feat(Upload): use local preview instead of base64 format#6157
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feat(Upload): use local preview instead of base64 format#6157
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Reviewer's GuideThis PR replaces the existing Base64-based image preview workflow with a faster, local object-URL approach by adding a file reader utility in JavaScript, wiring up a client-side preview URL API, and adjusting C# upload components and samples to use that API instead of Base64. File-Level Changes
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Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## main #6157 +/- ##
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Coverage 99.99% 99.99%
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Files 704 704
Lines 31093 31099 +6
Branches 4394 4395 +1
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+ Hits 31092 31098 +6
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Hey @ArgoZhang - I've reviewed your changes - here's some feedback:
- Consider revoking the created object URLs (via URL.revokeObjectURL) when they’re no longer needed to avoid accumulating memory leaks.
- You can simplify the preview logic by calling URL.createObjectURL(file) directly instead of reading into an ArrayBuffer and re-wrapping into a Blob.
Here's what I looked at during the review
- 🟡 General issues: 4 issues found
- 🟢 Security: all looks good
- 🟢 Testing: all looks good
- 🟡 Complexity: 2 issues found
- 🟢 Documentation: all looks good
Help me be more useful! Please click 👍 or 👎 on each comment and I'll use the feedback to improve your reviews.
| const preventHandler = e => e.preventDefault(); | ||
| const body = el.querySelector('.upload-drop-body'); | ||
| const upload = { el, body, preventHandler } | ||
| const inputFile = el.querySelector('[type="file"]'); |
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issue (bug_risk): inputFile can be null; add a null-check before usage
Add a guard or early return to handle cases where inputFile is null to avoid runtime errors.
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| /** | ||
| * @param {File} file | ||
| * @returns {Blob} |
Contributor
| /// </summary> | ||
| /// <param name="file"></param> | ||
| /// <returns></returns> | ||
| protected override async Task TriggerOnChanged(UploadFile file) |
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suggestion: Image preview logic duplicated here as well
Consider refactoring this logic into a shared base class or utility method to avoid duplication.
Comment on lines
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| // 从客户端获得预览地址不使用 base64 编码 | ||
| if (file.IsImage(AllowExtensions, CanPreviewCallback)) | ||
| { | ||
| await OnChange(file); | ||
| file.PrevUrl = await InvokeAsync<string?>("getPreviewUrl", Id, file.OriginFileName); | ||
| } | ||
| await base.TriggerOnChanged(file); |
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suggestion (bug_risk): Non-image files retain previous PrevUrl
Reset PrevUrl for non-image files to prevent showing outdated previews.
Suggested change
| // 从客户端获得预览地址不使用 base64 编码 | |
| if (file.IsImage(AllowExtensions, CanPreviewCallback)) | |
| { | |
| await OnChange(file); | |
| file.PrevUrl = await InvokeAsync<string?>("getPreviewUrl", Id, file.OriginFileName); | |
| } | |
| await base.TriggerOnChanged(file); | |
| // 从客户端获得预览地址不使用 base64 编码 | |
| if (file.IsImage(AllowExtensions, CanPreviewCallback)) | |
| { | |
| file.PrevUrl = await InvokeAsync<string?>("getPreviewUrl", Id, file.OriginFileName); | |
| } | |
| else | |
| { | |
| // 非图片文件重置预览地址，防止显示过期预览 | |
| file.PrevUrl = null; | |
| } | |
| await base.TriggerOnChanged(file); |
| }) | ||
| } | ||
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| export async function getPreviewUrl(id, fileName) { |
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issue (complexity): Consider refactoring getPreviewUrl to use early returns and optional chaining to reduce nesting and intermediate variables.
Here’s a way to flatten out the nesting in getPreviewUrl (and even drop the manual let url = '' accumulator) by using early-returns and optional chaining:
export async function getPreviewUrl(id, fileName) {
const files = Data.get(id)?.files;
if (!files) return '';
// find the File object
const file = Array.from(files).find(f => f.name === fileName);
if (!file) return '';
// readFileAsync → blob URL
const blob = await readFileAsync(file);
return blob ? URL.createObjectURL(blob) : '';
}If you’re not actually transforming the file (just wrapping it in a blob URL), you can simplify further and drop readFileAsync entirely:
export function getPreviewUrl(id, fileName) {
const files = Data.get(id)?.files || [];
const file = files.find(f => f.name === fileName);
return file ? URL.createObjectURL(file) : '';
}Both versions preserve the current behavior while reducing indentation, intermediate variables, and nested if blocks.
| * @param {File} file | ||
| * @returns {Blob} | ||
| */ | ||
| export function readFileAsync(file) { |
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issue (complexity): Consider removing or simplifying the readFileAsync helper to avoid unnecessary FileReader logic.
Suggested change
| export function readFileAsync(file) { | |
| The new `readFileAsync` helper isn’t needed since `File` already implements the `Blob` interface. You can either: | |
| 1. Drop the helper entirely and pass `file` wherever a `Blob` is expected, or | |
| 2. If you really need an immutable copy, use `File.prototype.slice` instead of a `FileReader` round‐trip. | |
| Example (identity / no‐op helper): | |
| ```js | |
| /** @param {File} file | |
| * @returns {Promise<Blob>} | |
| */ | |
| export function readFileAsync(file) { | |
| return Promise.resolve(file); | |
| } |
Or (clone via slice):
/** @param {File} file
* @returns {Promise<Blob>}
*/
export function readFileAsync(file) {
const blobCopy = file.slice(0, file.size, file.type);
return Promise.resolve(blobCopy);
}Both eliminate the 20+ lines of FileReader logic while preserving all functionality.```
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fixes #6156
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☑️ Self Check before Merge
Summary by Sourcery
Implement local preview for image uploads by replacing base64 image requests with Blob URL previews via a new JavaScript API, update upload components and samples to use the new mechanism, and adjust tests accordingly.
New Features:
Enhancements:
Tests: