RestController.cs:line 239
Code of Conduct

I agree to follow this project's Code of Conduct</issue_description>

<agent_instructions>Introduce as little new code as necessary. Ensure this and variants of this problem are resolved by creating as generic of a solution as possible. </agent_instructions>

Comments on the Issue (you are @copilot in this section)
@JerryNixon This is a DAB bug, not a user error.
What's Happening

The user correctly URL-encoded their filter value:

& → %26

spaces → %20

However, DAB (or the underlying framework) is double-decoding the URL. The %26 gets decoded back to &, which then causes the query string parser to split on that & — treating everything after it as a separate query parameter.

Result: The filter string gets truncated to region eq 'filter (note the unterminated quote), hence the error.

Root Cause

This is a known class of issue with URL encoding in ASP.NET / OData scenarios. The %26 is being decoded at the framework level before the OData filter parser receives it, so the filter parser never sees the encoded value — it sees a literal & which breaks query string parsing.

Workaround

Double-encode the ampersand: %2526 (encodes the % in %26)

Fix for DAB

The OData filter parser needs to receive the raw/encoded query string, or DAB needs to handle this edge case explicitly when parsing $filter values containing special characters.</comment_new>

Fixes [Bug]: Special characters in filter clause #3039

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Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

…ocumentation Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Copilot

Pull request overview

This PR fixes a critical bug where URL-encoded special characters in $filter and $orderby query parameters were being double-decoded, causing OData parsing failures. The issue occurred because HttpUtility.ParseQueryString() decodes parameter values before they reach the OData parser, which also expects to decode them.

Changes:

Added RawQueryString property to preserve URL-encoded query strings before decoding
Modified $filter and $orderby parsing to use raw (URL-encoded) values instead of decoded values
Added comprehensive unit and integration tests across all supported database types

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Core/Models/RestRequestContexts/RestRequestContext.cs	Added `RawQueryString` property to store the URL-encoded query string
src/Core/Services/RestService.cs	Populated `RawQueryString` before parsing query parameters
src/Core/Parsers/RequestParser.cs	Added `ExtractRawQueryParameter()` method and modified `$filter`/`$orderby` parsing to use raw values
src/Service.Tests/UnitTests/RequestParserUnitTests.cs	Added 14 unit tests validating URL encoding preservation in various scenarios
src/Service.Tests/SqlTests/RestApiTests/Find/*.cs	Added integration tests for all database types (MsSql, PostgreSQL, MySQL, DwSql)
src/Service.Tests/DatabaseSchema-*.sql	Added test data with special characters for integration tests

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RubenCerna2079 · 2026-02-02T19:27:35Z

/azp run

azure-pipelines · 2026-02-02T19:28:02Z

Azure Pipelines successfully started running 6 pipeline(s).

RubenCerna2079

Need to test more scenarios in which we use special characters not just &

RubenCerna2079 · 2026-02-02T22:47:41Z

src/Core/Parsers/RequestParser.cs

-                        context.FilterClauseInUrl = sqlMetadataProvider.GetODataParser().GetFilterClause(filterQueryString, $"{context.EntityName}.{context.DatabaseObject.FullName}");
+                        // Use raw (URL-encoded) filter value to preserve special characters like &
+                        string? rawFilterValue = ExtractRawQueryParameter(context.RawQueryString, FILTER_URL);
+                        if (rawFilterValue is not null)


Is there any situation where we would expect the rawFilterValue parameter to be null? If so then we should throw an exception for it.

Added exception handling in commit cffedaa. Now throws DataApiBuilderException with "Unable to extract $filter parameter from query string" if the parameter exists in ParsedQueryString but cannot be extracted from RawQueryString, indicating an unexpected state.

RubenCerna2079 · 2026-02-02T22:48:21Z

src/Core/Parsers/RequestParser.cs

-                        (context.OrderByClauseInUrl, context.OrderByClauseOfBackingColumns) = GenerateOrderByLists(context, sqlMetadataProvider, sortQueryString);
+                        // Use raw (URL-encoded) orderby value to preserve special characters
+                        string? rawSortValue = ExtractRawQueryParameter(context.RawQueryString, SORT_URL);
+                        if (rawSortValue is not null)


Is there any situation where we would expect the rawFilterValue parameter to be null? If so then we should throw an exception for it.

Added exception handling in commit cffedaa. Now throws DataApiBuilderException with "Unable to extract $orderby parameter from query string" if the parameter exists in ParsedQueryString but cannot be extracted from RawQueryString, indicating an unexpected state.

RubenCerna2079 · 2026-02-02T23:15:58Z

src/Service.Tests/SqlTests/RestApiTests/Find/FindApiTestBase.cs


+        /// <summary>
+        /// Tests the REST Api for Find operation with a filter containing special characters
+        /// like ampersand (&) that need to be URL-encoded. This validates that the fix for


Are there other special characters that we could test?

Added 3 additional integration test methods in commit cffedaa testing special characters: +, = (A+B=C), ampersand in different context (Tom & Jerry), and % (100% Complete). Test data added across all database schemas.

RubenCerna2079 · 2026-02-02T23:20:48Z

src/Service.Tests/UnitTests/RequestParserUnitTests.cs

+        /// parameter values, preserving special characters like ampersand (&).
+        /// </summary>
+        [DataTestMethod]
+        [DataRow("?$filter=region%20eq%20%27filter%20%26%20test%27", "$filter", "region%20eq%20%27filter%20%26%20test%27", DisplayName = "Extract filter with encoded ampersand")]


We should test other special characters besides the %26 which is &

Added 6 more test cases in commit cffedaa testing various special characters beyond &: encoded =, +, %, #, <, >, :, /, and ?. Total unit tests increased from 14 to 20, all passing.

RubenCerna2079 · 2026-02-02T23:25:36Z

src/Service.Tests/UnitTests/RequestParserUnitTests.cs

+        }
+
+        /// <summary>
+        /// Tests that ExtractRawQueryParameter handles edge cases correctly.


Give a better explanation of what are the edge cases

Improved documentation in commit cffedaa to clarify edge cases: duplicate parameters (returns first occurrence), case-insensitive parameter name matching, and malformed query strings with unencoded ampersands.

…nd improve documentation Co-authored-by: RubenCerna2079 <32799214+RubenCerna2079@users.noreply.github.com>

Copilot · 2026-02-02T23:32:22Z

Need to test more scenarios in which we use special characters not just &

Expanded test coverage in commit cffedaa:

6 new unit tests for special characters: =, +, %, #, <, >, :, /, ?
3 new integration tests with titles: A+B=C, Tom & Jerry, 100% Complete
Test data added across all DBs (MsSql, PostgreSQL, MySQL, DwSql)
20/20 unit tests passing

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Copilot AI assigned Copilot and JerryNixon Jan 23, 2026

Copilot started work on behalf of JerryNixon January 23, 2026 21:08 View session

Copilot AI and others added 5 commits January 23, 2026 21:12

Implement fix for special characters in filter clause

8b01458

Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Add test data and test case for filter with special characters

8f1c4c0

Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Add unit tests for RequestParser URL encoding preservation

f2d8fbd

Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Improve ExtractRawQueryParameter with better edge case handling and d…

55a1f98

…ocumentation Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Make code more terse and concise

7a8f2aa

Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix special characters issue in filter clause~~ Fix: URL-encoded special characters in $filter and $orderby break OData parsing Jan 23, 2026

Copilot AI requested a review from JerryNixon January 23, 2026 21:25

Copilot finished work on behalf of JerryNixon January 23, 2026 21:25

JerryNixon marked this pull request as ready for review January 23, 2026 21:29

JerryNixon requested review from Aniruddh25, RubenCerna2079, aaronburtle, anushakolan, neeraj-sharma2592, sourabh1007, souvikghosh04 and vadeveka as code owners January 23, 2026 21:29

Copilot AI review requested due to automatic review settings January 23, 2026 21:29

JerryNixon requested review from Alekhya-Polavarapu and rusamant as code owners January 23, 2026 21:29

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Merge branch 'main' into copilot/fix-filter-clause-issue

029d51b

JerryNixon approved these changes Feb 2, 2026

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github-project-automation bot moved this from Todo to Review In Progress in Data API builder Feb 2, 2026

Copilot started work on behalf of RubenCerna2079 February 2, 2026 23:27 View session

Address PR feedback: Add null checks, more special character tests, a…

cffedaa

…nd improve documentation Co-authored-by: RubenCerna2079 <32799214+RubenCerna2079@users.noreply.github.com>

Copilot AI requested a review from RubenCerna2079 February 2, 2026 23:33

Copilot finished work on behalf of RubenCerna2079 February 2, 2026 23:33

Fix: URL-encoded special characters in $filter and $orderby break OData parsing #3080

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Fix: URL-encoded special characters in $filter and $orderby break OData parsing #3080

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Sample Request(s)

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What hosting model are you using?

Which API approach are you accessing DAB through?

Relevant log output

Code of Conduct

Comments on the Issue (you are @copilot in this section)

What's Happening

Root Cause

Workaround

Fix for DAB

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Pull request overview

Reviewed changes

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