fix(net/gclient): fix form field value truncation when uploading files

[lingcoder]

What does this PR do?

Fixes #4156

When posting form data with file upload, if a field value contains = or &, the value was being truncated.

Example

data := g.Map{
    "file":      "@file:/path/to/file.txt",
    "fieldName": "aaa=1&b=2",
}
client.Post(ctx, "/upload", data)

Expected: Server receives fieldName = "aaa=1&b=2"
Actual (before fix): Server receives fieldName = "aaa" (truncated)

Root Cause Analysis

The issue was caused by three problems in the original code:

Problem 1: Global URL encoding disable (httputils.go)

// Original code - PROBLEMATIC
if urlEncode {
    for k, v := range m {
        if gstr.Contains(k, fileUploadingKey) || gstr.Contains(gconv.String(v), fileUploadingKey) {
            urlEncode = false  // Disables URL encoding for ALL values!
            break
        }
    }
}

When any value contained @file:, URL encoding was disabled for ALL values, causing "aaa=1&b=2" to remain unencoded. The & character was then treated as a parameter separator.

Problem 2: Split on all = characters (gclient_request.go)

// Original code - PROBLEMATIC
array := strings.Split(item, "=")  // Splits on ALL '=' characters

This caused "fieldName=aaa=1" to be split into ["fieldName", "aaa", "1"].

Problem 3: No URL decoding for field values

URL-encoded values were written directly to the multipart form without decoding.

Solution

Fix 1: Remove global URL encoding disable

Only @file: prefixed values are kept unencoded for file upload detection. Other values are properly URL-encoded.

Fix 2: Use SplitN to limit split count

array := strings.SplitN(item, "=", 2)  // Only split on first '='

Fix 3: Add URL decoding for field values

if v, err := gurl.Decode(fieldValue); err == nil {
    fieldValue = v
}

Compatibility Analysis

Scenario	Before	After	Compatible
Normal form POST (no file upload)	✅ Works	✅ Works	✅ Yes
File upload + normal field values	✅ Works	✅ Works	✅ Yes
File upload + field values containing = or &	❌ Truncated	✅ Works	✅ Fixed
Field value is @file: (no path)	✅ Works	✅ Works	✅ Yes
Field value starts with @file: but file doesn't exist	❌ Error	❌ Error	✅ Yes
User sends pre-encoded value like "aaa%3D1"	✅ Works	✅ Works	✅ Yes
Content-Type: application/json	✅ Works	✅ Works	✅ Yes
Content-Type: application/xml	✅ Works	✅ Works	✅ Yes

Breaking Change Assessment

No breaking changes. The fix only affects the file upload scenario where field values contain special characters (=, &). Previously this scenario was broken, now it works correctly.

Edge Cases

1. Literal @file: value: GoFrame treats @file: as a special marker for file upload. This is a framework design decision and remains unchanged.

2. URL decode failure: If URL decoding fails (e.g., invalid %XX sequence), the original value is preserved.

Test Coverage

Added comprehensive tests covering:

• Test_Issue4156 - Basic fix verification
• Test_Issue4156_MultipleSpecialChars - Multiple =, &, %, +, spaces
• Test_Issue4156_MultipleFields - Multiple fields with special characters
• Test_Issue4156_NoFileUpload - Normal POST without file upload
• Test_Issue4156_PreEncodedValue - Pre-encoded values like %3D
• Test_Issue4156_EmptyAndSpecialValues - Edge cases (= at start/end, only special chars)
• TestBuildParams_* - httputil.BuildParams comprehensive tests

All tests pass, including existing Test_Issue3748 which tests the @file: marker handling.

Files Changed

• internal/httputil/httputils.go - Remove global URL encoding disable, adjust @file: condition
• internal/httputil/httputils_test.go - Add comprehensive BuildParams tests
• net/gclient/gclient_request.go - Use SplitN, add URL decoding
• net/gclient/gclient_z_unit_issue_test.go - Add Issue 4156 test cases

[Copilot]

Pull request overview

This PR fixes a bug where form field values containing = or & characters were being truncated when uploading files via multipart form data.

Changes:

• Modified parameter parsing to use SplitN with limit 2 to only split on the first = character
• Added URL decoding for form field names and values in multipart requests
• Removed global URL encoding disable logic that was causing the truncation issue
• Added comprehensive test coverage for various edge cases

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
net/gclient/gclient_z_unit_issue_test.go	Added 7 comprehensive test functions covering the fix and edge cases including special characters, multiple fields, pre-encoded values, and various scenarios
net/gclient/gclient_request.go	Changed Split to SplitN for limiting splits and added URL decoding for field names and values; imported gurl package for decoding
internal/httputil/httputils_test.go	Added 5 test functions to verify URL encoding behavior, file upload marker handling, and parameter building
internal/httputil/httputils.go	Removed global URL encoding disable logic and simplified @file: marker detection; removed unused gstr import

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